Chapter 1 Introduction and Literature Review: Chemical ...shodhganga.inflibnet.ac.in/bitstream/10603/25187/5/5. chapter 1.pdf · Introduction and Literature Review: Chemical modifications

Ph. D. Thesis, Priya S. Deshpande, NMU, Jalgaon, 2013

1

Chapter 1

Introduction and Literature Review:

Chemical modifications of lipids for applications in chemical industry

The chemical process industries, all over the world, have been facing the

challenges of developing innovative processes and products in the wake of highly

globalized trade competition and stringent environmental regulations1. The term Green

Chemistry has been coined to promote the movement towards more environmentally

acceptable and sustainable chemical processes and products. The ‘Twelve Principles of

Green Chemistry’, which were formulated in the 1990s, provide guidelines for chemists to

develop clean, environmentally benign methodologies that are sustainable for the long

term and that reduces or eliminates the use or generation of hazardous substances in the

design, manufacture and application of chemical products2.

According to the seventh principle of Green Chemistry, a raw material or feedstock

should be renewable rather than depleting whenever technically and economically

practicable. The term ‘Renewable Resources’ primarily includes carbohydrates (starch,

cellulose, sugars) and lipids (animal and vegetable fats and oils, phospholipids etc.).

Carbohydrates are the most abundant organic compounds (around 75-80% of biomass) on

the planet. They constitute a suitable replacement for fossil fuels since they contain a

considerable amount of carbon and hydrogen. Utilization of natural products such as plant

oils and natural fats has attracted great attention in both scientific and industrial areas in

recent years. They can be used and are being used to produce valuable chemical

feedstocks and macrocyclic frameworks for natural product synthesis. The wide range of

renewable raw materials with varying properties and differing chemical compositions are

available at the annual production rate of approximately 170 billion tons3. Around 6

billion t/a (3.5%) are utilized in the form of timber, grain and other foodstuffs. The rapid

depletion of crude oil reserves, escalating fuel prices and the concern over climate change

catapulted into global interest for utilizing the remaining 96% (quantitatively in the order

of the total reserve of mineral oil) crop-based feedstocks as renewable alternatives to

petroleum-based feedstocks for energy generation and the synthesis of new platform

chemicals4-6

. Bio-based chemicals typically are cheap, readily available, low in toxicity,

CO2 sequestering, biodegradable and eco-friendly, making them prime candidates for an

alignment of industry to the principles of green chemistry and sustainability. In spite of

this fact, the applications that use biomass as starting materials are currently limited to


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only 10-12% of the overall organic chemical industry and include adhesives, textile and

leather chemicals, surfactants, cleaning agents, perfumes and flavours, cosmetics,

coatings/ paints, printing inks, crop protection, lubricants/ greases and dietary

supplements. Chemists have much to contribute to meet this challenge and the future of

green chemistry will depend on innovations that consolidate and integrate the Twelve

Principles as a framework for intentional design of routes for utilisation of renewable

materials. The detailed study of the chemistry of these renewable materials and the

exploration of their chemical derivatizations with due stress on techno-commercial

feasibility analysis, which is the objective of present investigations, is absolutely

necessary on the way to sustainable and economical usage of biomass as renewable

feedstock for organic chemical industries.

1.1 A. Vegetable oils and fats as feedstock for chemical industries, their world

production and economics

Lipids are water insoluble organic biomolecules that can be extracted from cells

and tissues by nonpolar organic solvents such as hexane, acetone, ether, chloroform etc.

and are widely distributed in nature. Lipids can be further classified as simple lipids (fats,

waxes), conjugated lipids (phospholipids, lipoproteins, glycolipids) and derived lipids

(terpenes, steroids, fat soluble vitamins [A, D, E, K], carotene, tocopherols, squalene).

The diverse utility as foods, fuels, lubricants and starting materials for other chemicals

result from the unique chemical structures and physical properties of lipids. Vegetable oils

are the most important renewable and readily available part of a large family of lipids.

The oils and fats of commerce are predominantly made up of triesters of glycerol

with fatty acids (FA) called triacylglycerol or triglycerides (Fig. 1.1). FA are almost

entirely straight chain aliphatic saturated, monounsaturated or polyunsaturated carboxylic

acids. The broadest definition includes all chain lengths, but most natural FA are C4 to C22,

with C18 most common. The principal raw materials from which the natural fatty acids are

derived are tallow, crude tall oil, coconut, palm kernel, sunflower, castor and soybean oils.

Crude oils or triglycerides, when first extracted (generally >95%), are accompanied by

diglycerides, monoglycerides and free FA, but they may also contain phospholipids, free

sterols and sterol esters, tocols (tocopherols and tocotrienols), triterpene alcohols,

hydrocarbons and fat-soluble vitamins. During refining, some of the minor components

are removed, wholly or in part, and useful materials may be recovered. For example,

phospholipids are separated during degumming, and deodoriser distillates contain fatty

acids, along with valuable sterols, sterol esters, tocols, etc.


3

R3

O

O

O

O

R1

OO

R2

Fig. 1.1 Structure of triglyceride (R1, R2, R3- alkyl parts of different fatty acids)

The world’s production and consumption of natural oils and fats has grown from

79.2 million metric tones7

(MMT) in 1990 to 117 MMT in 2001. The annual global

production of the major vegetable oils amounted in 2007/08 to 128 MMT, increasing in

2008/09 to 132 MMT, and in 2009/10 137 MMT are expected8. In addition, about 31

MMT of minor plant oils and animal fats were produced and consumed9. It is expected

that the average annual world oil production will increase in the years 2016 to 2020 to

184.7 MMT10

. Sunflower seed oil is obtained from Helianthus annuus grown mainly in

Russia and Ukraine, Argentina, Western and Eastern Europe, China and the United

States11

. World production of sunflower oil is around 9 MMT, amounting to 8% of the

total vegetable oil production12

. The projected production for 2008–2012, according to the

literature10,13

, would be 12 MMT. Soybeans (Glycine max) are grown mainly in the United

States, Brazil, Argentina and China11

. At almost 30 MMT per annum14

(2006-10 forecast

33.6 MMT)10

, soybean oil is produced in greater amounts than any other oil. Grown

mainly in Indonesia and the Philippines, the annual production of coconut oil [coconut

palm (Cocus nucifera)] exceeds 3 MMT11,14

. Castor oil (Ricinus communis) is produced

mainly in India, Brazil and China at a world production level of 0.4-0.5 MMT11,14

. India is

the world’s largest exporter of castor oil. Groundnut oil, obtained from the legume Arachis

hypogea, is also known as peanut oil, monkeynut oil or arachis oil. The plant is grown

widely, especially in India, China and the United States. Many of the nuts are consumed as

snacks, but crushing still yields about 5.5 MMT of oil each year11,14

. In general, Malaysia,

Indonesia, and Argentina are prominent excess-supply producers of oils and fats while

India, the European Union countries, and China are notable high-demand areas that

supplement regional production through imports. In India, in the Oil Year 2007-08 (Nov.

2007- Oct. 2008), the net availability of edible oils from all domestic sources was 8.654

MMT while the consumption of Edible Oils was 14.262 MMT (source: Net availability

and consumption of edible oils: Directorate of Vanaspati, Vegetable Oils & Fats, India).

Thus the surplus requirement was met mainly through imports. Despite overall increases


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in production of oils and fats, changes vary from year to year and individual oils may even

show a decline in particular years. The uneven changes from year to year result in

variations in the relation between supply and demand and consequently affect the stock

status. When stocks rise, prices fall, demand increases and production declines because it

becomes less profitable. On the other hand, when stocks fall, prices rise, demand is stifled,

but production then increases as profit margins grow. In this way the market takes care of

changes in agricultural production arising both from man-made decisions and from

changes in climate.

Oils and fats differ in composition of the alkyl chains depending on their origin.

Table 1.1 presents the FA composition of some commercially important vegetable oils.

Oils rich in saturated FA have poor low-temperature flow properties, and those rich in

polyunsaturated FA are of low oxidative resistance. Vegetable oils rich in

monounsaturated FA have optimum oxidative stability and low-temperature properties15

.

The edible uses of vegetable oils include the preparation of shortening/ bakery fat,

vanaspati, margarines, and mayonnaise, besides routine use as cooking and frying oil and

as salad oil. In addition to food uses, the long-chain unsaturated FA vegetable oils such as

soybean, sunflower, and rapeseed have found their way into the plastics, pharmaceutical

products, inks, adhesives, coatings and many other industries. For example, the use of

soybean oil in lubricants15

, oleochemicals16

, and bioplastics17

is reported. Vegetable oil-

based inks, which cost even less than the petroleum oil-based inks, have been formulated

for various specialized applications. Containing around 70% linoleic acid, the traditional

sunflower oil is semidrying oil and can be used, like soybean oil, in the manufacture of

resins for paint and press-ink formulations18

.

Mineral-based lubricants lead the lubricant market. However, with the

advancement of the need for biodegradable products, vegetable oils have become popular,

because they are also better lubricants. Vegetable oils with high oleic (C18:1) content are

considered to be the potential environmentally friendly base fluids to substitute

conventional mineral oil-based lubricating oils, synthetic fuels (biodiesel, biogasoline) and

synthetic ester19-21

. In view of the higher oxidative stability of high-oleic sunflower oil, it

is used as diesel and gasoline engine lubricant. The groundnut oil produced is virtually all

used within the countries of production for edible purposes. Coconut oil, the medium

chain saturated FA oil (mainly lauric C12 and myristic C14 FA), normally commands a

higher cost over other vegetable oils. It is an important source for the production of

emulsifiers, detergents, cosmetics etc. In toilet soap, high lauric content provides the quick


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lathering properties. Castor oil differs from all other commercial oils in being rich in

ricinoleic acid (~90%, 12-hydroxyoleic). This hydroxy acid has several interesting

properties and is converted to a range of useful products to substitute those obtained from

petroleum such as lubricant, surface coating, nylon, perfumery chemicals and organic

intermediates for several industries. Long chain saturated FA (mainly stearic C18 and

palmitic C16) oils such as palm oil, sal fat, mahuwa fat have relatively high oxidation

stability and provide the hard fat components of soaps.

1.1 B. Primary and secondary oleochemicals

The direct use of fatty oils for industrial purposes is limited to relatively small

applications. The chemistry and technology of oils and fats derived industrial products i.e.

oleochemicals run parallel to those of petrochemicals. Majority of the oleochemicals,

being derived from oils and fats, are straight long chain, even numbered, primary

functional compounds and their advantages including biodegradability and negligible

sulfur, nitrogen and heavy metal content can be illustrated by several of the principles of

green chemistry22,24

.

Oleochemicals derived from splitting (hydrolysis) or transesterification of natural

fats and oils such as fatty acids (FA), mono-alkyl (mostly methyl) fatty esters (biodiesel-

substitute for diesel fuel), and glycerol, are termed as basic oleochemicals. Further

processing of these basic oleochemicals and their various fractions by different unit

processes/ chemical modifications, such as transesterification and esterification (e.g.

sucrose polyesters, monoglycerides), saponification and coprecipitation (metallic soaps)

hydrogenation and hydrogenolysis (e.g. fatty alcohols), ethoxylation (e.g. alcohol ethers),

sulphonation and sulphation (e.g. ester sulphonates, turkey red oil), ammonolysis and

amidation (nitrogen derivatives), ozonolysis (azealic/ pelargonic acids), epoxidation and

hydroxylation, dimerization and polymerisation, pyrolysis, alkali fusion (Fig. 1.2),

produce secondary oleochemical or specialty chemical products for utilisation as

surfactants, emulsifiers, lubricants, plasticizers, additives, bactericides, fungicides, etc.

Sunflower oil, either traditional or high oleic, may be used in bio-carburant in the form of

methyl esters. The use of vegetable oils as a substitute for petroleum-based diesel has

been replaced by the use of their methyl or ethyl esters as biodiesel. The importance of

biodiesel as a partial or total substitute for petroleum-based fuels has increased in the last

two decades. The fatty acid methyl esters (FAME) of soyabean oil are blended with diesel

fuel at a ratio of 20:80 for use in ignition engines25

. The caproic to capric (C6–C10) fatty

acid fractions, comprising approximately 15% in coconut oil, are good materials for


6

plasticizer range alcohol and for polyol esters. The latter are used in high-performance oil

for jet engines and for the new generation of lubricants. These acid fractions are also the

basic material for the manufacture of medium-chain triglycerides, a highly valued dietary

fat. Glyceryl monoesters and wax esters find application as food emulsifiers, mold release

agents, and lubricants for the plastic industry. In a variety of polymer applications, such as

coatings, large amount of solvents has to be used. Use of hydrocarbon and chlorinated

solvents provide volatile organic emissions with photochemical ozone creation potential.

Ester solvents, typically produced from FA and/or fatty alcohols, represent the largest

group of green solvents26

. The production of FAME of soyabean oil as environmentally

friendly solvent is reported27,28

.

The main non-food use of oleochemicals is in the production of surfactants. The

amphiphilic properties of fatty acids, exploited for centuries in the use of soaps, can be

modified by changing the carboxyl group into other hydrophilic groupings, giving anionic,

cationic, amphoteric and nonionic surfactants. Soap is one of the oldest known

oleochemical surfactant manufactured from saponification of oils. Fatty amines, produced

by the reaction of fatty acids with ammonia and hydrogen, are the most important nitrogen

derivatives of fatty acids. Polyglycol ethers, produced by the reaction of fatty alcohol with

ethylene oxide, constitute the most important class of nonionic surfactants. Monoalkyl

phosphate, fatty alcohol ether phosphate, and fatty alcohol sulfosuccinate are some of the

specialty surfactants derived from fatty alcohol with specific applications in the cosmetics

and other chemical industries. Alkanolamides, formed by the reaction of fatty acids or

esters with monoethanolamine or diethanolamine are popularly used as foam boosters for

shampoos and detergent products.

Parallel to the growth of the petrochemical industry, the fats and oils industry has

grown, and the oleochemistry has become an important area of research and technology in

several institutions and industries over the years. For long it has been considered that oil

and fat consumption was shared between food, feed, and industrial use in the ratio 80:6:14,

but with increasing production of biodiesel this is probably now closer to 74:6:20 29

. Many

new FA plants, with a cumulative capacity of 1.5 MMT have been built in Southeast

Asia30

(coconut and palm oil producing region). Consumption of fatty acids in the United

States, Western Europe, and Japan totaled 2.5 MMT in 2001. There was a sharp decline in

production and consumption of fatty acid in North America after the events of September

2001. However, growth is expected at the rate of 2.3% for the consumption of split acids

for the period 2000–2006. Growth in Western Europe is expected at the rate of 1.2%/yr for


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Table 1.1 Fatty acid composition of major vegetable oils

Sr.

No.

Name of

the Oil ρ S. V. I. V.

% Fatty Acid Composition

C14 C16 C18 C18:1 C18:2 C18:3 C20 Any special fatty acid

1 Castor 0.945-0.965/

250C

177-187

H.V.-160 83-86 ---- 2.0 1.0 7.0 5.0 ---- ----

Ricinoleic:86-90; 9,10

Dihydroxy Stearic: 0.7

2 Coconut 0.917-0.919/

250C

251-263 7.5-

10.5

13.0-

19.0

8.0-

11.0

1.0-

3.0 5.0-8.0 0-1.0 ----

0-

0.5

C6: 0-0.8, C8: 5.0-9.0, C10: 6.0-

10.0, C12: 44.0-52.0,

Palmitoleic: tr -2.5

3 Groundnut 0.910-0.915/

250C

188-195 84-

100 ----

6.0-

9.0

3.0-

6.0

52.0-

60.0

13.0-

27.0 ----

2.0-

4.0

Lignoceric: 1-3, Behenic acid:

1-3

4 Mustard 0.906-0.910/

250C

169-176 98-

110 ---- 1.5 0.4 22.0 14.2 6.8 ----

Erucic: 47.0 Behenic:2.0

5 Soyabean 0.916-0.922/

250C

189-195 128-

143 tr.0.5

7.0-

11.0

2.0-

6.0

22.0-

34.0

43.0-

56.0

5.0-

11.0 ----

----

6 Sunflower 0.915-0.919 /

250C

188-194 125-

140 ----

3.0-

6.0

1.0-

3.0

14.0-

35.0

44.0-

75.0 ----

0.6-

4.0

Behenic: 0.8

7 Cottonseed 0.915-0.926

/150C

191-196 103-

115 0.4 20.0 2.0 35.0 42 ---- ----

----

8 Palm 0.921-0.925

/150C

196-205 48-58 0.5-

2.0

32.0-

45.0

2.0-

7.0

38.0-

52.0 5.0-11.0 ---- ----

----

9 Linseed 0.931-0.938/

150C

189-196 170-

180 ----

4.0-

7.0

2.0-

5.0

12.0-

34.0

17.0-

24.0

35.0-

60.0

0.3-

1.0

----

ρ: specific gravity, I. V.: Iodine value, S.V.: Saponification value, H.V.: Hydroxyl value, C6: Caproic acid, C8: Caprylic acid, C10: Capric acid,

C12: Lauric acid, C14: Myristic acid , C16 : Palmitic acid, C18: Stearic acid, C18:1: Oleic acid , C18:2 : Linoleic acid , C18:3: linolenic acid , C20 :

Arachidic acid.

http://en.wikipedia.org/wiki/Caproic_acid

http://en.wikipedia.org/wiki/Caprylic_acid

http://en.wikipedia.org/wiki/Capric_acid

http://en.wikipedia.org/wiki/Lauric_acid

http://en.wikipedia.org/wiki/Myristic_acid

http://en.wikipedia.org/wiki/Palmitic_acid

http://en.wikipedia.org/wiki/Stearic_acid

http://en.wikipedia.org/wiki/Oleic_acid

http://en.wikipedia.org/wiki/Linoleic_acid

http://en.wikipedia.org/wiki/Gamma-linolenic_acid

http://en.wikipedia.org/wiki/Arachidic_acid


8

the period 2001–2006. Japan’s consumption is expected to decline30

. Recent data for the

Philippines listed a capacity of 25,000 t of alcohol products from coconut oil by the fatty acid

hydrogenation process for Cocochem and 4,000 t for Colgate. Philippians’ Kao produced

30,000 t of alcohol products from coconut oil using the methyl ester hydrogenation process31

.

In 2008, biodiesel production and capacity amounted globally to 11.1 and 32.6 MMT,

respectively32

. This is most remarkable because biodiesel as fatty acid methyl ester can also

be used as chemical feedstock. Moreover, genetic engineering offers a new way of

optimizing the properties of oleochemicals by controlling the FA distribution. This allows us

to change the composition of plant oils to control the structures that produce oleochemicals

with better properties. Thus the oleochemical industry is fairly well developed and its future

share of chemical industries, which currently stands at 10%, may go up because of a reliable

supply of raw materials.

1.1 C. Chemical modifications of vegetable oils for synthesis of oleochemicals

The physical and chemical properties of oils and fats can be modified through the use

of diverse derivatization pathways as shown in Fig. 1.2. In fact, chemical modifications of

vegetable oils constitute an important route to develop new efficient and environmentally

friendly reaction pathways leading to new products or to find new applications for already

existing oleochemicals33

.This strategy can contribute to decrease our dependence on non-

renewable, and therefore limited, natural resources such as mineral oil. For example, a high

degree of multiple C=C unsaturations in the fatty acid (FA) chain (mainly linoleic C18:2 and

linolenic C18:3 FA) of many vegetable oils (e.g. soybean/ linseed/ sunflower/ safflower etc.)

causes poor thermal and oxidative stability and confines their use as lubricants to a modest

range of temperature. The bis allylic protons in FA chain are highly susceptible to radical

attack and subsequently undergo oxidative degradation to form polar oxy compounds, which

ultimately results in insoluble deposit formation and an increase in oil acidity and viscosity34

.

Vegetable oils also show poor corrosion protection and the presence of ester functionality

renders these oils susceptible to hydrolytic breakdown. Although use of additives35

(antioxidants and pour point depressants) can overcome these shortcomings to some extent,

the major way to improve these properties of vegetable oils is chemical modifications of fatty

acid chains of triglycerides at the sites of double bonds and carboxyl groups.

Thus the chemical modifications through application of various unit processes, as

shown in Fig. 1.2, are essential for obtaining oleochemicals with multifunctionality,

improved oxidative, thermal and photostability and good low temperature properties for

explorations in chemical industries36,37

.


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Fig. 1.2 Oleochemicals derivatization pathways

Hydro

-genation

Sulfonation

Diols /

Polyols

Hydroxylation

Fatty alcohol

sulfates

Azealic /

Pelargonic acids

Sebacic acid /

Octanol

Hydrogenated

Castor oil

Turkey red oil

Splitting

FAME/

bio-

diesel

Ozonolysis

Alkali fusion

Amidation

Epoxidation

Ethoxylation / Propoxylation

Hydrogenation

Sulfation

Esterification

Transesterification

Fat

ty A

lcoh

ol

Chlorination

Ethoxylation

Propoxylation

Sulfation

Esterification Esters

α-Sulfo FA esters

FA

alkanolamides

Epoxidised

triglycerides

Alkoxylated

triglycerides

Fatty alcohol

alkoxylates

Alkyl chlorides

Guerbet alcohols Fatty alcohol

ether sulfates

Fatty alcohol

ether

phosphates

Fatty alcohol

sulfosuccinates

Phosph-

atization

Sulfitation

Sulfation

Guerbet

reaction

Esterification

Epoxidation

Ethoxylation

Polymerisation

Conjugation

Esterification

Fat

ty A

cid

s (F

A)

Self

Metathesis

Dibasic esters,

Hydrocarbons

Dimer acids

Saturated FA

Partial glycerides

Triacetin

Fatty Acid esters

Alkyl epoxy esters

FA ethoxylates

Conjugated FA

Glycerol

Hardening

Oil

s a

nd

Fa

ts


10

The exact FA composition of various plant oils (Table 1.1) gives indications of the

most likely transformations and the probable characteristics of the oleochemicals formed

after chemical modifications, which are required to improve the physicochemical and

performance characteristics of these derivatives. The main compositional difference is the

chain-length distribution of the fatty acids associated with the fats or oils. The chain length of

the feed stock, C12-C14 from lauric oils, C22 from high erucic rape and fish oils, and C16-C18

from most other sources, can be used to modify solubility, hydrophobicity and other

characteristics. The chemical modification of triglycerides is performed using the reactivity

of the functional groups in their structure. In respect of chemical modifications, oils and fats

carry following active chemical sites that can be used for derivatisation, functionalisation or

polymerization:

i) The terminal functional group mostly ester or carboxyl group- Traditionally,

industrial oleochemistry has concentrated predominantly on exploiting synthetic methods-

esterifications38

, transesterifications39

, hydrogenolysis, saponifications, acylation40

etc.

applied to the carboxylic group of FA to synthesize major industrial oleochemicals.

ii) Single or multiple double bonds- Chemical modification of seed oils at the

unsaturated bond sites results in changes to the physical properties of the substrate and allows

products to be tailored to meet specific applications. Currently less than 10% of the

modifications have involved the hydrocarbon backbone of the fatty acid41,42

.

iii) Carbon atom to the functional group- although the most reactive sites in fatty

acids are the carboxyl group and double bonds, methylenes adjacent to them are activated,

increasing their reactivity. Only rarely do saturated chains show reactivity.

iv) Secondary OH group- The presence of hydroxyl group on castor oil makes it vital

industrial raw material.

v) Other special functional groups- e.g. epoxy group in Vernolic acid present in oil

obtained from Euphorbia lagascae.

Carboxyl groups and unsaturated centers usually react independently, but when in

close proximity, both may react through neighboring group participation. The industrial

exploitation of oils and fats, both for food and oleochemical products, is based on chemical

modification of one of these five active sites. The continued development of oleochemistry

opens up for several reaction routes involving selective transformation of the alkyl chain, for

example sulfonation, with the potential of producing new highly-branched and charged

hydrophobes from abundant natural material43

. The transformations by reactions of the


11

carbon-carbon double bonds in the fatty acids such as epoxidation and epoxy ring-opening20

hydrogenation44

, hydroformylation, hydrocarboxylation, ozonolysis, estolides formation45

,

metathesis46

and dimerization, are becoming increasingly important industrially for the

improvement in the oxidative stability and attaining the optimal characteristics for extreme

applications47

. There is also scope for functionalizing the aliphatic chain, but this has not

been widely used commercially. Introducing functionality to the alkyl chain through radical,

electrophilic, nucleophilic, pericyclic, and transition metal catalyzed addition to carbon-

carbon double bonds leads to novel compounds with commercial potential. The chemical

transformation of triglycerides affords a wide variety of monomers for the synthesis of

linear45

, hyper-branched48

or cross-linked structures49

.

Subsequent sections present literature review on chemical modifications undertaken

in present investigations.

1.2 Sucrose esters

Although scientists have reported numerous ways of making surfactant linkages

(amphiphilic) for a large number of different carbohydrates used, it is clear from an industrial

perspective that only a few carbohydrates such as sucrose fulfil the criteria of price, quality,

and availability to be an interesting raw material source. Sucrose (C12H22O11) is one of the

most abundant, renewable and inexpensive international agricultural carbohydrate products in

the world, found in sugar cane, sugar beet and many other plants. It is produced at a very high

scale of production volume of 130 MMT per annum [The figure, estimated by Cerestar,

Henkel, is based on the crop cycle of 2002-03]. According to the revised estimate of ISMA

(Indian Sugar Mill Association), the annual production of sugar in 2012 at the end of

sugarcane season would be 24.3 MMT. The data indicates the abundant availability of sugar

as raw material for chemical industries. Chemical transformations of sucrose are much

developed in the fermentation domain, in order to produce alcohol, yeast, organic acids, etc.

Another strategy (sucrochemistry) is to keep the disaccharidic structure with the goal of

taking advantage of its physical properties (polarity, hydrophilicity, biodegradability, higher

compatibility with biological systems, low toxicity, skin-compatibility etc.) and bringing

them into a new molecule. In this respect, the targets are nonionic surfactants, eco-friendly

detergents, associative polymers, rheology modifiers, sweeteners, body builder, fat

substitutes, non digestible oligosaccharides etc50-52

.

Sucrose monoester (SE) is a green surfactant while sucrose polyester (SPE) is a low

calorie fat substitute, both being derived by transesterifying sucrose with edible oil/ fatty

acids or esters either by chemical or enzymatic processes. Development of the technique for


12

synthesis of sucrose esters was one of the first major achievements of the Sugar Research

Foundation53

.

1.2.1 Synthesis and characterization of sucrose esters

Considering the amphiphilic structure of a typical surfactant with a hydrophilic head

group and a hydrophobic tail, it has always been a challenge to attach a sucrose molecule as

the perfect hydrophilic group, due to the numerous (eight) hydroxyl groups, to a fat and oil

derivative such as fatty acid/ester/ alcohol54

. Sucrose is a disaccharide of α-glucose and

fructose. These two moieties are connected at their anomeric carbon atoms. It does not

contain a hemi-acetal linkage and so, it is a nonreducing sugar. Its chemistry is then limited to

its eight hydroxyl groups, of which three are primary (C1, C6’ and C6) and five are secondary,

which compete during the derivatization step with methyl esters of fatty acids derived from

edible fats and oils including hydrogenated fats and oils such as stearic acid, palmitic acid,

erucic acid and other fatty acids. The primary site for transesterification appears to be the 6th

position of the glucose portion of the molecule55

. The base catalyzed transesterification

reaction proceeds faster than its acid catalyzed counterpart56

.

Typically, the sucrose esters are prepared through the base catalyzed

transesterification of sucrose with vegetable oils/ fatty acid methyl esters, using sodium

methoxide or potassium carbonate or alkali metal soaps as a catalyst and in the presence of

suitable basic solvents such as dimethyl formamide (DMF), dimethyl sulfoxide (DMSO),

isobutanol, or methyl ethyl ketone57,58

(Fig. 1.3). Methanol is released as a by-product

through this reaction. Its removal by distillation during synthesis (semi-batch process) drives

the equilibrium in favor of the sucrose ester and improves the yield of the desired product.

Lithium soap, as catalyst, will shorten ester exchange time 2-3 hr relative to other method and

the yield of production is high. In general, mixed alkali metal soap (lithium oleate and

sodium oleate) with proper ratio as catalyst can improve the yield of sucrose ester59

. A

complex product mixture consisting of mono-, di-, tri, tetra-, and pentaesters is formed. The

reaction is stopped by the addition of lactic acid to neutralize the reaction mixture. Through

the choice of sucrose to fatty acid mole ratio, reaction time, speed of methanol removal, the

ratio of mo-, di-, and polyester can be influenced. It is difficult to obtain pure monoesters by

this route because they disproportionate to sucrose and diesters. Hence diester predominates

at lower reactant ratios60

(2:1). Co-proportionation of diesters with sucrose resulted in

monoesters which still contained 10% diester. By varying the degree of esterification of the

sucrose molecule it is possible to obtain emulsifiers with HLB values ranging from 1 up to 16


13

for the high SE content. SPE products (higher degree of substitution) are very hydrophobic

and of limited application potential.

O

OHOH

OH

O

OH

OHO

OH

OH

OH

O

OROR

OR

O

OR

ORO

OR

OR

OR

R'COOMe

MeOH

+

-

Sucrose Sucrose ester

R= R’CO, H R’= C12, C16, C18, C18:1

Fig. 1.3 Synthesis of sucrose esters by base catalysed (K2CO3) transesterification with

FAME.

The conventional base-catalyzed high temperature production of sucrose esters has a

low selectivity, forming coloured derivatives as side products61,62

. Several methods have been

developed to achieve higher selectivity in the reaction or provide economical purification

procedures and, as a result, a high quantity of hydrophilic monoester or hydrophobic

polyester. Increase in the monoester content was achieved in a sucrose laurate product by

alcoholysis with methanol63

. An alternate improved one-step process involves dissolving

sucrose ester in propylene glycol and emulsifying methyl esters into this solution followed by

thin film reactive distillation. The glycol is distilled off and in the distillation process,

transesterification takes place. It permits greater yields of the polyesters at 110-1450C within

5 hrs, eliminating use of toxic solvents and more efficient removal of byproducts64,65

. Procter

& Gamble holds two patents on synthesis of SPE66,67

during 2005-06. The direct esterification

of sucrose with fatty acid chlorides68

is reported. Powdered white granulated sugar and

methyl carbityl palmitate were reacted using different metal soaps as catalyst at 1850C

59.The

base-catalyzed synthesis of four sucrose fatty acid esters (caprylate, laurate, myristate, and

palmitate) was performed in DMSO by transesterification of sucrose with the corresponding

vinyl esters using disodium hydrogen phosphate as catalyst. In using a molar ratio sucrose/

vinyl ester 4:1 and mild reaction conditions (400C and atmospheric pressure), yields were

higher than 85%. The isolated sucroesters had a higher percentage of monoesters (around

90%) and a lower content of diesters in comparison with commercial derivatives. In all cases,

2-O-acylsucrose was the major product (around 60%) in the monoester fraction. For example,

72% yield of 2-O-lauroyl sucrose was obtained at 400C for 5 hrs with vinyl laurate as acyl

donor69

. The author holds patent for this improved procedure70

. A highly regioselective


14

conversion of sucrose into 6-O-acyl derivatives is reported. First sucrose was transformed

into the dibutyltin acetal, thus enhancing the nucleophilicity at the C6 oxygen and restricting

the subsequent acylation reaction71

. The enzyme-catalyzed synthesis of sugar esters provides

regio- and stereo selective products72-74

. Enzymatic sugar ester syntheses catalyzed by an

immobilized lipase were investigated, including the solubility, water content, molar ratio of

sugar/acyl donor, and enzyme stability75

. Enzymatic synthesis of fatty acid esters of di- and

tri-saccharides is limited by the fact that most biological catalysts are inactivated by the polar

solvents (e.g. DMSO, DMF) where these carbohydrates are soluble. To overcome this

limitation, the uses of mixtures of miscible solvents (e.g. DMSO and 2-methyl-2-butanol)

were proposed as a general strategy to acylate enzymatically hydrophilic substrates.

However, most of the above methods remain limited to laboratory scale because of

the process economics. Standard technology (conventional method, Fig. 1.3) for production

of SE/ SPE is still the transesterification combined with a series of purification steps to

remove impurities and residual solvents. The purification procedures include the use of

solvents, special extraction and crystallization techniques, and equilibrium reactions. The

sugar was precipitated from the reaction mixture by adding toluene, xylene, butanol or

isobutanol as a solvent. The solvent permits separation into a plurality of layers containing

sucrose esters of different degrees of substitution, which are recovered from the separate

layers. Mixing with water and freeze-drying the aqueous mixture may further refine the

separate layers. Reaction and extraction solvents and methanol are removed by the distillative

concentration/ purification processes. Vacuum may be applied to accomplish the distillation

at lower temperature. As a consequence of the manufacturing process, several trace

impurities may be found in the final purified products. An optimized solvent-free process

using water for removal of impurities and spray process for drying of product has been

described76

. Transesterification of sucrose in excess FAME (without additional solvent) at

about 1400C (around 20 hrs) and simultaneous removal of methanol to form sucrose esters

with a high degree of esterification (DE= 4), subsequent alcoholysis of the sucrose ester by

addition of methanol at 750C in two steps (step 1 transesterification: 45 min, step 2

transesterification: 75 min) to form sucrose monoester and FAME, and removal of residual

methanol and FAME using a thin-film evaporator (1600C, 0.2–0.3 mbar)

63 permit high yield

of sucrose monoesters. Product analysis by high-performance liquid chromatography shows

the increase of the sucrose monoester (SE) content to 48% (DE= 1.8, reaction A) and 57%

(DE= 1.6, reaction B) relative to sucrose diester and sucrose oligoesters (SPE). The Japanese


15

firm of Dai- Nippon has utilized large excess of sucrose and K2CO3 as a catalyst, for

manufacture at 900C under vacuum

77. Today, the major producers of sucrose esters are Dia-

Ichi Kogyo Seiyaku and Mitsubishi in Japan, Croda in the United States, Sisterna (a joint

venture of Dai-Ichi with Suiker Unie from The Netherlands), and Goldschmidt in Germany.

Thin layer chromatography (TLC) has been widely used as a preliminary qualitative

technique for the analysis of SE/ SPE to give an impression of the reaction. This technique is

considered as a rapid, advantageous and simple method for the preliminary investigation of

SE/ SPE synthesis. HPLC is an efficient tool for analyzing and quantifying SE/ SPE in a

reaction mixture. This technique is more convenient than gas chromatography as it does not

require previous derivatization of the sample. Many procedures for SE/ SPE separation with

HPLC were reported with the different eluent systems.

1.2.2 Reaction mechanism and kinetics of synthesis of sucrose esters

The transesterification reaction mechanism78

of base catalyzed synthesis of sucrose

esters is shown in Fig. 1.4 which proceeds by a two stage transesterification process.

nCH3

O

OCH3 + Sugar-O

nCH3 OCH3

O-

OSugar

nCH3

O

OSugar + CH3 O

-

nCH3 OCH3

O-

OSugar

Sugar OH + Base Sugar O-

+ Base H+

Fig. 1.4 Reaction mechanism of base catalyzed transesterification between sugar

polyols and FAME78

Potassium soaps provide a homogeneous melt of sucrose and fatty acid methyl esters.

Initially, the base reacts with the alcohol, producing an alkoxide and the protonated catalyst.

The alkoxide then attacks the carbonyl group of the fatty acid methyl ester. This nucleophilic

attack generates a tetrahedral intermediate. The alkyl ester and the anion of the fatty acid are

then formed. The anion deprotonates the catalyst and generates an active species which reacts

with a molecule of the alcohol, starting another catalytic cycle.

The rate constants, activation energies, Arrhenius factor and mechanism of inhibition

for base catalyzed hydrolysis of sucrose laurate, sucrose sulphenyl laurate and sucrose ethyl

laurate were investigated at several temperatures in pH 11 buffer. At 270C sucrose laurate


16

hydrolyzed fastest and sucrose ethyl laurate slowest79

. A kinetic model for the synthesis of

the sucrose esters without solvent is developed. It implies a solid/solid/liquid reaction

between sucrose (solid) and methyl palmitate (liquid). The second solid (potassium

carbonate) acts as a catalyst. The reaction medium is heterogeneous and pasty. The viscosity

increases with the chemical reaction extent. Activation step of sucrose (solid) by potassium

carbonate (solid) is taken into account which corresponds to the overcrossing of the

interfacial barrier and the contact between the two solids and is associated to the viscosity of

the medium. The second important parameter is molar ratio, which takes into account the

hydrophobic effect during the formation of diesters80

. The literature describes several

molecular models of heterogeneous kinetics, for example:

• Park and Levenspiel model81

: it represents conversion versus time with S shape

curves.

• Hao-Tanaka model82

: it describes the reaction between two solids and takes into

account the number of contact points between the particles.

• The shrinking core model and the uniform conversion model83

.

1.2.3 Properties and applications of sucrose esters

Sucrose esters (SE/ SPE) occur as white to yellow-brown powdery or massive

substances, or as colourless to red-brown, viscous resinous or liquid substances. Sucrose

monolaurate forms clear, low viscous aqueous solutions at 30% strength while those of C16-

C18 fatty acids forms gels. SPEs, however, are completely water insoluble. They are stable at

pH 4 to 8 and at temperatures up to 1800C. Sucrose monooleate, however, decomposes at

1200C. The physical and chemical properties, including the lipophilic character, of the

sucrose esters vary depending on (i) the alkyl chain length of acyl group, (ii) the degree of

substitution or number of hydroxyl groups replaced by ester groups in the compound, (iii) the

degree of unsaturation of the acyl chain.

i) SE as non-ionic surfactant

Sucrose ester with three or lesser fatty acids is suitable as surfactants and food

additives because of their emulsifying, stabilizing, and conditioning properties84,85

. The

amphiphilic behavior of sucrose based surfactants result from the hydrophilic free hydroxyl

groups and hydrophobic alkyl chain. The uses of surfactants are determined by the particular

functionality with respect to their solubility in oil and water which can be expressed and

quantified as their hydrophilic-lipophilic balance or HLB value. Wide range of HLB values

ranging from zero to twenty, are obtained by changing the characteristics of the fatty acid

used in their preparation86

. Unlike the alkyl ethoxylates, the sucrose esters do not


17

significantly change their HLB with increasing temperature. Consequently, increasing the

temperature does not induce a phase inversion in micro emulsion systems based on sucrose

esters, as was observed in micro emulsions based on alkyl ethoxylate87

. The properties of

sucrose esters can range from water soluble surfactants (high HLB, most hydrophilic) to oil

soluble surfactants (low HLB, most hydrophobic) as shown in Table 1.2. HLB values of

some pure SE is as given below88

: sucrose monostearate(C18)-11.2, sucrose

monopalmitate(C16)-11.8, sucrose monomyristate(C14)-12.4. Thus with decrease in chain

length from C18 to C14, the hydrophilicity of SE increases. The softening temperature and

surface tension of 1% solution of sucrose monolaurate were 90-910C and 33.4 dynes/cm.

respectively89

. The CMC (mol/lit) of 6-O-lauroyl sucrose and 6-O-myristyl sucrose at 300C

were found to be 5.14-5.31 X 10-4

and 0.71-0.88 X 10-4

, respectively. These CMC values are

lower than those of ethoxylates71

. Thus SE of fatty acids having 12 or more carbon atoms (at

low degree of substitution, preferably monoester) are expected to display surface active

properties. Long chain SE have shown promise as surfactant and compare well in foaming,

wetting, emulsification and overall detergency performance with other surface-active

compounds and for some applications even superior58,90

. They are not sensitive to hard water,

and some of the SEs are moderate foaming agents91

. Mixtures of regioisomers, as well as

mono-, di- and triesters are used as emulsifiers, whose resulting physicochemical properties

depend on the average degree of substitution and fatty acid chain length.

Table 1.2 Approximation of HLB values of surfactants as a function of their solubility in

water 92

Solubility in water HLB Values* Description

Insoluble 4-5 Water in oil emulsifier

Poorly dispersible 6-9 Wetting agent

Translucent to clear 10-12 Detergent

Very soluble 13-18 Oil in water emulsifier

*HLB = (L/T) x 20 (L and T referred to the molecular weight of the hydrophilic (sucrose) part of the

molecule and the total molecular weight, respectively)

Sucrose esters have a wide variety of applications. SE has excellent non ionic

surfactant and emulsifier properties that are desirable and promising in food, personal care,

detergent, bleaching booster, cosmetic, fine chemical, oral-care and medical applications93-97

.

Besides this, they have received considerable attention due to their recent availability in

commercial quantities, together with their tasteless, odourless, nontoxic, biocompatible,

biodegradable and noncumulative characters98,99

. SEs were approved in 1959 for use as food


18

additives in Japan90

. They are mild toward the skin and eye and possess lower hemolytic

activity than many other types of surfactants. However, depending on the nature of the

hydrophobic moiety, some sugar-based surfactants possess rather high haemolytic activity.

Sucrose esters have been studied for effective preservation of the quality of fresh produce100

.

Phosphorylated sucrose stearate showed a higher solubility and better emulsifying properties

than sucrose stearate and improved the thermal behaviour of potato starch by increasing the

gelatinization temperature, decreasing the viscosity and inhibiting retrogradation101

.

Fatty acid esters of mono- and di-saccharides, produced commercially by Mitsubishi-

Kagaku (Tokyo, Japan) and Sisterna PV (Roosendaal, Netherlands), are effective emulsifiers

found in a variety of food, cosmetic, and pharmaceutical products such as chocolate,

toothpaste, lotions, shampoo, and lipstick87,102,103

. They possess excellent antimicrobial

activity as well104

. Some possible applications for sucrose based polymers are drug delivery

systems, dental medicine, bioimplants, contact lenses, and tissue engineering105,106

. The most

common pharmaceutical application of SE is for the modification of bioavailability, often

with the hot-melt method. Use of SE as surfactants in the development of microparticulate

systems for parenteral delivery of protein and gene medicines was investigated107

.

SE has shown remarkable use as surfactant in stabilized synthesis of nanoparticles.

Huang108

synthesised indium sulfide nanorods in water-in-oil (w/o) microemulsion system

using food grade SE as biosurfactant. Titanium dioxide nanoparticles were prepared via

hydrothermal processing route, which utilized SE as a stabilizing agent109

.

Sucrose esters are more soluble in t-pentanol than glucose esters. Dimethyl sulfoxide

provides good solvency, especially in the case of glucose and sucrose monoesters110

. Sucrose

esters display significant activity against several clinical isolates. They have increasing

interest due to advantages with regard to the performance, the consumer health and the

environmental compatibility compared to petrol-derived standard products62

. They have

antibacterial properties and can also be used as lubricants97

. SE also shares a number of

insecticidal properties with other surfactant111

. SEs composed of C6-C12 fatty acids have

desirable insecticidal properties against many soft-bodied arthropod pests112

. Sucrose esters

are currently used as additives in the food industry which makes them especially attractive as

safe and effective insecticides. The combination of particular characteristics such as

emulsifying, anti-adhesive (inhibition and disruption of biofilms formed in food contact

surfaces) and antimicrobial activities presented by sucrose esters suggests potential

application as multipurpose ingredients or additives113

.


19

ii) Sucrose polyesters (SPE) as fat substitute

SPE has physical and organoleptic properties similar to those of cooking and frying

fats and are digested as a blend of sucrose and fatty acids in the stomach93

. Olestra, a non-

caloric fat substitute, is a SPE with moderate to high degree of substitution (six or more fatty

acids per sucrose molecule) and has been developed by Proctor and Gambel in the early

1970s and marketed under the brand name Olean114

. It has been approved by the FDA as a

food additive used in preparing low-fat deep-frying foods such as savoury snacks. These

compounds are lipophilic, nondigestible and nonabsorbable molecules with physical and

chemical properties similar to those of triglycerides, but it is not digestible by lipolytic

enzymes.

1.3 Epoxidation of vegetable oils and fatty acids

Epoxidation is the reaction (Fig. 1.5) between double bonds in olefinic compounds

(unsaturated fatty acid, alkyl ester, or oil) and organic peroxy acid [RC(=O)OOH, oxygen

transfer reagent] to obtain (three-membered) cyclic ethers called epoxides. The reaction is

catalysed by homogeneous catalysts such as H2SO4, p-toluene sulfonic acid115

, heterogeneous

catalysts such as transition metals of variable valence, acidic ion exchange resin116

or

enzymes117

. The peracid is either preformed or prepared in situ by equilibrium reaction (Fig.

1.5) between hydrogen peroxide (preferably high strength e.g. 70% w/w) and carboxylic acid

[formic or acetic acid or other acids]/ corresponding anhydride or acid chloride. The

carboxylic acid is regenerated after epoxidation which proceeds by a concerted mechanism,

giving cis stereospecific addition

118 (Fig. 1.6). Thus, a cis olefin leads to a cis epoxide and a

trans olefin to a trans epoxide. For example, epoxidation of oleic acid generates cis-9, 10-

epoxy stearic acid, while that of linoleic acid gives a mixture of two cis, cis diastereoisomeric

bis- epoxides. The carboxylic acid produced is a stronger acid than the strongly hydrogen

bonded peracid and may lead to subsequent ring opening reactions especially in the case of

formic acid producing dihydroxy and hydroxy carboxylates as byproducts. Hence complete

epoxidation is never achieved in the acidic medium.

RCOOH + H2O2

H+

R

O

O OH

+ OH2

+CH3

CH3

CH3

CH3

RCOOH +CH3

CH3

CH3

CH3

O

R

O

O OH

Fig. 1.5 In situ peracid epoxidation reaction


20

+O

ROO

H

CH3CH3

CH3CH3

O

CH3CH3

CH3CH3

+O R

OH

Fig. 1.6 Mechanism of peracid epoxidation118

1.3.1 The performic/ peracetic epoxidation process

The industrial scale epoxidation process, referred as “Prileschajew reaction”, is most

frequently carried out with preformed or in situ generated peroxyacetic acid or peroxyformic

acid due to their low cost (particularly the peracetic acid process) and easy availability119,120

.

Moreover epoxidation with peracids is irreversible (if the acid does not contain

admixtures). On the other hand, problems related to this method are associated with the

strongly exothermic character of this reaction and the risk of explosion resulting from the

necessity of operations with concentrated solutions of peracids. These problems imply the

necessity for strict control of temperature and reaction time. The in situ generation of

peracids is mostly preferred because, when the organic peroxyacid is preformed, there are

some safety issues associated with its storage since the concentrated peroxyacid is unstable

and explosive121,122

. Moreover the in situ process operates with a lower concentration of

aliphatic acids. On the other hand, the presence of an acid during in situ epoxidation causes

the opening of the oxirane ring with formation of undesirable secondary products. In ex situ

process, the acid is eliminated from preformed peracid by neutralizing it with a buffer or

filtering. With preformed peroxyacetic acid, the conversions, yields and selectivity were

higher than those with the in situ formed peroxyacetic acid.

The rate of generation of peroxyformic acid is much greater than that of peracetic

acids. Formation of peroxyacetic acid requires an acidic catalyst such as sulfuric acid123

.

Between the in situ-generated performic and peroxyacetic acid, latter has certain advantages

such as need of minimum amounts of reactants in the preparation of epoxidizing reagent and

convenience and safety of preparation, handling and stability of peroxyacetic acid at

moderate temperatures124

. Patwardhan et al125

worked on the epoxidation of cottonseed oil

using in situ generated peracetic/ performic acid catalysed by liquid inorganic acid. While the

rate of formation of oxirane was higher with formic acid, acetic acid was more effective

oxygen carrier, promoting the transport of the oxygen from the aqueous phase to the oil

phase126

. It also functions as a catalyst in the formation of the oxirane ring127

. H2SO4 was

found to be the most efficient and effective catalyst. But being strong acid, it leads to many

side reactions such as oxirane-ring opening to diols, hydroxyesters, estolides and other dimer


21

formations. Furthermore it causes the equipment corrosion and must be neutralized and

removed from the end product128

. Ikhuoria et al129

observed that the in situ peracetic acid

epoxidation of the methyl esters of parkia biglobosa seed oil could be carried out in a

moderate temperature range of 50-700C. Peracetic acid resulted in a 10% higher conversion

of double bonds to oxirane116

and caused the lower amount of undesirable products formed

over that by performic acid. An explanation for this is that due to the very high activity of the

formic acid, the hydrogen peroxide is rapidly decomposed leaving the batch oxygen

depleted37

. Cationic ion-exchange resins are versatile heterogeneous catalysts and offer

several advantages over the homogeneous acid catalysts. Use of acidic ion exchange resin

catalysts would reduce corrosion problem, avoid disposal of strong acids, and present better

product recovery. The catalyst can be recycled, shows better selectivity, and avoids side

reactions130

. However the rate of resin catalysed epoxidation slows down in comparison to

that of homogeneous epoxidation. The heterogeneous method seems to be tedious due to the

difficulty of separating the product from the resin.

1.3.2 Other techniques of epoxidation

A cheap and green epoxidiser would be molecular O2. But when used in the

epoxidation of vegetable oil, it leads to the degradation of the oil to low molecular weight

volatile compounds such as aldehydes and ketones as well as short chain dicarboxylic

acids131

. Organic peroxy acids, other than peroxyformic or peroxyacetic acids, may be more

convenient in the laboratory or for small-scale reactions. These include the peroxy acids

derived from trifluoroacetic, lauric, benzoic, m-chlorobenzoic acids, and m-nitrobenzoic acid.

Monoperoxy acids derived from succinic, maleic, and phthalic anhydrides can also be used.

The order of reactivity of some peracids is: m-chloroperbenzoic > performic > perbenzoic >

peracetic; electron withdrawing groups promote the reaction. Some of these can be safely

stored at 0-200C to avoid hazards of its decomposition. Small scale reactions are carried out

with m-chloroperbenzoic acid in a halocarbon or aromatic solvent, in the presence of

bicarbonate to neutralize the carboxylic acid as it is formed132

.

Recent studies have attempted enzymatic procedures to improve the efficiency of

epoxidation under milder conditions that minimize the formation of byproducts. Chemo-

enzymatic epoxidation133

uses the immobilized lipase from Candida antartica (Novozym

435) to catalyze conversion of fatty acids to peracids with 60% hydrogen peroxide. The fatty

acid is then self-epoxidized in an intermolecular reaction. The lipase is remarkably stable

under the reaction conditions and can be recovered and reused 15 times without loss of

activity. Competitive lipolysis of triacylglycerols is inhibited by small amounts of fatty acid,


22

allowing the reaction to be carried out on intact oils134

. Rapeseed oil with 5% of rapeseed

fatty acids was epoxidised in 91% yield with no hydroxy byproducts. Sunflower, soybean,

and linseed oils have been satisfactorily epoxidised by this route using 35% hydrogen

peroxide with 5 mol% of free fatty acid134

and in a batch stirred tank reactor at atmospheric

pressure135

. Corn oil rich in oleic and linoleic acids, was also epoxidized in a similar manner

but using stearic acid as an active oxygen carrier136

. Methyl esters are also epoxidized

without hydrolysis under these conditions.

Epoxidation is also feasible with dimethyl dioxirane (DMDO), made from potassium

peroxymonosulfate (KHSO5) and acetone. The most common of inorganic peroxides is nitrile

hydrogen peroxide, which catalysed by a transition metal catalyst131

. Halohydrines, using

hypohalous acids (HOX) and their salts as reagents, are also used for the epoxidation of

olefins with electron deficient double bonds. But the process is not ecofriendly.

Different novel approaches to epoxidation have recently been reviewed137,138

.

Compounds of second-row transition metals- rhodium and ruthenium and the oxides of

rhenium and tungsten have attracted particular interest as catalysts to affect the epoxidation

of olefins, some with excellent regio-, stereo- and enantio- selectivities. Silver, however,

produces very low rates of double bond conversion and is also only effective on very simple

ethylenic substances. Methyltrioxorhenium (MTO, MeReO3) or tungstates catalyses direct

epoxidation by hydrogen peroxide. MTO reacts with hydrogen peroxide to give

organorhenium peroxo complexes. The reaction is carried out in presence of large excess of

nitrogenous bases, particularly pyridine under biphasic conditions, avoiding acidic conditions

detrimental to high epoxide yield and uses less concentrated hydrogen peroxide (30%) than

other methods139

.This method epoxidized soybean140

and metathesized soybean oil in high

yield141

with higher product selectivity and catalyst lifetime. The epoxidized metathesized oil

was more stable to polymerization than that produced using m-chloroperbenzoic acid,

presumably because it was free of acidic impurities. Hyeon et al142

fabricated molybdenum

oxide nanoparticles incorporated into a mesoporous silica shell that are coated on dense

silica-coated magnetite nanoparticles and demonstrate a magnetically recyclable epoxidation

catalyst. Alumina catalysed sol-gel process was evaluated for the epoxidation of unsaturated

fatty esters using anhydrous or aqueous hydrogen peroxide as oxidant and ethyl acetate as

solvent. The alumina shows a good catalytic activity and excellent selectivity towards the

epoxides. The sol-gel alumina was more efficient and when using aqueous hydrogen

peroxide, it could be recycled several times143

. None of these methods have yet found

feasibility at industrial scale.


23

1.3.3 Influence of reaction parameters on extent of epoxidation and kinetic and

thermodynamic modelling of epoxidation

Epoxidation is a consecutive reaction and its success depends on the control of

available conditions for minimisation of opening the rings. The rate of performic acid

production, for ex situ process, is at least 4 X 104 faster than the rate of epoxidation

144. This

means that whenever a performic acid molecule reacts, another performic acid molecule is

generated before any further epoxidation occurs. On the other hand, peracids are unstable,

and the reaction is exothermic. The concentration of peracid is therefore kept low by using a

low concentration of the carboxylic acid either in the neat oil or in a hydrocarbon solvent.

Industrial epoxidation is conducted in two-phase polar (aqueous H2O2)-organic (oil plus

solvent) systems. The presence of an inert solvent (e.g. xylene, toluene) in the reaction

mixture appeared to stabilize the epoxidation product and minimize the side reaction such as

the opening of the oxirane ring, especially at higher temperatures145

. It is important to

minimize the presence of protons originating from either the acid or the catalyst and work at

low temperatures. Ring opening cannot be totally avoided, but proper control may be attained

by working at low temperatures, say 20-350C. The progress of the epoxidation reaction, as

measured by the changes of the hydroxyl value, iodine number and epoxy number, is used to

estimate the fractional conversion, yield, and the selectivity of transformation to epoxidized

oil/ fatty acids/ ester. The structures of the products are confirmed by thin layer

chromatography (TLC), fourier transform infrared spectroscopy (FTIR), and nuclear

magnetic resonance (NMR) analysis.

The influence of the several reaction parameters such as temperature, hydrogen

peroxide: peracid: vegetable oil molar ratio, type of peracid, type and loading of catalyst,

stirring speed and reaction period on epoxidation rate as well as the oxirane ring stability for

the in situ inorganic acid catalysed (homogeneously catalysed) peroxyacid epoxidation of

rapeseed oil146

, mahua oil131

(Madhumica indica), cottonseed oil125

, soybean oil and jatropa

oil147

were examined. Elevation of the temperature from 30 to 600C caused a decrease of the

iodine number, while the value of the epoxy number rapidly decreased above 600C for the

formation of epoxidised rapeseed oil. Increasing temperature showed a favorable effect on

the formation of peracetic acid during the epoxidation of mahua oil. Acetic acid was found to

be superior to formic acid for the in situ cottonseed oil epoxidation. In general, with an

increase in hydrogen peroxide-to-ethylenic unsaturation molar ratio, there was a progressive

increase in the rate of oxirane formation. However, the correlation between decrease in the

final iodine value and the corresponding increase in the final oxirane value were relatively


24

less when the ratio was increased beyond particular magnitude, specific to individual oils.

This may be attributed to the higher hydrogen peroxide concentration leading to an

accelerated rate of oxirane ring decomposition. To attain the maximum oxirane oxygen

content in peroxyacetic acid epoxidation, the optimum level of the acetic acid should be used

where both the effects (catalytic effect counteracting hydrolysis) are balanced considering the

amount of acid required in the formation of peracetic acid. The maximum reaction conversion

was 83.3% for the epoxidation of soybean oil and 87.4% for the epoxidation of jatropha oil. It

was possible to obtain up to 78% relative conversion to oxirane with very less oxirane

cleavage by in situ sulfuric acid catalysed epoxidation of cottonseed oil. The order of

effectiveness of catalysts was found to be sulfuric acid > phosphoric acid > nitric acid >

hydrochloric acid. For a two-phase epoxidation reaction mixture, different solubility of

peracid in the organic phase can have a large effect on the kinetics. Thus to safely avoid mass

and heat transfer effects, a stirring speed of higher order feasible with the given system

should be chosen. Okieimen et al121

have shown that the negligible oxirane cleavage and

almost complete epoxidation of rubber seed oil by in situ peroxyacetic acid process could be

achieved.

In a similar manner, the effect of different reaction variables on heterogeneous in situ

cationic exchange resin- Amberlite IR-120 catalysed peracid epoxidation of soybean oil148

,

jatropha oil124

and castor oil149

was evaluated. With an acidic ion exchange resin as the

catalyst for the epoxidation of vegetable oils, the porous structure of the solid catalyst and the

size of the natural unsaturated triglycerides were found to minimize side reactions and thus

improve selectivity150

. At lower temperatures (30, 50 and 700C), peroxyformic acid was

found to be more efficient, while at higher temperature (850C), peroxyacetic acid was equally

good and an optimum in the ion exchange resin catalyst reactivity was observed at 700C for

the formation of epoxidised jatropha oil. The extent of the side reaction is negligible with

peracetic acid in the entire temperature range and somewhat higher with performic acid at

850C for epoxidation of castor oil. The optimal conditions (91% conversion, 5.99% epoxide

content in product) for peracetic epoxidation of soybean oil were found to be: 0.5 mole of

glacial acetic acid and 1.1 mole of hydrogen peroxide (30%) per mole of ethylenic

unsaturation, 750C, 8 hrs, 5 wt% of the resin catalyst

148.

The rate law that holds for epoxidation of all oils and FAME is shown in Eq. 1.1:

d[DB]r = = k [DB] [PFA] Eq. 1.1

dt


25

Where r is the rate of disappearance of carbon-carbon double bonds, [DB] is the

concentration of double bonds, [PA] is the concentration of peracid and k is the second-order

rate constant. For ex situ and sometimes for in situ process, the epoxidation reaction can be

assumed to be pseudo-zero order in peracid concentration because the rate of formation of

peracid is much faster than the rate epoxidation. The epoxidation and ring opening for in situ

epoxidation of anchovy oil with partially preformed peracetic acid in the presence of a resin

catalyst151

were described, by applying the principle of the stationary state, by a pseudo first-

order reaction. Two studies of the kinetics of the in situ epoxidation of oleic acid with

hydrogen peroxide and acetic acid and of methyl esters of palmolein by performic and

peracetic acid, both carried out in the presence of sulfuric acid as a catalyst, concluded that

the rate-determining step of the epoxidation process was the formation of peracetic (or

performic) acid145,152

. Rangarajan et al120

reported kinetic parameters for the in situ

epoxidation of soybean oil by peracetic acid, again in the presence of sulfuric acid as the

catalyst, but treated it as a two-phase system. Significantly higher rates were obtained in

kinetically controlled regimes. Jankovic et al153

proposed the mathematical model that

describes the kinetics of reaction systems for the in situ epoxidation of unsaturated fatty acid

esters or triglycerides with organic peracids. Kinetic studies of epoxidation of soybean oil

with peroxoacetic acid and peroxoformic acid have been reported and found to be pseudo-

first order with respect to both double bonds as well as peroxy acid37

.

The magnitude of rate constants (kepo) in cm3mol

-1s

-1 and the energy of activation

(Ea) in Kcal/mol for conc. sulfuric acid catalysed preformed (ex situ) peracetic epoxidation of

undecylenic acid, methyl undecylenate, and ethyl undecylenate undecylenic acid over 25-

350C were found to be- 0.06-0.09 and 20.78, 0.096-0.12 and 6.95 and 0.046-0.11 and 15.34,

respectively130

. The apparent activation energy using Arrhenius relationship, for the in situ

formation of epoxidised jatropha oil was found to be 53.6 kJ/mol124

which compared well

with the corresponding value of 48.6 kJ/mol, as obtained by154

for a similar acidic ion

exchange resin catalysed epoxidation of a vegetable oil. The epoxidation of castor oil with

performic and peracetic acid generated in situ in presence of cation exchange resin

(Amberlite IR-120) was found to be first order with respect to the conversion of ethylenic

unsaturation. The rate constants for the epoxidation with peracetic acid were 0.067, 0.184,

0.55, and 1.12 (hr-1

) at 300C, 50

0C, 70

0C and 85

0C, respectively, while those for the

performic acid were 0.125, 0.287, 0.645, and 0.981 (hr-1

). Activation energies of the peracetic

acid and performic acid epoxidation were found to be 48.2 kJ/mol and 35.4 kJ/mol,

respectively149

. The kinetic modelling of Novozym 435 catalysed epoxidation of oleic acid


26

based on ternary complex mechanism was reported155

. Following kinetic parameters were

deduced at 300C: Vmax= maximum epoxidation velocity=2.229 X 10

5-3.614 X 10

5

(mmol/L/min/g enzyme) and KiA= dissociation constant for enzyme-oleic acid complex

59.986- 65.618 (mmol/L/g enzyme). At low temperatures, the rate of epoxidation was faster

than the rate of deactivation of the enzyme by hydrogen peroxide.

Table 1.3 provides the kinetic constants (kepo and Ea) and thermodynamic parameters

[enthalpy of activation-ΔH, average entropy of activation- ΔS, and free energy of activation-

ΔG ] reported by different investigators for sulphuric acid catalysed peracetic acid in situ

epoxidation of different oils/ esters. These thermodynamic data show that the epoxidation is

a non-spontaneous process.

In Eq. 1.1, if triglyceride structure is going to have any effect on epoxidation reaction

kinetics, the only parameter that can be affected is the rate constant implying likely influence

of the FA composition on the value of the rate constant. The rate constants of noncatalysed,

ex situ epoxidation were determined by reacting preformed formic acid with a number of oils

(cottonseed/ corn/ olive/ soybean oil etc.) model triglycerides (triolein, trilinolein) and model

fatty acid methyl esters (FAME)144

. In triglycerides, the double bonds of oleic acid and

linoleic acid were equally reactive, and the double bonds of linolenic acid were

approximately three times more reactive than oleic and linoleic acids. For FAME, the rate

constants of epoxidation increased as the level of unsaturations increased. Furthermore, the

rate constants of epoxidation for the FAME were higher than their respective triglycerides.

These results showed that the FA composition had a significant effect on the value of the

epoxidation rate constant and were interpreted on the basis of the steric and electronic effects

on epoxidation kinetics. The double bonds further from the glycerol center are more reactive

than double bonds near the glycerol center and double bonds on different FA have different

reactivities. Steric factors inherent in the triglycerides structure reduce the reactivity of the

unsaturated sites in comparison to the same site on FAME. As the number of double bonds

increases, the electron density increases, this causes an increase in the rate constant for

epoxidation of linolenic acid. These results were used to derive a model that predicts the

epoxidation kinetics of oils from their FA composition. The relative rates of epoxidation for

oleic, linoleic and linolenic acids are 1.0, 1.0 and 1.7, respectively. The triacylglycerols are

slightly more reactive than the acids with values of 1.9, 3.0 and 4.9, respectively11

.

Twelve epoxidised oil derivatives based on rubber seed oil, Madhuca oil (Mee oil)

and Neem oil and their hydrolysed products were prepared by optimised conditions on a

comparatively large scale without solvent extraction procedures. It was found that more than


27

80% of the reaction was completed within three hours at 600C. The level of epoxidation could

be controlled reasonably by limiting the reagents. The solubility parameter values calculated

from the molar attraction constant values G, using Small’s equation, were comparable with

those of conventional plasticizers used in the PVC industry156

.

Table 1.3 Kinetic and thermodynamic parameters for sulphuric acid catalysed peracetic

acid in situ epoxidation of different oils/ esters

Oil/ esters

Kinetic constants Thermodynamic parameters Literature

reference kepo,

L mol-1

s-1

Ea ΔH ΔS ΔG

Cotton

seed oil

0.39-5.42

X 10-6

(temp. range

30–750C)

11.7

kcal/mol

11.0

kcal/mol

-51.4 cal

mol-1

K-1

28.1

kcal/mol 125

mahua oil

0.2-6.8

X 10-6

(temp. range

30–850C)

14.5

kcal/mol

13.8

kcal/mol

-51.1 cal

mol-1

K-1

30.6

kcal/mol 131

methyl esters

of parkia

biglobossa

seed oil

3-5 X 10-7

(temp. range

50-700C)

51.963

kJ/mol

13.8

kJ/mol

-3.55 kJ

mol-1

K-1

1.51

kJ/mol 129

1.3.4 Ring opening and synthesis of multifunctional derivatives

A lot of trifunctional compounds (introduction of hydroxyamines, hydroxynitriles,

diols, etheralcohols, hydroxyalkylamides etc. in FA or triglycerides) are the result of splitting

of oxirane ring by nucleophilic compounds (secondary amines, hydrogen cyanide, water,

alcohols, amides etc.). Applications for these interesting oleochemicals have not yet been

fully investigated.

The three-step synthesis of several diesters from commercially available oleic acid

and common fatty acids was reported157

. The key step of ring opening of epoxidized oleic

acid with different fatty acids (octanoic, nonanoic, lauric, myristic, palmatic, stearic and

behenic acids) was achieved using p-toluenesulphonic acid (PTSA) as catalyst. The

esterification reaction of these compounds with octanol was further carried out in the

presence of H2SO4 giving diester compounds. This study described a systematic approach to

improve the low temperature pour property of oleic acid derivatives. Salimon et al24

also

reported the oxirane ring opening of epoxidized oleic acid using behenic acid and PTSA as

catalyst followed by esterification with octanol and 2-ethylhexanol to form diesters for


28

industrial biolubricant applications. Moser158

also reported the preparation of branched chain

ethers from oleic acid in a three-step synthesis. Esterification of oleic acid was followed by

the epoxidation of double bond and then a ring-opening step by an alcohol (alkyl: propyl,

isopropyl, octyl, 2-ethylhexyl) using propionic and octanoic acid medium without the need

for either solvent or catalyst.

O

O

O

O

O

O

CH3

O

CH3

O O

O O

CH3

O

O

O

O

O

O

CH3

CH3

CH3

OHOROR OH

OR OH

OR OH OH OR

ROH, H2SO4 1200C, 3Hrs

Fig 1.7 Ring opening of epoxidised oils

For the production of lubricants from vegetable oils, the oils are first epoxidized, and

then the oxirane ring is opened with either acetic acid or a low chain aliphatic alcohol like

methanol or ethanol159

. Epoxidized oils were ring opened by a one-pot, one-step process by

using a predetermined amount of allyl alcohol mixed with tetrafluoroboric acid catalyst.

Allylic double bonds were successfully incorporated into triglycerides of epoxidized oils

through a ring-opening nucleophilic addition reaction of allyl alcohol. The reaction is facile

with high conversion under mild conditions160

. The epoxidation of natural oils and

subsequent ring opening with acrylic acid has been well studied161

. Acrylation kinetic model

that predicts rate constants from fatty acid distributions in the oil were established144

. Thus,

the rate constant of acrylation increased as the number of epoxides per fatty acid decreased.

Multiple epoxides per fatty acid decrease the reactivity of the epoxides because of steric

hindrance effects and the oxonium ion, formed as an intermediate during the epoxy-acrylic

acid reaction, is stabilized by local epoxide groups.

Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by boron

trifluoride diethyl etherate (BF3.OEt2) in methylene chloride was conducted in an effort to

develop useful biodegradable polymers162

. Epoxidized diethanolamides were synthesized by

reacting diethanolamine (DEA) with mixture of epoxidized palmolein (40% w/w) and refined


29

bleached deodorized palmkernel olein (60% w/w) at 1:3 molar at 800C for 5 hrs and

continued at 1100C for another 4 hrs of reaction time. Synthesized diethanolamides with high

content of epoxides were reacted with isocyanate in the presence of AlCl3-THF complex

catalyst to produce oxazolidone linkages in polyurethane network. The rigid polyurethane

foam produced is of better quality as compared to the commercially available foam163

.

The kinetic study on the oxirane cleavage of palmolein methyl ester164

has been

reported. The first degradation reaction is first order with respect to the epoxide concentration

and second order with respect to the solvated acetic acid126

[kAA(700C) = 4.27 ± 0.12×10

-5

l2mol

-2min

-1; EaAA = 12.9 ± 0.64 kcal mol

-1]. The degradation increases notoriously the lower

the pH of the reacting media is; the increase is directly proportional to the concentration of

protons, as is usually found in homogeneous catalysis (for very low pH, the reaction is almost

instantaneous). Likewise, the degradation reaction with peracetic acid is first order with

respect to the epoxide [kPAA(700C) = 4.31 ± 10

-4 l

2 mol

-2 min

-1; EaPAA = 10.6 ± 0.38 kcalmol

-1]

and it also increases linearly with proton concentration. Although the specific attack on the

ring by the peracid is almost 10 fold harsher, acetic acid is constantly being regenerated

during the industrial process, so that its concentration is always far larger than that of

peracetic acid. Thus, under process conditions the degradation of the oxirane ring is mostly

caused by the carboxylic acid. A systematic investigation of the impact of the various

consecutive reactions of oxirane ring-opening on the yield of the epoxidised soybean oil was

carried.

1.3.5 Applications of epoxidised oils and fatty acids

Oils, mainly soybean and linseed, are epoxidized on an industrial scale (0.2 MMT per

year) for utilization as stabilizers and plasticizers for PVC polymers11

. Epoxidised oils are

also used as plasticizer in the production of packing materials such as wrapping foils.

Plasticizer is an additive for plastic formulations to enhance their plastic workability and

flexibility and is generally produced from petroleum derivatives such as phthalate

compounds. The plasticizing efficiency of epoxidised oils is equivalent to that of dioctyl

phthalate. Besides this, epoxidised oils also improve UV light and heat stability of PVC

plastic due to the presence of the oxirane rings36,45,165,166

. The typical stabilization action for

PVC167

is derived from the fact that the reactive epoxide groups scavenge hydrogen chloride

produced by the degradation of the PVC polymer168,169

, interrupt the formation of polyene

sequences in the polymer170

and retard the apparition of discoloration171

. They are generally

regarded as secondary stabilizers used to enhance the effectiveness of metal soaps. The

marked effect on the thermal stabilization of PVC by epoxidised oils requires the synergistic


30

presence of metallic soaps172,173

. The esterification and etherification reactions which occur

with allylic chlorine groups in PVC provide an explanation for the synergism observed in the

stabilization of PVC containing a combination of an epoxy compound with metal soap168,171

.

Epoxidized oils transesterified with low-molecular weight alcohols are also used as

plasticizers of polyvinyl chloride174-176

. In particular, methyl esters of epoxidized soybean oil

represent a renewable substrate that is readily converted into surfactants, fuel additives, and

other industrial products177

.

A significant lubricant market of some nine million metric tons per year of industrial

and automotive lubricants exists and there has been a constant demand for environmentally

friendly or green lubricants. As lubricants, vegetable oils possess superior lubricity, good

anticorrosive properties, better viscosity-temperature characteristics and low evaporation loss

which are important in industrial applications such as rolling, cutting, drawing, quenching

operations, and greases159,178

. Their low volatility and narrow range of viscosity changes with

temperature are due to the high molecular weight of the triglyceride molecule. Polar ester

groups in vegetable oils are able to adhere to metal surfaces and, therefore, possess good

boundary lubrication properties. In addition, vegetable oils have high solubilizing power for

polar contaminants and additive molecules. From the environmental point of view, their

importance is evident especially in areas of total loss lubrication, military applications, and in

outdoor activities such as forestry, mining, railroads, dredging, fishing and agriculture

hydraulic systems. In spite of these facts, vegetable oils currently provide only a fraction of

the lubricant market due to the poor stability and low temperature properties. For the

production of lubricants from vegetable oils with improved oxidation stability and pour point

characteristics, the oils are first epoxidized, and then the oxirane ring is opened with either

acetic acid or a low chain aliphatic alcohol like methanol or ethanol159

followed by the

reaction of the epoxide function with linear and branched-chain alcohols. Epoxy esters144

, due

to the overall good lubrication characteristics, are being actively investigated as biolubricants.

Salimon et al24

reported the oxirane ring opening of epoxidized oleic acid using behenic acid

and p-toluenesulfonic acid as catalyst followed by esterification reaction with octanol and 2-

ethylhexanol to form diesters for biolubricant industrial applications. Epoxidized soybean oil

functionalized with diamine is an excellent antioxidant and lubricant, and has been proven as

an antifriction agent. Because of its amphiphilic character it is added to base grease oils to

improve their application properties179

. Activity of epoxidised oils is essentially related to the

amount of oxirane oxygen, but the plasticization, lubrication and cost parameters play a role

in their selection and use.


31

Due to the high reactivity of the oxirane ring in epoxidized oils, they are used as

renewable raw materials for manufacturing such intermediate products as alcohols, glycols,

alcoxyalcohols, hydroxyesters, N-hydroxyalkylamides, mercaptoalcohols, hydroxynitriles,

alkanolamines, and carbonyl compounds131,180

. Thus, epoxidised oils/ fatty acid derivatives

are used as intermediates for a large number of commodities such as agricultural and

pharmaceutical molecules, flavors and fragrances, surfactants, adhesives, sealants181-184

. With

sodium iodide and an appropriate solvent, epoxy esters are converted to keto esters

(RCOCH2R’ and RCH2COR’). Natural vernolic acid (12, 13-epoxyoleic acid) is being

examined as an antirust additive (as its C4-C6 amides) and as a source of dibasic acids and of

high-value products such as the pheromone bombykol (CH3(CH2)2CH=CH CH=CH(CH2)8

CH2OH) and the plant wound hormone traumatic acid (HOOC(CH2)8CH=CHCOOH).

Limonene epoxide has traditionally been used as a precursor for the synthesis of perfumes,

drugs, and food additives185

.

Petrochemical based resins such as epoxy, polyester and vinyl ester find more

engineering applications because of their advantageous material properties such as high

stiffness and strength. However these resins have serious drawbacks in terms of

biodegradability, initial processing cost, energy consumption and health hazards. Renewable

epoxy esters can be used as diluents in paints and so replace volatile organic solvents.

Reaction of epoxidised oils or fatty acids with acrylic acid (CH2=CHCOOH) gives an

acrylate which can be cured by exposure to UV photoinitiated free radical or cationic

polymerization186-188

. Polyhydroxy compounds produced by reaction of epoxides with diols

and triols (glycerol) serve as a source of polyurethanes through reaction with isocyanates155

.

Green nanocomposite coatings with excellent film properties and good biodegradability have

been obtained with epoxidised soybean and linseed oil and γ-glycidoxypropyl

trimethoxysilane189

.

1.4 Synthesis and characterization of dimer acids

One finds number of patents on polymers based on vegetable oils190

as number of

different dimers and oligomers are produced from fatty acids and alcohols. The term dimer

acid191-195

is applied to the branched-chain acyclic or cyclic dicarboxylic acids (predominantly

the C36) formed by the thermal (260-4000C) or catalytic (acid activated clay or other cationic

catalysts) polymerization reactions of two or more C18 unsaturated fatty acids or monohydric

esters of semi-drying oils such as tall oil, sunflower, soybean and rapeseed oils or drying oils

such as dehydrated castor oil. Typical manufacturing conditions196

are: 4% montmorillonite

clay catalyst at 2300C for 4-8 hours under steam pressure. Dimerization is usually carried out


32

in the presence of a little water (1-2%) to prevent decarboxylation at high temperature. The

extent of reaction was determined by measuring changes in refractive index, molecular

weight and acid values of the dimerized oil samples. After the desired reaction is complete,

the mixture is cooled, a metal complexing agent, usually phosphoric acid, is added and the

crude product is filtered. The product is a complex mixture of acyclic, cyclic, and bicyclic C36

dimer acids as the main product (Fig. 1.8), apart from some C54 tricarboxylic trimer acids and

higher condensed polymer acids as well as unreacted and structurally modified (e.g. isostearic

acid) monocarboxylic acids42

. The monomers are recovered as overhead product by vacuum

distillation. The separation from trimer and higher homologs is achieved by molecular

distillation or wiped film evaporator.

CH3

OH

O

CH3 OH

O

CH3

OH

O

4% Montmorillonite clay

2300C, 4-8 hrs

Fig. 1.8 Dimerization of polyunsaturated fatty acid

Other catalysts investigated for this reaction include peroxides197

, hydrofluoric acid198

and sulphonic ion exchange resin199

. The reaction also has been investigated under corona

discharge200

. Catalysis by super acids has received considerable attention in recent years201-

205. The sulphate-treated zirconia super acid catalyst has high chemical stability, and being a

solid does not pose any corrosion problems. Dimerization of fatty acids derived from

dehydrated castor oil and safflower oil was carried out on the sulphate-treated zirconia

catalyst and trifluoromethane sulphonic acid (triflic acid) under autogeneous pressure in the

temperature range of 160-2400C. Triflic acid was observed to be highly active; however, the

product obtained was deeply colored. Zirconia exhibited high activity for the reaction. The

important features of this catalyst were the lower cost in comparison to triflic acid, the high

selectivity for dimer (low yields of trimer) and no significant coloration of the products206

.

Anyaogu et al207

as well as Boot and Speek208

have reported the optimum condition for the

polymerization of soybean oil to include 3500C, 0.0025% iodine catalyst and a reaction time

of 20 min under inert atmosphere. None of these methods has succeeded commercially.

The diversification of the sources of precursors for the production of dimer acids will

reduce the pressure on the regular oils which are already in use in many domestic and

industrial applications. The physical properties of dimer are affected by the raw materials

used in the manufacture, reaction conditions and content of monomer, dimer and trimer.


33

These branched dibasic compounds possess significantly lower melting points than straight

chain structures of similar molecular weight. All the dimer acids are liquid at 250C, even

though their molecular weight is about 560. This phenomenon can be attributed to the

presence of large number of isomers which tend to lower the melting point. Dimer and trimer

acids as well as monomer acids derived from dimer acid processing are neither flammable

nor combustible. Fully saturated dimers have excellent oxidative stability. This and their

extended liquid range are exploited in their use as lubricants and cosmetic additives. Dibasic

dimer acids react with polyamines to give reactive polyamides as epoxy curing agents in the

formulation of anticorrosive coatings and nonreactive polyamides for utilization in printing

inks hot melt adhesives and petroleum exploration operations with outstanding chemical,

physical and mechanical properties209

. Imidazole derivatives are used as corrosion inhibitors

and esters as lubricants. Dimer acids also find wide applications as source of polybasic acids

for the synthesis of polyester and polyamidoamines. Isostearic acids, byproduct in dimer

production, are important intermediates in the production of biodegradable lubricants,

emollients, and hydraulic fluids. The scope and potential of the zeolite-catalyzed synthesis of

isostearic acids starting from oleic acid is examined210

.

1.5 Alkali fusion of castor oils

The broad and versatile use of castor oil is because of its unique structure and comes

from its main component, ricinoleic acid (12-hydroxy-9-cis-octadecenoic acid), which

represents 90% of the vegetable triglycerides. This triglyceride has three chemical groups

subject to modifications: hydroxyl (C12), C-C double bond (C9), and acid carbonyl, giving a

variety of derivatives217

. The hydroxyl group at 12th

position is so reactive that the molecule

can be split at that point by high-temperature pyrolysis and by caustic fusion to yield useful

products of shorter chain length. Sebacic acid (1,8-octane-dicarboxylic acid or decanedioic

acid), a linear saturated C10 dicarboxylic acid, is manufactured by heating castor oil to high

temperatures (about 2500C) with alkali. This treatment results in saponification of the castor

oil to sodium ricinoleate that is then cleaved to give capryl alcohol (2-octanol) and sebacic

acid (Fig. 1.9).

Although the sebacic acid yields by above route are low, the route has been found to

be cost competitive and used commercially by Union Camp in Dover, Ohio and by Hokoku

Oil Company, Japan196

for mass production of sebacic acid in either a batch or continuous

process. The castor oil or ricinoleic acid and caustic are fed to a reactor at a temperature of

180-2700C, where the ricinoleic acid undergoes the series of reaction with evolution of

hydrogen to give disodium sebacate and capryl alcohol. When the reaction is complete, the


34

soaps are dissolved in water and acidified to a pH of about 6. At this pH, the soaps of

monobasic acids are converted to free acids that are insoluble in water. The disodium

sebacate is the only partially neutralised to the half acid salt, which is water soluble. The oil

and aqueous layers are separated. The aqueous layer containing the half salt is acidulated to a

pH of about 2, causing the resulting sebacic acid to precipitate from the solution. It is then

filtered, water washed, and finally dried. 2-Octanol, 2-octanone, and sebacic acid were

determined by GC and GC/MS analysis, and purity of sebacic acid was further assessed by its

acid value (444) and melting point (1340C). The crystals of sebacic acids are monoclinic

leaflets (ρ-1.231). It is only slightly soluble in water even at 1100C. It is soluble in alcohol

and ether but nearly insoluble in benzene.

Castor oil + 3 NaOH 3 Sodium Ricinoleate + Glycerol

Sodium Ricinoleate

NaOH,180-2500C

(CH2)8

O

ONa

O

NaO + CH3 (CH2)5 CH(OH) CH3

CH3 (CH2)5CH(OH) CH2 CH CH(CH2)7C

O

ONa

Disodium Sebacate Capryl alcohol

Fig. 1.9 Alkali fusion of castor oil

The mechanism for the conversion of ricinoleic acid to sebacic acid218

is shown Fig.

1.10. The first step is the dehydrogenation of ricinoleic acid to a β, γ-keto acid, followed by

isomerisation of double bond to give α, β-unsaturated keto acid intermediate in the presence

of alkali. At elevated temperature, this intermediate should undergo a retro- aldol type of

reaction to give a saturated ketone and a ω-aldehydo acid in the presence of water. The

methyl hexyl ketone takes hydrogen from the first step of dehydrogenation for reduction to

form 2-octanol. On the other hand, two possible reactions may take place with the aldehyde

of decanoic acid. One reaction is a reversible reaction of hydrogenation (the hydrogen being

made available from the first step of dehydrogenation) to form 10-hydroxy decanoic acid,

while in the presence of strong alkali at elevated temperature, the ω-aldehydo acid would

undergo an irreversible oxidation to yield sebacic acid. Since only one mole of hydrogen is

available in situ after dehydrogenation of ricinoleic acid and the same is likely to get

distributed for the subsequent hydrogenation of methyl hexyl ketone and aldehyde of

decanoic acid, the presence of suitable catalyst, which may work as oxygen donor, favours

the oxidation reaction of aldehyde of decanoic acid. Longer reaction period (such as 13 hrs),


35

lower temperature range (458-463 K) and use of 1 mol of sodium or potassium hydroxide per

ricinoleate promote formation of 10-hydroxydecanoic acid. Using 2 mol of alkali per 1 mol

of ricinoleate at 513-549 K and with a shorter reaction cycle produces sebacic acid. Hydrogen

was also formed with excess alkali219

.

A number of process improvements have been described and include the use of white

mineral oil having a boiling range of 300-4000C or the use of mixture of cresols

220. These

materials act to reduce the reaction mixture’s viscosity and thus improve mixing. The

normally expected theoretical yields of 2-octanol and sebacic acid from alkali pyrolysis of

castor oil containing 84% ricinoleic acid are 35.7 and 43.6%, respectively. Higher sebacic

acid yields are claimed by the use of catalysts such as barium salts221

, cadmium salts222

, lead

oxide and salts223

, sodium nitrate224

and zinc oxide225

. The presence of barium is to provide a

process which enables the recovery of sebacic acid without neutralisation of fusion bath. The

role of adjuncts in enhancing the yields of the desired products is, however, not very explicit

in the literature. Alkali pyrolysis at 280 ± 20C for 5 hrs using an overall ratio of alkali to

diluent (white mineral oil) of about 8:27 and 1% red lead catalyst in a cylindrical reactor

yielded 70.1% 2-octanol and 72.5% sebacic acid on the basis of their respective theoretical

yields226

. The oxygen donating effect of Pb3O4 may play an important role in increasing the

yield of sebacic acid by oxidation of aldehyde of decanoic acid and suppressing the other

forward reaction of hydrogenation of the aldehyde of decanoic acid to form 10-hydroxy

decanoic acid.

Heating and driving chemical reactions by microwave energy has been an

increasingly popular theme in the scientific community227

. Azcan et al 228

studied the effect of

microwave irradiation on alkali fusion of castor oil using different NaOH/oil ratios (8:15,

12:15, and 14:15), reaction temperatures (473, 493, 503, 513, and 523 K), and reaction times

(15, 20, 25, and 30 min) in the presence of 1% Pb3O4 catalyst. Maximum yields of

oleochemicals were obtained using methylated then presaponified castor oil (sodium

ricinoleate), 14/15::NaOH/oil ratio at temperature 513 K and 20 min reaction time.

Sebacic acid finds applications as monomeric and polymeric plasticizers for PVC,

dioctyl sebacate for jet engine lubricants and air-cooled combustion engines and polymer

intermediates for 6,10 nylons, polyesters and polyurethanes used in adhesives, coatings,

fibers, inks and resins. It is also used as a mineral floatation agent and for producing

emulsifiers, defoaming and anti-bubbling agents. 2-Octanol (capryl alcohol) is used in

plasticizers in the form of dicapryl esters of various dibasic acids229

.


36

CH3 CH2 CH

OH

CH2 CH CH CH2 COO-

5 7

Dehydrogenation

CH3 CH2 C

O

CH2 CH CH CH2 COO-

5 7

Isomerisation

5

CH3 CH2 C

O

CH CH CH2 COO-

8

Retro - Aldol fission

5

CH3 CH2 C

O

CH3OHC CH2 COOH+

(2 - Octanone) C -10 Aldehydo acid

5

CH3 CH2 CH

OH

CH3

2 - Octanol

8

CH2 CH2 COOHOH

8

HOOC CH2 COOH

8

Sebacic acid10 - Hydroxydecanoic acid

Fig. 1.10 Mechanism of alkali fusion of castor oil218

Background of present investigations

Structurally, fatty acids and esters closely resemble materials (petroleum

hydrocarbons) already recognized and understood by the current chemical industry based on

nonrenewable feedstock. Raw material familiarity will be an important component in

transitioning the industry from nonrenewables to renewables, and general technology and

equipment/ plant design present in the chemical industry today can be easily adapted/

retrofitted to the production of oleochemicals. Epoxidation of olefins present the glaring

example of this transition. Current research efforts in oleochemicals have focused only on

biodiesel as an area of investigation which is simply one of many products that are derived


37

from the oleochemical unit operations. The state of the art in chemical modification of fatty

acids/oils focuses almost entirely on simple, incremental changes at the COOH group of the

molecule. Shifting the focus from a single product to the much broader oleochemical

platform, as stated under initial para of introduction, is absolutely necessary on the way to the

sustainable and economical usage of lipids as renewable feedstock for organic chemical

industries. For example, application of mature technologies well known to the chemical

industry could lead to some of their traditional building blocks when applied to low value

mixed fatty acids. This research work will detail important R&D opportunities for

development of different chemical modification technologies for fatty acid/oil conversions.

A key barrier to the oleochemical unit operation is acceptance of a new form of raw

material by the chemical industry. The hydrocarbon nature of fatty acids and esters, with

appropriate development of new technology, can serve as an important transitional raw

material as the chemical industry evolves from nonrenewable to renewable raw materials.

However, use of crude oil still dominates the industry, while oleochemistry remains a

specialty sidelight. This situation, as is the case with any commodity technology, could

change radically upon introduction of new conversion technology for the raw materials and a

realization of their potential by the chemical industry. Demonstration of that potential and

addressing the important barriers in utilization of oils and fats are the objectives of present

investigations.

The broad range of vegetable oil sources lead to diverse fatty acid structures. These

structural units can be used to introduce new functionality that can be translated into

marketplace properties. The major vegetable oil sources in the U. S. are soybean and

cottonseed while those for European Union are rapeseed and sunflower oil. The economics of

Malaysia is governed by palm and palmkernel oil. India is the largest producer of groundnut

oil, castor oil and many native nontraditional oils. Developing of new or optimization of

technologies for the invention of next generation products are feasible in the most promising

growth areas such as surfactants, lubricants, additives and polymers. Improved products and

technology, exhibiting properties deemed of value, will allow capture of a greater proportion

of these markets by renewable oils and fats. Research efforts in the areas of transformations

related to the COOH group, in present work, is mainly concentrated on process optimization

and modeling studies in synthesis of sucrose ester. From a research viewpoint, a great

opportunity exists to develop cost effective and efficient technology for the selective

structural modification of fatty acid side chains. The chemical transformations in

hydrocarbon chain of fatty acids have the additional advantage of being able to draw on the


38

broad knowledge possessed by the petrochemical industry. Thus it is essential to explore the

breadths of the catalytic processes (alkali fusion in present work) available and examine their

feasibility. In a similar manner, the examination of unsaturated oils and their transformations

(epoxidation, ring opening, Dimerization in present work), which may fulfill the interests of

the oleochemical industry, was undertaken.

1. Surfactants and specialty chemicals: An area of potential opportunity is in the production

of sucrose ester. These are surfactants based entirely on renewables as starting materials, and

are the result of the reaction between a carbohydrate (sucrose) and a fatty acid methyl ester/

oil to give an amphiphilic molecule possessing a polar sugar based head group and a long

nonpolar oleochemical tail. The research challenge in producing these materials arises in

developing technology suitable for the selective reaction of a fatty acid at a single site of the

carbohydrate molecule without the requirement of a complex series of protection/

deprotection sequences. While there are currently commercial products based on this

technology, the materials are mixtures of mono, di, and triesters, which limit their utility to

particular applications. Given that the performance of these materials will be based on their

structure, process optimization for selective transesterification and modeling studies based on

the concepts of Reaction Engineering were the objectives of research investigations.

2. Polymers and coating: Another very large potential market for consumption of fatty acid

derivatives is the polymer market. Use of oleochemicals, particularly diacids, as polymer

components is known but its share of the otal polymer market is very small. The portion of

the polymer market is dominated (87%) by materials such as adipic or terephthalic acid,

while use of oleochemically derived diacids accounts for only 0.5% of the total. Displacing

the commodity acids will be difficult; however, the use of oleochemical diacids offers access

to an interesting suite of properties including elasticity, flexibility, impact strength, hydrolytic

stability, hydrophobicity, lower Tg, and flexibility42

. In present research, synthesis of diacids

such as sebacic acid by catalytic alkali fusion of castor oil and dimer acids by catalytic

thermal polymerisation of polyunsaturated oils and fatty acids/ esters have been carried.

3. Additives and lubricants: The market opportunity exists in the production of

biolubricants from oleochemicals. Petrochemically derived lubricants possess an

environmental problem in that they are often released during their use, for example, in

various engines, metal working, chain saws, etc. Epoxidation of the double bonds in fatty

acids is an area of current interest, as oil epoxides have utility as additives for PVC. Mustard

oil has been epoxidized and ring opening studies have been carried to obtain biolubricants.


39

The kinetic and thermodynamic studies on epoxidation and ring opening reactions and

comparative engineering evaluations of different reactor options were also focused.

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