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Lipids
Anna Drew
with grateful acknowledgement for inspirational teaching received at
The School of Pharmacy, University of London
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LIPIDS
Simple: fixed oils, fats, waxes
Complex: phosphatides, lecithins may contain P, N as well as C, H, O
widely distributed in plant and animal kingdom in all living cells
sometimes accumulate to be commercially useful plants - food reserve (fruit and seeds)
animals insulation, energy sources, protection
Lipids or fatty esters are an important group long chain fatty acid + alcohols eg glycerol
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Fixed oils & fats
Esters of glycerol:
3 fatty acids may be involved => triglyceride (main
component of oils and fats)
some may exist as free acids
[Fish oils may have 12 fatty acids which vary]
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Simple triglyceride (triacylglycerol)
all fatty acid groups the same
Mixed triglyceride
fatty acid groups different
more usual in nature
-> yields 3
molecules of
palmatic acid
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Saturated or unsaturated:
unsaturated acids: oleic, linoleic, linolenic, palmitolinic
saturated acids: palmitic, myristic, stearic
Fatty acid content determines properties
large amount of saturated -> solid at room temp.
large amount of unsaturated -> liquid at room temp.
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most vegetable products contain a high number of
triglycerides with unsaturated fatty acids liquid
most animal products opposite
where large number of unsaturated fatty acids readily
oxidizes
eg whale, fish oils, linseed
Expect a good (fixed) oil to be:
odourless, tastleless and non-volatile
soluble in a lipid solvent
fairly readily air-oxidized -> rancid oil (depending on
degree of saturation)
leave a permanent grease stain on filter paper
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Determination of structure
by hydrolysis or saponification in 2 ways:
i) Alkaline hydrolysis with KOH splits triacylglycerol into parent glycerol and releases all
fatty acids
arrangement of fatty acids is unknown ii) Can use an enzyme (pancreatic lipase)
hydrolyses two outer glycerides
and then remove final group with KOH
Detecting fatty acids
GLC not volatile so have to form a methyletherand separate them by chain length
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Chemical tests
solubility
freezing point, melting point
refractive index (and sometimes optical rotation)
density
volatile acidity, unsaponifiable matter, acetyl value
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Waxes
contain appreciable quantities of esters derived from higher monohydric alcohols (one OH
group) of the methyl (1y) alcohol series
combined with fatty acids (C16 C32)
most are solids at room temperature can only be saponified by alcoholic alkali
often contain free acids, hydrocarbons, free alcohols and sterols
saponification and acid values higher, iodine values lower
commercially important examples Vegetable: carnuba
Animal: spermaceti, beeswax, wool fat
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Uses
readily absorbed through skin ointments
protect from entry of water eg cod liver oil, linseed oil
vehicles for injections
waxes in enteric coatings
pharmacological substances vitamin A and D in cod liver oil
food source eg peanut oil
may contain essential fatty acids (linoleic acid, arachidonic acidrequired in prostaglandin formation)
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Olive oil
salad oil, sweet oil
From ripe fruits ofOleo europoea(Oleaceae)
Mediterranean, California native of Palestine, known in Egypt in 7th
century B.C., introduced into Spain early on
pale yellow with greenish tinge
(chlorophyll and carotene)
bland, slight odour, goes pasty/cloudy at10oC
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tested for absence of arachis oil, cotton-seed oil, sesameoil, peanut oil and tea-seed oil (Camellia sasanqua)
Composition:
high iodine value, low acid value
Uses salad oil, soaps, plasters
manufacture of parenteral preparations (low acid value, free ofwater)
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Arachis oil
From seeds ofArachis hypogaea (Leguminosae) -groundnut
cultivated in tropical Africa, India, Brazil, southern USA
and Australia worlds 4th largest source of a fixed oil
seeds contain 40-50% oil
fruits shelled by a machine kernels difficult to express; crushed and cooked at low
pressure
seed cake fed to cattle
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Composition:
oleic acid ~ 60%
linoleic acid 24%
palmitic acid 9%
arachidonic acid
GU3, GSU2 like olive oil
acid and saponification values similar to olive oil
if fatty acids are separated (hydrolysis) the
presence of arachidonic acid gives a meltingpoint >710C used as a test for adulteration of olive oil
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Castor oil
From seeds ofRicinus communis (Euphorbiaceae)
India, Africa, Europe
Contains ricinoleic acid 91%, glycerides GU3 must be free of ricin
pale yellow, very viscous, acrid tasting
soluble in ethanol (unlike most oils) due to so much
hydroxy- acid
Used in toothpaste, nail varnish remover, lubricantindustry and pharmacy (as derivatives)
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Almond oil
From Prunus amygdalus v. amara (bitter used inpharmacy), v. dulcis (sweet)
native to Far East, grown in Mediterranean, N.California
Oil is highly unsaturated with oleic acid 77%, linoleic acid 17%
83% GU 3, 17% GSU2
Bitter almond oil also contains amygdalin (glycoside)
which decomposes to benazldehyde + HCN
Used in pharmacy in oily injections and ointments prone to oxidation so has to be kept air-free or goes rancid
transfer to smaller bottle to exclude air
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Theobroma oil
Cocoa butter
From seeds ofTheobroma cacao (Sterculaceaea)
Central America, also cultivated in Brazil,W
.Africa(Nigeria)
Solid oil
high steric and palmitic acid content (35%, 25%), oleic acid 3%
GS2U 52% melting point 31-350C
low iodine value because saturated
most expensive commercial fixed oil (adulterated)
Mainly used in suppositories
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Animal products
Cod and Halibut liver oils
mixed triglycerides, mainly unsaturated C16-22 acidsand decahexanoic acid
Used for Vitamin A and D content (halibut > cod)
Beeswax
yellow and white from honeycomb
simple esters of 1y alcohols with a high degree ofmyricyl palmitate (80%) (C15H31OOC30H61)
ester:acid ratio value 3.3-4.2
Used in paraffin ointment, plasters and enteric coating
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Carnuba wax
an adulterate of beeswax From the cuticle of the South American palmCopenicia cerifera
Used in tablet coatings
Spermaceti
From the head of sperm (Physeter macrocephalus)and bottle-nosed whales (Hyperodon rostratus) justabove right nostril) 500lb from 1 whale
simple esters of cetyl alcohol CH3(CH2)4CH2OH cetyl palmitate, cetyl myistate 90-93%
no longer used pharmaceutically, can be replaced byjojoba oil
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Wool fat
From the wool of sheep (Ovis aries) Complex composition:
esters of cholesteryl and isocholesteryl + estolidic32-33%
esters of normal aliphatic alcohols with fatty acids48-49%
Used as an emollient base for creams andointments
major component of most ointments melting point 30-42oC
readily absorbed through skin
absorbs twice its own weight in water so makes anemulsion
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Extraction
enzymes in cells can break down oils in
cells
some oils highly unsaturated and easilyoxidized heat in air > rapid oxidation
[1] Cold expression[2] Steam treatment + expression
[3] Solvent extraction
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[1] Cold method
Castor beans
roll to break down testa
winnow to separate seed coat from seed
Olives
put into press
light pressure applied
gives the 1st
grade oil used in pharmacy oil washed to remove pigment
floats to the top and is skimmed off
30-40% oil recovered not economical
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[2] Steam treatment + expression
material left over from [1] undergoes steamtreatment repressed to get 2nd fraction of oil
[3] Solvent extraction
to get 100% of oil out
last portion gives a low grade used to industrial paintsetc
left with high protein+fibre fed to animals once ricinremoved
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Cocoa seeds
fat is solid so cant cold express
use hot expression with steam treatment oil is a byproduct of the cocoa industry
Cod liver and halibut
livers heated by steam process in an inertatmosphere
mixture separated by centrifugation
oil dried in drying towers
gives a clear bright highly refined oil
cooled to 0oC to remove saturated stearic fats leaves polyunsaturated triglycerides
standardised for vitamin content
stored in airtight containers in the dark
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Spermacetin
ensure well separated from normal triglycerides
washed with alkali
W
ool fat has to be cleaned up
acidified to precipitate waxes
free fatty acids removed by forming salts
wax extracted with acetate
product can be bleached to give light yellow colour or
left as dark yellow wax
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Volatile oils
different from fixed
components of plants that are highly odiferous
generally occur as they are
secreted in oil cells in specialised structures ducts, cavities, glandular hairs
frequently associated with other substances
gums, resins (resinify on exposure to air)
mainly terpenoid some phenol ethers and phenols
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Terpenoids
based on the 5C isoprene unit
Monoterpenes
most important, most volatile
di-, tri-, sesquiterpenes also important
contain 2 condensed 5C units head-tail most formed from geranyl pyrophosphate
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Monoterpene components
Hydrocarbons
Alcohols
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Aldehydes
all produced via the terpenoid pathway
Ketones
Citral
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Esters
Oxides
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Sesquiterpenes (C15)
Hydrocarbons Phenols Phenolic
esters
Anethole
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Chemical and physical properties
volatile liquids with no colour keep in amber bottles with minimum air
odour
asymetric centres, isomers with optical activity only one isomer occurs naturally
refractive index normally high is a means to characterise the oil
miscible in water and soluble in organic solvents
more soluble if contains OH fatty acids reasonably heat stable
can be steam distilled
tend to be used as solvents for resins
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Families
Economically only a few family groups arecommercially useful
[1] Labiatae
Lavender, Mentha Sp. large number, tend to hybridise
oil occurs in special organs synthesized in glandular trichomes (mint)
burst easily releasing oil
[2] UmbelliferaeFruits (best if ripe): anise, caraway, fennel, coriander
found in vittae in the outer layer is characteristic
steam distill to remove oils
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[3] PinaceaePine, juniper
found in resin ducts in outer old xylem or bark
released when bark removed
[4] RutaceaeCitrus fruits
typical ductless sacs in outer part of fruit rind
found at various depths before albino layer (white bitter pithypart)
oil is there under pressure and will burst open when rasped
less stable, need more care
[5] LauraceaeCinnamon, camphor
from region immediately below bark
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Method of extraction
depends where oils lies and its stability
Steam distillation gentle, herb + water heated and oil distilled over
Water distillation wood chips in chamber and heated until water distills over
crushed sample must be stable
Cold expression citrus fruit oil (lemon, orange, bergamot)
rasping process breaks oil sacs in rind
pour cold water over and then separate oil and water
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Enfleurage petals (rose) placed between glass sheets covered in sheep or
pig fat
oil seeps into fat and can be extracted with methanol
Destructive distillation produces a different product from the one started with
pine and juniper heated to exclude air over aqueous part - wood naphtha (ethanol and crude acetic acid) to
attract juniper oil
non-aqueous part resin (pine tar) to attract C5-C20 moleculesincluding monoterpenes
like a fractional distillation
Menthol and camphor nearly solid at room temperature can isolate by freezing oils out
cheaper to synthesize camphor but generally extracted fromplants
camphor
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Usesas inhalations, orally, gargles, mouthwashes, trans-dermally
[1] Flavours & carminatives
Labiatae
Mentha piperita (peppermint oil) 50-75% menthol, also contains menthone etc
used mainly in toothpastes
Mentha spicata (spearmint oil) 50-75% L-carvone
some minor components similar to peppermint but major
components differ giving different smell and taste Lavendura officinalis (lavender oil)
35-45% linalyl acetate, also geraniol, limonene, cineole
some varieties have a lower % so other compoundcharacteristics dominate
growing environment will affect quality
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Rutaceae
Citrus oils D-limonene 90%, citral 4% + esters, pinene, d-limonene (small
amount) high proportion of limonene desirable
but a lot is removed after isolation by distillation underreduced pressure
leaves oil high in citral which deteriorates on storage givinga turpentine odour
Citrus flower oils no citral, other constituents that give a different odour and
flavour of orange flower oil
used in confectionary
Umbelliferae
Pimpinella anisum (anise), Foeniculum vulgare (fennel) 90% anethole
some fennel variaties contain fenchone giving a bitter taste
Carum carvi(carraway) carvone
Coriandum sativum (coriander)
60-80% linalool
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[2] Local stimulants and antiseptics
(containing phenols)
Pinaceae
Pinus paulastrus
destructive distillation
phenol p-cresol
Juniperus oxycedrus cadenine
Clove Syzygium aromaticum
eugenol 82% used on sore teeth to deaden pain
Eucalyptus oil 1,8-cineole 70%
(sesquiterpene)
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[3] Perfumes
Rose oil
R
osa gallica,R
. damescena trans-geraneol
and isomer cis-nerol
Lavender oil
Citrus oil
[4] Insect repellant, antimating device
Citronella oil
from grass
doesnt work well
[5] Starting materials
Turpentine
(for synthesis of other compounds)