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1 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
ENVIRONMENTALLY BENIGN AND
CATALYTIC PROCESSES LABORATORY
PRACTICE
Production of Raw Materials for the Chemical
Industry by Homogeneous Catalytic Hydrogenation
and Catalytic Transfer Hydrogenation Reactions
BME, Department of Chemical and Environmental Process
Engineering
Budapest
2018
2 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
Introduction
Our excessively wasteful and environmentally damaging lifestyle is highly depended on
products of chemical industry. One of the main aims of chemistry is to create such new and
effective technologies, which have less negative impact on the environment. Gamma-
valerolactone (GVL) was considered as a promising renewable platform chemical, which can
easily be produced from avaiable biomass-based feedstocks including waste stream reducing
the excluding edible carbohydrates- without unethically producing chemical raw materials from
foodstuff. Due to its advantageous physical and chemical properties, it can be equally applied
as an organic platform molecule, solvent, octane booster, fuel additive etc..
Primarily solar-, wind-, hydro- and geothermal energy are used as renewable energy
sources. We need to pay extra attention to the biomass based energy production,i because
carbohydrates, the most common organic compounds on Earth, are regenerated from carbon
dioxide and water by solar energy, can be utilized as a renewable raw material even in large
scale.ii There is approximately 170 billion tons of biomass generated on the planet annually, of
which 75% is carbohydrate, still humanity utilizes only about 3-4% of this significant amount.iii
The composition of the biomass strongly depends on the source. In general, biomass consists
of 38 – 50% of cellulose, 23 – 32% of hemicellulose and 15 – 25% of lignin. (Fig 1.). The
cellulose is an unbranched-chained, water-insoluble polysaccharides, that can consists of
hundreds or even tens of thousands of glucose units. The cellulose is the most common
naturally occurring biopolymer, that is assumed to be generated around 2 x 109 tons annually.
The hemicellulose is a polymer that has amorphous structure, has lower molceular weight, than
cellulose, its monomers are hexoses (glucose, mannose and galactose) and pentoses (mainly
arabinose and xilose). The third constituent is lignin, which is an intensely cross-linked
polymer, it consists of three types of phenylpropene components, and functions as some kind
of glue, connecting the cellulose and hemicellulose threads.
3 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
Figure 1. Average composition of the plant origin biomass
The most common carbohydrates are the pentose and hexose containing five and six
carbon atoms, respectively. Nowadays, the most sought for and most produced monosaccharide
is glucose obtained from corn, rice or potato extracted starch, its amount is approximately 5
million tons per year.iv The diversity of carbohydrates offers much more possibilities for us
(Fig 2.).
Figure 2. Industrial processes for converting carbohydrates
Conversion of the biomass into carbonaceous compounds is therefore becoming more
and more importance. István Horváth and his colleagues demonstrated first that the dehydration
of carbohydrates combined with hydrogenation involves the preparation of various oxygen-
containing compounds, furfuryl alcohol, levulinic acid (LA), gamma valerolactone (GVL), 2-
4 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
methyltetrahydrofuran (2-Me-THF), through further hydrogenation processes, even alkanes can
be produced (Fig 3).v This proposed cycle involves sustainability (cyclicality), free from ethical
issues (as it does not start from edible carbohydrates), its versatility is demonstrated by the
variance of products.
Figure 3. The proposed conversion of carbohydrates
Laboratory practice focuses on the use of GVL as a solvent in transfer hydrogenation
reactions, as well as reduction of furfural to furfuryl alcohol, which is the major step in the
production of GVL from hemicellulose. Since most chemical reactions take place in the
presence of a catalyst, therefore the appropriate selection of the catalyst, separation and
recovery of the catalyst from the reaction mixture are crucial points for all catalytic processes.
In the case of homogeneous catalysis, the separation of the product and the catalyst, which are
in the same phase, can be carried out in several ways. One option is to change the polarity of
the reaction medium. An example: conversion of levulinic acid to γ-valerolactone in the
presence of water-soluble ruthenium catalyst. After removing water and GVL (e.g. distillation),
the precipitated catalyst complex can be re-dissolved and reused for the production further γ-
valerolactone molecules. Another possibility is the membrane separation process based on the
difference in size of the molecules.
-valerolactone
5 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
Homogeneous catalytic reduction of 2-furfural to furfuryl alcohol in various solvent is
known in the literature, but the reduction using Ru(acac)3/BDPP catalyst system was very
recently demonstrated by Tukacs et al. It was shown that the activity of the Ru-based catalyst
systems can be increased by the application of bidentate phosphine ligands (Ph2P(CH2)nPPh2,
n = 1 – 3) keeping the environmentally benign benefits of a solvent-free system (Fig 4.).vi,vii
Furthermore, the activity was also influenced by the number of the methylene spacers between
the phosphorus atoms of the bidentate ligands e.g. by the size of the chelate ring of the active
form of the catalyst. Main advantages of this method are the good solubility and stability of the
catalyst (not susceptible to oxidation).
Figure 4. Two-way phosphine ligands
Purpose of the practice
Production of chemical raw materials (1-phenyl-ethanol, i-propyl-alcohol, gamma-
valerolactone, cinnamonalcohol, furfuryl alcohol, etc.) by homogeneous catalytic reduction
using molecular hydrogen and catalytic transfer hydrogenation reaction. During the reactions,
the Ru-based catalyst system is used, while as a solvent – in case of the catalytic transfer
hydrogenation reactions (if necessary) – gamma-valerolactone (sustainable liquid) is applied,
which can also be obtained from natural biomass.
Scheme of the chemical reaction
Figure 5. Homogeneous catalytic reduction of Furfural
6 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
Structure of the applied Ru-based catalyst
Applied green chemistry principles:
Use of renewable raw materials
Application of catalyst
Development of less dangerous syntheses
Design of safer products
Required chemicals
Name Formula M (g mol-1)
2-furfural C5H4O2 96.1
1,4-bis(diphenyl-
phosphino)butane
DPPB
C28H28P2 426.5
Ruthenium(III)-
acetylacetonate
Ru(acac)3
(C5H7O2)3Ru 398.4
Ru(acac)3
Ruthenium(III) acetylacetonate
7 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
Equipment
Measuring cylinder (30 mL), 120 mL Hastelloy-C Parr reactor (Fig 6.), analytical scale
for accurate weighing in, sample containers (2 – 4 mL).
Figure 6. High pressure reactor system
Experimental work
1. During the experiment, pour 30 ml of 2-furfural into the Hastelloy-C Parr reactor, then
add 0.038 g of Ru(acac)3 and 0.416 g of DPPB.
2. Place the clamps on the reactor, connect it to the H2 cylinder, then flush the reactor
several times, then set the desired pressure.
3. After installing the heating block, set the appropriate temperature (80 – 160 °C) and the
mixing speed (500 – 600 rpm) on the user interface.
4. During the 2 hours reaction the decrease in pressure has to be corrected for.
5. After the desired reaction time, the sample prepared directly from the single-phase
mixture is analysed by gas chromatography and the conversion is determined. During
the analysis, 10 µL of toluene (internal standard) is added to 10 µL of the reaction
mixture, 1 mL of dichloro-methane is used as the solvent. Additionally, 1H- and 13C-
NMR spectroscopic analysis of the final product of the reaction, spectral evaluation.
Toluene internal standard is used to determine the sample purity.
8 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
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Transfer hydrogenation
Transfer hydrogenation is an alternative process where hydrogenation is carried out with
a non-gaseous hydrogen donor, therefore these reactions are executed under mild conditions at
atmospheric pressure. Since alternative hydrogenation molecules tend to be more soluble in
substrates, the reaction time is shortened. Most commonly, mono- or bivalent alcohols, formic
acid, formates, or cyclic ethers, amines, aldehydes or water are used as hydrogen sources.viii
The general equation for transfer hydrogenation is shown in Fig 7., where S is the substrate to
be reduced, DH2 indicates the alternative hydrogen donor.
Figure 7. The general equation of transfer hydrogenation
Catalytic transfer hydrogenation of levulinic acid to GVL has not been previously
described in the literature. Viktória Fábos presented in her doctoral dissertation in 2009 that
using a formic acid (HCOOH) as a hydrogen donor, in the presence of a ruthenium-based
catalyst the reaction can be successfully implemented.ix The formic acid that is a co-product of
the production of levulinic acid from biomass, is capable of the reduction of the levulinic acid
during transfer-hydrogenation. During the process carbon-dioxide (CO2) and 4-hydroxyvaleric
acid (4-HVA) are produced, the cyclisation of the latter, together with water loss, result the
final product, gamma-valerolactone (Fig 8.).
Figure 8. Transfer hydrogenation of levulinic acid in the presence of formic acid and catalyst
Transfer hydrogenation using diruthenium-complex {[2,5-Ph2-3,4-(p-MePh)2(η5-
C4CO)]2H}Ru2(CO)4(μ-H) as catalyst proposed by Shvo and latter Casey led to a yield of GVL
nearly 100%. The method was patented.x The reaction showed an excellent selectivity, also the
9 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
overhydrogenated byproducts were missed from product mixtures. The highest conversions
were achieved at 2-fold formic acid / levulinic acid molar ratio with a levulinic acid / catalyst
molar ratio of 1200 and 2400 – 8 hours reactions led to the formation of GVL with a yield of
>99.9% at 100 °C (Fig 9.).
Figure 9. Transfer hydrogenation of levulinic acid with Shvo-catalyst
General reaction equation
Figure 10. General reaction equation
Application of Ruthenium-based catalyst (Shvo-catalyst)
The preparation of the catalyst is a three-step process (Fig 11.). Providing the
cyclopentadienyl ring of the catalyst firstly the 2,5-diphenyl-3,4-bis(4'-methylphenyl)
cyclopentadienone (4) and the ruthenium-containing triruthenium dodecacarbonyl (3) reagents
must be prepared. The physical and physico-chemical properties of the various types of Shvo
catalysts can be easily modify by fine tuning of the substituents on the phenyl rings of the (4)
ligand.
10 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
Figure 11. Preparation of Shvo-catalyst
Figure 12. Precursor of Shvo catalyst (1) and the active form (2)
The Shvo-catalyst precursor (Fig 12.) is a symmetric ruthenium complex {2,3,4,5-
Ph4(η5-C4CO)]2H}Ru2(CO)4(μ-H) bounded by a hydride bridge, originally used to reduction of
aldehydes, ketones, alkenes and alkines. Shvo and colleagues have shown that in the presence
of formic acid and hydrogen {[2,3,4,5-Ph4(η5-C4CO)]2H}Ru2(CO)4(μ-H)-diruthenium complex
and various phenyl-substituted derivatives are capable for the reduction of aliphatic, cyclic or
aromatic ketones and aldehydes forming the corresponding alcohol product.
While the reduction of ketones were highly selective, in case of aldehydes aldol
condensation products were also observed in the reaction mixture. The experimental results
clearly show that the excess of formic acid accelerates the reaction, but at the same time the it
promotes the formation of formate esters. To eliminate this issue, sodium formate and a small
amount of water were added to the reaction mixture. Reduction experiments of unsaturated
aldehydes and ketones has shown that when not conjugated double bonds are existing in the
11 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
substrate, hydrogenation is selective for the carbonyl group, resulting alcohols, whereas double
bonds are reduced when conjugated double bonds are in the substrate. They also confirmed if
the reaction is carried out in a solvent it has an effect on the rate of reaction. The mechanism of
reduction was also studied, in which it was found that the active intermediate involved in the
reaction is formed from the diruthenium complex and contains a relatively acidic hydroxyl
group on the cyclopentadienyl ring as well as a hydride directly connected to ruthenium.
Reaction analysis
Atom-efficiency (e.g. transfer hydrogenation of levulinic acid)
C5H8O3 + H2 → C5H8O2 + H2O
M = 116.11 M = 2 M = 100.16 M = 18
Hatom = 100 * Mproduct / Mstarting materials = 100*(100.16/116.11+2) = 84,8 %
Required chemicals
Name Formula M (g mol-1)
Levulinic acid C5H8O3 116.12
Acetone C3H6O 58.08
Acetophenone C8H8O 120.15
Cinnamaldehyde C9H8O 132.16
Equipments
Measuring cylinder (10 mL), 8 mL glassreactor, stirring bar, analytical scale for accurate
weighing in, sample containers (2 – 4 mL).
Safety instructions
During the experimental work, protective goggles and lab coat must be worn. Due to
the high temperature of the reactor, care must be taken while working with it.
Experimental work
6. During the experiments acetofenone, levulinic acid, acetone, cinnamaldehyde are used
as model substrate. Since acetofenone containes two types of functional groups
12 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
(carbonyl- and phenyl group), its reduction is suitable to follow-up the selectivity of the
catalyst. It should be noted that the electron withdrawing properties of the phenyl group
promotes the reduction of the carbonyl group
7. Measure into the reactor tube (Hach tube) 0.5 mL (5.22 mmol) of GVL, 0.0021 g (0.002
mmol) of catalyst, 0.2 mL (5.22 mmol) of HCOOH and 0.3 mL of substrate (2.61 mmol).
Close up the reactor tube and place it into the thermostat bath preheated to 95°C
previously. Set the magnetic mixer to 375 rpm. The reaction time is 2 hours. After the
desired reaction time sample taken from the reaction mixture analyzed by
gaschromatographic method using toluene as internal standard.
To be submitted
A brief summary of the experimental work
Writing up the chemical equations for the reactions
Determination and calculation of the conversion and selectivity of the products
produced with different hydrogenation reactions
Attach chromatograms and spectra
Test questions (example)
Write up the equation for the GVL production!
What is atomic efficiency and what is the atomic efficiency of the examined test reaction like?
What kind of safety instructions must be taken during practice?
Which metal atom does the catalyst contain used during practice?
Draw the Shvo-catalyst precursor and its active form!
13 ENVIRONMENTALLY BENIGN AND CATALYTIC PROCESSES LABORATORY
PRACTICE
Literature
i Tuck, C. O.; Pérez, E.; Horváth, I. T.; Sheldon R. A.; Poliakoff, M., Science, 2012, 695.
ii Fábos V., PhD Thesis, ELTE, Budapest, 2009.
iii Corma, A.; Iborra, S.; Velty, A., Chem. Rev., 2007, 107, 2411.
iv Lichtenthaler, F. W., Acc.Chem. Res., 2002, 35, 728.
v Mehdi, H.; Tuba, R.; Mika, L. T.; Bodor, A.; Torkos, K.; Horváth, I. T., „Renevable Resources
and Renevable Energy, Taylor and Francis, 2006, Boca Raton, 2007, 55.
vi O. Kröcher; R.A. Köppel and A. Baiker; Chem. Commun. 1997, 453.
vii J. M. Tukacs; M. Novák; G. Dibó; L. T. Mika; Catal. Sci. Technol. 2014, 4, 2908.
viii Joó, F., Aqueus Organometallic Catalysis, Kluwer Academic Publisher, 2001.
ix Fábos, V.; Koczó G.; Mehdi, H.; Boda, L.; Horváth, I. T., Energy & Environ. Sci., 2009, 2,
767.
x Horváth I.T; Mehdi, H.; Fábos V.; Kaposy, N., 2008: Szabadalom HU 08 00662