Base-Catalysed Hydrogenation of Sulphur-Containing Aldehydes

Article abstract of DOI:10.1002/adsc.200390056

The present work reports the first selective catalytic hydrogenation of bifunctional compounds containing a carbonyl and sulphur moieties, using hydrogen transfer from alcohols and a basic catalyst. The reaction was performed in batch at 371 K at atmospheric pressure with 3- mercaptopropionaldehyde, thiophene-2-carboxaldehyde, 5-bromothiophene-2- carboxaldehyde and 4-methylthiobenzaldehyde. The only product of reaction was the alcohol, formed with yields > 80%, except with 3-mercaptopropionaldehyde which did not give the alcohol but rather afforded unidentified heavy products. 5-Bromothiophenemethanol was obtained with 100% yield in 3 h. The reaction obeys a mechanism of competitive adsorption of the reactants, and the reaction rates are higher than those reported for supported rhodium catalysts.

Full text of DOI:10.1002/adsc.200390056

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Base-Catalysed Hydrogenation of Sulphur-Containing Aldehydes
Thi-Thu-Ha Vu,a Pramod S. Kumbhar,b FranÁois Figuerasa,*
a
Institut de Recherches sur la Catalyse du CNRS, 2 avenue Albert Einstein, 69626 Villeurbanne Cedex, France
Fax: ( ‡ 33)-472-44-53-99, e-mail: figueras@catalyse.univ-lyon1.fr
b
J. F. Welch TechnologyCentre, GE India TechnologyCentre, Plot 122, Export Promotion Industrial Park, Hoodi Village,
Whitefield Road, Bangalore 560066, India
Fax: ( ‡ 91)-80-8412111, e-mail: pramod.kumbhar@geind.ge.com
Received: October 18, 2002; Accepted: January10, 2003
Abstract: The present work reports the first selective rather afforded unidentified heavyproducts. 5-Bro-
catalytic hydrogenation of bifunctional compounds mothiophenemethanol was obtained with 100% yield
containing a carbonyl and sulphur moieties, using in 3 h. The reaction obeys a mechanism of compet-
hydrogen transfer from alcohols and a basic catalyst. itive adsorption of the reactants, and the reaction
The reaction was performed in batch at 371 K at rates are higher than those reported for supported
atmospheric pressure with 3-mercaptopropionalde- rhodium catalysts.
hyde, thiophene-2-carboxaldehyde, 5-bromothio-
phene-2-carboxaldehyde and 4-methylthiobenzalde- Keywords: basic catalysis; 5-bromothiophene-2-car-
hyde. The only product of reaction was the alcohol, boxaldehyde; hydrogen transfer; hydrotalcites; selec-
formed with yields > 80%, except with 3-mercapto- tive hydrogenation of aldehydes; thiophenecarboxal-
propionaldehyde which did not give the alcohol but dehyde
Introduction
solvent, therefore basic catalysis is preferable for the
synthesis of alcohols. This reaction has now been
extended to the hydrogenation of benzaldehyde,[6]
The preparation of alcohols byreduction of the carbon-
oxygen double bond of aldehydes and ketones is one of citral,[7,8] aryl alkyl ketones,[9] and propiophenone.[10]
the most fundamental and useful transformations in The reduction of carbonyl compounds based on thio-
organic chemistry. Catalytic methods have been report- phene permits one to synthesise the corresponding
ed and are considered in terms of ease, efficiency, and thiophenemethanols which are intermediates for the
commercial viability, as the most attractive procedures synthesis of some herbicides[11] and pharmaceutical
for reduction. Carbonyl reduction can be performed at compounds.[12,13] This prompted us to investigate an
relativelyhigh pressures, using hydrogen and metals
extension of the base-catalysed hydrogen transfer to
such as Pt/C, RaneyNi, and Pd/C. [1] However carbonyl substrates containing sulphur moieties.
compounds containing sulphur moieties cannot be
reduced using supported metal catalysts, as the metal
itself gets poisoned bythe sulphur; almost no conversion Results and Discussion
is observed. Recently, an immobilised cationic rho-
dium(I) catalyst bearing the diphosphine 1,1'-bis(diiso- The experiments were performed in 2-propanol at 355 K
propylphosphino)ferrocene as ligand has been pro- with 3-mercaptopropionaldehyde, thiophene-2-carbox-
posed.[2,3] In spite of the good stabilityof the complex,
aldehyde (Equation 1, X ˆ H), 5-bromothiophene-2-
some leaching of Rh was observed in the first runs, and carboxaldehyde (Equation 1, X ˆ Br) and 4-methyl-
theseRh(DiPFc)/Al2O3 catalystsareextremelyexpensive. thiobenzaldehyde (Equation 2). The only products of
We reported earlier that the Meerwein Ponndorf
the reactions are the alcohol (products 2 and 4), and
Verley(MVP) reduction of 4- tert-butylcyclohexanone fairlyhigh yields ( > 80%) were reached at this temper-
and unsaturated aldehydes to the corresponding unsa- ature, except with 3-mercaptopropionaldehyde which
turated alcohol could be catalysed in the liquid phase at gave not the alcohol but unidentified heavyproducts.
353 K bythe mixed oxides derived from hydrotalcites
From their GC-MS these products could correspond to a
and 2-propanol as hydrogen donor.[4] The acid and basic partial decomposition of a dimer. The simpler path to
catalysis for the MVP reduction were compared using dimerisation is here aldolisation which is known to
MgAl mixed oxides and BEA zeolites:[5] basic catalysis proceed rapidlyand with a favourable thermodynamic
gave selectivelythe alcohol whereas acid catalsyis
yielded the ether by consecutive reaction with the that this hydrogenation cannot probably be extended to
equilibrium below room temperature.[14] This suggests
Adv. Synth. Catal. 2003, 345, No. 4
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Thi-Thu-Ha Vu et al.
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Figure 2. Arrhenius plot of the initial rates of hydrogenation
of thiophene-2-carboxaldehyde by reaction with 2-butanol.
Figure 1. Yields of alcohol as a function of time for thio-
phene-2-carboxaldehyde (TCA), 5-bromothiophene-2-car-
boxaldehyde (BrTCA) and 4-methylthiobenzaldehyde
(MTB) for the reactions with 2-propanol at 355 K and with
2-butanol at 371 K.
enolisable aldehydes, and indeed the best results were
obtained with non-aldolisable substrates. The results of
this reaction with 2-propanol at 355 K are reported in
Figure 1.
ꢀ1†
Equation 1. Hydrogenation of thiophene-2-carboxaldehyde
[1a, X ˆ H] and 5-bromothiophene-2-carboxaldehyde [1b,
X ˆ Br] with 2-propanol.
Figure 3. Influence of the concentration of thiophene-2-
carboxaldehyde on the initial rate of reaction with 2-butanol
at 371 K.
plot of the initial rate at low conversion against
reciprocal temperature (Figure 2) gives an activation
energyof 74 kJ/mol.
ꢀ2†
It is interesting to compare the activities reached by
this process to those reported for immobilised homoge-
neous Rh(DiPFc)/Al2O3 catalysts. This is reported in
Table 1 for the three substrates, in which basic catalysis
compares favourablywith hydrogenation over support-
ed Rh. In particular, bromobenzaldehyde, which is
debrominated on Pd/C and shows a low reactivityon
Equation 2. Hydrogenation of 4-methylthiobenzaldehyde
with 2-propanol.
Since the reaction time was long using 2-propanol, the immobilised homogeneous Rh catalysts, is quantitative-
reaction was also studied at 371 K using 2-butanol as lyhydrogenated over the mixed oxide, therefore HDTis
hydrogen donor and solvent. In this case the time the first catalytic system to reach a good selectivity in
required to reach the final conversion of thiophenecar- this difficult hydrogenation.
boxaldehyde decreases from 41 h to 2 h, without loss of
selectivity(Figure 1). At 355 K the initial reaction rate
The influence of the concentration of substrate was
investigated in the case of 2-thiophenecarboxyaldehyde
with 2-butanol is twice that observed with 2-propanol, at 371 K. The results reported in Figure 3 show a
thus the better yield in 2-butanol results from the sum of maximum of the rate at a concentration of about 0.1
two factors: a higher reaction temperature and better mol LÀ1. The usual mechanism accepted for MVP
hydrogendonor. Therateofhydrogenationofthiophene- hydrogenation involves the coordination of the alde-
carboxaldehyde (0.1 M) to thiophenemethanol was hyde to a surface alkoxide.[15] The competition for
measured at several temperatures in 2-butanol. The adsorption between the two substrates (aldehyde and
494
Adv. Synth. Catal. 2003, 345, 493 496

Base-Catalysed Hydrogenation of Sulphur-Containing Aldehydes
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Table 1. Comparison of the results[a] of hydrogen transfer hydrogenations using 2-butanol at its boiling point and
hydrogenation on Rh and Pd catalysts from ref.[2]
Substrate
Catalyst
Alcohol Yield [%]
Reaction Time [h]
1a Thiophenecarboxaldehyde
Rh(DiPFc)/Al2O3
10% Pd/C
HDT
Rh(DiPFc)/Al2O3
10% Pd/C
HDT
Rh(DiPFc)/Al2O3
Pd/C
HDT
100
8
100
37.2
0
100
100
5
18
18
3
18
18
3
18
18
3
1b 5-Bromothiophene-2-carboxaldehyde
2 4-Methylthiobenzaldehyde
100
[a]
Reaction conditions: for the immobilised complex: 293 K, 100 psi H2; molar ratio substrate/Rh ˆ 300 350, concentration:
0.1 M, solvent 10 mL of 2-PrOH/H2O (1/1 v/v); for Pd/C: 293 K, 14 psi H2, concentration 0.1 M, 10 mg of 10% Pd w/w for
reaction 1 (X ˆ H) and 2.5 mg for reaction 1 (X ˆ Br), solvent 10 mL of 2-PrOH/H2O (1/1 v/v); for hydrotalcites standard
conditions: 371 K, atmospheric pressure, concentration 0.1 M, 0.1 g of catalyst corresponding to 1.2 wt % of the reaction
mixture, solvent 10 mL of 2-PrOH.
necked glass reactor using 2-propanol or 2-butanol as hydro-
gen donors at their boiling points. The pre-treated catalyst
(0.15 g of original solid, reduced to about 0.1 g after activation)
was carefullytransferred to the reactor swept bya small flow of
nitrogen and containing the alcohol (10 mL, Aldrich) at the
reaction temperature without exposure to air. Afterwards the
substrate (1 mmol, purity99% from Aldrich) was introduced.
The amount of catalyst in the reaction mixture is therefore
about 1.2 wt %. Periodicallywithdrawn samples were analysed
on a Shimadzu GC 14B gas chromatograph using a Super-
cowax capillarycolumn (30 m, 0.5 mm ID and 0.3 mm film
thickness). The products were identified byGC-MS analysis
and calibrations were done using authentic samples of the
corresponding alcohols.
alcohol) leads to the maximum in the rate observed here.
A lower but still acceptable rate is, however, observed in
more concentrated solutions. Since MgAl mixed oxides
contain about 0.4 meq/g of active sites,[16] at the optimal
concentration, the catalyst converts 25 mol per active
site in 2 h, therefore the reaction is trulycatalytic. On the
same reaction, the supported Rh catalyst converts 320
mol per mol Rh in 16 h, therefore the activities per active
site are of the same magnitude.
Conclusion
We have shown for the first time that the mixed oxides
obtained bycalcination of MgAl hydrotalcites can be
successfullyused to selectivelyreduce carbonyl com-
pounds to alcohols in the presence of sulphur moieties.
The selectivityis also excellent, with retention of Br,
with 5-bromothiophenecarboxaldehyde. The process
uses an inexpensive catalyst, operates at atmospheric
pressure and low temperature. The hydrotalcite can be
regenerated several times bycalcination provided it
contains no chlorine at the surface.[17] These catalysts are
suitable for aldolisation[18] and hydrogen transfer hydro-
genation[4] and can be reused several times after
calcination at 723 K in air.
Acknowledgements
TTHV acknowledges a grant from the French government.
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