Vapour phase transfer hydrogenation of α,β-unsaturated carbonyl compounds. Thermodynamic and experimental studies

• Transfer hydrogenation (TH) of α,β-unsatd. carbonyl compounds over MgO is studied.
• The 1st thermodynamic description of hydrogenation/transfer hydrogenation is given.
• The formation of unsaturated alcohols is not favoured thermodynamically.
• Very high chemoselectivity towards allyl alcohol was noted in TH of acrolein.
• Reactivity of 2-PrOH highly exceeded that of EtOH in TH, except with acrolein.

This paper presents the first systematic thermodynamic study of the vapour phase transfer hydrogenation of α,β-unsaturated carbonyl compounds at temperatures: 423.15–723.15 K. Calculations were made for four compounds, namely: acrolein, α-methylacrolein, β-methylacrolein and methyl vinyl ketone. The Gibbs free energies and equilibrium mole fractions (EMFs) were calculated for transfer hydrogenation with ethanol and 2-propanol as hydrogen donors. It was noted that for transfer hydrogenation and hydrogenation with hydrogen the formation of the unsaturated alcohol (UOL) is the least thermodynamically favoured reaction and that saturated alcohol (SOL) and saturated aldehyde or ketone (SAL or SON) are the main products.A set of eight carbonyl compounds have been transfer hydrogenated with ethanol and 2-propanol in the presence of MgO as the catalyst. The main conclusions are that: (a) the reduction of a carbonyl group into a carbinol group occurs with a very high selectivity, (b) for almost all carbonyl compounds, except acrolein, the reactivity of 2-propanol highly exceeded that shown by ethanol and (c) the high chemoselectivity of transfer hydrogenation of acrolein with alcohols resulted from the kinetic control caused by the presence of magnesium oxide.

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