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The enantioselective hydrogenation of ethyl benzoylformate over (−)-cinchonidine (CD)-modified Pt/Al2O3 catalyst in semi-batch and continuous fixed bed reactors was studied as a function of the modifier concentration and reaction temperature. The kinetic results from the semibatch reactor showed a higher enantioselectivity and lower initial rate as the amount of modifier was increased. The results from the fixed bed reactor demonstrates that continuous enantioselective hydrogenation is possible and that continuous feeding of (−)-CD is needed to maintain a high steady-state enantioselectivity.

The enantioselective hydrogenation of ethyl benzoylformate (EBF) to (R)-ethyl mandelate over (−)-cinchonidine (CD)-modified Pt/Al2O3 catalyst in toluene in a semi-batch reactor was studied as a function of modifier concentration, reaction temperature, stirring rate and catalyst particle size. The kinetic results showed higher enantioselectivity and lower initial rates tending asymptotically to a constant value as the amount of modifier increased. The maximum enantiomeric excess (ee) and the initial hydrogenation rate or turnover frequency obtained under optimized conditions with an initial concentration of 5.6 mmol L−1 EBF at 25 °C over 5% (w/w) Pt/Al2O3 were 85% (modifier-to-surface Pt of 1.28) and 109 h−1 (modifier-to-surface Pt of 0.16), respectively. Additionally, catalyst deactivation due to the presence of impurities in the feed was prominent in some cases; therefore activated carbon was used as a cleaning agent of the raw material to remove impurities prior to catalyst addition.

Solvent effects in the enantioselective hydrogenation of ethyl benzoylformate (EBF) to (R)-ethyl mandelate over (−)-cinchonidine (CD)-modified Pt/Al2O3 catalyst were studied in a semi-batch reactor. Solvents of different nature were used: protic (2-propanol, 1-propanol, 1-octanol and ethanol), aprotic polar (methyl acetate, acetone, ethyl acetate and tetrahydrofuran) and apolar solvents (methyl cyclohexane and toluene). The effects of pure solvents and binary solvent mixtures on hydrogenation rates and enantioselectivity were investigated. The highest enantiomeric excess (ee) of 72 % was obtained in ethyl acetate, decreasing nonlinearly with increasing dielectric constant (e) being close to 20 % in ethanol. The highest value of the initial hydrogenation rate was obtained in the apolar solvents (21 mmol dm−3 min−1g cat −1 ) while the lowest one was observed in tetrahydrofuran (2 mmol dm−3 min−1 g cat −1 ). A kinetic model was proposed for the enantioselectivity dependence on dielectric constant based on Kirkwood treatment. The non-linear dependence of ee on (e) was included in the model to describe quantitatively the variation of ee in different solvents. The results showed a good fit for ee as a function of e.