Abstract
A novel chiral modifier, (R)-2-(1-pyrrolidinyl)-1-(1-naphthyl) ethanol (PNE), has been synthesised and tested in the enantioselective hydrogenation of ethyl pyruvate over Pt/alumina. An enantiomeric excess in (R)-ethyl lactate of up to 75% was achieved. The influence of solvent, pressure, temperature, and concentrations of the components (reactant, modifier, catalyst) on the reaction rate and enantiodifferentiation was investigated. Among various polar and nonpolar solvents, acetic acid was found to be most suitable for reaching good enantioselectivity. Favorable reaction conditions are 1-10 bar hydrogen pressure, 0-25°C, and a catalyst loading ≥ 15 g liter−1. The efficiency of PNE is demonstrated by the very low modifier : reactant molar ratio (1 : 30,000) which is required to obtain maximum enantioselectivity. The performance and stability of the aminoalcohol-type modifier are compared to those of cinchona alkaloids. At low hydrogen pressure, the enantiodifferentiation of PNE is comparable to that of 10,11-dihydrocinchonidine.
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