Asymmetric reduction of acetophenone in membrane reactors: comparison of oxazaborolidine and alcohol dehydrogenase catalysed processes

Abstract

The enantioselective reduction of acetophenone was studied in two different ways. Chemical borane reduction using a homogeneously soluble polymer-bound oxazaborolidine catalyst was carried out in a continuously operated membrane reactor and yielded ( R)-phenylethanol in good enantiomeric excess with high space–time yields. An enzymatic reduction using a dehydrogenase two-enzyme system as the catalyst and formate as the hydrogen source was carried out in an extractive bi-membrane reactor and yielded ( S)-phenylethanol in excellent enantiomeric excess with a low enzyme consumption. A comparison of the two systems with respect to space–time yield, total turnover number and other parameters is made.