Enantiomeric enrichment of cyanohydrins

An enzymatic process for the enantiomeric enrichment of a chiral cyanohydrin of the structure ##STR16## comprising the steps:

• (a) bringing said mixture of chiral cyanohydrins into contact at a pH of 3.5 to 5.5 with an enantioselective dehydrocyanation catalyst selected from the group consisting of (R)- and (S)- oxynitrilase and cyclic peptides until one of said chiral cyanohydrins is converted in a dehydrocyanation reaction to dehydrocyanation reaction products comprising hydrogen cyanide and an aldehyde or ketone of the structure ##STR17## (b) simultaneously reducing the concentration of at least one of said dehydrocyanation reaction products by a method selected from a liquid-liquid extraction, a liquid-gas extraction, a membrane-based separation, a chemical conversion, and combinations thereof where
• (i) R.sub.1 and R.sub.2, taken together, form a diyl hydrocarbon chain containing 3 to 5 carbons, or
• (ii) R.sub.1 and R.sub.2 are different and R.sub.1 is selected from straight and branched chain alkyl, cycloalkyl, heterocyclic and aryl groups, said cycloalkyl, said heterocyclic and said aryl groups being unsubstituted or substituted with a substituent selected from the groups consisting of halo, hydroxy, lower alkyl, lower alkoxy, lower alkylthio, cycloalkyl, carbamoyl, trifluoromethyl, phenyl, phenoxy, nitro, alkylsulfonyl, arylsulfonyl, alkylcarboxamide, and . .acrylcarboxamido,.!. arylcarboxamido, and R.sub.2 is selected from hydrogen and R.sub.1.