Process for the preparation of (S)-Cyanhydrines

Preparation of (S)-cyanohydrin compounds of formula (I) comprises enzyme-catalysed reaction of carbonyl compounds of formula (II) with hydrocyanic acid, or a substance which releases hydrocyanic acid or CN, in the presence of a catalytic amount of an (S)-oxynitrilase immobilised on a nitrocellulose carrier. R, R' = H; 1-18C alkyl, 2-18C alkenyl or 2-18C alkynyl (all optionally substituted by ≥ 1 amine, imine, OH, 1-6C alkoxy, halo, carboxyl, 3-20C cycloalkyl and/or Het substituents, where the cyclic substituents are themselves optionally substituted by ≥ 1 halo, OH, 1-8C alkyl, 2-8C alkenyl or 2-8C alkynyl); or a (hetero)aromatic group containing 5-22 ring atoms, in which up to 4 ring C atoms may be replaced by N, O and/or S atoms, the ring being optionally substituted by ≥ 1 amine, imine, OH, 1-8C alkoxy, aryloxy, halo, carboxy or 1-22C optionally unsaturated alkyl, where ≥ 2 of the ring substituents may combine to form a cyclic group; Het = an aromatic ring with up to 22C atoms which is optionally substituted by N, O or S heteroatoms; provided that R' and R are not both H.