Method of preparing optically active cyanohydrins

A method of preparing an optically active cyanohydrin by addition of hydrogen cyanide to a carbonyl compound, selected from aldehydes and ketones which allow addition of hydrogen cyanide, in a biphasic solvent system, comprising a homogeneous aqueous solution of hydroxynitrile lyase, and a suitable organic solvent which is at least substantially immiscible with water, said method being characterized in that said homogeneous aqueous solution is buffered with a buffer solution having a pH between 3 and 6, said buffer solution being selected from an acetate buffer and a non-acetate buffer, wherein said acetate buffer has a buffer concentration of between 0.005 and 0.1 mole per liter and wherein said non-acetate buffer is selected from citrate, succinate, glutamate and phthalate buffers, that the volume ratio organic phase:aqueous phase is between approx. 5:1 and approx, 1:5, and that a solution of hydrogen cyanide and said carbonyl compound in said organic solvent is properly mixed to ensure sufficient interfacial area between the phases during the reaction period with said homogeneous aqueous solution of hydroxynitrile lyase.