Cyanohydrins can be reduced to phenylacetonitriles by the aid of commercially available phosphorous pentasulfide. 0.2-1.1 moles of P2S5 per mole of cyanohydrin is employed, preferably around 0.5 moles, but larger amounts are not deleterious to the yields. The reaction is performed in an inert solvent, preferably an intert hydrocarbon having a boiling point between 50-150°C, such as hexane, heptane, benzene and toluene.
As an example 2 mmol of a cyanohydrin in 5ml toluene is heated to 85°C with 1 mmol phosphorous pentasulfide for one hour, and the reaction was quenched with water (H2S evolution!) and the reaction mixture was extracted with a non-polar solvent, dried and filtered, the solvent evaporated and the residue distilled to give the phenylacetonitrile in high yield.
Reference: US Pat 4,952,718