GB416007A - Improvements in or relating to the manufacture of cyanhydrins - Google Patents

Abstract

Ketone cyanhydrins of the aliphatic series are manufactured by adding to an aliphatic ketone, maintained at boiling point and containing a base dissolved therein, an equimolecular proportion of hydrocyanic acid in the gaseous or, preferably, in the liquid state. Suitable bases are: alcoholic or aqueous caustic soda, gaseous or aqueous ammonia, pyridine, piperidine, quinoline, primary, secondary or tertiary amines, potassium or sodium cyanide. The cyanhydrin is recovered by acidification, preferably with a non-volatile mineral acid, e.g. sulphuric acid, which may be in 50 per cent excess over the base present, followed by distillation under reduced pressure. The cyanhydrins may be converted into unsaturated nitriles of homologues of acrylic acid by dehydration with a powerful dehydrating agent, e.g. phosphorus pentoxide, in the presence of a soluble base, preferably in the presence of a diluent, e.g. tetrahydronaphthalene, which may be added before or after the dehydrating agent. The dehydrating agent may be added to the mixture of cyanhydrin and base with efficient cooling, or the dehydrating agent may be added first followed by the base. In examples: (1) liquid hydrocyanic acid is added to a boiling solution of piperidine in acetone and the acetone cyanhydrin is isolated and converted to methacrylonitrile by adding quinoline followed by phosphorus pentoxide, if desired with the addition of a diluent, e.g. tetrahydronaphthalene; (2) hydrocyanic acid is added to a boiling solution of pyridine in acetone and the reaction mixture is cooled and worked up for the production of methacrylonitrile by the addition of pyridine followed by gradual addition of phosphorus pentoxide and then of more pyridine, or by the addition first of the phosphorus pentoxide and then of the pyridine.