GB728522A - Improvements in the production of pure adiponitrile - Google Patents

Abstract

Pure adiponitrile is obtained from crude adiponitrile containing 1-cyano-cyclopentanone-(2) and/or its imide by treating the crude adiponitrile, preferably at elevated temperature, with hydrocyanic acid, and distilling off the pure adiponitrile from the higher-boiling reaction products of the hydrocyanic acid with said impurities. When the crude adiponitrile is obtained by reacting 1.4-dichlorobutane and excess sodium cyanide the amount of hydrocyanic acid necessary for reaction with the said impurities may be obtained by adding to the reaction mixture, before distilling off the adiponitrile formed, a small amount of an aqueous solution of hydrochloric, sulphuric or phosphoric acid or of an alkyl or aryl sulphonic acid at temperatures of from about 40 DEG to 100 DEG C. When the crude adiponitrile is obtained by catalytically reacting adipic acid with excess ammonia the hydrocyanic acid may be introduced into the vapours leaving the catalyst but instead of ready-made hydrocyanic acid there may be employed corresponding amounts of formamide or methyl formate which are added to the reaction mixture at a temperature above 160 DEG C. at which temperature the formamide splits up into hydrocyanic acid and water and the methyl formate reacts with the excess ammonia to form hydrocyanic acid, water and methanol. In examples (1) a mixture of pure adiponitrile and 1-cyanocyclopentanone-imide (2) and/or the corresponding ketone is heated to 60-80 DEG C. and hydrocyanic led in. The mixture is allowed to stand at 60-100 DEG C. and then distilled in vacuo; (2) sodium cyanide is added to pure adiponitrile and reacted with 1.4-dichlorobutane at 180-190 DEG C. A small amount of sulphuric acid which may either be concentrated or diluted to 50 per cent with water, is then added and after stirring for 1 to 2 hours the mixture is distilled to yield an additional amount of pure adiponitrile; (3) ammonia is led through molten adipic acid at 330-350 DEG C. and the resulting adiponitrile, after the addition of formamide, is led at about 200 DEG to 300 DEG C. over a short layer of pieces of chamotte containing phosphoric acid, the vapours leaving the chamber being condensed to recover adiponitrile containing less than 0.1 per cent of 1-cyano-cyclopentanone-(2)-imide.