GB703398A - Preparation of unsaturated nitriles - Google Patents

Abstract

Alpha-beta unsaturated nitriles are produced by the pyrolysis of an alkoxyamide of formula <FORM:0703398/IV(b)/1> in which R1, R2, R3 may be hydrogen, or un substituted alkyl, cycloalkyl, aralkyl or aryl radicals and R4 is an alkyl group. R1, R2, R3 may be, for example, methyl, ethyl, propyl, butyl, cyclohexyl, benzyl, phenyl, tolyl or xylyl, R4 may be, for example, methyl, ethyl, propyl or butyl. The starting material is heated to a temperature in the range 250 DEG -550 DEG C. and preferably the pyrolysis takes place in the vapour phase. The a -b unsaturated nitrile produced is isolated from the reaction mixture, most suitably by distillation. Preferably the starting material is a compound of formula R5O-CH2-(R6)-CH-CONH2 where R5 is an alkyl group and R6 is hydrogen or aralkyl group. The pyrolysis is preferably carried out in the presence of a pyrolysing catalyst, e.g. alumina, bauxite, silica gel, active earths, acid activated earths, mixed alumina-silica gel catalysts, strong acids such as sulphuric acid and phosphoric acid, esters of strong acids such as isopropyl sulphate, metal oxides or catalyst supports containing mineral acids such as phosphoric acid, or salts thereof, or metal oxides. The pyrolysis may also be carried out in the presence of an inert diluent, such as nitrogen or steam, in addition to the steam produced in the process of dehydration. Preferably, the reaction is carried out in the presence of a small amount of volatile acid and/or a small amount of an acid, for example, a mineral acid, is added to the reaction products so as to neutralise any ammonia or amines found during the reaction. The most suitable acid is acetic acid. The reaction may be represented by the following equation <FORM:0703398/IV(b)/2> The process is of particular application in the production of acrylonitrile by the pyrolysis of 3-methoxypropionamide and of 2-methacrylonitrile by the pyrolysis of 3-methoxy-isobutyramide. In the examples acrylonitrile is prepared by the pyrolysis of 3-methoxypropionamide in the presence of acetic acid. Specification 703,399 is referred to.