Preparation of unsaturated nitriles

摘要

Alpha-beta unsaturated nitriles are produced by the pyrolysis of an alkoxy nitrile of formula in which R1, R2, R3 may be hydrogen, unsubstituted alkyl, cycloalkyl, aralkyl and aryl radicals and R4 is an unsubstituted alkyl group. R1, R2 and R3 may be, for example, methyl, ethyl, propyl, butyl, cyclohexyl, benzyl, phenyl, tolyl or xylyl radicals and R4 may be, for example, methyl, ethyl, propyl or butyl radicals. The starting material is heated to a temperature between 250 DEG and 500 DEG C. and the reaction is preferably carried out in the vapour phase. The alpha-beta unsaturated nitrile is isolated from the reaction mixture preferably by distillation. Preferably the starting material is R5O-CH2-(R6)CH-CN where R5 is an alkyl group and R6 is hydrogen or an alkyl group. The pyrolysis is preferably carried out in the presence of a pyrolysing catalyst, e.g. alumina, 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, ion, zinc or calcium oxide, 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 carbon dioxide. The reaction is preferably carried out in the presence of a small amount of a volatile acid and/or a small amount of an acid, for example, a mineral acid is added to the reaction products before they are isolated. The most suitable acid for this purpose is a fatty acid such as acetic acid. The process is of particular application in the production of acrylonitrile by the pyrolysis of 3-methoxy-propionitrile and of 2-methacrylonitrile by the pyrolysis of 3-methoxyisobutyronitrile. It is also applicable to the production of atroponitrile by the pyrolysis of alphaphenyl-betamethoxy propionitrile or of cinnamonitrile by the pyrolysis of betaphenylbetamethoxy propionitrile. In the examples 3-methoxypropronitrile is converted to acrylonitrile in the presence of various catalysts. Specification 703,398 is referred to.