GB728656A - Preparation of cyanoalkenes - Google Patents

Abstract

Mono-cyanoalkenes are prepared by the oxidation of the corresponding mono-cyanoalkanes, containing at least 3 carbon atoms, in the vapour phase with molecular oxygen present in an amount of from 0.1 to 2 mols. per mol. of nitrile. Oxidation is effected, in general, at about 250-900 DEG C. or higher, if desired in the presence of an oxidation catalyst effective in vapour phase oxidation. Oxidation inhibitors may also be present. The oxygen may be used alone or with an inert diluent such as nitrogen or carbon dioxide, and may be introduced at a plurality of points along the reaction vessel. The oxidation product is condensed and distilled to remove first the water formed and then the cyano-alkene; the residue is recycled to the oxidation stage with additional cyano-alkane feed. Suitable oxidation catalysts are iodine, hydrogen bromide, diphenylamine, metals of Group IB and their oxides, metals of Groups II to VII and their oxides, including compounds giving rise to these oxides under the reaction conditions, sulphates, silicates and phosphates, alone or supported on various carriers; silica-gel and boric oxide-silica gel. Specified oxidation initiators are phenols, benzene, naphthalene, anthracene, methane, higher alkanes, ethers, aldehydes, ketones, nitro compounds, oxides of nitrogen, sulphur, sulphur oxides, hydrogen cyanide and peroxy compounds. In typical examples illustrating the conversion of propionitrile and isobutyronitrile to acrylonitrile and methacrylonitrile respectively; (2) propionitrile containing 2 per cent phenol is passed with 0.49 mol. of oxygen through a quartz tube at 535 DEG C.; similarly, (6) propionitrile and air are passed at 260 DEG C. through a glass tube containing silica gel granules impregnated with a mixture of cadmium and uranium nitrates; (7) propionitrile vapour and air are injected into the bottom of a boiling bed of silica gel powder impregnated with uranium nitrate and maintained at 448-497 DEG C.; (13) isobutyronitrile containing 2 per cent iodine is passed with air through a quartz tube at 630 DEG C. The propionitrile and isobutyronitrile may also be introduced in the form of their corresponding amides, the cyano alkanes being formed in situ. The oxidation of propionitrile is stated to yield trace amounts of acetonitrile, isobutyronitrile and methacrylonitrile.ALSO:A catalyst for use in the oxidation of propionitrile to acrylonitrile (see Group III) is prepared by washing silica gel granules with dilute nitric and hydrochloric acids, igniting the washed granules, then impregnating the granules by introducing thereto an aqueous solution of cadmium and uranyl nitrates and applying a vacuum and finally drying. Another catalyst is prepared in like manner from silica gel powder, aqueous uranyl nitrate only being used in the impregnation.