GB774345A - Improvements in or relating to reductive n-alkylation process - Google Patents

Abstract

In a process for the reductive alkylation of an aromatic compound containing at least one amino or nitro group in the presence of hydrogen with a ketone, during which an alcohol is inherently formed, the effluent products of the reductive alkylation comprising an alcohol fraction contaminated with an amino compound or compounds are separated, substantially all the amino compounds are removed from the separated alcohol fraction, and the purified alcohol is dehydrogenated to a ketone which is recycled to the reductive alkylation. The process of the invention is particularly applicable to the production of N:N1-di-sec.-alkyl-p-phenylene diamines, several of which are specified. Specified aromatic compounds containing amino and/or nitro groups are aniline, phenylene diamines, nitrobenzene, dinitrobenzenes, nitroanilines, diaminonitrobenzenes, o - nitro - p - phenylene diamine, dinitroanilines, a - or b -amino- or -nitro-naphthalenes and amino and/or nitro substituted anthracene and phenanthrene compounds. The amino and/or nitro compounds may also contain other substituents such as alkyl, aryl, aralkyl, alkaryl, cycloalkyl, alkoxy, hydroxy, sulphonic acid and halogen. Specified ketones are dialkyl ketones having C1-C20 groups. Specified catalysts for the reductive alkylation are nickel, nickel-kieselguhr composites, nickel or copper or molybdenum sulphides, platinum and palladium, the preferred catalyst being a mixture of copper oxide, chromium oxide and barium oxide. The product of the reductive alkylation comprises hydrogen, the N-alkyl aromatic amine, water, unreacted ketone and the secondary alcohol containing amino-compounds. The N-alkylamino-product and unreacted ketone are separated, the ketone being recycled. The alcohol is freed from water (e.g. by azeotropic distillation) and then may be freed from amino compounds by solvent extraction, preferential adsorption on a solid adsorbent, or by azeotropic distillation, but fractionation is preferred. In the reductive alkylation of p-nitroaniline with methyl ethyl ketone, for example, the sec.-butyl alcohol formed is contaminated with mono- and di-sec.-butyl amines and possibly with minor amounts of cyclohexylamine and other amines. Specified catalysts for the dehydrogenation are zinc oxide, copper and copper oxide but brass catalysts are preferred. A Figure (not shown) is given illustrating in a flow diagram a continuous process of the invention. In examples: (1) p-nitroaniline is reacted with hydrogen and an excess of methyl ethyl ketone at elevated temperature and pressure and in the presence of a mixture of barium oxide, chromium oxide and copper oxide as catalyst, N : N1-di-sec.-butyl-p-phenylene diamine is separated from the reaction products, hydrogen and unreacted ketone are recycled, the sec.-butyl alcohol formed is freed from amino compounds by fractionation, dehydrogenated by passing over a heated brass catalyst and the resultant methyl ethyl ketone is recycled; (2) the dehydrogenation of sec.-butyl alcohol recovered from a reductive alkylation is compared when using purified and unpurified material.