GB904413A - Improvements in processes for preparing caprolactam - Google Patents

Abstract

Nitrosyl sulphate is prepared (Example 3) by passing SO2 into a mixture of nitric acid, oleum and nitrosyl sulphate at 0 DEG C. with intermittent additions of oleum until a partly solid mass is obtained, whereupon additional oleum is added and the mixture heated at 40 DEG C. to provide a solution of the nitrosyl sulphate in oleum. The solution is used as a nitrosylation agent in the production of caprolactam from cyclohexylaryl ketones (see Group IV(b)).ALSO:Caprolactam is prepared by reacting a ketone of the general formula <FORM:0904413/IV (b)/1> wherein Ar is an aryl radical, with a nitrosylation agent capable of providing NO+ ions in the reaction medium, in the presence of free sulphuric acid. Suitable nitrosylation agents include nitrous gases (N2O3), nitrosyl halides, nitrosyl sulphate, alkyl nitrites, nitrogen monoxide and salts of nitrous acid, e.g. sodium nitrite, and nitrosyl sulphuric anhydride. Reaction may be effected in oleum at temperatures above -20 DEG C., preferably -15 DEG to +45 DEG C; in the absence of SO3, higher temperatures of up to 150 DEG C. may be used. Preferably at least 2.5 moles of sulphuric acid are used per mole of NO+ ion supplied by the nitrosylation agent. The reaction yields as by-product an aromatic or nitrated aromatic carboxylic acid. Examples describe the reaction of cyclohexyl aryl ketones, wherein Ar represents phenyl, naphthyl, p-toluyl, cumyl or xylyl, in oleum or 95% H2SO4 with each of the above types of nitrosylation agents, reaction sometimes being effected in the presence of cyclohexane refluxing under reduced pressure or boiling liquid SO2, ethyl chloride or dichloro-tetrafluoroethane to control the temperature. The purification of the resulting crude lactam, comprising alkaline washing and solvent extraction, is described. The cyclohexyl aryl ketones are prepared from hexa hydro benzoyl chloride, the aromatic hydrocarbon and aluminium trichloride.