GB1021197A - Process for the manufacture of lactams - Google Patents

Abstract

Lactams of formula <FORM:1021197/C2/1> where n is an integer between 7 and 17 are prepared by heating to a temperature between 60 DEG and 200 DEG C. A mixture of the corresponding oxime of formula <FORM:1021197/C2/2> with phosphoric acid in which the concentration by weight of P2O5 is between 72 and 80%, then separating the formed lactam and recovering the phosphoric acid, which is re-cycled for the following operation, being periodically purified before recycling. The preferred minimum proportion of phosphoric acid to oxime is 0.7 parts to 1 part by weight; more advantageously 1 to 2 parts of acid to 1 part of oxime are used. The reaction mixture is diluted with water to bring the concentration of orthophosphoric acid to below 60% by weight before extraction of the lactam.ALSO:Nitrogenous and other organic impurities can be removed from phosphoric acid in one of the following ways. (1) Treatment with concentrated nitric acid and heating. The organic materials are destroyed by nitric acid and nitrous fumes are evolved. The quantity of nitric acid necessary depends on the amount of impurities and can easily be determined when the evolution of nitrous fumes ceases. The nitric acid is suitably used in 50 to 100% concentration. To prevent foaming the temperature is raised gradually and the nitric acid is added slowly. (2) Treatment of a dilute solution with cation exchange resins. Suitable resins contain sulphonic groups such as sulphonated polystyrene. The concentration of phosphoric acid should be at most 50%, preferably 20-40%. (3) Treatment of a dilute solution with chlorine. When a current of chlorine is passed into an aqueous solution of phosphoric acid any organic impurities separate as a thick oil containing chlorinated organic products which can be separated by filtration or extraction. The preferred concentration of phosphoric acid in aqueous solution is from 30-60%.