GB597794A - Manufacture of 4-aryl-piperidine-4-carboxylic acid esters - Google Patents

Abstract

4-Aryl-piperidine-4-carboxylic acid esters are obtained by heating (e.g. at 200-250 DEG C.) 4-aryl-piperidine-4-carboxylic acid betaines having hydrocarbon radicals attached to the piperidine nitrogen atom, e.g. by dry distillation, with or without applying reduced pressure, or in a solvent of high boiling point. The aryl nucleus may be substituted whilst the piperidine nitrogen atom may have attached thereto methyl, ethyl, propyl, ally, benzyl or penylethyl radicals, and the piperidine nucleus may contain further substituents. In examples, 1 : 1-dimethyl-, 1 : 1-diethyl-, and 1 : 1 : 2-trimethyl - 4 - phenyl - piperidine - 4 - carboxylic acid betaines are heated alone or in a solvent of high boiling point, e.g. decahydronaphthalene, to produce the corresponding ester; 1 : 1-methyl-benzyl-4-phenyl-, 1 : 1-methyl-allyl-4-phenyl and 1 : 1-dimethyl-4-tolyl-piperidine-4-carboxylic acid betainers are heated under reduced pressure to produce the benzyl, allyl and methyl esters respectively; 1 : 1-methylethyl - 4 - phenyl - piperidine - 4 - carboxylic acid betaine is rapidly distilled without applying reduced pressure to produce 1-ethyl-4-phenyl - piperidine - 4 - carboxylic acid methyl ester. 4-Aryl-piperidine-4-carboxylic acid betaines are obtained by the hydrolysis, e.g. by means of mineral acids, with subsequent treatment with strong alkalis, e.g. potassium hydroxide, calcium hydroxide, or silver oxide, of 4-aryl-4-cyano-piperidinium salts, e.g. 1 : 1-dimethyl-4-phenyl-, 1 : 1-diethyl-4-phenyl-, 1 : 1 : 2-trimethyl-4-phenyl-, 1 : 1-methyl-benzyl-4-phenyl-, 1 : 1-methyl-allyl-4-phenyl, 1 : 1-dimethyl-4-p-tolyl, and 1 : 1-methy-ethyl-4-phenyl-4-cyanopiperidinium bromide. Specification 591,992 is referred to.