GB623323A - Preparation of n-aryl-2-4-diketo-tetrahydro-quinoline - Google Patents

Abstract

N-Aryl-2 : 4-diketo-tetrahydroquinolines are prepared by heating the corresponding N-monoaryl-o-aminobenzoic acid with acetic anhydride in the presence of added glacial acetic acid. The amount of glacial acetic acid added may be as low as 1 : 10 or as high as 20 : 1 of the weight of the N-monoaryl-o-aminobenzoic acid and is preferably in the ratio of from 1 : 2 to 5 : 1. The acetic anhydride is preferably present in an excess over the theoretical proportions. The preferred reaction temperature is from about 70-100 DEG C. In an example acetic anhydride is added to N-(21-methoxyphenyl)-anthranilic acid in glacial acetic acid at 80 DEG C. giving N-(21 methoxyphenyl)- 2 : 4-diketo-tetrahydroquinoline. Other monoaryl-o-amino-benzoic acids which may be used are those in which the aryl radical on the N atom is of the benzene or naphthalene series and may be substituted by alkyl, cycloalkyl, alkoxy, aryloxy or an aryl group or a halogen atom such as chlorine or bromine or an amino, hydroxy, carboxy or nitro group.ALSO:Azo dyes.-N -(21-Methoxyphenyl)-2 : 4-diketo-tetrahydroquinoline may be used as a coupling component in the manufacture of azo dyes.