The Tautomeric Equilibria of 4-(Dialkylamino)azobenzene Derivatives. II. 2- and/or 2′-Methyl-4-(dimethylamino)azobenzene Derivatives

Abstract

Abstract The tautomeric equilibrium constants, Kt=[ammonium ion]/[azonium ion], of the first conjugate acids of 2- and/or 2′-methyl-4-dimethylaminoazobenzene derivatives were estimated by the spectrophotometric method. The effects of the 2- and 2′-methyl groups on the basicity of the amino and the azo nitrogens were examined in order to explain the effects on the tautomeric equilibrium. The effects of the 2- and 2′-methyl groups on the basicity of the amino nitrogen is an inductive one only, while the effects on the basicity of the azo nitrogens are both electronic and steric. The latter effect of the 2′-methyl group is very large, but that of the 2-methyl group is not significant. The order of Kt in a series of compounds is almost the same as that of the basicity of the azo nitrogens. That is to say, the magnitude of Kt is mainly governed by the basicity of the azo nitrogens.