Kinetics of the tautomeric conversions of monoazo-substituted chromotropic acids in solution

Abstract

1. The kinetics of the tautomeric conversions of monoazo-substituted chromotropic acids in aqueous solution have been studied by the temperature-jump method. In acid solution the quinone hydrazone equilibrium is established in < 10−5 sec; in alkaline solution, in <10−3 sec. 2. Tautomeric transitions proceed by a dissociative mechanism via acid-base catalysis, and in alkaline solution at pH < 11 are also catalyzed by H2O molecules. 3. It has been shown by pulse photolysis that in alkaline solution the azo-substituted chromotropic acids can undergo cis-trans photoisomerization. Cis-trans transitions do not take place in acid medium because of the formation of a quasiaromatic ring that stabilizes the trans form.