PROTOLYTIC EQUILIBRIA OF INDOLE AND SEVERAL INDOLECARBOXYLIC ACIDS INMICELLAR MEDIA

The influence of two cationic micellar systems on the absorption and f luorescence spectra and on the acid-base equilibria of indole and indo le-2-, 3-, 4- and 5-carboxylic acid are studied. Indole-2- and indole- 4-carboxylic acid on the one hand, and the 3- and 5-substituted deriva tives on the other, show similar values of pK(COOH) in the micellar me dia of hexadecyltrimethylammonium bromide and benzyldimethylhexadecyla mmonium chloride. The same equilibrium in the excited state shows a de crease in the acid character of the 4- and 5-carboxylic derivatives. I n the excited state, all the compounds show two equilibria associated with protonation of the heterocyclic ring and deprotonation of pyrroli dine nitrogen. The pK(a1)() and pK(a3)(*) values of indole and carbox ylic acid derivatives are influenced by the nature of the medium, the position of the carboxyl group and the nature of the hydrocarbon chain of the surfactant.