Acid dissociation constants of N-alkyl p/o-hydroxy styryl pyridinium dyes in surfactant solutions

Some N-alkyl p/o-hydroxy styryl pyridinium halides, the alkyl moieties being methyl, hexyl and decyl, have been synthesised and the acid dissociation constants of these compounds in aqueous and surfactant solutions have been determined using spectrophotometric method. The alkyl chain does not have any substantial effect on the pK(a) values in aqueous and cationic surfactant (cetyl trimethylammonium bromide: CTAB) system. However, with longer alkyl chain the pK(a) values increase in anionic surfactant (sodium dodecyl sulphate: SDS). These results have been attributed to the variation in solubilization sites of the surfactants.