Collection of Czechoslovak Chemical Communications - digital archive 

Abstract

The effect of cationic (hexadecylpyridinium bromide, hexadecyltrimethylammonium bromide, Septonex), anionic (sodium dodecyl sulfate) and nonionic (Brij 35, Triton X-100) surfactants on the deprotonation of the phenolic oxygen in bromophenol red, bromophenol blue and bromocresol green is studied. The conditional dissociation constants K_ai^* depend on the surfactant concentration and, in the alkylpyridinium surfactant series, on the alkyl chain length at a constant concentration of inert electrolyte, and on the concentration of the inert electrolyte (Cl^-, Br^-, NO₃^-, SO₄^2-, H₂PO₄^-, CH₃COO^-, HCOO^-, ClO₄^-) or of the sulfophthalein dye at a constant concentration of a cationic surfactant. In acid and alkaline solutions, cationic surfactants (tensides, T) and the dyes (H₂L) form ionic associates with the stoichiometric composition {T⁺, LH^-} and {T₂⁺, L^2-}, respectively, exhibiting absorption maxima at 400-430 nm (ε = 1.3-2.0 m² mmol^-1) and at 570-630 nm (ε = 3.5-4.5 m² mmol^-1), respectively, formation of these associates was confirmed for chloroform extracts by the continuous variations and molar ratios methods.