T. Shibusawa, T. Uchida
Jun 10, 1988
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Sen-i Gakkaishi
Abstract
Effects of the concentrations of sodium and hydrogen ions on the binding equilibria of 4-aminoazobenzene derivatives (model azo disperse dyes) by sodium salts of ƒÀ-naphthalenesulfonic acidformaldehyde condensates (ƒÀNSF) in water were determined spec trophotometrically; a ƒÀNSF with degree of condensation, N=40, was used. The detailed analysis of the results indicates that the binding of dye by the ƒÀNSF of a compact conformation is successfully described by an ion-exchange mechanism. At first, a trace amount of hydrogen ion in the solution is attached to the ƒÀ-azo nitrogen of the dyes, then the protonated dye (DH) competes with sodium (Na) and hydrogen (H) ions for the dyeing sites in the ƒÀNSF, -SO3-•@ The values of ion-exchange constants determined in the pH ranges of 4.126-4.9505 and 5.010-5.508 at 25•Ž were KH DH = 0.14-0.60 and KNa DH 3.8-9.2•~10-4 , respectively. The values of KDH obtained indicate the fact that the sulfonic acid group in the ƒÀNSF of a compact conformation behaves as a weak acid.