Complexation of polymer-bound imino diacetate-type chelating agents with some transition-metal ions. Effect of charged polymer chains on chelate formation reactions

Abstract

Acid dissociation constants (K_a) of the polymer-bound imino diacetate analogue, 4-vinylbenzylamine-N, N′-diacetate co-styrenesulphonte (P-SS) and 4-vinylbenzylamine-N, N′-diacetate co-N-vinylpyrrolidone (P-VPRo), and the formation constants of (P-SS)–M²⁺(M = Co, Ni, Cu) chelates have been determined by means of potentiometric titration and spectrophotometry, respectively. The values of K_a1 and K_a2 of P-SS and P-VPRo are smaller than those of the corresponding low molecular weight model compound, benzylamine-N, N′-diacetate (BDA), and the formation constants of the (P-SS)–M²⁺ chelates are larger than those of the corresponding BDA–M²⁺ chelates by a factor of 10–10², depending on the metal ions. The results obtained in the polymer system are largely explained in terms of a powerful microheterogeneous field effect of the anionic polyelectrolyte chain.