Potentiometric and Thermodynamic Studies of 4-Sulfamethazineazo-3-methyl-1-phenyl-2- pyrazolin-5-one and Its Metal Complexes

Abstract

Proton–ligand dissociation constants of 4-sulfamethazineazo-3-methyl-1-phenyl-2- pyrazolin-5-one (SMP) and metal–ligand stability constants of its complexes with bivalent metal ions (Mn²⁺, Co²⁺, Ni²⁺ , Cu²⁺, and Zn²⁺) have been determined potentiometrically in 0.1 M KCl, and a 40% (v/v) ethanol–water mixture. The order of the stability constants of the complexes was found to be Mn²⁺ < Co < Ni < Cu < Zn. The dissociation constants, pK ^H, of SMP and the stability constants, log K, of its complexes were determined at different temperatures and the corresponding thermodynamic parameters (Δ G, Δ H, and Δ S) were derived and discussed. The dissociation process is nonspontaneous, endothermic, and entropically unfavorable. The formation of the complexes were found to be spontaneous, endothermic, and entropically favorable.