Studies of Polymeric Flocculants. IX. The Formation of Poly(methacrylohydrazide)–Copper(II) Complexes

Abstract

Abstract Formation constants for the complexes of poly(methacrylohydrazide) (PMH) with the copper(II) ion were measured by using a modification of Bjerrum’s method proposed by Gregor and his coworkers. The pKa1 and pKa2 values of PMH determined in an aqueous solution with an ionic strength of 0.1 (KNO3) at 25 °C were 3.20 and 10.61 respectively. Therefore, when the PMH-copper(II) complexes were formed above pH 7, the average number of ligands combined with one metal ion could be calculated approximately without using the first acid dissociation constant. The pKa2 value decreased with an increase in the ionic strength and temperature. The formation curves of the complexes showed that one copper(II) ion formed a coordination compound with six hydrazide groups in a high pH region (about pH 9). The formation constants increased with an increase in TCu/THL (the ratio of the total concentration of the copper(II) ion to the total concentration of the ligand) in the range higher than 0.1. The formation constants were unaffected by the degree of polymerization of PMH in the range from 64.1 to 5470, but the formation constants were affected by the kind of anion in copper(II) salts and neutral salts added and they increased in the order of NO3−<SO42−<Cl−. The thermodynamic parameters for the above reaction were determined by Ringbom’s method.