Kinetic studies of the solvent extraction of metal complexes—I: The rate of extraction and back-extraction of Zr(IV) 1-phenyl-3-methyl-4-benzoyl-pyrazolonate chelate in aqueous sulphate solution-chloroform systems

Abstract

The rate of forward extraction of Zr(IV) from 2M sulphuric acid into 1-phenyl-3-methyl-4-benzoyl-pyrazole-5-one (HP z) dissolved in chloroform and backward extraction of the tetrakis-chelate, Zr(Pz) 4 have been measured under various conditions. The rate of forward reaction is proportional to [Zr 4+], [HP z] 2 and [H +] −2, while that of back extraction to [Zr(Pz) 4] org, [HP z] org −2 and [H +] 2. The rate determining step in the forward extraction is established to be the formation of the second complex between the dissociated form of HPz, Pz − and the Zr(H 2O) 2SO 4Pz + species in the aqueous phase while it is the reverse in the backward extraction. The velocity constants for both rate controlling steps have been determined and the extraction constant agrees with the value obtained from the equilibrium data.