Mechanism of Solvent Extraction of Copper with 2Thiophenecarbaldehyde 2-Benzothiazolylhydrazone

Abstract

The equilibrium and rate of solvent extraction of copper (II) in 0.1 mol⋅dm-3 aqueous perchlorate media with 2-thiophenecarbaldehyde 2-benzothiazolylhydrazone (TBH) in benzene have been studied at 15-30°C. The plots of both log D'M vs. log[H+] and log D'M vs. log [HR]org showed straight lines with slope 2, where D'Mand [HR]og represent the distributi on ratio of copper and the TBH concentration in benzene, respectively. It was proved from the analysis of an electron spin resonance spectrum that the extracted copper (II) complex in benzene was paramagnetic. Consequently, the extracted species was assumed to be CuR2. The equilibrium constants of the copper (II) complex were determined; the extraction constant (log Kex), the distribution constant (log KDC) and the stability constants (log β1, log β2) were found to be 1.25, 2.45, 13.40 and 26.76, respectively. The rate of reaction w as found to be first-order with respect to the copper (II) ion and TBH concentrations, and zeroand inverse first-order with respect to the hydrogen ion concentration. On the basis of these results, the rate-determining step was assumed to be the formation of the 1: 1 chelate of copper (II) with TBH in aqueous phase. The formation reaction proceeds through two rea ction paths: the reactions of copper (II) with undissociated TBH (rate constant: 1.2 × 10⁴mol^-1 ⋅dm³⋅ s^-1) and with dissociated TBH (rate constant: 2.7 × 10¹⁰mol^-1 ⋅dm³⋅ s^-1). The temperature dependence of these rate constants was examined and the thermodynamic constants were calculated.