Kinetic studies on the reaction between copper(II) ions and some dithiocarbonates using stopped-flow technique

The kinetics of the self-redox reaction of bis(R-dithiocarbonato)copper(II) complexes (R=Me, Et, i-Pr, i-Bu, 2-Bu, Oct) formed in situ by the mixing of water/alcohol solutions of Cu(II) salts and the corresponding alkali salts of the ligands are studied using stopped-flow spectrophotometric technique. It was found that: (i) maximal absorbance at 425 nm due to the studied complex is reached at Cu(II)/ligand ratio=1:2; (ii) reduction of Cu(II) to Cu(I) follows the kinetics of a second-order reaction in respect to the bis-chelate; (iii) the measured rate constants decrease with increasing the size of the remote ligand substituents; (iv) the rate constant depends on the type and the concentration of the alcohol in the solvent. The obtained results are discussed in terms of a self-redox reaction between Cu(II) and thiols proceeding within the associate between two bis(R-dithiocarbonato)copper(II) molecules without the formation of free radicals from the ligands.