POLYMER-SUPPORTED METAL-COMPLEXES AS CATALYSTS FOR THE OXIDATION OF THIOSALTS BY MOLECULAR-OXYGEN .5. THE POLYTHIOSEMICARBAZIDE-CU(II) COMPLEX

Polythiosemicarbazide obtained by the condensation of N,N prime -diaminopiperazine with methylene bis(4-phenyl isothiocyanate) has been complexed with copper(II) and used to catalyse the oxidation of S//2O//3**2** minus and S//4O//6**2** minus by molecular oxygen in a batch reactor, employing the catalyst as a 2% (w/v) slurry. The oxidation rate of S//2O//3**2** minus was several times higher than that of S//4O//6**2** minus , while the rates of both the thioanions were significantly influenced by the thioanion concentration, the pH and the temperature. The product distribution pattern in batch oxidation may be modelled by a three-stage reaction mechanism. In stage I, a part of the S//2O//3**2** minus in the feed is rapidly oxidized to S//4O//6**2** minus by an electron-transfer redox reaction with the polymeric Cu(II) complex, while in stage II S//2O//3**2** minus and S//4O//6**2** minus are oxidized to SO//4**2** minus by O//2 on the catalyst by series-parallel reaction paths. In stage III, which begins with the disappearance of S// 2O//3**2** minus , S//4O//6**2** minus is oxidized by O//2 to SO//4**2** minus on the catalyst.