The promoting role of polycations in the cobalt(ii) phthalocyanine tetrasodium sulfonate catalysed oxidation of thiols

Abstract

The oxidation of 2-mercaptoethanol with polymer-bound cobalt(II) phthalocyanine catalysts has been investigated. Poly(vinyl amine) (PVAm), poly(ethylenimine) (PEI), poly (L-ly sine) (PLL) and 2,4-, 2,6- and 2,10-ionene hydroxide have been studied as polymeric ligands. All these ligands appear to enhance the reaction rate considerably in comparison with their monomeric analogues and all exhibit a similar behaviour towards the effect of salt and pH. The reaction rate appears to increase virtually linearly with the linear charge density on the ionenes, which is consistent with recent findings for copolymers of vinyl amine and vinyl alcohol. Three main parameters seem to provide the enhanced polycationic catalytic effect: a high linear charge density on the polymer, a large amount of base groups in the polymer domain and a low ionic strength for the reaction solution. Furthermore, a comparison of the linear charge density, catalytic activity and activation parameters for the ionene catalysts with those obtained earlier for the vinyl amine-vinyl alcohol copolymers shows that the presence of hydrophilic side-groups has a promoting effect on the oxidation of the hydrophilic thiol. From catalyst re-use experiments, it appears that the polyamine catalysts (PVAm, PEI and PLL) have a poor stability, but that the ionene hydroxides can be re-used many times, probably as a result of the chemical inertness of the quaternary ammonium groups in the ionenes.