INFLUENCE OF THE MOLECULAR-WEIGHT OF IONENES ON THE COBALTPHTHALOCYANINE-CATALYZED AUTOXIDATION OF MERCAPTOETHANOL

In order to study the promoting effect of polycations on the cobalt(II )phthalocyanine-tetrasodiumsulphonate (CoPc(NaSO3)(4))-catalysed autox idation of thiols, it is imperative to know the molecular weight depen dence of the polymer. Monodisperse oligomers can often supply a lot of information. To elucidate the mechanism of the promoting effect of 2, 4-ionene, a poly(quaternary ammonium)salt, on the CoPc(NaSO3)(4)-catal ysed autoxidation of 2-mercaptoethanol, a series of monodisperse 2,4-i onene oligomers were prepared. Trimeric 2,4-ionenes, containing two qu aternary ammonium groups separated by four methylene groups, showed a high co-catalytic activity, and active Co-aggregates were detected wit h visible light spectroscopy. The spectroscopic behaviour was in close agreement with that of high molecular 2,4-ionene/CoPc(NaSO3)(4) compl exes. In order to achieve this aggregation several oligomeric ionenes have to act concertedly. If the distance between the ionic sites is sh ort, the trimer acts as a simple salt in stabilizing the aggregates. W ith respect to the catalytic activity the optimum polycation/catalyst ratio, expressed as the N+/Co ratio, decreased with increasing chain l ength and reached a constant level of 50 at a 2,4-ionene nonamer. For the trimers and pentamers this ratio is affected by the type of end-gr oup. All synthesized 2,4-ionene oligomers exhibited excellent co-catal ytic properties at the optimum N+/Co ratio, with maximum turnover freq uencies of 4600 mol thiol/(mol Co s), i.e. 50 times higher than those obtained for the polymer-free system. In the case of monodisperse 2,4- ionene pentamer with bromo end-groups, double Michaelis-Menten kinetic s were observed, as also was exhibited by high molecular weight ionene .