Reactions at the lower potential limit in aprotic medium at a platinum cathode revisited: their role in indirect electrochemical reductive degradation of polymers

Formation of hydroxyl ions when reduction of residual water occurs at the l ower potential limit at a Pt cathode in a tetrabutylammonium perchlorate so lution in dimethylformamide (DMF), results not only in splitting of TEA (+) cations via the Hofmann reaction, but also in hydrolysis of the solvent th rough an intermediate charged complex into dimethylamine (DMA) and a formic acid anion. These solvent hydrolysis products can play a significant role in reactions, which may occur in electrochemical organic systems. For examp le, such products formed by electrochemical reduction of the background sol ution at a Pt cathode, interact with some electrophilic compounds present i n the solution. In the case of polymers, it results both in dehydrohalogena tion of halogenated polyolefins (polyvinyl chloride, poly(vinylidene fluori de), etc.) and in degradation of ester bonds in polycarbonates. That is, th e solvent hydrolysis products are the active agents of the indirect electro chemical reductive degradation (ECRD) of polymers. The results obtained sug gest that an intermediate charged complex of an aprotic solvent (DMF, MeCN) with OH ions plays the governing role in the indirect ECRD of halogenated polyolefins. Furthermore, this complex and the DMA which appeared due to DM F hydrolysis are the agents of an indirect ECRD of polycarbonates. Undoubte dly, the electrochemically induced hydrolysis reactions can be minimized bo th in the thoroughly dried solutions, which have by our CV data a lower pot ential limit at Pt at about - 3.0 V versus SCE, in the case of cathode mate rials with a high hydrogen overpotential. (C) 2000 Elsevier Science S.A. Al l rights reserved.