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 lower potential limit at a Pt cathode in a tetrabutylammonium perchlorate solution in dimethylformamide (DMF), results not only in splitting of TBA+ cations via the Hofmann reaction, but also in hydrolysis of the solvent through 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 example, such products formed by electrochemical reduction of the background solution at a Pt cathode, interact with some electrophilic compounds present in the solution. In the case of polymers, it results both in dehydrohalogenation of halogenated polyolefins (polyvinyl chloride, poly(vinylidene fluoride), etc.) and in degradation of ester bonds in polycarbonates. That is, the solvent hydrolysis products are the active agents of the indirect electrochemical reductive degradation (ECRD) of polymers. The results obtained suggest 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 DMF hydrolysis are the agents of an indirect ECRD of polycarbonates. Undoubtedly, the electrochemically induced hydrolysis reactions can be minimized both in the thoroughly dried solutions, which have by our CV data a lower potential limit at Pt at about −3.0 V versus SCE, in the case of cathode materials with a high hydrogen overpotential.