Ion exchange membranes as solid polymer electrolytes ( spe) in electro-organic syntheses without supporting electrolytes

Abstract

Ion exchange membranes can function as solid polymer electrolytes ( spe) in non-conductive liquids and therefore electro-organic syntheses are possible without supporting electrolytes. This approach can reduce the process steps for separating and recycling of supporting electrolytes and also side-reactions with such electrolytes are impossible. Advantages of the spe process have been verified by reactions using cation or anion exchange membranes combined with various electrode materials in aqueous and non-aqueous media, using galvanostatic experiments with current densities of 0.12–1.0 kA/m 2, membrane areas up to 250 cm 2 and in continuous operation up to eight months. The methoxylation of furane showed that reactions take place in the spe process without supporting electrolyte only at the electrodes but not in the inert cell liquid. Alkoxylations of N-alkylamides, without any additive in nonaqueous media, give selectivities of nearly 100% at low cell voltages. Important factors in the spe process are an optimal contact in the electrode/membrane combination and the electro-osmotic transport through the membrane, which enhances the mass transfer at the electrodes giving improved selectivity. A pretreatment of the membrane by intensified swelling benefits both these parameters.