(750h) Understanding the Roles of Water during Electrochemical C-H Activation in Thermodynamically Non-Ideal Blended Electrolytes

Water represents an abundant and benign oxygen-atom (O-atom) source in the context of organic synthesis which can be activated through the application of an electrical potential. Many organic substrates we may wish to oxidize, however, are not soluble in water at high concentrations. This warrants the implementation of blended aqueous/nonaqueous liquid electrolytes which contain water as an O-atom source, an electrochemically stable organic solvent to facilitate substrate solubility, and a suitable electrolyte salt to provide conductivity. We demonstrate the efficacy of such an electrolyte in enabling C-H activation of xylene with water as the O-atom source to selectively form the partially oxidized product p-tolualdehyde. In studying the mechanism of this electrochemical reaction, we show that measurements of the dependence of the reaction rate on water concentration are obscured by non-idealities due to mixing in the blended electrolyte system. We argue for the necessity of the quantification of such non-idealities when seeking mechanistic insights pertaining to reactions taking place in blended aqueous/nonaqueous electrolytes. We present our method for accounting for solvent non-idealities in the context of our blended electrolyte system, as well as a revised order of the reaction with respect to water. We also offer interpretation for our results, evaluating the complex interplay of water as O-atom source, proton acceptor, and co-solvent.