Towards the electroreduction of very weak acids

Abstract In order to improve the understanding of the synthesis of electrogenerated bases (EGB), the electrochemical reduction of two weak acids, 2-pyrrolidone (p K a (DMSO)=24.2 and hexamethyldisilazane (HMDS, p K a (DMSO)=26), has been compared in DME+HMPA+Et 4 NBF 4 solution using the sacrificial magnesium anode method in an undivided cell under constant current. Both acids are reduced at transition metal cathodes to form dihydrogen and their conjugate base (as evidenced by their deprotonation abilities) whereas no gas evolution is observed at non-catalytic surfaces such as glassy carbon. Kinetic studies of dihydrogen evolution at Pt, stainless steel, Fe and Ni, throughout the electrolysis showed different behavior: a theoretical current efficiency (CE=1) characterizes 2-pyrrolidone, but HMDS needs a latency period with slow gas evolution mainly corresponding to reduction of HMPA, followed by a faster and linear evolution period during which HMDS is predominantly reduced (51 K a value for ‘category II acids’, which corresponds to a diffusion controlled process, while HMDS behaves differently without any observable reduction peak, probably showing a charge transfer controlled mechanism.