Electrosynthesis in room-temperature ionic liquids: benzaldehyde reduction

The electrochemical reduction of benzaldehyde at Pt microelectrodes in 1-butyl-1-methyl pyrrolidinium triflimide ([Bmpyr][NTF2]) room temperature ionic liquid is reported. At high potential sweep rates (>1000 V s(-1)) reduction occurs as two reversible one-electron reduction processes corresponding to the reversible formation of the radical anion (at -1.6 V versus Pt) and the dianion species (at -2.2 V versus Pt). The second order rate constant for radical anion-radical anion dimerisation was 1.4 x 10(4) mol(-1) dm(3) s(-1), while the pseudo-first-order rate constant for the subsequent formation of the alcohol (or electroinactive alcoholate) was 1000 s(-1). Kinetically, the electrochemistry is similar to that in acetonitrile or alkaline ethanol. At lower potential sweep rates, a third irreversible reduction occurs which appears to be the reduction of the pyrrolidinium cation as an ion-associated species with the anion products of the initial reductions. (C) 2004 Elsevier Ltd. All rights reserved.