Cryo-electrochemistry in tetrahydrofuran: The regioselective electrochemical reduction of a phenyl sulfone: Fast-scan cyclic voltammetry investigations

Abstract

Cryo-electrochemistry in tetrahydrofuran (THF) with microdisc chronoamperometry and bulk electrolysis has been applied to the reductive, alkyl–sulfur bond cleavage of the phenyl sulfone: [(3-{[trans-4-(methoxymethoxy)cyclohexyl]oxy}propyl)-sulfonyl]benzene (RSO2Ph). Preparative electrolyses show that the aliphatic carbon atom is cleaved both at room and low temperature. In the latter case, a higher yield of the reduced product: trans-1-(methoxymethoxy)-4-propoxycyclohexane (RH), was obtained as a consequence of the lower reactivity and stabilisation of the radical anion intermediate to follow-up chemical reactions. This can be inferred from the fact that the number of electrons, n, involved in the electrochemical reduction of RSO2Ph is greater than 1 at 298 K but close to 1 at low temperature as determined from microdisc-chronoamperometric experiments. In addition, fast-scan cyclic voltammetry at a microdisc electrode at both room temperature and low temperature (253 K) has allowed kinetic data to be extracted as a function of temperature. Both chronoamperometric and voltammetric analyses performed at low temperature proved significantly advantageous over room-temperature analyses. In particular, voltammetric waves and peaks were better resolved from the solvent window allowing accurate step potentials to well-defined steady-state plateaus used in chronoamperometric experiments, with voltammetric potential sweeps reversed without significant scanning into the solvent-decomposition window. The error involved in chronoamperometric fitting parameters, such as the number of electrons transferred, n, is shown to be smaller when the temperature is lowered. Finally, fast-scan cyclic voltammetry has been shown to be applicable for use in tetrahydrofuran and at low temperatures.