Electro-oxidation of Benzyl Alcohol in a Biphasic System Consisting of Supercritical CO2 and Ionic Liquids

Abstract

Electro-oxidation of benzyl alcohol was conducted by electrolysis in an ionic liquid/supercritical CO2 (IL/SC CO2) two-phase system in an undivided cell at 318.2 K and up to 10.3 MPa, and two ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF6]), were used as the solvents and electrolytes. It was demonstrated that benzyl alcohol could be efficiently electro-oxidized to benzaldehyde. [Bmim][BF4] was more effective medium for the electro-oxidation of benzyl alcohol. The effects of various factors, such as pressure and the concentration of benzyl alcohol, on the reaction were studied as [Bmim][BF4] was used. The Faradic efficiency (FE) and selectivity of benzaldehyde increased with the pressure of CO2 when the pressure was lower than about 9.3 MPa, while the FE decreased as the pressure was increased further. This interesting phenomenon could be explained reasonably on the basis of solubility difference of the reactants and products...