Binary composite ionic liquids [bmim][BF4] and [bmim][Ac] for electrochemical reduction of nitrobenzene

The binary composite ionic liquid mixtures composed of 1-butyl-3-methylimidazolium tetrafluoroborate (bmim]BF₄]) and 1-butyl-3-methylimidazolium acetate (bmim]Ac]) were studied and used in electroreduction of nitrobenzene for the first time. ¹H NMR and Fourier transform infrared (FTIR) spectroscopy were carried out to acquire a deep understanding of the interaction of binary ionic liquids, and UV/Vis spectroscopy was used to study the interaction between the mixture of ionic liquids and nitrobenzene. It was found that chemical shifts of all protons were changed and significant changes in the anion IR bands were induced, and the UV maximum absorption wavelength and absorbance of nitrobenzene in binary ionic liquids were different from those in the neat ionic liquid. The electrochemical reduction behavior of nitrobenzene in binary composite ionic liquids on platinum electrode was studied by cyclic voltammetry, in situ Fourier transform infrared spectroscopy, and constant potential electrolysis. Results indicated that the reduction of nitrobenzene in binary composite ionic liquids demonstrated higher current densities with a more positive potential, and the product (azobenzene) showed higher yield and selectivity in the composite ionic liquids than in the neat ionic liquids; the concentrations of water in the binary mixtures of ionic liquids had great effect on the electrochemical behavior of nitrobenzene. In the end, the mechanism of reduction of nitrobenzene in binary mixtures of ionic liquids was discussed.