Electrochemistry of 1‐Ethyl‐3‐methylimidazolium Chloride in Acetonitrile

The electrochemistry of 1-ethyl-3-methylimidazolium chloride (EMIC) is important because the reduction of the 1-ethyl-3-methylimidazolium cation (EMI + ) defines the negative potential limit of room temperature molten salt electrolytes made by mixing EMIC with AlCl 3 . Since EMIC constitutes both part of the solvent and the supporting electrolyte in the molten salt, it is difficult to examine its electrochemistry quantitatively in the melt. Thus, EMIC has been studied as an analyte at a glassy carbon electrode in acetonitrile with 0.1 M tetra-n-butylammonium perchlorate (TBAP) as the supporting electrolyte. EMI + is reduced at - 2.35 V measured vs. a reference electrode consisting of a silver wire in 0.1 M TBAP/CH 3 CN. Controlled potential coulometry indicates that the reduction is a one-electron process. Subsequent voltammograms exhibit two small oxidation peaks at -0.45 and -0.65 V but no new reduction peaks. Exhaustive oxidation of these two peaks gives less than 15% as many coulombs as for the initial reduction peak, indicating that the reduction of EMI' is irreversible. Comparison of the voltammograms to those for 1-methylimidazole indicates that the reduction process does not cleave the ethyl group from the five-membered ring to give the precursor of EMIC. Mass spectra of the reduction product shows no evidence of dimer formation. The dominant product of EMI + reduction is not electroactive within the accessible voltage window of acetonitrile or the molten salt. Thus, slight degradation of the electrolyte should not interfere with the operation of EMIC/AlCl 3 molten salt cells