Electrochemical and Spectroscopic Studies of 9,10‐Anthraquinone in a Room Temperature Molten Salt

Abstract : The electrochemical and spectroscopic properties of 9,10-anthraquinone (AQ) in the low-temperature AlCl3:n-butylpyridinium chloride (BuPyCl) molten salt system have been studied as a function of melt acidity. Infrared spectroscopic data indicate that AQ exists in the uncomplexed state in the basic melt (0.8 AlCl3:1.0 BuPyCl). The electrochemical behavior in this region involves a single-process two-electron reduction (with slow electron transfer) of AQ to its dianion, the reduction mechanism probably proceeding by an ECE pathway. Oxidation of the dianion back to AQ occurs at a potential considerably positive (600mV) of the potential for AQ reduction, thus indicating some interaction of the dianion with the melt. The complexation of AQ by Al2Cl7 - in the acidic melt (1.2 AlCl3:1.0 BuPyCl produces AQ.2AlCl3 as indicated both by infrared spectroscopy and chemical analysis. This complexation results in a shift in potential for the reduction process compared to the corresponding potential for AQ reduction in the basic melt of +1.4V. The reduction of AQ.2AlCl3 also involves a single-wave two-electron process (with faster electron transfer than in the basic melt), thought to proceed by a disproportionation mechanism.