Electrochemical Investigation of Quinone Complexation by Lewis Acids in a Chloroaluminate Ionic Liquid

Abstract

The electrochemical behavior of 9,10-anthraquinone (AQ) has been investigated in the initially neutral aluminum chloride : 1-ethyl-3-methylimidazolium chloride ionic liquid. It has been found that AQ is characterized by a single irreversible redox process in the neutral melt. Additions of AlCl3 cause a positive potential shift, first by the formation of two reversible redox processes corresponding to AlCl3 complexes of AQ under mildly acidic conditions, and then by the appearance of a shifted irreversible redox process in an acidic melt. HfCl4 additions cause similar behavior, except that the reversible systems persist at higher Lewis acid levels than for AlCl3. At the 11:1 Lewis acid: AQ point, AQ is still soluble as an orange solution for AlCl3 additions, but a yellow solid precipitates from a yellow (amber) solution for HfCl4 additions.