Interaction of 9, 10‐Anthraquinone with Tetrachloroaluminate and Proton in Basic Aluminum Chloride: 1‐ethyl‐3‐methylimidazolium Chloride Room‐Temperature Molten Salts

Abstract

The electrochemical behavior of 9, 10‐anthraquinone (AQ) in a basic room‐temperature molten salt composed of a mixture of AlCl3 and 1‐ethyl‐3‐methylimidazolium chloride false(normalImClfalse) is described. In the absence of a proton source, AQ is reduced via a quasireversible two‐electron transfer to AQfalse(AlCl3)2− . The homogeneous chemical steps coupled to the electron transfers are displacement of Cl− from AlCl4− to form AQfalse(AlCl3)22− . Addition of a proton source, imidazolium hydrogen dichloride false(ImHCl2false) , causes the coupled chemical reactions to shift from solvent leveling of reduced AQ by AlCl4− to more facile protonation steps. Visible spectroscopy of AQ in 0.8:1 melt and neat ImHCl2 show that AQ is present as the neutral, unprotonated quinone in its oxidized form. The two‐electron, two‐proton reduction product 9, 10‐dihydroxyanthracene false(AQH2false) is formed under these conditions but is unstable in the AlCl3:normalImCl melt. It is converted to AQfalse(AlCl3)22− , which is the reoxidizable form, regardless of whether protons are present in the melt. AQH2 is stable on the voltammetric time scale in neat ImHCl2 . Under these conditions, the hydroquinone is formed exclusively and the electrochemistry tends toward that of the classical 2 e−, 2 H+ case found in aqueous systems. Experiments in molten normalImCl , at 90°C, show that the quinone anion radical and dianion are stable only under conditions where no Lewis acid is available for adduct formation.

Quinone Based Materials as Renewable High Energy Density Cathode Materials for Rechargeable Magnesium Batteries

“…This is an important limitation, especially for Mg electrolytes, which are mostly based on ether solvents that have significantly lower oxidative limits than carbonate solvents, typically used in Li-ion batteries. Although no voltage upshift was reported in the MTC electrolyte, some older literature reports and recently published battery studies show a considerable upshift of AQ redox potential in AlCl 3 containing Al and Mg electrolytes [11,12,28,29]. Thus, we wanted to check if the effect could be generalized also on other electroactive groups in MAC electrolyte, which contains AlCl 3 .…”

Electrochemical reduction of quinones in ethaline chosen as an example of deep eutectic solvent

“…In relation with the present work, some investigations have concerned the reduction of quinone in ionic liquids that have been analyzed in view of the mechanisms reported in molecular solvents taking into account the strength of the hydrogen-bonding characteristics of the ionic liquids. [14][15][16][17][18] Quinones were notably selected as model compounds for evaluating the properties of ionic liquids as electrolytes and compared with molecular solvents. [18] Besides the basic studies, this also led to electrochemical applications in selected ionic liquids as the CO 2 separation from a gas mixture.…”

Quinone Reduction in Ionic Liquids for Electrochemical CO2 Separation

“…Protonation in acidic media and the consequent hydrogen-bonding shift the second reduction to more positive potentials. , Because of their varying degrees of ionicity, , ILs, which act as both the electrolyte and the solvent, can have more a specific influence on the quinone reduction than do more conventional solvents . A few studies have reported quinone reduction in imidazolium-based ILs in the solution phase − and when bound to the electrode surface . In these studies, in order to eliminate the complications associated with metal speciation when using metal-based redox agents, quinones were selected as model redox probes for the evaluation of the IL properties as electrolytes.…”