Electrochemical Studies of 9,10-Anthraquinone in Adiponitrile
Authors: Cheek Graham T. 
Published: February 2020

Introduction

The electrochemical behavior of quinones, as well as other carbonyl compounds, has been explored in many solvents (1), allowing the effect of additives to be examined in great detail (2,3). The extent of these interactions depends on the basicity of the carbonyl functions, the polarity of the solvent, and the nature of the additive. In the present work, adiponitrile has been chosen because it has not been widely applied to electrochemical investigations of organic compounds. The wide potential range, high boiling point, and reasonable polarity of adiponitrile (4,5) make it useful as a solvent for capacitors and battery systems (5,6), and these same qualities are expected to provide a good solvent system for organic compounds as well.

Experimental

Adiponitrile, 9,10-anthraquinone (AQ), and aluminum trifluoromethansulfonate [aluminum triflate, Al(TfO)3] were obtained from Aldrich Chemical Co. Tetraethylammonium tetrafluoroborate [TEA BF4] was purchased from Southwestern Analytical Chemicals (SACHEM). Voltammograms were acquired with a PAR283 potentiostat using PowerSuiteTM software. Potentials are reported with respect to a Ag/AgCl (0.1M EMICl in EMI BF4) reference electrode (Cypress Systems). Vitreous carbon electrodes were obtained from Cypress Systems. All experiments were carried out in a Vacuum Atmospheres drybox.

Results and Discussion

Cyclic voltammograms reveal that 9,10-anthraquinone undergoes two successive, reversible redox processes in adiponitrile / 0.20 M TEA BF4 ( Figure 1), as is also the case in acetonitrile (7). Upon addition of aluminum triflate to the solution, a new reduction peak, shifted to -0.40 V vs Ag/AgCl, appears. This peak is assigned to the reduction of AQ complexed by an aluminum cation. At the 1:1 AQ : Al(TfO)3 point, the peak at -0.40 V becomes completely dominant and is paired with an oxidation process at +0.60 V. For 9-fluorenone / Al(TfO)3 in adiponitrile, by contrast, the shifted reduction process is completely irreversible, with no corresponding anodic process. Another difference between 9-fluorenone and 9,10-anthraquinone in adiponitrile is the lack of interaction of the AQ dianion with the solvent in adiponitrile (8). This behavior is evidently due to the less basic nature of the AQ dianion compared to the 9-fluorenone dianion.

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Figure 1. Cyclic voltammogram of 14 mM 9,10-anthraquinone in adiponitrile / 0.20 M TEA BF4.

Vitreous carbon, 1 mm diameter, 100 mV / s

(a) 14 mM AQ only [ black curve ]

(b) With added Al(TfO)3, 0.40 mol Al(TfO)3 : 1.00 mol AQ [ red curve ]