Electrochemical Studies of 9,10-Anthraquinone in Adiponitrile

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 PowerSuite^TM    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.

References

1. N. A. Macýas-Ruvalcaba and D. H. Evans,  J. Phys. Chem. C, 114, 1285 (2010).
2. N. Gupta and H. Linschitz,  J. Am. Chem. Soc., 119, 6384-6391 (1997).
3. D. Yu Ge, L.  Miller, T. Ouimet, and D. K. Smith,  J. Org. Chem.,  65 (26), (2000).
4. P. G. Sears, J. A. Caruso, and A. I. Popov,  J. Physical Chemistry, 71 (4), 905 (1967).
5. H. Duncan,  N. Salem, and Y. Abu-Lebdeh,  J. Electrochem. Soc., 160 (6), A838 (2013).
6. A. Brandt, P. Isken, and A.  Lex-Balducci,  J. Power Sources, 204, 213 (2012).
7. L.  Jeftic and G. Manning,  J. Electroanal. Interfacial Echem, 26, 195 (1970).
8. Electrochemical Society 224^th Meeting, Fall 2013, San Francisco, CA, ECS Abstract I1-2481.

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 ]