Studies of Adiponitrile As a Solvent for Ketone Electrochemistry
Authors: Cheek Graham T. 
Published: February 2020

Introduction

Recent work in this laboratory has involved the use of adiponitrile [NC(CH2)4CN] as an electrochemical solvent (1). For some applications, adiponitrile combines such desirable characteristics as moderately high dielectric constant, high boiling point, and an extremely wide potential range (2, 3). At this point, adiponitrile has been mostly confined to work with capacitors (4) and Li-ion batteries (3). The present abstract represents work involving the use of adiponitrile as an electrochemical solvent for organic electrochemistry, specifically dealing with the complexation of the ketone 9-fluorenone by added aluminum ions. Recent work involving 9-fluorenone has been carried out in acetonitrile (5) and the ionic liquids 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate [BMPY TfO] and 1-ethyl-3-methylimidazolium tetrafluoroborate [EMI BF4] (1,6,7), providing useful comparisons to the present work.

Experimental

Adiponitrile, 9-fluorenone, 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 taken 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

In adiponitrile / 1.0 M TEA BF4, 9-fluorenone undergoes two successive one-electron redox process as shown in the figure at the end of this abstract. The second process is not strictly reversible due to proton donation from adiponitrile to the fluorenone dianion (1). Upon addition of aluminum triflate, two changes are observed in the voltammogram. First, a new reduction process appears at -0.6 V vs Ag / AgCl and is due to complexation of fluorenone by the aluminum cation. There is also an extensive shift of the usual first fluorenone reduction process from -1.25 V to -1.1V, due to interaction of the fluorenone radical anion with aluminum cation during the fluorenone reduction process. It should be noted that aluminum triflate is reducible in adiponitrile only as a broad, low-current process from approximately -2 V to -3 V, so that aluminum reduction does not interfere with the voltammetry shown in the figure. It is also planned to present interesting comparisons between fluorenone / Al3+interactions in adiponitrile and in the 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate [BMPY TfO] ionic liquid system.

These results indicate that adiponitrile is useful for studies of Lewis acid interactions with the model ketone 9-fluorenone. The wide potential range of adiponitrile / 1.00 M TEA BF4 allows the full characterization of those interactions.

References

1. G. Cheek, Abstract I1-2481, 224thElectrochemical Society Meeting, San Francisco, CA, 29 October 2013.

2. P. G. Sears, J. A. Caruso and A. I. Popov, Journal
of
Physical
Chemistry, 71(4), 905 (1967).

3. H. Duncan, N. Salem, and Y. Abu-Lebdeh,
J. Electrochem. Soc., 160 (6) A838-A848 (2013).

4. A. Brandt, P. Isken, A. Lex-Balducci, A. Balducci, Journal of Power Sources, 204, 213 (2012).

5. D. S. Canby and G. T. Cheek, ECS Trans., 3(35), 609 (2007).

6. G. T. Cheek, ECS Trans., 35(16), 17 (2011).

7. D. Canby, E. Sanders, and G.T. Cheek, J.Electrochem. Soc., 160(7), G3159 (2013).

Figure : Cyclic voltammograms in adiponitrile (1.00 M TEA BF4) at 1 mm diameter vitreous carbon, 100 mV/s.

(a) 45 mM 9-fluorenone [ black curve ].

(b) After addition of 1 : 1 Al(TfO)3 : fluorenone [ red curve ].