Recent investigations from this laboratory have shown that adiponitrile  (NCCH₂CH₂CH₂CH₂CN) / tetraethylammonium tetrafluoroborate  (TEABF₄)  is  a versatile solvent system  for organic electrochemistry (1,2).   The  extraordinarily wide  eight volt potential window noted in earlier work (3) has been confirmed and applied to the measurement of water (1) and electrodeposition of metals (4).  The positive limit at +5 V vs Ag/AgCl opens up another 2 V for study, compared to that of most other solvents.  The present paper addresses the usefulness of the positive potential region for oxidation of hydrocarbons.

Experimental

       Adiponitrile was obtained from Sigma-Aldrich, and tetraethylammonium tetrafluoroborate was purchased from Southwestern Analytical Chemicals. Cyclic voltammograms were obtained on a PAR 283 potentiostat using PowerSuite software.  Potentials are referenced against a Ag/AgCl reference electrode (1).

Results and Discussion

       A cyclic voltammogram of 15 mM naphthalene in adiponitrile / 0.2 M TEABF₄  is shown in the attached figure.  The reversible reduction of naphthalene is observed at -2.5 V, followed by an irreversible oxidation process at +1.74 V. Scan reversal at +2.00 V shows no reduction current associated with the oxidation process at 100 mV/s. If the potential scan is continued to +5.0 V,  considerable filming is observed, and the peak currents for the redox processes at -2.5 V are considerably lessened.  Similar behavior for naphthalene oxidation has been observed in acetonitrile (5), and the irreversible nature of the oxidation was ascribed to rapid coupling of naphthalene radical cations. These results show that the entire positive potential range in adiponitrile is available for study of the representative aromatic hydrocarbon naphthalene. 

References

1. G.T. Cheek,  ECS Trans., 58(46),  45-51 (2014).
2. G.T. Cheek,  ECS Trans., 61(30),  19-24 (2014).
3. H. Duncan, N. Salem, and Y. Abu-Lebdeh, J. Electrochem. Soc., 160 (6) A838-A848 (2013).
4. G.T. Cheek,  ECS Trans., 61(24),    9-14 (2014).
5. M.N. Cortona, N. Vettorazzi,  J. J. Silber, and L. Sereno, J. Electroanal. Chem., 394, 245-251 (1995).