1080
J. Phys. Chem. 1981, 85,1069-1075
low-frequency permittivity so drastically because of the long dielectric relaxation times. The ion-solvent interactions can also play an important role in determining ionic mobilities in solutions, as discussed by Evans, Tominaga, Hubbard and Wolynes.” Further studies of depolarization in other hydrogen-bonding and aprotic solvents should help to define the relative magnitudes and importance of kinetic and static interaction effects; such studies by Winsor are underway in this laboratory. Finally, we believe that the results show the usefulness of time domain methods for study of solutions with ap(17) Evans, D. F.; Tominaga, T.; Hubbard, J. B.; Wolynes, P. G. J. Phys. Chem. 1979,83, 2669.
preciable conductivities. The accuracy of the methods used in this work was adequate for the principal objectives and has since been considerably improved by digital signal averaging rather than X-Y analog recording of the transients. It also seems possible to increase the upper frequency limit by modified cell design for smaller and better defined propagation effects.
Acknowledgment. We are indebted to both Lars Onsager and Joseph Hubbard for several stimulating and helpful discussions. Support of the National Science Foundation by Grant CHE-7822209 and by the Materials Science Program at Brown University is also acknowledged.
Studies of the EE Mechanism. Evidence for Reversible Dimer Formation in Electrochemical Oxidation of a Cyclic Dlthloether M. D. Ryan, Department of Chemistry, Marqueffe University, Milwaukee, Wisconsin 53233
D. D. Swanson, R. S. Glass, and G. S. Wllson’ Department of Chemistry, University of Arizona, Tucson, Arizona 85721 (Received: July 3, 1980; In Final Form: November 7, 1980)
The electrochemical oxidation of 1,5-dithiacyclooctane(DTCO) in acetonitrile has been shown to result in two closely spaced (AI3 = 20 mV) reversible one-electron-transfersteps. A reversible second-order chemical reaction is observed to follow production of the cation radical thus resulting in dimer formation. As the dimer is not electroactive at the potential of the initial process, its further oxidation or reduction must be preceded by dissociation. These conclusions are supported by cyclic voltammetry, controlled potential electrolysis, rotating disk electrode studies, and semiintegral analysis. The unusual ease of the second electron-transfer step is attributed to interactions between the two mesocyclic sulfur atoms.
The general mechanism involving two successive closely-spaced charge transfer steps (EE) has been the subject of a number of investigation~.l-~This situation may be represented by the following reactions:
A + B + e-
Elo’
B + B’
+ eB’ + C + eB
C
(1) (2)
EzO’
(34
E30’
(3b)
If Ezo’ >> Elo’that is, the second step (reaction 3a) is significantly more difficult than the first, two distinct successive steps are observed by cyclic voltammetry. The D. S. Polcyn and I. Shain, Anal. Chem., 38, 370 (1966). R. L. Myers and I. Shain, Anal. Chem., 41, 980 (1969). W. H. Smith and A. J. Bard, J. Electround Chem., 76, 19 (1977). M. D. Ryan, J . Electrochem. SOC.,125, 547 (1978). D. D. Macdonald, “Transient Techniques in Electrochemistry”, Plenum, New York, 1977. (6) D. L. Langhus and G. S. Wilson, Anal. Chem., 51, 1139 (1979). (7) G. S. Wilson, D. D. Swanson, J. T. Klug, R. S.Glass, M. D. Ryan, and W. K.Musker, J. Am. Chem. Soc., 101, 1040 (1979). (8) F. Ammar and J. M. Saveant, J. Electrounul. Chem., 47, 115 (1) (2) (3) (4) (5)
related disproportionation reaction
2B+A+C K (44 B + B’=A + C K’ (4b) with equilibrium constant, K, is defined by the relation Elo‘- E z O ’ (5) = log-’ 0.059
(
)
However, as Saveantlohas pointed out, under the condition Ezo’ >> El0’,reaction 4a does not occur significantly and the interpretation of the current-voltage curves is correspondingly straightforward. On the other hand, if EzO’5 Elo’or E30‘5 E
