Supporting Information for:
Electrochemical reduction of 3-phenyl-1,2-benzisoxazole 2-oxide on boron-doped diamond
M. Kociolek*, J. Bennett, and J. Casbohm
School of Science, Penn State Erie, The Behrend College, 4205 College Drive, Erie, PA 16563
*Correspondence, mgk5@psu.edu
Contents:
1. Electrochemical analysis of reduction peak I
2. Supporting Figures
Figure S1: Plot of the reduction I peak potential as a function of the log scan rate
Figure S2: Comparison between the experimental cyclic voltammogram obtained for 3
mM 1a at a rate of 0.5 V/s with simulations approximated using the proposed
mechanism and electron transfer values of either 1 or 2 moles, respectively
The following analysis of the electrochemical data was performed to support the
determination that reduction peak I is indeed a 1-electron process. Since the reduction is
irreversible, the peak potential (Ep) should follow equation S1, where  is the transfer
coefficient, n is the number of electrons, ko is the apparent electrochemical rate constant, v is the
scan rate, and the remaining variables having there normal meaning:[1, 2]
Ep = E +
æ RTk ö æ 2.303RT ö
2.303RT
log ç
+ç
÷ log n
a nF
è a nF ÷ø è a nF ø
(S1)
Therefore a plot of Ep vs. log v will yield a slope of (2.303RT/nF) with the rest of the right side
of the equation representing the y-intercept. A plot of the Ep obtained from the voltammetric i-E
curves in Figure 2 as a function of log v is shown in Figure S1. As mentioned above, the
absolute slope of 0.1922 V/decade must equal (2.303RT/nF). A simple rearrangement can then
be used to calculate an n product of 0.30 (at T = 295 K). Since  tends to be in the range of
0.3-0.7 for most reactions,[3] an n value of 1-electron can be concluded.
S1
Reduction I Peak Potential
(V)
-2.3
y = -0.1922x - 2.6011
R² = 0.98775
-2.35
-2.4
-2.45
-2.5
-2.55
-2.6
-1.5
-1
-0.5
0
Log of Scan Rate (V/s)
Figure S1. Plot of the reduction I peak potential as a function of the log of scan rate.
Furthermore, by extrapolating the reduction peak potential values back to zero scan rate,
an estimated standard reduction potential of -2.33 V can be found. By substituting this value as
well as the n product of 0.30 into the y-intercept above, the apparent electrochemical rate
constant can be calculated to be 0.45 cm/s. This is similar to that used by Soucaze-Guillous and
Lund for benzaldoxime (1 cm/s) in 0.1 M TBATFB/DMF.[4]
Finally, a simulation of the proposed square scheme involving 1a, 2a, 2c and 2e was
approximated using the CH Instruments software and the calculated kinetic parameters from
above (including n = 1) as well as one using an n = 2 assumption (and  = 0.15 accordingly).
The apparent rate constant of 0.45 cm/s was used to model both the reduction I and the oxidation
II and the chemical steps, which experimentally appear to be comparatively fast, were estimated
at 100 s-1. A scan rate of 0.5 V/s was used and the simulations were compared to the
experimental data as shown in Figure S2. It is important to note that this software does not have
the ability to account for the high solution resistance, which exists in the 0.1 M TBATFB/ACN
solution, and so these results are merely an approximation and by no means a complete
evaluation. Regardless, it is clear that the experimental data for reduction I more closely
resembles the peak current associated with the 1-electron simulation. The difference in Ep and
S2
peak width of the simulation compared to the experimental curve is assumed to be due to the
unaccounted solution resistance.
Current (A)
500
0
-500
Experimental
1-electron reduction
2-electron reduction
-1000
-1500
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
Potential (V)
Figure S2. A comparison between simulated voltammetric i-E curves and that
obtained experimentally for 3 mM 1a. An apparent electron transfer rate constant of
0.45 cm/s and n product of 0.3 was used for both electrochemical steps. The rate
constant for the chemical steps was estimated to be 100 s-1 to make them fast
compared to the electrochemical steps.
Supporting References
[1]
[2]
[3]
[4]
E. Laviron, Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1979, 101, 19.
C. V. Uliana, G. S. Garbellini, K. Yamanaka, Journal of Applied Electrochemistry 2012, 42, 297.
A. J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications, 2nd ed., John
Wiley & Sons, New York, 2001.
B. Soucaze-Guillous, H. Lund, Acta Chemica Scandinavica 1998, 52, 417.
S3