The oxidation of tetra‐n‐butylammonium acetate, propionate, and pivalate was studied in rigorously anhydrous acetonitrile by conventional linear sweep and convolution voltammetry (LSV and ConV, respectively). The results suggest oxidation occurs via a concerted dissociative electron transfer pathway (RCO2−→R⋅+CO2+e−). The addition of water lowers the intrinsic barrier, signaling a possible change in mechanism to stepwise dissociative electron transfer. In rigorously dry acetonitrile, the oxidation potentials of CH3CO2−(0.60±0.09), CH3CH2CO2−, (0.47±0.05) and (CH3)3CCO2−(0.40±0.04 V vs. Ag/AgNO3(CH3CN, 0.1 M)) are reported. These values parallel the stabilities of the resulting free radicals, consistent with a possible concerted pathway, although differential solvation of the carboxylate anions cannot be completely excluded as a contributor to this trend.
The electrochemical reduction of several α,β ‐epoxyketones was studied using cyclic (linear sweep) voltammetry, convolution voltammetry, and homogeneous redox catalysis. The results were reconciled to pertinent theories of electron transfer. α,β ‐Epoxyketones undergo dissociative electron‐transfer reactions with C−O bond cleavage, via both stepwise and concerted mechanisms, depending on their structure. For aliphatic ketones, the preferred mechanism of reduction is consistent with the “sticky” concerted model for dissociative electron transfer. Bond cleavage occurs simultaneously with electron transfer, and there is a residual, electrostatic interaction in the ring‐opened (distonic) radical anion. In contrast, for aromatic ketones, because the ring‐closed radical anions are resonance‐stabilized and exist at energy minima, a stepwise mechanism operates (electron transfer and bond cleavage occur in discrete steps). The rate constants for ring opening are on the order of 108 s−1, and not significantly affected by substituents on the 3‐membered ring (consistent with C−O bond cleavage). These results and conclusions were fully supported and augmented by molecular orbital calculations.
more » « less- NSF-PAR ID:
- 10200353
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemPlusChem
- Volume:
- 85
- Issue:
- 11
- ISSN:
- 2192-6506
- Page Range / eLocation ID:
- p. 2387-2396
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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