Publication
604
J. Am. Chem. Soc. , 128, 8726 -8727, 2006.
DOI: 10.1021/ja0621750
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Carboxylates as Proton-Accepting Groups in Concerted
Proton-Electron Transfers. Electrochemistry of the 2,5-Dicarboxylate
1,4-Hydrobenzoquinone/2,5-Dicarboxy 1,4-Benzoquinone Couple
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Cyrille Costentin, Marc Robert, and Jean-Michel Savéant*
Contribution from the Laboratoire d'Electrochimie Moléculaire, Université de Paris 7-Denis Diderot, 2 place Jussieu,75251 Paris Cedex 05, France
Concerted proton and electron transfers (CPET) currently attract considerable
theoretical and experimental attention, notably in view of their likely
involvement in many enzymatic reactions. The role of carboxylate groups as
proton-accepting sites in CPET reactions is explored by means of a cyclic
voltammetric investigation of the 2,5-dicarboxy
1,4-benzoquinone/2,5-dicarboxylate 1,4-hydrobenzoquinone couple in a nonaqueous
medium. The presence of carboxylate groups ortho to the phenol groups induces
the removal of an electron to be coupled with the transfer of the phenolic
proton to a carboxylate oxygen. The kinetics of the electrochemical reaction and
the observation of a significant hydrogen/deuterium kinetic isotope effect
unambiguously indicate that electron transfer and proton transfer are concerted,
thus providing an additional demonstration of the role of carboxylate groups as
proton-accepting sites in concerted proton-electron transfer reactions. |
