Investigation of the Mechanisms of Electrogeneration of Anions
Recent studies of the mechanism of reduction of weak acids resulting in the formation of active anions are reviewed. The acids that were investigated included CH, NH and OH acids with pKa (DMSO) ranging from 1.6 to 19.8. Acids with pKa up to about 6 were reduced by a CE scheme involving prior dissociation of the acid giving the anion (conjugate base) and the solvated proton, the latter being discharged at the platinum cathode to produce dihydrogen. Acids with pKa greater than 6 cannot dissociate rapidly enough to produce the diffusion-controlled reduction currents that are seen. These acids are reduced by a different mechanism, direct discharge with simultaneous electron transfer and element-hydrogen bond breaking producing the anion and an adsorbed hydrogen atom. The CH acids in this group are thought to undergo tautomerization to OH or NH forms prior to reduction. In the case of ethyl nitroacetate and 2,4-pentanedione tautomerization is slow enough to become the rate-limiting step in the overall reaction scheme.
KeywordsDissociative Electron Transfer Direct Discharge Conjugate Base Solvate Proton Dichloroacetic Acid
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