The Effect of H-Bonding and Proton Transfer on the Voltammetry of 2,3,5,6-Tetramethyl-p-phenylenediamine in Acetonitrile. An Unexpectedly Complex Mechanism for a Simple Redox Couple

作者：Clare Laurie A; Rojas Sligh Lydia E; Maciejewski Sonia M; Kangas Karina; Woods Jessica E; Deiner L Jay; Cooksy Andrew; Smith Diane K^*

来源：Journal of Physical Chemistry C, 2010, 114(19): 8938-8949.

DOI：10.1021/jp100079q

The voltammetry of 2,3,5,6-tetramethyl-p-phenylenediamine, H(2)PD, has been studied and compared to that of its isomer N,N,N',N'-tetramethyl-p-phenylenediamine, Me(2)PD. Both undergo two reversible electron transfer processes in acetonitrile that nominally correspond to 1 e- oxidation to the radical cations, Me(2)PD(+) and H(2)PD(+), and a second 1 e- oxidation at more positive potentials to the quinonediimine dications, Me(2)PD(2+) and H(2)PD(2+). While the voltammetry of Me(2)PD agrees with this simple mechanism, that of H(2)PD does not. The second voltammetric wave is too small. UV vis spectroelectrochemical experiments indicate that the second wave does correspond to oxidation of H(2)PD(+) to H(2)PD(2+) in solution. The fact that the second wave is not present at all at the lowest concentrations (5 mu M), and that it increases at longer times and higher concentrations, indicates that H(2)PD(+) is not the initial solution product of the first oxidation. A number of lines of evidence suggest instead that the initial product is a mixed valent, H-bonded (timer between one H(2)PD in the full reduced, fully protonated state, H(4)PD(2+), and another in the fully oxidized, fully deprotonated state, PD. A mechanism is proposed in which this dimer is formed on the electrode surface through proton transfer and H-bonding. Once desorbed into solution, it breaks apart via reaction with other to give 2 which is the thermodynamically favored species in solution.

• 出版日期2010-5-20