The electrochemical reduction of 1,2-di(4-pyridyl) ethylene in an aqueous medium

The electrochemical reduction of 1,2-di(4-pyridyl)ethylene has been examined between H-0=-2 and pH 14. For pH>6.5 a global 2e(-), 3H(+) or 2e(-), 2H(+) surface reversible reaction leads to the quinoidal form already proposed by Volke and Holubek (Cell. Czech. Chem. Commun. 27 (1962) 1777); it is followed by an internal transfer of two protons to give 1,2-di(4-pyridyl)ethane. The rate constant for this first order process varies from 47 s(-1) below pH 8.5 to 5.5 s(-1) above pH 11.5. The variations of the global rate constant of the electrochemical reaction with pH are analyzed; the process is controlled by the first 1e(-) stage; the elementary surface rate constants are larger than 2 x 10(5) s(-1). (C) 1997 Elsevier Science S.A.