Pyrene electrochemistry in MeCN-water solvent mixtures.

E.L. SVARTMAN; W. REATEGUI ROMERO; E. J. VASINI; J. A. CARAM; M. V. MIRÍFICO*

Los Cocos. Córdoba, Argentina.

Conferencia; 9th CLAFQO. 9a Conferencia Latinoamericana de Físico-Química Orgánica. 9th Latin American Conference on Physical Organic Chemistry.; 2007

It has been recently shown that quinone/hydroquinone redox couples can be obtained by the electroxidation of pyrene molecules covalently attached1 or physisorbed2 to an electrode submerged in an aqueous electrolyte. The possibility of a friendly electrochemical synthesis of pyrenequinones is studied in this work. Since pyrene is almost totally insolube in water the partial electrochemical oxidation of pyrene at platinum working electrode (WE) en MeCN-water mixtures was studied. The water concentration range extended from nominally dry MeCN to 20 M water. Cyclic voltammetry (CV) and controlled potential electrolysis (CPE) were performed in varied experimental conditions. In a typical  CV scan, a quasi reversible anodic peak was observed at ca. 1,2 V (p1a) (all potentials vs. SCE), as a shoulder of a larger anodic peak at ca. 1.4 V (p2a). The reverse scan showed a reversible couple at ca. -0.5 V. The couple at -0.5 V was also observed in CV experiments were the WE was withdrawn from the pyrene solution, washed, and submerged in a supporting electrolyte solution. A conducting gold-colored film, that remained attached to the electrode surface through the washing process, was deposited on the anode during the anodic scan. This film is believed to be responsible for the couple at -0.5 V. The increase of the water/MeCN ratio causes p2a to shift to lower potentials, at 1 M water concentration both peaks merge. The current intensities of p1a and p2a increase with water content up to a 1 M water concentration. The intensity of the merged peaks remains constant on further increase of the water content. The yield and current efficiency of the electroxidation products and their dependence of the different experimental parameters of the PCE experiments are reported. References 1) M. Mazur, G. J. Blanchard, Bioelectrochemistry, 66, 89-94 (2005). 2) M. Mazur, G. J. Blanchard, J. Phys. Chem. B, 108, 1038-1045 (2004).