SCANNING ELECTROCHEMICAL MICROSCOPY .27. APPLICATION OF A SIMPLIFIED TREATMENT OF AN IRREVERSIBLE HOMOGENEOUS REACTION FOLLOWING ELECTRON-TRANSFER TO THE OXIDATIVE DIMERIZATION OF 4-NITROPHENOLATE IN ACETONITRILE

Scanning electrochemical microscopy (SECM) was employed to study the r ate of the second-order homogeneous reaction of a species electrogener ated at an ultramicroelectrode tip. Oxidation of 4-nitrophenolate in a cetonitrile to the phenoxyl radical took place at a gold ultramicroele ctrode (5-mu m diameter) held in close proximity to a larger substrate electrode that detected the tip-generated species. A radical dimeriza tion rate constant of 1.2 (+/-0.3) X 10(8) M(-1) s(-1) was determined. Approximate analytical equations for the treatment of irreversible ki netics following electron transfer were developed to simplify the anal ysis of feedback and collection data for both first- and second-order reactions. The effect of possible interference by the reference materi al added to allow precise determination of the tip-substrate spacing ( benzoquinone or ferrocene) was also investigated.