Electrohydrodimerization Reactions VI . Rotating - Ring Disk Electrode and Macroscale Electrolysis Studies of the Second Reduction Wave of Diethyl Fumarate

The react ions occurr ing at potent ia ls of the second reduct ion wave of die thyl fumara t e (DEF) in d ime thy l fo rmamide solutions, where a cur ren t dip is f r equen t ly observed in the vo l t ammograms in the absence of added pro ton donors, was invest igated, The over -a l l react ion order was de te rmined by ro t a t ing disk e lec t rode studies of the var ia t ion in the current at the dip wi th DEF concentra t ion and theore t ica l resul ts obta ined by digi ta l s imulat ions, Ana l ysis of products of macroscale e lectrolyses by NMR and mass spectroscopy was also under taken . Severa l mechanisms are considered and one in which the e lec t rogenera ted dianion is p ro tona ted by the pa ren t DEF to produce a ca rb anion which can in i t ia te format ion of d imer ic and t r imer ic species is proposed. In recent years the re have been numerous inves t igations deal ing with the e lect rochemical reduct ion of diac t iva ted olefins in aprot ic media (1). For example , Baizer et al. (2) car r ied out polarographic , cyclic vol tammetr ic , and macroscale e lectrolysis exper iments and showed that the po la rog raphy of these compounds is character ized by two separa te reduct ion waves. Numerous expe r imen ta l studies of such systems (3-11), ut i l iz ing such e lect rochemical techniques as cyclic vo l tammetry , double potent ia l s tep chronocoulometry, ro ta t ingr ing disk e lect rode (RRDE) vo l tammetry , and e lect ron spin resonance (ESR) spectroscopy have shown tha t the p redominan t pa thway of the e lec t rohydrod imer iza t ion (EHD) react ion for reduct ion at the first wave consists of format ion of the rad ica l anion, RH2, fol lowed by d imer iza t ion and pro tona t ion RH2 + e -> RH2 " [1]