In the course of studying a series of aromatic amines it was found that in some cases upon electrochemical oxidation, benzyl-type radicals were formed and these rapidly coupled ~'2. There appears to be a paucity of data in the literature concerning the reactivity of benzyl-type free radicals, as opposed to phenyl radicals 3, so a study was undertaken to determine the reaction pathways of nitrobenzyl radicals generated by electrochemical reduction of the isomeric nitrobenzyl halides in non-aqueous media. A study of these compounds takes on added significance in light of their importance in the mechanism of antibacterial action 4 and in chigger and nematode control 5.6.
Shortly after the present work was submitted for publication, Hawley and co-workers 7 reported similar studies. They found that bibenzyl formation predominated for the o-and p-nitrobenzyl halides whereas the only detectable electrolysis product from the m-nitrobenzyl halides was m-nitrotoluene. Their studies were carried out at approximately milliformal concentrations in acetonitrile (MeCN). Our investigations included concentrations varying from 10-1 to 10-5 F in both MeCN and N,N-dimethylformamide (DMF) and utilized e.p.r, spectroscopy as a sensitive probe to detect the various radical species formed. In addition, the effects of oxygen on these systems was investigated in some detail.
EXPERIMENTAL
All of the isomeric nitrobenzyl halides, nitrotoluenes, nitrobenzaldehydes and nitrobenzoic acids were obtained commercially and purified by recrystaUization, sublimation or vacuum distillation. The 2,2'-and 4,4'-dinitrobibenzyls were also commercial products and were purified by recrystallization. The 3,3'-dinitrobibenzyl was prepared from m-nitrobenzyl bromide via an Ullman synthesis using Baker copper powder as catalyst and no solvent.
N,N-Dimethylformamide (DMF) was purified by first drying it over calcium hydride for several days and then distilling it twice from phthalic anhydride at reduced pressure, each time retaining only the middle 60 % fraction. It was then stored over Linde type 4A molecular sieves until it was used. Acetonitrile (MeCN), supporting electrolyte (tetraethylammonium perchlorate--TEAP), cells, electrodes and electrochemical instrumentation were as previously described, as were the spectrophotometric cells and apparatus 8.