Mechanistic studies on the electrochemical reductive coupling of some polyhalogenonitrobenzenes. A new example of a radical anion dimerization

Coupling processes with loss of one halogen atom per ring are observed when heavily substituted polyhalogenonitrobenzenes (polyfluoro- and polychloro-) are electrochemically reduced in DMF. Product analyses and cyclic voltametry mechanistic studies suggest that in the particular case of pentafluoronitrobenzene, direct dimerization of the radical anions occurs prior to CF bond fragmentation. On the contrary, reduction of the nitro group is the only observed process when less substituted polyhalogenonitrobenzenes are used in the same conditions. Nitro group reduction is also the main process for all the studied polyhalogenonitrobenzenes when the reactions are carried out in protic solvents. © 1994.