The electrochemical oxidation of 4-chloroaniline, 2,4-dichloroaniline and 2,4,6-trichloroaniline in acetonitrile solution

The electrochemical oxidation of 4-chloro-, 2,4-dichloro- and 2,4,trichloroanilines was investigated in acetonitrile solution. Based on the experimental results, it can be stated that the mechanism introduced by J. Bacon and R.N. Adams (J. Am. Chem. Sec. 90 (1968) 6596) describing the voltammetric oxidation of 4-substituted aniline derivatives in acidic aqueous media is the main electrochemical oxidation route in acetonitrile as well. It is shown, that in the cases of 4-chloro- and 2,4-dichloroanilines, the substituent in the para position is not only eliminated at the electrochemically initiated dimerization step, but it was oxidized to chlorine, which substitutes the free ortho position of the starting chloroaniline. As a consequence of that oxidized form of chlorinated 4-amino-diphenylamines is formed also besides chlorinated anilines. 2-Amino-4',5-dichloro-diphenylamine has been found as a product of oxidation at the oxidation of 4-chloroaniline. This can be explained by dimerization of 4-chloroaniline at the ortho position by the one electron oxidized substrate. In the case of both monomer compounds, the role of 'head-to-head' coupling found negligible (azobenzene type compounds). Chlorination did not take place at the oxidation of 2,4,6-trichloroaniline, because the rejected chloride ion can be oxidized only to chlorine. The oxidation products prepared by controlled potential electrolysis (CPC), were isolated and identified by different techniques (GC-ECD, GC-MS and ES-MS: gas chromatography, gas chromatograph-mass spectrometry and electrospray mass spectrometry). Cyclic voltammograms of the chloroaniline type substrates and n-tetrabutylammonium chloride have been recorded before and after the CPC electrolysis, and were also used for product identification. (C) 2001 Elsevier Science Ltd. All rights reserved.