Electrochimica Acta, Vol.46, No.22, 3405-3414, 2001
The electrochemical oxidation of 4-bromoaniline, 2,4-dibromoaniline, 2.4,6-tribromoaniline and 4-iodoaniline in acetonitrile solution
The electrochemical oxidation of 4-bromo-, 2,4-dibromo-, 2,4,6-tribromo- and 4-iodoanilines was investigated in acetonitrile solution. Based on the experimental results, it can be stated that the Bacon-Adams mechanism (J. Am. Chem. Soc. 90 (1968) 6596) is the main electrochemical oxidation route in acetonitrile solution similar to the 4-chloroanilines. In the cases of 4-bromo- and 2,4-dibromoanilines, the substituent in the para position eliminated in the dimerisation step, following its oxidation to bromine, which quantitatively substitutes the free ortho position of the starting bromoaniline. As a consequence of this, oxidised form of brominated 4-amino-diphenylamines is formed besides brominated anilines, Halogenisation did not take place at the oxidation of 2,4,6-tribromo- and 4-iodoaniline because the rejected halide ion can only be oxidised to elemental halogen (bromine and iodine). In the case of all bromo monomer compounds, the role of 'head-to-head' coupling was found negligible (azobenzene type compounds). 4,4 ' -Diiodo-azobenzene has been observed as by-product in traces at 4-iodoaniline oxidation. The electrochemical oxidation of 4-bromoaniline resulted in the 'ortho-coupling' product in a considerable less degree in contrast with 4-chloroaniline. The oxidation products prepared by controlled potential electrolysis (CPC) were isolated and identified by different techniques: GC-ECD (gas chromatography), GC-MS (gas chromatograph-mass spectrometry), and ES-MS (electrospray mass spectrometry). Cyclic voltammograms of the 4-halogenoaniline type substrates and n-tetrabutylammonium halides, have been recorded before and after the CPC electrolysis, and were also used for product identification.