M. Kádár, Z. Nagy, T. Karancsi
Aug 1, 2001
Citations
0
Influential Citations
30
Citations
Journal
Electrochimica Acta
Abstract
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.