Acid-promoted decomposition of benzenesulphenanilides and N-aryl bis(benzenesulphen)amides

Abstract

The decomposition of 4′-substituted benzenesulphenanilides (1a–d) in the presence of trifluoroacetic acid (0.6 equiv.) leads to N-arylbis(benzenesulphen)amides (6a–d) in variable yields, depending on the 4′-substituent, in addition to disulphide (4) and anilines (3a–d), whereas products arising from sulphenylation of the N-aryl ring result from 3′-methoxybenzenesulphenanilide (1g). The 4′-nitro- and 3′-nitro-benzenesulphenanilides (1e,f) react with a slight excess of trifluoroacetic acid to give only (4), the thiosulphonate (5), and aniline (3e,f). The findings are interpreted in terms of possible nucleophilic attack at the S–N bond of a protonated sulphenanilide by the nitrogen or the N-aryl ring of another sulphenanilide unit, according to the nature of the substituent and its position, with displacement of aniline (3). The reaction of (1a–d) with 1.5 equiv. of trifluoroacetic acid leads to complete disappearance of the initially formed amides (6a–d) with concomitant formation of phenazines (9) and/or p-quinone di-imines (8). Similar results are obtained by using boron trifluoride–diethyl ether. Di-imines (8) and phenazines (9) are explained on the basis of a mechanism initially involving nucleophilic attack by (1) and/or (6) and/or (3) at the ortho and para positions of an intermediate cation, possibly (18A) or (18B), and loss of the disulphide (4).