Surfactant control of the ortho/para ratio in the bromination of anilines. 2.

Abstract

We report the bromination of some N,N-disubstituted anilines (N-ethyl-N-methylaniline, N,N-diethylaniline, N-butyl-N-methylaniline, 1-phenylpyrrolidine, 1-phenylpiperidine) both in aqueous suspension of cetyltrimethylammonium tribromide (CTAB 3) and in homogeneous solution (CHCl 3). In the presence of surfactant we observed a regioselectivity different from that observed in homogeneous conditions. The regioselectivity seems to depend on the nature of the substituents on the nitrogen of the aniline as well as on the temperature. An explanation based on specific interactions between the aniline and the packed structure of the aggregate is proposed. On the basis of the results we obtained in the bromination reaction of 1, 2 3 and 5 in the presence of CTAB 3, it could be argued either that the orientation of the amino group of these anilines is mostly toward the water phase as compared to 4 or that, most probably, they are localised in larger grooves where the interaction with the aggregate and the brominating agent is looser. It seems evident that both hydrophobicity of the amino group and a tight interaction with the aggregate should be necessary to bring the ortho position close to the brominating agent.