Surfactant control of the Ortho/Para ratio in the bromination of anilines. 4

The bromination of N,N-disubstituted anilines was performed in aqueous suspension of 1-hexadecylpyridinium tribromide (CPyBr3), using the surfactant counterion as reagent. The experiments carried out at room temperature showed the same regioselectivity observed in homogeneous solutions, with the prevalence of the para-bromo product. On the contrary, at 0 °C the [ortho-bromo]/[para-bromo] ratio increased. This result can be ascribed to the location of the aniline at the solid–water interphase and to the tight packing at low temperature.