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The rates of Bamberger-type rearrangement of phenylhydroxylamine (1 a) and its derivatives (1 b-d) to the corresponding paminophenols were determined in sulphuric acid solution. Plots of the pseudo-first-order rate constants against pH (or Ho) indicate that the active species at [H,SO,] < 1 .OON (pH region) is the 0-protonated arylhydroxylamine (ArNHO 'H,) which exists in equilibrium with the N-protonated species (ArN+H,OH), while the diprotonated species (ArN+H,O+H,) contributes significantly to the observed reaction rate at [H,SO,] > 1.OON (H, region). The slope of Hammett plots (p) which was obtained by plotting kobM at [H,SO,] 1.OON against the Hammett CT values was -3.1 9. It was also established that the ASt values for the four substrates are all positive. These results suggest that the Bamberger rearrangement occurs by an S , 1 mechanism and that the elimination of water from ArNHOS H2 is rate determining.

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