The rates of Bamberger-type rearrangement of phenylhydroxylamine (1a) and its derivatives (1b-d) to the corresponding p-aminophenols were determined in sulphuric acid solution. Plots of the pseudo-first-order rate constants against pH (or H0) indicate that the active species at [H2SO4] < 1.00N (pH region) is the O-protonated arylhydroxylamine (ArNHO+H2) which exists in equilibrium with the N-protonated species (ArN+H2OH), while the diprotonated species (ArN+H2O+H2) contributes significantly to the observed reaction rate at [H2SO4] > 1.00N (H0 region). The slope of Hammett plots (ρ) which was obtained by plotting kobs at [H2SO4] 1.00N against the Hammett σ values was -3.19. It was also established that the ΔS‡ values for the four substrates are all positive. These results suggest that the Bamberger rearrangement occurs by an SN1 mechanism and that the elimination of water from ArNHO+H2 is rate determining.
|Number of pages||5|
|Journal||Journal of the Chemical Society, Perkin Transactions 2|
|Publication status||Published - 1981|
All Science Journal Classification (ASJC) codes