Kinetics of Bamberger rearrangement of N-phenylhydroxylamine in a reusable homogeneous system: CH3CN-H2O-CF3COOH

4-Aminophenol is an important raw material for several products in the field of dyes, photographs and pharmaceutics. For instance, paracetamol (N-acetyl-4-aminophenol) a widely employed analgesic and antipyretic [1]. Bases of the present research have been the recent results in the Beckmann rearrangement of the cyclohexanone oxime to caprolactam in CH3CN-CF3COOH solvent catalytic system [2]. The system CH3CN-CF3COOH in that reaction is fully reusable because of the acidity of the CF3COOH does not allow formation of the caprolactam salt and does not need neutralization [2]. Here we study the reactivity of the CH3CN-H2O-CF3COOH system in the Bamberger rearrangement of N-phenylhydroxylamine to 4-aminophenol the former being the key intermediate in the selective hydrogenation of nitrobenzene to 4-aminophenol. The reaction is carried out in a thermostatted reactor and the kinetics has been followed by HPLC and UV-Vis measurements. Both H2O and CF3COOH are in large excess and in any case an apparent first order has been observed, then a first order kobs have been reported. The influence of the operative variable has been studied and in particular the influence of CF3COOH and H2O concentration on reaction rate is shown in Figure 1. The increase of CF3COOH correspond to an increase of the reaction rate, on the contrary H2O inhibits the kinetics. These results suggest that H2O competes in one stage of the rearrangement thus reducing the overall rate, for instance, H2O may influence protonation equilibria.