Bamberger rearrangement on solid acids

Bamberger rearrangement of phenylhydroxylamine (PHA) to para-aminophenol (PAP) is investigated at 353 K, with water as solvent, on a series of solid acid catalysts. The catalysts are characterized by a micro-calorimetric technique using the adsorption of ammonia for acid strength. The solid acid catalysts under study include beta zeolite, K10 clay, sulphonated silica, and sulphated zirconias, obtained by different procedures. Both activity and selectivity are affected by the choice of the catalyst. The selectivity towards PAP is found to be 17% for K10 clay, 70% for sulphonated silica, 84% for beta zeolite and >90% for sulphated zirconia, respectively. The reaction obeys a first-order rate law and the rate constant shows a linear dependence on the number of acid sites. On sulphated zirconia calcined at 973 K, a quantitative reaction is obtained, and the catalyst can be recycled, giving the first example of selective Bamberger rearrangement catalysed by solids.