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.

Graphical abstractSelective Bamberger rearrangement has been reported for the first time using solid acids as catalysts. The solid acids were characterized by the measurement of their surface area and acidity. The surface area was determined from the adsorption isotherm of nitrogen at 77 K, on samples activated in N2 flow for 2 h at 523 K. The acid properties were determined by adsorption of NH3 using a calorimetric method.Figure optionsDownload full-size imageDownload as PowerPoint slide