Solvent effects in the liquid phase Beckmann rearrangement of 4-hydroxyacetophenone oxime over H-Beta catalyst

N-acetyl-para-aminophenol (APAP) or acetaminophen was first synthesized via the environmentally benign liquid phase Beckmann rearrangement of 4-hydroxyacetophenone oxime over zeolite H-Beta. The reaction represents a typical case of active solvent participation. The results of co-adsorption of substrate and solvent suggest that the facility of protonation of oxime is mainly dependent upon the competitive adsorption between substrate and solvent. On the other hand, a solvent having a higher dielectric constant or more polar nature is preferred in the subsequent 1,2-H-shift and rearrangement steps. Consequently, the choice of a suitable solvent balancing between the two competitive aspects is the most important factor enhancing the performance of the reaction. (C) 2000 Elsevier Science B.V. All rights reserved.