Beckmann rearrangement of acetophenone oximes to the corresponding amides organo-catalyzed by trifluoroaceticacid for sustainable NSAIDs synthesis

tThe Beckmann rearrangement of acetophenone oximes to the corresponding amides (4-hydroxyacetophenone oxime to N-acetyl-4-hydroxyacetanilide and acetophenone oxime toN-phenylacetamide) is investigated by using trifluoroacetic acid (TFA) as catalyst. The reactionoccurs either in the presence or in the absence of a suitable solvent. High selectivity and practicallyquantitative yield to amide is achieved in both cases at TFA/substrate > 3. Both TFA and the solvent(whenever present) could be easily reused by distillation since no protonation of amides occurs. Thereaction proceeds via a multistep reaction path and the role of TFA is related not only to its aciditybut also mainly to its ability on forming reactive trifluoroacetylated intermediates. In particular, thehighly reactive trifluoroacetylated amide is actually the effective catalyst. Finally, a likely reaction pathis proposed.