on the Beckman rearrangement of ketoximes : a kinetic study in trifluoromethansulphonic acid

The formation and the destruction of an intermediate involved in the Beckmann rearrangement of 2,4,6-trimethylacetophenone oxime have been studied in concentrated trifluoromethanesulfonic acid by kinetic and spectroscopic measurements. observed (k(obs)) and thermodynamic rate constants (k(o)) have been estimated and the values compared with the ones obtained in perchloric, sulfuric, and methanesulfonic acids. In the range 80-100 wt% of sulfuric acid, combined analysis of k(obs) and k(o) rates shows a specific catalysis due to [H2SO4] species. In trifluoromethanesulfonic acid, lower rate constants, compared to the values in sulfuric acid, have been observed which differ at 99 wt% by a factor of 10(3) ca. The catalytic effect of different strong acids, the structure of the intermediate inferred from Raman and NMR spectra, and the role of the ion-pairs involved in the reaction are discussed