The Beckmann Rearrangement in Concentrated Sulfuric Acid. Studies by Means of NMR and Kinetic Isotope Effect

Abstract

Abstract The mechanism of the Beckmann rearrangement of acetophenone (a) and 1-phenyl-2-propanone (b) oximes in concd sulfuric acid was elucidated by means of NMR spectroscopy and the carbon-14 kinetic isotope effect. For (a), the postulated reactive species acetophenone oxime hydrogensulfate was detected, the absence of hydrolysis of the oxime during the course of the reaction being verified. Positive carbon-14 kinetic isotope effect at the phenyl-1, k12/k14=1.026 at 40 °C and 1.019±0.005 at 60 °C, confirmed a definite change in bonding of the phenyl-1 carbon in the transition state of the reaction. Concertedness of the rearrangement was thus established. For (b), sulfonation of the benzene ring prior to the rearrangement was observed, kinetic isotope effect study being found to be useless.