Kinetics study of the acid-catalysed rearrangement of 1, 2-oxazines

Abstract EN

The fates of acid-catalyzed rearrangements of 6-ethoxy-5, 6-dihydro-3-phenyl-4H-1, 2-oxazines have been investigated in H2SO4 / methanol, MeCN and Me2SO by means of spectrophotometry methods.

Pseudo first order rate constants were obtained in each case.

Results in methanol supported an Al type mechanism.

Also investigated were the correlation of reaction rates with Hammet acidity function (H0) by application of the Bunnet criterion where a slope of -0.

67 was obtained.

Further, the solvent effect was considered from two points of mechanistic, views: the thermodynamic transfer functions of MeOH to MeCN and Me2SO where the rate was found to be fast in MeCN and slow in Me2SO and the Kirkwood-Buff preferential solvation with aqueous MeOH, MeCN and Me2SO.

The techniques supported the proposed transition state structure.