N-Hetarylethylenes. XII. Influence of the Substituent at the Double Bond and the Nature of the Heterocycle on the Acid Hydrolysis of N-Alkenyl Derivatives of Phenoxazine, Phenothiazine, and Carbazole

The kinetics of acid hydrolysis of N-vinylphenothiazine, N-vinylphenoxazine, N-isopropenylcarbazole, N-isopropenylphenoxazine, N-(1-phenylvinyl)phenothiazine, and N-(1-phenylvinyl)phenoxazine in 60% aqueous dioxane have been studied. The activation parameters and kinetic isotope effects (k_H/k_D = 3.1-5.2) indicate that the hydrolysis follows AS_E2 mechanism with proton transfer from the medium to substrate in the rate-determining stage. The results are compared with the previous data for N-alkenyl derivatives of carbazole, phenothiazine, and phenoxazine. The existence of isokinetic relationship in the coordinates In k (313 K) - In k (334 K) provides an additional evidence for the similarity of the mechanisms of hydrolysis of these compounds. 10-Phenothiazinyl substituent exerts the strongest activating effect on the double bond. In the series of compounds with the same substituents, the rate of hydrolysis increases in going from cis to trans and then to geminal arrangement of the substituents at the double bond.