Kinetics and mechanism of hydrolysis of aryl N-methoxycarbamates and their derivatives

Abstract

Hydrolysis kinetics have been studied of 3- and 4-substituted phenyl N-methoxycarbamates and their N-methyl derivatives in aqueous buffers at 60 °C. The N-methyl derivatives show linear dependence of the rate constants on concentration of hydroxyl ion in the pH range measured. Hydrolysis of aryl N-methoxycarbamates is independent of hydroxyl ion concentration at higher pH values. Logarithms of the rate constants have been correlated with the substituent constants σ. The calculated values 0.9 for N-methyl derivatives, 4.5 and 3.3 for aryl N-methoxy-carbamates in the region of linear pH-dependency and pH-independency, respectively, suggest that the hydrolysis follows the BAC2 and ElcB mechanisms in the case of the N-methyl derivatives and aryl N-methoxycarbamates, respectively. Difference between the two ρ constants for the hydrolysis of aryl N-methoxycarbamates agrees with the found value ρ = 1.2 for dissociation constants of these compounds. The elimination mechanism has been confirmed by reaction of the isocyanate formed with added aniline to give the respective urea.