Basic hydrolysis of quinolinyl N,N‐dimethylcarbamates: a two‐step mechanism

Abstract

The reactivity of 6-quinolinyl and 8-quinolinyl N,N-dimethylcarbamates was examined in several aqueous basic media. A quadratic dependence was observed for the constant rates upon hydroxide concentration for both compounds, which is a typical behaviour of a mechanism involving a base-catalysed deprotonation of the tetrahedral intermediate with the formation of a dianion at high concentrations of hydroxide ion, while at lower concentrations a specific-base catalysed addition-elimination mechanism seems to be predominant. The reactivity of 8-quinolinyl N,N-dimethylcarbamate was also studied in several amine buffers, showing specific base catalysis. The reactivity of 6-quinolinyl N,N-dimethylcarbamate was studied in H 2 O and in D 2 O and the solvent isotope effect supports the proposal of a mechanism involving a specific-base hydrolysis. All results confirm the existence of a mechanism with a rate determining step involving the substrate anion and a second mole of hydroxide ion. This mechanism was so far unknown for carbamate reactivity, being only known to occur with amides. In the present study, the hydrolysis 8-quinolinyl and 6-quinolinyl N,N-dimethylcarbamates (compounds 1 and 2, respectively) were studied in several basic media, and a similar behaviour to the one showed by activated anilides was observed, in which kinetic constants show a quadratic dependence on hydroxide concentration.(wileyonlinelibrary.com)