Environmentally friendly method of producing carbamates by transesterification: kinetics and mechanism†

Abstract

The kinetic profile of the reaction of O-methyl-N-aryl carbamates with aliphatic alcohols in the presence of their respective alkoxide catalysts was investigated across a temperature range from 323 K to 373 K. In alcoholic media, the reaction exhibits selectivity and follows first-order kinetics relative to the substrate carbamate. Kinetic constants for the O-methyl-N-aryl carbamate reaction with a series of alcohols were quantified. The mechanistic pathway was elucidated, revealing that the nucleophilic attack by the alkoxide ion on the carbonyl carbon dominates under the examined conditions. Correlation equations were employed to articulate the impact of alcohol structural characteristics on the interaction rate with O-methyl-N-phenyl carbamates, demonstrating that less polar alcohols promote faster reactions. The Hammett equation was applied to describe how substituents on the aromatic moiety of O-methyl-N-phenyl carbamate influence the reaction kinetics with ethanol and isopropanol, showing that electron-withdrawing substituents facilitate the process, consistent with the established mechanistic framework. Activation parameters relevant to this reaction series were evaluated, revealing isokinetic temperatures that suggest a change in the reaction mechanism at 100–250 K above the experimental temperatures. The experimental data were applied to the synthesis of chlorpropham (O-isopropyl-N-(3-chlorophenyl)carbamate), demonstrating their practical utility in herbicide production.