Kinetics and mechanism of the aminolysis of aryl N-ethyl thiocarbamates in acetonitrile

Article abstract of DOI:10.1021/jo0484676

The aminolysis of aryl N-ethyl thiocarbamates (EtNHC(=O)SC ₆H₄Z) with benzylamines (XC₆H ₄-CN₂NH₂) in acetonitrile at 30.0 °C is investigated. The rates are faster than the corresponding values for aryl N-phenyl thiocarbamates (PhNHC(=O)SC₆H₄Z), reflecting a stronger push to expel the leaving group by EtNH than the PhNH nonleaving group in a concerted process. The negative ρ_XZ (-0.86) and failure of the reactivity-selectivity principle found are consistent with the concerted mechanism. The kinetic isotope effects involving deuterated nucleophiles (k _H/k_D = 1-5-1.7) and low ΔH? with large negative ΔS? values suggest a hydrogen bond cyclic transition state.