Kinetics and mechanism of the aminolysis of aryl N-ethyl thiocarbamates in acetonitrile.
The aminolysis of aryl N-ethyl thiocarbamates (EtNHC(=O)SC(6)H(4)Z) with benzylamines (XC(6)H(4)CN(2)NH(2)) in acetonitrile at 30.0 degrees C is investigated. The rates are faster than the corresponding values for aryl N-phenyl thiocarbamates (PhNHC(=O)SC(6)H(4)Z), reflecting a stronger push to expel the leaving group by EtNH than the PhNH nonleaving group in a concerted process. The negative rho(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 Delta H(++) with large negative Delta S(++) values suggest a hydrogen bond cyclic transition state.
Oh
Hyuck Keun
HK
Department of Chemistry, Chonbuk National University, Chonju 560-756, Korea.
Park
Jie Eun
JE
Sung
Dae Dong
DD
Lee
Ikchoon
I