Aminolysis of Aryl N-Ethyl Thionocarbamates: Cooperative Effects of Atom Pairs O and S on the Reactivity and Mechanism

[reaction: see text] The aminolysis reactions of aryl N-ethyl thionocarbamates (ETNC/EtHN-C(=S)-OC6H4Z) with benzylamines (XC6H4CH2NH2) in acetonitrile are investigated at 30.0 degrees C. The rate of ETNC is slower by a factor of ca. 3 than the corresponding aminolysis of aryl N-ethyl thiocarbamate (AETC/EtHN-(C=O)-SC6H4Z), which has been interpreted in terms of cooperative effects of atom pairs O and S on the reactivity and mechanism. For concerted processes, these effects predict a rate sequence, -C(=S)-S- < -C(=S)-O- < -C-(=O)-S- < -C-(=O)-O-, and the present results are consistent with this order. The negative cross-interaction constant, rho(XZ) = -0.87, the magnitude of betaZ (= 0.36-0.50) and failure of the RSP are in accord with the concerted mechanism. The normal kinetic isotope effects, kH/kD = 1.52-1.78, involving deuterated benzylamines suggest a hydrogen-bonded cyclic transition state. Other factors influencing the mechanism are also discussed.