Kinetics and Mechanism of Anilinolyses of Aryl Methyl and Aryl Propyl Chlorothiophosphates in Acetonitrile

摘要

Nucleophilic substitution reactions of Y-aryl methyl (8) and Y-aryl propyl (10) chlorothiophosphates with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at 55.0 °C. A concerted mechanism is proposed for 8 based on the negative pxy (= -0.23) value, while a stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed for 10 based on the positive pxy (= +0.68) value. The deuterium kinetic isotope effects (DKIEs; k_H/k_D) are 0.89-1.28 and 0.62-1.20 with 8 and 10, respectively. Primary normal and secondary inverse DKIEs are rationalized by a frontside attack involving hydrogen bonded, four-center-type transition state and backside attack involving in-line-type transition state, respectively.