Kinetics and mechanism of anilinolyses of aryl methyl and aryl propyl chlorothiophosphates in acetonitrile

Abstract

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 ρXY (= -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 ρXY (= +0.68) value. The deuterium kinetic isotope effects (DKIEs; kH/kD) 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.