Kinetics and Mechanism of the Anilinolysis of O,O-(o-Phenylene) Phosphorochloridate in Acetonitrile

초록

Abstract: The nucleophilic substitution reactions of O,O-(o-Phenylene) phosphorochloridate with substituted anilines (XC6H4NH2) and deuterated anilines (XC6H4ND2) are investigated kinetically in acetonitrile at -15.0 oC. The studied substrate of O,O-(o-Phenylene) phosphorochloridate (1) is cyclic five-membered ring of phosphorus ester, and the anilinolysis rate of (1) is much faster than its acyclic analogue (2: ethyl phenyl chlorophosphate) because of extremely small magnitude of the entropy of activation of 1 compared to 2. The Hammett and Bronsted plots exhibit biphasic concave upwards for substituent X variations in the nucleophiles with a break point at X = 3-Me. The values of deuterium kinetic isotope effects (DKIEs; kH/kD) change from secondary inverse (kH/kD H/kD > 1) with the weakly basic anilines. The secondary inverse with the strongly basic anilines and primary normal DKIEs with the weakly basic anilines are rationalized by the transition state (TS) variation from a predominant backside attack to a predominant frontside attack, in which the reaction mechanism is a concerted SN2 pathway. The primary normal DKIEs are substantiated by a hydrogen bonded, four-center-type TS.