Kinetics and mechanism of the anilinolysis of aryl ethyl isothiocyanophosphate in acetonitrile

초록

The nucleophilic substitution reactions of Y-aryl ethyl isothiocyanophosphates with substituted X-anilines and deuterated X-anilines are investigated kinetically in acetonitrile at 75.0 oC. The free energy relationships with X in the nucleophiles exhibit biphasic concave downwards with a break point at X = H. A stepwise mechanism with a rate-limiting bond formation for more basic anilines and with a rate-limiting bond breaking for less basic anilines is proposed based on the negative and positive ρXY values, respectively. The deuterium kinetic isotope effects (DKIEs; kH/kD) are gradually changed from primary normal with more basic anilines, via primary normal and secondary inverse with aniline, to secondary inverse with less basic anilines. Primary normal and secondary inverse DKIEs are rationalized by a frontside attack involving hydrogen bonded four-center-type TSf and backside attack involving in-line-type TSb, respectively.