Kinetics and Mechanism of the Anilinolysis of Aryl Ethyl Isothiocyanophosphates in Acetonitrile

Abstract

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

Structure‐Reactivity Insights on the Alkaline Hydrolysis of Organophosphates: Non‐Leaving and Leaving Group Effects in a Bilinear Brønsted‐Like Relationship

“…These values can be used for the construction of More'O'Ferral Jencks plot, allowing to infer on the reaction mechanism. Due to the information that can be extracted from Brønsted plots they are extensively used to study organophosphorus reactivity and some examples are: aminolysis of a phosphate triester, [14] aminolysis, pyridinolysis and phenolysis of phosphate and thiophosphate triesters, [15] substitution reaction in phosphate monoesters assisted by intramolecular catalysis, [16] anilinolysis of aryl ethyl isothiocyanophosphates, [17] among several others. In the review by Lassila and coworkers they present a detailed mechanistic interpretation of beta values, briefly discussed above, for reactions of organophosphates mono, di and three substituted [1] …”