Dual Nucleophilic Substitution Reactions of O,O-Diethyl 2,4-dinitrophenyl Phosphate and Thionophosphate Triesters

The reactions of the title compounds with phenoxides, secondary alicyclic (SA) amines, and pyridines, in 44 wt% ethanol–water, at 25°C and an ionic strength of 0.2 M, were subjected to kinetic and product studies. From analytical techniques (HPLC and NMR), two pathways were detected (nucleophilic attack at the phosphoryl center and at the C‐1 aromatic carbon) for the reactions of all the nucleophiles with the phosphate (2) and for the pyridinolysis of the thionophosphate (1). Only aromatic nucleophilic substitution was found for the reactions of 1 with phenoxides and SA amines. For the dual reactions, the nucleophilic rate constants (kN) were separated in two terms: \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$k_{\rm N}^{\rm P}$\end{document} and \documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}$k_{\rm N}^{{\rm Ar}}$\end{document}, which are the rate constants for the corresponding electrophilic centers. The absence of a break in the Brønsted‐type plots for the attack at P is consistent with concerted mechanisms. The Brønsted slopes, βAr 0.32–0.71, for the attack at the aromatic C‐1, are in agreement with stepwise mechanisms where formation of a Meisenheimer complex is the rate‐determining step. © 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 202–211, 2013