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Nucleophilic substitution reactions of diethyl 4-nitrophenyl phosphate triester: Kinetics and mechanism

✍ Scribed by Enrique A. Castro; Daniela Ugarte; M. Fernanda Rojas; Paulina Pavez; José G. Santos

Publisher
John Wiley and Sons
Year
2011
Tongue
English
Weight
200 KB
Volume
43
Category
Article
ISSN
0538-8066

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✦ Synopsis

Abstract

The reactions of diethyl 4‐nitrophenyl phosphate (1) with a series of nucleophiles: phenoxides, secondary alicyclic (SA) amines, and pyridines are subjected to a kinetic study. Under excess of nucleophile, all the reactions obey pseudo‐first‐order kinetics and are first order in the nucleophile. The nucleophilic rate constants (k~N~) obtained are pH independent for all the reactions studied. The Brønsted‐type plot (log k~N~ vs. p__K__~a~ nucleophile) obtained for the phenolysis is linear with slope β=0.21; no break was found at p__K__~a~ 7.5, consistent with a concerted mechanism. The Brønsted‐type plots for the SA aminolysis and pyridinolysis are linear with slopes β=0.39 and 0.43, respectively, also suggesting concerted processes. The concerted mechanisms for the latter reactions are proposed on the basis of the lack of break in the Brønsted‐type plots and the instability of the hypothetical pentacoordinate intermediates formed in these reactions. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 708–714, 2011

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