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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 4
BKCSDE 32(4)
April 20, 2011

Title	Kinetics and Mechanism of the Pyridinolysis of Aryl Phenyl Chlorothiophosphates in Acetonitrile
Author	Md. Ehtesham Ul Hoque, Shuchismita Dey, Chan Kyung Kim, Hai Whang Lee
Keywords	Biphasic concave upward/downward free energy correlation, Phosphoryl transfer reaction, Pyridinolysis, Y-aryl phenyl chlorothiophosphates
Abstract	Kinetic studies for the reactions of Y-aryl phenyl chlorothiophosphates with X-pyridines have been carried out in acetonitrile at 35.0 ºC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = 3-Ph, while the Hammett plots for substituent Y variations in the substrates are biphasic concave downwards (and partially upwards) with a break point at Y = H. The signs and magnitudes of the cross-interaction constant (ρ XY) are strongly dependent upon the nature of substituents, X and Y. The proposed mechanism is a stepwise process with a rate-limiting step change from bond breaking with the weaker electrophiles to bond formation with the stronger eletrophiles. The nonlinear free energy correlations of biphasic concave upward plots for substituent X variations in the nucleophiles are rationalized by a change in the attacking direction of the nucleophile from a backside with less basic pyridines to a frontside attack with more basic pyridines.
Page	1138 - 1142
Full Text	PDF

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