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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 7
BKCSDE 32(7)
July 20, 2011

Title	Kinetics and Mechanism of the Pyridinolysis of O,O-Dimethyl S-Aryl Phosphorothioates in Dimethyl Sulfoxide
Author	Hasi Rani Barai, Hai Whang Lee *
Keywords	Biphasic concave upward free energy correlation, Phosphoryl transfer reaction, Pyridinolysis, O,O-Dimethyl Z-S-aryl phosphorothioates
Abstract	Kinetic studies for the reactions of O,O-dimethyl Z-S-aryl phosphorothioates with X-pyridines have been carried out in dimethyl sulfoxide at 85.0 ºC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = H, while those for substituent Z variations in the leaving groups are linear. The negative sign of the cross-interaction constant (ρXZ) implies that the reaction proceeds through a concerted mechanism for both the strongly and weakly basic pyridines. The magnitude of ρXZ (= –0.35) for the strongly basic pyridines is greater than that (ρXZ = –0.15) for the weakly basic pyridines, indicating a change of the nucleophilic attacking direction from frontside for the strongly basic pyridines to backside for the weakly basic pyridines. The early transition state is proposed on the basis of the absence of positive deviations from both the Hammett and Brönsted plots for the strong π-acceptor, X = 4-Ac, and small values of ρXZ and βX.
Page	2339 - 2344
Full Text	PDF / Supporting Information

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