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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 12
BKCSDE 32(12)
December 20, 2011 
 
Title
 Kinetics and Mechanism of the Benzylaminolysis of O,O-Dimethyl S-Aryl Phosphorothioates in Dimethyl Sulfoxide
Author
 Keshab Kumar Adhikary, Hasi Rani Barai, Hai Whang Lee *
Keywords
 Phosphoryl transfer reaction, Benzylaminolysis, Deuterium kinetic isotope effect, Discrete free energy correlation, O,O-Dimethyl S-aryl phosphorothioate
Abstract
 Kinetic studies of the reactions of O,O-dimethyl Z-S-aryl phosphorothioates with X-benzylamines have been carried out in dimethyl sulfoxide at 85.0 °C. The Hammett (log k2 vs σX) and Brönsted [log k2 vs pKa(X)] plots for substituent X variations in the nucleophiles are discrete with a break region between 4-Me and H, while the Hammett plots (log k2 vs σZ) for substituent Z variations in the leaving groups are linear. The sign of the crossinteraction constant (ρXZ) is positive for both the strongly and weakly basic nucleophiles. Greater magnitude of ρXZ (= 2.54) value is observed with the weakly basic nucleophiles compared to with the strongly basic nucleophiles (ρXZ = 0.17). The deuterium kinetic isotope effects (kH/kD) involving deuterated benzylamines [XC6H4CH2ND2] are primary normal (kH/kD > 1). The proposed mechanism is a stepwise with a rate-limiting leaving group expulsion from the intermediate involving a frontside nucleophilic attack with a hydrogen bonded, four-center-type transition state for both the strongly and weakly basic nucleophiles.
Page
 4304 - 4308
Full Text
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