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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 10
BKCSDE 32(10)
October 20, 2011 

Kinetics and Mechanism of the Benzylaminolysis of O,O-Diethyl S-Aryl Phosphorothioates in Dimethyl Sulfoxide
Keshab Kumar Adhikary, Hai Whang Lee *
Phosphoryl transfer reaction, Benzylaminolysis, O,O-Diethyl Z-S-aryl phosphorothioate, Crossinteraction constant, Concave downward free energy correlation
The reactions of O,O-diethyl Z-S-aryl phosphorothioates with X-benzylamines are kinetically investigated in dimethyl sulfoxide at 85.0 °C. The Hammett (log k2 vs σX) and Brönsted [log k2 vs pKa(X)] plots are biphasic concave downwards for substituent X variations in the nucleophiles with a break point at X = H. The signs of the cross-interaction constants (ρXZ) are positive for both the strongly and weakly basic nucleophiles. Considerably great magnitude of ρXZ (= 6.56) value is observed with the weakly basic nucleophiles, while ρXZ = 0.91 with the strongly basic nucleophiles. Proposed reaction mechanism is a stepwise process with a ratelimiting leaving group expulsion from the intermediate involving a backside nucleophilic attack with the strongly basic nucleophiles and a frontside attack with the weakly basic nucleophiles. The kinetic results are compared with those of the benzylaminolysis of O,O-diphenyl Z-S-aryl phosphorothioates.
3587 - 3591
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