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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 29, Number 4
BKCSDE 29(4)
April 20, 2008 

 
Title
Pyridinolysis of O,O-Diphenyl S-Phenyl Phosphorothiolates in Acetonitrile
Author
Keshab Kumar Adhikary, Bilkis Jahan Lumbiny, Chan Kyung Kim*, Hai Whang Lee*
Keywords
O,O-Diphenyl S-phenyl phosphorothiolate, Pyridinolysis, Cross-interaction constants, Frontside
attack, Negative ρZLg)
Abstract
The reactions of O,O-diphenyl Z-S-phenyl phosphorothiolates with X-pyridines have been studied kinetically in acetonitrile at 35.0 oC. The Hammett plots for substituent (Z) variations in the leaving group (log k2 vs. σZ) are biphasic concave downwards with breaks at Z = H. The large magnitudes of ρXρnuc), βXρnuc), and the cross-interaction constant, ρXZ, suggest frontside nucleophilic attack toward the leaving group. The sign reversal of ρ Z from positive in σZ ≤ 0 to negative in σZ ≥ 0 is interpreted as the change in mechanism from concerted to stepwise with rate-limiting expulsion of the leaving group. The anomalous negative sign of ρZ for leaving groups with electron-withdrawing substituents is interpreted as the intramolecular ligand exchange process of the leaving group from the equatorial position in the intermediate to the apical position in the TS.
Page
851 - 855
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