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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 ρ_Z (ρ_Lg)
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. σ_Z) are biphasic concave downwards with breaks at Z = H. The large magnitudes of ρ_Xρ_nuc), β_Xρ_nuc), and the cross-interaction constant, ρ_XZ, suggest frontside nucleophilic attack toward the leaving group. The sign reversal of ρ Z from positive in σ_Z ≤ 0 to negative in σ_Z ≥ 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 ρ_Z 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
Full Text	PDF

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