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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 33, Number 7
BKCSDE 33(7)
July 20, 2012 

 
Title
Kinetics and Mechanism of the Pyridinolysis of Dimethyl Isothiocyanophosphate in Acetonitrile
Author
Keshab Kumar Adhikary, Hai Whang Lee*
Keywords
Phosphoryl transfer reaction, Pyridinolysis, Dimethyl isothiocyanophosphate, Biphasic discrete free energy relationship
Abstract
The kinetics and mechanism of the pyridinolysis (XC5H4N) of dimethyl isothiocyanophosphate are investigated in acetonitrile at 55.0 oC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles exhibit two discrete slopes with a break region between X = 3-Ac and 4-Ac. These are interpreted to indicate a mechanistic change at the break region from a concerted to a stepwise mechanism with a rate-limiting expulsion of the isothiocyanate leaving group from the intermediate. The relatively large βX values imply much greater fraction of frontside nucleophilic attack TSf than that of backside attack TSb. The steric effects of the two ligands play an important role to determine the pyridinolysis rates of isothiocyanophosphates.
Page
2260 - 2264
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