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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 34, Number 11
BKCSDE 34(11)
November 20, 2013 

Kinetics and Mechanism of Pyridinolyses of Ethyl Methyl and Ethyl Propyl Chlorothiophosphates in Acetonitrile
Hasi Rani Barai, Hai Whang Lee*
Thiophosphoryl transfer reaction, Pyridinolysis, Ethyl methyl and ethyl propyl chlorothiophosphates, Biphasic concave upward free energy relationship, Stepwise mechanism
The kinetic studies on the reactions of ethyl methyl (2) and ethyl propyl (4) chlorothiophosphates with Xpyridines have been carried out in acetonitrile at 35.0 oC. The free energy correlations with X show biphasic concave upwards with a break point at X = H (2) and 3-Ph (4), respectively. A stepwise mechanism with a ratelimiting leaving group expulsion from the intermediate is proposed based on the magnitudes of selectivity parameters for both substrates. The considerably large values of βX = 1.50(2) and 1.44(4) with strongly basic pyridines and relatively small values of βX = 0.43(2) and 0.36(4) with weakly basic pyridines are interpreted as a change of the attacking direction of the X-pyridines from a frontside to a backside attack toward the chloride leaving group.
3372 - 3376
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