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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 35, Number 2
BKCSDE 35(2)
February 20, 2014 

Kinetics and Mechanism of Pyridinolyses of Aryl Methyl and Aryl Propyl Chlorothiophosphates in Acetonitrile
Hasi Rani Barai, Hai Whang Lee*
Biphasic free energy correlation, Thiophosphoryl transfer reaction, Pyridinolysis, Aryl methyl and propyl chlorothiophosphates
The nucleophilic substitution reactions of Y-aryl methyl (8) and Y-aryl propyl (10) chlorothiophosphates with X-pyridines are studied kinetically in acetonitrile at 35.0 ºC. The Hammett and Brönsted plots with X in the nucleophiles for both substrates exhibit biphasic concave upwards with a break region between X = 3-Me and H. The obtained values of the cross-interaction constants (XY) are negative with 8 while positive with 10 despite the same free energy correlations with X for both substrates. A stepwise mechanism with a rate-limiting bond formation is proposed with 8, whereas a stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed with 10 based on the sign of XY, negative and positive with 8 and 10, respectively. A frontside nucleophilic attack is proposed with strongly basic pyridines based on the considerably great magnitudes of X and X values while a backside attack is proposed with weakly basic pyridines based on the relatively small magnitudes of X and X for both substrates.
483 - 488
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