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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 10
BKCSDE 32(10)
October 20, 2011 

 
Title
Kinetics and Mechanism of the Pyridinolysis of S-Aryl Phenyl Phosphonochloridothioates in Acetonitrile
Author
Keshab Kumar Adhikary, Bilkis Jahan Lumbiny, Hai Whang Lee *
Keywords
Biphasic free energy correlation, Phosphoryl transfer reaction, Pyridinolysis, S-Aryl phenyl phosphonochloridothioates
Abstract
Kinetic studies on the reactions of Y-S-aryl phenyl phosphonochloridothioates with X-pyridines have been carried out in MeCN at 55.0 ºC. The Hammett and Brönsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = H. The Hammett plots for substituent Y variations in the substrates are biphasic concave upwards with a break point at Y = H, and the sign of ρY is changed from unusual negative (ρY < 0) with the weaker electrophiles to positive (ρY > 0) with the stronger electrophiles. The stepwise mechanism is proposed on the basis of the ρX, βX, and ρXY values as follows: a ratelimiting leaving group departure from the intermediate involving a frontside attack and product-like TS for the stronger nucleophiles and weaker electrophiles; a rate-limiting leaving group departure from the intermediate involving a backside attack and product-like TS for the weaker nucleophiles and electrophiles; a rate-limiting bond formation involving a frontside attack for the stronger nucleophiles and electrophiles; a rate-limiting bond formation involving a backside attack for the weaker nucleophiles and stronger electrophiles. The substituent effects of X and Y on the pyridinolysis mechanisms of R1R2P(=S)Cl-type substrates are discussed.
Page
3743 - 3747
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