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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 28, Number 10
BKCSDE 28(10)
October 20, 2007 

Kinetics and Mechanism of the Pyridinolysis of Diphenyl Phosphinic and Thiophosphinic Chlorides in Acetonitrile
Md. Ehtesham Ul Hoque, Nilay Kumar Dey, Arun Kanti Guha, Chan Kyung Kim, Bon-Su Lee*, Hai Whang Lee*
Pyridinolysis, Diphenyl phosphinic chloride, Diphenyl thiophosphinic chloride, Biphasic Hammett and Bronsted plots, Deuterium kinetic isotope effects
The kinetics and mechanism of the nucleophilic substitution reactions of diphenyl phosphinic (1) and thiophosphinic (2) chlorides with substituted X-pyridines are investigated kinetically in acetonitrile at 35.0 and 55.0 oC, respectively. A concerted mechanism with backside nucleophilic attack is proposed for the pyridinolysis of 1, on the basis of the linear Bronsted plot with the βX value of 0.68. In the case of the pyridinolysis of 2, the Hammett and Bronsted plots are biphasic concave upwards with the break point at 3- phenyl pyridine. These results indicate a change in mechanism from a concerted SN2(P) process with direct backside nucleophilic attack for less basic nucleophiles (X = 3-CN-3-Ph) to a stepwise process with frontside attack for more basic nucleophiles (X = 4-MeO-3-Ph). Apparent secondary inverse kinetic isotope effects with deuterated pyridine (C5D5N), kH/kD < 1, are observed for the pyridinolysis of 1 and 2.
1797 - 1802
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