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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 32, Number 12
BKCSDE 32(12)
December 20, 2011 

Kinetics and Mechanism of the Pyridinolysis of Bis(2,6-dimethylphenyl) Chlorophosphate in Acetonitrile
Hasi Rani Barai, Hai Whang Lee *
Phosphoryl transfer reaction, Pyridinolysis, Bis(2,6-dimethylphenyl) chlorophosphate, Biphasic concave upward free energy correlation, Transition state imbalance
The nucleophilic substitution reactions of bis(2,6-dimethylphenyl) chlorophosphate (5), containing the four ortho-methyl substituents, with X-pyridines are investigated kinetically in MeCN at 65.0 oC. The free energy correlations for substituent X variations in the nucleophiles exhibit biphasic concave upwards with a breakpoint at a X = 3-Cl. Unusual positive ρX (= +5.40) and negative βX (= –0.83) values are obtained with the weakly basic pyridines. The pyridinolysis rate of 5 is hundreds times slower compared to that of bis(phenyl) chlorophosphate because of the steric hindrance of the four ortho-methyl substituents in the two phenyl rings. Ion-pair mechanism is proposed and positive ρX and negative βX values are substantiated by an imbalance of the transition state.
4179 - 4184
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