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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 25, Number 7
BKCSDE 25(7)
July 20, 2004 

Kinetic Studies on the Structure-Reactivity of Aryl Dithiomethylacetates
Hyuck Keun Oh*, Jie Eun Park, Hai Whang Lee
Nucleophilic substitution reaction, Pyridinolysis, Cross-interaction constant, Zwitterionic tetrahedral intermediate, Stepwise mechanism
Kinetic studies of the pyridinolysis (XC5H4N) of aryl dithiomethylacetates (CH3CH 2C(=S)SC6H4Z, 1) are carried out in acetonitrile at 60.0 oC. A biphasic Bronsted plot is obtained with a change in slope from a large ( βX ? 0.8) to a small ( βX ? 0.2) value at pKa o = 5.2, which is attributed to a change in the rate limiting step from breakdown to formation of a zwitterionic tetrahedral intermediate, T±, in reaction path as the basicity of the pyridine nucleophile increases. This mechanism is supported by the change of the cross-interaction constant ρXZ from a large positive ( ρXZ = +1.36) for the weakly basic pyridines to a small negative ( ρXZ = -0.22) value for the strongly basic pyridines. The magnitudes of ρZ and activation parameters are also consistent with the proposed mechanism.
1041 - 1045
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