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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 31, Number 8
BKCSDE 31(8)
August 20, 2010

Title	Kinetics and Mechanism of Pyridinolysis of Aryl Dithiocyclopentanecarboxylates in Acetonitrile
Author	Hyuck Keun Oh
Keywords	Nucleophilic substitution reaction, Pyridinolysis, Cross-interaction constant, Zwitterionic tetrahedral intermediate, Stepwise mechanism
Abstract	Kinetic studies on the pyridinolysis of aryl dithiocyclopentanecarboxyaltes 2 were carried out at 60.0 ^oC in acetonitrile. In the aminolysis of 2, the β_X values were 0.5 - 0.8 with anilines, and there was no breakpoint. However, in the pyridinolysis of 2, biphasic Brönsted plots were obtained, with a change in slope from a large value (β_X ≠ 0.7) to a small value (β_X ≠ 0.4) at pK_a⁰ = 5.2. This was attributed to a change in the rate-limiting step from breakdown to the formation of a zwitterionic tetrahedral intermediate, T^±, in the reaction path, with an increase in the basicity of the pyridine nucleophile. An obvious change in the cross-interaction constant _ρXZ from a large positive (_ρXZ = +1.02) value to a small negative value (_ρXZ = -0.17) supports the proposed mechanistic change.
Page	2357 - 2360
Full Text	PDF

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