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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 33, Number 7
BKCSDE 33(7)
July 20, 2012 

 
Title
Kinetics and Reaction Mechanism for Aminolysis of Benzyl 4-Pyridyl Carbonate in H2O: Effect of Modification of Nucleofuge from 2-Pyridyloxide to 4-Pyridyloxide on Reactivity and Reaction Mechanism
Author
Ji-Sun Kang, Ik-Hwan Um*
Keywords
Aminolysis, Brønsted-type plot, Nucleofuge, Concerted mechanism, Stepwise mechanism
Abstract
Pseudo-first-order rate constants kamine have been measured spectrophotometrically for the reactions of benzyl 4-pyridyl carbonate 6 with a series of alicyclic secondary amines in H2O at 25.0 oC. The plots of kamine vs. [amine] curve upward, indicating that the reactions proceed through a stepwise mechanism with two intermediates, a zwitterionic tetrahedral intermediate T± and its deprotonated form T–. This contrasts to the report that the corresponding reactions of benzyl 2-pyridyl carbonate 5 proceed through a forced concerted pathway. The kamine values for the reactions of 6 have been dissected into the second-order rate constant Kk2 and the thirdorder rate constant Kk3. The Brønsted-type plots are linear with βnuc = 0.94 and 1.18 for Kk2 and Kk3, respectively. The Kk2 for the reaction of 6 is smaller than the second-order rate constant kN for the corresponding reaction of 5, although 4-pyridyloxide in 6 is less basic and a better nucleofuge than 2-pyridyloxide in 5.
Page
2269 - 2273
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