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A kinetic study on aminolysis of t-butyl 4-pyridyl carbonate and related compounds: Effect of leaving and nonleaving groups on reaction mechanism

Title
A kinetic study on aminolysis of t-butyl 4-pyridyl carbonate and related compounds: Effect of leaving and nonleaving groups on reaction mechanism
Authors
Kang J.-S.Lee J.-I.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2012
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 33, no. 9, pp. 2971 - 2975
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants k N have been measured spectrophotometrically for nucleophilic substitution reactions of t-butyl 4-pyridyl carbonate 8 with a series of alicyclic secondary amines in H 2O at 25.0 ± 0.1 °C. The Brønsted-type plot for the reactions of 8 is linear with β nuc = 0.84. The βnuc value obtained for the reactions of 8 is much larger than that reported for the corresponding reactions of t-butyl 2-pyridyl carbonate 6 (i.e., β nuc = 0.44), which was proposed to proceed through a forced concerted mechanism. Thus, the aminolysis of 8 has been concluded to proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate T±, in which expulsion of the leaving-group from T± occurs at the rate-determining step (RDS). In contrast, aminolysis of benzyl 4-pyridyl carbonate 7 has been reported to proceed through two intermediates, T± and its deprotonated form T- on the basis of the fact that the plots of pseudo-first-order rate constant k obsd vs. amine concentration curve upward. The current study has demonstrated convincingly that the nature of the leaving and nonleaving groups governs the reaction mechanism. The contrasting reaction mechanisms have been rationalized in terms of an intramolecular H-bonding interaction, steric acceleration, and steric inhibition.
DOI
10.5012/bkcs.2012.33.9.2971
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자연과학대학 > 화학·나노과학전공 > Journal papers
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