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Kinetics and mechanism of michael-type reactions of ethyl propiolate with alicyclic secondary amines in H2O and MeCN: Solvent effect on reactivity and transition-state structure

Title
Kinetics and mechanism of michael-type reactions of ethyl propiolate with alicyclic secondary amines in H2O and MeCN: Solvent effect on reactivity and transition-state structure
Authors
Kim S.-I.Baek H.-W.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2009
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 30, no. 12, pp. 2909 - 2912
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
The amines studied in this study are less reactive toward ethyl propiolate (3) in MeCN than in H2O although they are 7 to 9 pKa units more basic in the aprotic solvent. The reactivity of morpholine and deuterated morpholine toward 3 is found to be identical, indicating that proton transfer occurs after rate-determining step (RDS). The fact that kinetic isotope effect is absent excludes a stepwise mechanism in which proton transfer occurs in RDS as well as a concerted mechanism in which nucleophilic attack and proton transfer occur concertedly through a 4-membered cyclic transition state (TS). Thus, the reactions have been concluded to proceed through a stepwise mechanism in which proton transfer occurs after RDS. Brønsted-type plots are linear with small βnuc values, i.e., βnuc = 0.29 in H2O and βnuc = 0.51 in MeCN, indicating that bond formation is not advanced significantly in RDS. The small βnuc value also supports the conclusion drawn from the study of kinetic isotope effect.
DOI
10.5012/bkcs.2009.30.12.2909
Appears in Collections:
자연과학대학 > 화학·나노과학전공 > Journal papers
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