View : 576 Download: 0
Unexpected medium effect on the mechanism for aminolysis of aryl phenyl carbonates in acetonitrile and H2O: transition-state structure in the catalytic pathway
- Title
- Unexpected medium effect on the mechanism for aminolysis of aryl phenyl carbonates in acetonitrile and H2O: transition-state structure in the catalytic pathway
- Authors
- Um, Ik-Hwan; Song, Ji-Hyun; Bae, Ae-Ri; Dust, Julian M.
- Ewha Authors
- 엄익환
- SCOPUS Author ID
- 엄익환
- Issue Date
- 2018
- Journal Title
- CANADIAN JOURNAL OF CHEMISTRY
- ISSN
- 0008-4042
1480-3291
- Citation
- CANADIAN JOURNAL OF CHEMISTRY vol. 96, no. 12, pp. 1011 - 1020
- Keywords
- aminolysis; aryl phenyl carbonates; cyclic transition-state structure; activation parameters; deuterium kinetic isotope effects
- Publisher
- CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS
- Indexed
- SCIE; SCOPUS
- Document Type
- Article
- Abstract
- Upward curvature in the kinetic plots of pseudo first-order rate constants (k(obsd)) vs. [amine] for the aminolysis of aryl phenyl carbonates (5a-5j) in MeCN demonstrates that these reactions proceed via a zwitterionic tetrahedral intermediate (T-+/-) that partitions between catalyzed and uncatalyzed routes to give the products. Yukawa-Tsuno plots for the reactions of 5a-5j with piperidine result in excellent linear correlations with rho(Y) = 4.82 and r = 0.47 for the uncatalyzed reaction versus rho(Y) = 2.21 and r = 0.21 for the catalyzed reaction. Brensted plots for reactions of 4-(ethoxycarbonyl)-phenyl phenyl carbonate isp with a series of cyclic secondary amines exhibit excellent linear correlations with beta(nuc) = 0.87 and 0.58 for the uncatalyzed and catalyzed reactions, respectively. The Delta H-double dagger and Delta S-double dagger values are 0.92 kcal/mol and -50.1 cal/mol K, respectively, for the catalyzed reaction of 5f with piperidine. Deuterium kinetic isotope effects found for reactions of 5f with piperidine/deuterated piperidine are 0.84 (uncatalyzed) and 1.42 (catalyzed). Multi-parameter analysis supports a concerted catalytic pathway involving a six-membered cyclic transition state rather than a traditionally accepted stepwise pathway with an anionic intermediate. The current unexpected results, where P is the essential central intermediate in this aminolysis, contrast with previous calculation studies that deemed T +/- unstable in gas phase or MeCN.
- DOI
- 10.1139/cjc-2018-0204
- Appears in Collections:
- 자연과학대학 > 화학·나노과학전공 > Journal papers
- Files in This Item:
There are no files associated with this item.
- Export
- RIS (EndNote)
- XLS (Excel)
- XML