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Kinetic Study on Nucleophilic Displacement Reactions of Phenyl Y-Substituted Phenyl Carbonates with 1,8-Diazabicyclo[5.4.0]undec-7-ene: Effects of Amine Nature on Reaction Mechanism

Title
Kinetic Study on Nucleophilic Displacement Reactions of Phenyl Y-Substituted Phenyl Carbonates with 1,8-Diazabicyclo[5.4.0]undec-7-ene: Effects of Amine Nature on Reaction Mechanism
Authors
Park, Kyoung-HoKim, Min-YoungUm, Ik-Hwan
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2016
Journal Title
BULLETIN OF THE KOREAN CHEMICAL SOCIETY
ISSN
0253-2964JCR Link1229-5949JCR Link
Citation
vol. 37, no. 1, pp. 77 - 81
Keywords
1,8-Diazabicyclo[5.4.0]undec-7-eneSteric hindranceBronsted-type plotHammett plotYukawa-Tsuno plot
Publisher
WILEY-V C H VERLAG GMBH
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants (k(N)) for nucleophilic displacement reactions of phenyl Y-substituted phenyl carbonates (7a-7l) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in 80 mol % H2O/20 mol % DMSO at 25.0 +/- 0.1 degrees C have been measured spectrophotometrically. The Bronsted-type plot for the reactions of 7a-7l with DBU is linear with beta(lg) = -0.48, indicating that the reactions proceed through a concerted mechanism, which is in contrast to the stepwise mechanism reported previously for the corresponding reactions with ethylamine (a primary amine) and piperidine (a secondary amine). The Hammett plots correlated with sigma(-) and sigma(o) constants exhibit many scattered points. In contrast, the Yukawa-Tsuno plot results in an excellent linear correlation with rho(Y) = 1.27 and r = 0.57, implying that a negative charge develops partially on the O atom of the leaving group in the transition state. The bulky DBU is less reactive than the primary and secondary amines toward substrates possessing a weakly basic leaving group. It has been concluded that steric hindrance exerted by DBU in the plausible intermediate (T-+/-) forces the reactions to proceed through a concerted mechanism because expulsion of the leaving group from T-+/- could reduce the steric hindrance.
DOI
10.1002/bkcs.10627
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자연과학대학 > 화학·나노과학전공 > Journal papers
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