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Aminolysis of Y-substituted phenyl 2-thiophenecarboxylates and 2-furoates: Effect of modification of nonleaving group from 2-furoyl to 2-thiophenecarbonyl on reactivity and mechanism

Title
Aminolysis of Y-substituted phenyl 2-thiophenecarboxylates and 2-furoates: Effect of modification of nonleaving group from 2-furoyl to 2-thiophenecarbonyl on reactivity and mechanism
Authors
Um I.-H.Min S.-W.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2008
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 29, no. 3, pp. 585 - 589
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants (kN) have been measured for reactions of Y-substituted phenyl 2-thiophenecarboxylates (6a-h) with morpholine and piperidine in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Brønsted-type plot for the reactions of 6a-h with morpholine is linear with βlg = -1.29, indicating that the reactions proceed through a tetrahedral zwitterionic intermediate (T±). On the other hand, the Brønsted-type plot for the reactions of 6a-h with piperidine exhibits a downward curvature, implying that a change in the rate-determining step occurs on changing the substituent Y in the leaving group. Dissection of kN into microscopic rate constants (i.e., k1 and k2/k -1 ratio) has revealed that k1 is smaller for the reactions of 6a-h than for those of Y-substituted phenyl 2-furoates (5a-h), while the k2/k-1 ratio is almost the same for the reactions of 5a-h and 6a-h. It is also reported that modification of the nonleaving group from the furoyl (5a-h) to the thiophenecarbonyl (6a-h) does not influence pKao (defined as the pKa at the center of the Brønsted curvature) as well as the k2/k -1 ratio.
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자연과학대학 > 화학·나노과학전공 > Journal papers
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