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Pyridinolysis of 2,4-dinitrophenyl phenyl thionocarbonate: Effect of changing electrophilic center from c=o to c=s on reactivity and mechanism

Title
Pyridinolysis of 2,4-dinitrophenyl phenyl thionocarbonate: Effect of changing electrophilic center from c=o to c=s on reactivity and mechanism
Authors
Son M.J.Kim S.-I.Um I.-H.
Ewha Authors
엄익환
SCOPUS Author ID
엄익환scopusscopus
Issue Date
2011
Journal Title
Bulletin of the Korean Chemical Society
ISSN
0253-2964JCR Link
Citation
vol. 32, no. 4, pp. 1165 - 1169
Indexed
SCI; SCIE; SCOPUS; KCI WOS scopus
Abstract
Second-order rate constants (kN) have been measured spectrophotometrically for nucleophilic substitution reactions of 2,4-dinitrophenyl phenyl thionocarbonate 4 with a series of Z-substituted pyridines in 80 mol % H 2O/20 mol % DMSO at 25.0 ± 0.1 oC. The Brønsted-type plot for the reactions of 4 exhibits downward curvature (i.e., β1 = 0.21 and β2 = 1.04), indicating that the reactions proceed through a stepwise mechanism with a change in rate-determining step. It has been found that 4 is less reactive than its oxygen analogue, 2,4- dinitrophenyl phenyl carbonate 3, although the thionocarbonate is expected to be more electrophilic than its oxygen analogue. The pKa° at the center of the Brønsted curvature, defined as pKa o, has been analyzed to be 6.6 for the reactions of 4 and 8.5 for those of 3. Dissection of k N into the microscopic rate constants k1 and k 2/k-1 ratio has revealed that the reactions of 4 result in smaller k1 values but larger k2/k-1 ratios than the corresponding reactions of 3. The larger k2/k-1 ratios have been concluded to be responsible for the smaller pKa° found for the reactions of 4.
DOI
10.5012/bkcs.2011.32.4.1165
Appears in Collections:
자연과학대학 > 화학·나노과학전공 > Journal papers
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