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Leaving-group substituent controls reactivity and reaction mechanism in aminolysis of phenyl y-substituted-phenyl carbonates
- Leaving-group substituent controls reactivity and reaction mechanism in aminolysis of phenyl y-substituted-phenyl carbonates
- Kang J.-S.; Song Y.-J.; Um I.-H.
- Ewha Authors
- SCOPUS Author ID
- Issue Date
- Journal Title
- Bulletin of the Korean Chemical Society
- vol. 34, no. 7, pp. 2023 - 2028
- SCI; SCIE; SCOPUS; KCI
- A kinetic study is reported for the nucleophilic substitution reactions of phenyl Y-substituted-phenyl carbonates (5a-5k) with piperidine in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The plots of k obsd vs. [piperidine] for the reactions of substrates possessing a strong electron-withdrawing group (EWG) in the leaving group (i.e., 5a-5i) are linear and pass through the origin. In contrast, the plots for the reactions of substrates bearing a weak EWG or no substituent (i.e., 5j or 5k) curve upward, indicating that the electronic nature of the substituent Y in the leaving group governs the reaction mechanism. Thus, it has been suggested that the reactions of 5a-5i proceed through a stepwise mechanism with a zwitterionic tetrahedral intermediate (i.e., T±) while those of 5j and 5k proceed through a stepwise mechanism with two intermediates (i.e., T± and its deprotonated form T-). The slope of the Brønsted-type plot for the second-order rate constants (i.e., kN or Kk2) changes from -0.41 to -1.89 as the leaving-group basicity increases, indicating that a change in the rate-determining step (RDS) occurs. The reactions of 5a-5k with piperidine result in larger k1 values than the corresponding reactions with ethylamine. Copyright © 2005 KCSNET.
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