Leaving-Group Substituent Controls Reactivity and Reaction Mechanism in Aminolysis of Phenyl Y-Substituted-Phenyl Carbonates 


Vol. 34,  No. 7, pp. 2023-2028, Jul.  2013
10.5012/bkcs.2013.34.7.2023


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  Abstract

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 oC. The plots of kobsd 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.

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  Cite this article

[IEEE Style]

J. Kang, Y. Song, I. Um, "Leaving-Group Substituent Controls Reactivity and Reaction Mechanism in Aminolysis of Phenyl Y-Substituted-Phenyl Carbonates," Bulletin of the Korean Chemical Society, vol. 34, no. 7, pp. 2023-2028, 2013. DOI: 10.5012/bkcs.2013.34.7.2023.

[ACM Style]

Ji-Sun Kang, Yoon-Ju Song, and Ik-Hwan Um. 2013. Leaving-Group Substituent Controls Reactivity and Reaction Mechanism in Aminolysis of Phenyl Y-Substituted-Phenyl Carbonates. Bulletin of the Korean Chemical Society, 34, 7, (2013), 2023-2028. DOI: 10.5012/bkcs.2013.34.7.2023.

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ISSN(Print) 0253-2964
ISSN(Online) 1229-5949