Kinetic Study on Nucleophilic Displacement Reactions of Y-Substituted-Phenyl 2-Methylbenzoates with Cyclic Secondary Amines in Acetonitrile: Effects of Modification of 2-MeO in Benzoyl Moiety by 2-Me on Reactivity and Reaction Mechanism 


Vol. 34,  No. 12, pp. 3795-3799, Dec.  2013
10.5012/bkcs.2013.34.12.3795


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  Abstract

The second-order rate constants (kN) have been measured spectrophotometrically for nucleophilic substitution reactions of Y-substituted-phenyl 2-methylbenzoates (6a-e) with a series of cyclic secondary amines in MeCN at 25.0 ± 0.1 oC. Comparison of the kN values for the reactions of 4-nitrophenyl 2-methylbenzoate (6d) with those reported previously for the corresponding reactions of 4-nitrophenyl 2-methoxybenzoate (5) reveals that 6d is significantly less reactive than 5, indicating that modification of 2-MeO in the benzoyl moiety of 5 by 2- Me (i.e., 5 → 6d) causes a significant decrease in reactivity. This supports our previous report that aminolysis of 5 proceeds through a six-membered cyclic intermediate, which is highly stabilized through intramolecular H-bonding interactions. The Brønsted-type plot for the reactions of 6d with a series of cyclic secondary amines is linear with βnuc = 0.71, which appears to be a lower limit of βnuc for a stepwise mechanism with breakdown of an intermediate (T±) being rate-determining step (RDS). The Brønsted-type plot for the reactions of 6a-e with piperidine is curved, i.e., the slope of Brønsted-type plot (βlg) decreases from –1.05 to –0.41 as the leavinggroup basicity decreases. The nonlinear Brønsted-type plot has been taken as evidence for a stepwise mechanism with a change in RDS (e.g., from the k2 step to the k1 process as the leaving-group basicity decreases). Dissection of kN into the microscopic rate constants associated with the reactions of 6a-e with piperidine (e.g., k1 and k2/k–1 ratio) also supports the proposed mechanism.

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  Cite this article

[IEEE Style]

J. Lee, M. Kim, I. Um, "Kinetic Study on Nucleophilic Displacement Reactions of Y-Substituted-Phenyl 2-Methylbenzoates with Cyclic Secondary Amines in Acetonitrile: Effects of Modification of 2-MeO in Benzoyl Moiety by 2-Me on Reactivity and Reaction Mechanism," Bulletin of the Korean Chemical Society, vol. 34, no. 12, pp. 3795-3799, 2013. DOI: 10.5012/bkcs.2013.34.12.3795.

[ACM Style]

Ji-Youn Lee, Mi-Yeon Kim, and Ik-Hwan Um. 2013. Kinetic Study on Nucleophilic Displacement Reactions of Y-Substituted-Phenyl 2-Methylbenzoates with Cyclic Secondary Amines in Acetonitrile: Effects of Modification of 2-MeO in Benzoyl Moiety by 2-Me on Reactivity and Reaction Mechanism. Bulletin of the Korean Chemical Society, 34, 12, (2013), 3795-3799. DOI: 10.5012/bkcs.2013.34.12.3795.

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