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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 35, Number 8
BKCSDE 35(8)
August 20, 2014 

Kinetic Study on Aminolysis of Y-Substituted-Phenyl Picolinates: Effect of H-Bonding Interaction on Reactivity and Transition-State Structure
Min-Young Kim, Tae-Ah Kang, Jung Hwan Yoon, Ik-Hwan Um*
Aminolysis, Phenyl picolinate, H-bonding interaction, Intermediate, Reactivity-selectivity principle
A kinetic study is reported on nucleophilic substitution reactions of Y-substituted-phenyl picolinates (7a-7h) with a series of cyclic secondary amines in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 oC. Comparison of the kinetic results with those reported previously for the corresponding reactions of Y-substituted-phenyl benzoates (1a-1f) reveals that 7a-7h are significantly more reactive than 1a-1f. The Brønsted-type plot for the aminolysis of 4-nitrophenyl picolinate (7a) is linear with βnuc = 0.78, which is typical for reactions proceeding through a stepwise mechanism with expulsion of the leaving group being the rate-determining step. The Brønsted-type plots for the piperidinolysis of 7a-7h and 1a-1f are also linear with βlg = –1.04 and –1.39, respectively, indicating that the more reactive 7a-7h are less selective than the less reactive 1a-1f to the leavinggroup basicity. One might suggest that the enhanced reactivity of 7a-7h is due to the inductive effect exerted by the electronegative N atom in the picolinyl moiety, while the decreased selectivity of the more reactive substrates is in accord with the reactivity-selectivity principle. However, the nature of intermediate (e.g., a stabilized cyclic intermediate through the intramolecular H-bonding interaction for the reactions of 7a-7h, which is structurally not possible for the reactions of 1a-1f) is also responsible for the enhanced reactivity with a decreased selectivity.
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