期刊
JOURNAL OF ORGANIC CHEMISTRY
卷 79, 期 15, 页码 7025-7031出版社
AMER CHEMICAL SOC
DOI: 10.1021/jo5011872
关键词
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资金
- Basic Science Research Program through the National Research Foundation of Korea (NRF) - Ministry of Education, Science and Technology [2012-R1A1B-3001637]
- Grenfell Campus-Memorial University (Vice-President's Research Fund)
A kinetic study is reported for SNAr reactions of 1-(Y-substituted-phenoxy)-2,4-dinitrobenzenes (1a-1h) with amines in MeCN. The plots of pseudo-first-order rate constant versus amine concentration curve upward, indicating that the reactions are catalyzed by a second amine molecule. The Bronsted-type plots for the reaction of 1-(4-nitrophenyl)-2,4-dinitrobenzene (1a) with secondary amines are linear with beta(nuc) = 1.10 and 0.85 for the uncatalyzed and catalyzed reactions, respectively, while the Yukawa-Tsuno plots for the reactions of 1a-1h with piperidine result in excellent linear correlations with rho(Y) = 1.85 and r = 0.27 for the uncatalyzed reaction and rho(Y) = 0.73 and r = 0.23 for the catalyzed reaction. The catalytic effect decreases with increasing amine basicity or electron-withdrawing ability of the substituent Y in the leaving group. Activation parameters calculated from the rate constants measured at five different temperatures for the catalyzed reaction of la with piperidine are Delta H double dagger = 0.38 kcal/mol and Delta S double dagger = -55.4 cal/(mol K). The catalyzed reaction from a Meisenheimer complex (MC +/-) is proposed to proceed through a concerted mechanism with a cyclic transition-state rather than via a stepwise pathway with an anionic intermediate, MC-. Deuterium kinetic isotope effects provide further insight into the nature of the concerted transition state.
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