- Kinetic study on SNAr reaction of 1-(Y-Substituted-phenoxy)-2,4- dinitrobenzenes with cyclic secondary amines in acetonitrile: Evidence for cyclic transition-state structure
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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 Br?nsted-type plots for the reaction of 1-(4-nitrophenyl)-2,4- dinitrobenzene (1a) with secondary amines are linear with βnuc = 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 ρY = 1.85 and r = 0.27 for the uncatalyzed reaction and ρY = 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 1a with piperidine are ΔH? = 0.38 kcal/mol and ΔS? = -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.
- Um, Ik-Hwan,Kim, Min-Young,Kang, Tae-Ah,Dust, Julian M.
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Read Online
- Studies of Tertiary Amine Oxides. Part 8. Rearrangement of N-(2,4-Dinitrophenyl)-piperidines and -morpholine N-Oxides in Aprotic Solvents
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The N-oxides of N-(2,4-dinitrophenyl)-piperidines and -morpholine undergo thermal rearrangement to the substituted hydroxylamines.The kinetics of the rearrangement were studied in aprotic solvents at four or five temperatures.Steric and polar factors have
- Khuthier, Abdul-Hussain,Al-Mallah, Khawla Y.,Hanna, Salim Y.
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p. 109 - 112
(2007/10/02)
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