title: 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.
abstract: 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 Brønsted-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.
authors.affiliation: Department of Chemistry and Nano Science and Department of Life Science, Ewha Womans University , Seoul 120-750, Korea.
authors.forename: Ik-Hwan
authors.initials: IH
authors.lastname: Um
authors.forename: Min-Young
authors.initials: MY
authors.lastname: Kim
authors.forename: Tae-Ah
authors.initials: TA
authors.lastname: Kang
authors.forename: Julian M
authors.initials: JM
authors.lastname: Dust
mesh_terms: D000097:Acetonitriles / Q000737:chemistry*; D000588:Amines / Q000737:chemistry*; D003500:Cyclization; D004136:Dinitrobenzenes / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure
chemical_list: C000595011:1-(4-nitrophenyl)-2,4-dinitrobenzene; D000097:Acetonitriles; D000588:Amines; D004136:Dinitrobenzenes; C032159:acetonitrile