32101-47-6Relevant articles and documents
The α-effect in the SNAr reaction of 1-(4-nitrophenoxy)-2,4-dinitrobenzene with anionic nucleophiles: Effects of solvation and polarizability on the α-effect
Um, Ik-Hwan,Kim, Min-Young,Cho, Hyo-Jin,Dust, Julian M.,Buncel, Erwin
, p. 1109 - 1114 (2015/10/06)
A kinetic study on SNAr reactions of 1-(4-nitrophenoxy)-2,4-dinitrobenzene (1a) with various anionic nucleophiles in 80 mol% water-20 mol% DMSO at 25.0 °C is reported. The Bronsted-type plot for the reaction of 1a with a series of substituted phenoxides and HOO- results in an excellent linear correlation with βnuc = 1.17. However, OH- exhibits dramatic negative deviation from the Bronsted-type plot, while N3-, C6H5S-, and butane-2,3-dione monoximate (Ox-) deviate positively from linearity. HOO- is 680-fold more reactive than OH- but does not exhibit the α-effect. In contrast, Ox- is 166-fold more reactive than isobasic 4-Cl-C6H4O- and exhibits the α-effect. Differential solvation effects have been suggested to be responsible for the α-effect in this study, i.e., Ox- exhibits the α-effect, since it is 5.7 kcal/mol less strongly solvated than 4-Cl-C6H4O- in the reaction medium, while HOO- does not show the α-effect due to a strong requirement for partial desolvation before nucleophilic attack. The highly enhanced reactivity of polarizable N3- and C6H5S- and extremely decreased reactivity of nonpolarizable OH- are in accord with the hard-soft acid and base principle.
The α-effect in SNar reaction of y-substituted-phenoxy-2, 4-dinitrobenzenes with amines: Reaction mechanism and origin of the α-effect
Cho, Hyo-Jin,Kim, Min-Young,Um, Ik-Hwan
, p. 2448 - 2452 (2014/09/17)
Second-order rate constants (kN) have been measured spectrophotometrically for SNAr reactions of Ysubstituted-phenoxy-2, 4-dinitrobenzenes (1a-1g) with hydrazine and glycylglycine in 80 mol % H 2O/20 mol % DMSO at 25.0 ± 0.1 °C. Hydrazine is 14.6-23.4 times more reactive than glycylglycine. The magnitude of the α-effect increases linearly as the substituent Y becomes a stronger electron-withdrawing group (EWG). The Bronsted-type plots for the reactions with hydrazine and glycylglycine are linear with βlg = -0.21 and -0.14, respectively, which is typical for reactions reported previously to proceed through a stepwise mechanism with expulsion of the leaving group occurring after rate-determining step (RDS). The Hammett plots correlated with so constants result in much better linear correlations than s- constants, indicating that expulsion of the leaving group is not advanced in the transition state (TS). The reaction of 1a-1g with hydrazine has been proposed to proceed through a five-membered cyclic intermediate (TIII), which is structurally not possible for the reaction with glycylglycine. Stabilization of the intermediate TIII through intramolecular H-bonding interaction has been suggested as an origin of the α-effect exhibited by hydrazine.
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
Um, Ik-Hwan,Kim, Min-Young,Kang, Tae-Ah,Dust, Julian M.
, p. 7025 - 7031 (2014/08/18)
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.
