1094-62-8Relevant articles and documents
Alkali-Metal Ion Catalysis and Inhibition in SNAr Displacement: Relative Stabilization of Ground State and Transition State Determines Catalysis and Inhibition in SNAr Reactivity
Um, Ik-Hwan,Cho, Hyo-Jin,Kim, Min-Young,Buncel, Erwin
, p. 13337 - 13344 (2014)
We report here the first observation of alkali-metal ion catalysis and inhibition in SNAr reactions. The plot of kobsd versus [alkali-metal ethoxide] exhibits downward curvature for the reactions of 1-(4-nitrophenoxy)-2,4-dinitrobenzene with EtOLi, EtONa, and EtOK, but upward curvature for the corresponding reaction with EtOK in the presence of 18-crown-6-ether (18C6). Dissection of kobsd into the second-order rate constants for the reactions with the dissociated EtO- and the ion-paired EtOM (i.e., k EtO - and kEtOM, respectively) has revealed that the reactivity increases in the order EtOLi-+, Na+, and K+ ions but is catalyzed by 18C6 K+ ion. The reactions of 1-(Y-substituted-phenoxy)-2,4-dinitrobenzenes have been proposed to proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the rate-determining step based on the kinetic result that σo constants exhibit a much better Hammett correlation than σ- constants. Alkali-metal ion catalysis or inhibition has been discussed in terms of differential stabilization of ground-state and transition-state complexes through a qualitative energy profile. A π-complexed transition-state structure is proposed to account for the kinetic results.
Kinetic study on SNAr reaction of 1-Y-substituted-phenoxy-2,4- dinitrobenzenes with hydroxide ION: Effect of substituent y on reactivity and reaction mechanism
Kang, Tae-Ah,Cho, Hyo-Jin,Um, Ik-Hwan
, p. 2135 - 2138 (2014/11/08)
A kinetic study is reported for the SNAr reaction of 1-Y-substituted- phenoxy-2,4-dinitrobenzenes (1a-1h) with OH- in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The second-order rate constant (kOH-) increases as the substituent Y in the leaving group changes from an electron-donating group (EDG) to an electronwithdrawing group (EWG). The Bronsted-type plot for the reactions of 1a-1h is linear with βlg = -0.16, indicating that the reactivity of substrates 1a-1h is little affected by the leaving-group basicity. A linear Bronsted-type plot with βlg = -0.3 ± 0.1 is typical for reactions reported previously to proceed through a stepwise mechanism in which formation of a Meisenheimer complex is the rate-determining step (RDS). The Hammett plot correlated with σY o constants results in a much better correlation than that correlated with σY - constants, implyng that no negative charge is developing on the O atom of the leaving group (or expulsion of the leaving group is not advanced at all in the TS). This excludes a possibility that the SNAr reaction of 1a-1h with OH- proceeds through a concerted mechanism or via a stepwise pathway with expulsion of the leaving group being the RDS. Thus, the current reactions have been concluded to proceed through a stepwise mechanism in which expulsion of the leaving group occurs rapidly after the RDS.
