1268380-08-0Relevant articles and documents
Kinetic study on nucleophilic displacement reactions of phenyl Y-substituted phenyl carbonates with 1,8-diazabicyclo[5.4.0]undec-7-ene: Effects of amine nature on reaction mechanism
Park, Kyoung-Ho,Kim, Min-Young,Um, Ik-Hwan
, p. 77 - 81 (2016)
Second-order rate constants (kN) for nucleophilic displacement reactions of phenyl Y-substituted phenyl carbonates (7a-7l) with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C have been measured spectrophotometrically. The Br?nsted-type plot for the reactions of 7a-7l with DBU is linear with βlg = -0.48, indicating that the reactions proceed through a concerted mechanism, which is in contrast to the stepwise mechanism reported previously for the corresponding reactions with ethylamine (a primary amine) and piperidine (a secondary amine). The Hammett plots correlated with σ- and σo constants exhibit many scattered points. In contrast, the Yukawa-Tsuno plot results in an excellent linear correlation with ρY = 1.27 and r = 0.57, implying that a negative charge develops partially on the O atom of the leaving group in the transition state. The bulky DBU is less reactive than the primary and secondary amines toward substrates possessing a weakly basic leaving group. It has been concluded that steric hindrance exerted by DBU in the plausible intermediate (T±) forces the reactions to proceed through a concerted mechanism because expulsion of the leaving group from T± could reduce the steric hindrance.
Nucleophilic substitution reactions of phenyl y-substituted-phenyl carbonates with butane-2,3-dione monoximate and 4-chlorophenoxide: Origin of the α-effect
Kim, Min-Young,Min, Se-Won,Um, Ik-Hwan
, p. 49 - 53 (2013/08/24)
Second-order rate constants have been measured spectrophotometrically for the reactions of phenyl Ysubstituted- phenyl carbonates 7a-g with butane-2,3-dione monoximate (Ox-) in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The α-nucleophile Ox- is 53-95 times more reactive than the corresponding normalnucleophile 4-ClPhO- toward 7a-g, indicating that the α-effect is operative. The magnitude of the α-effect (e.g., the kOx/k4-ClPhO ratio) is independent of the electronic nature of the substituent Y. The cause of the α- effect for the reactions of 7a-g has been suggested to be ground-state (GS) effect rather than transition-state (TS) stabilization through a six-membered cyclic TS, in which Ox- behaves a general acid/base catalyst. This idea is further supported by the result that OH- exhibits negative deviation from the linear Bronsted-type plot composed of a series of aryloxides, while Ox- deviates positively from the linearity. Differential solvation of the GS of Ox- and 4-ClPhO- has been suggested to be responsible for the α-effect exerted by Ox-.
A kinetic study on nucleophilic displacement reactions of phenyl Y-substituted-phenyl carbonates with alkali metal ethoxides: Metal ion effect and reaction mechanism
Um, Ik-Hwan,Seo, Ji-Yoon,Kang, Ji-Sun,An, Jun-Sung
, p. 1007 - 1013,7 (2020/08/24)
Pseudo-first-order rate constants (kobsd) have been measured for reactions of phenyl Y-substituted-phenyl carbonates with alkali metal ethoxides (EtOM, M = Li, Na, and K). The plot of kobsd vs. [EtOM] curves upward for the reaction of diphenyl carbonate with EtOM but is linear for that with EtOK in the presence of 18-crown-6-ether (18C6), indicating that the reaction is catalyzed by M+ ions and the catalytic effect disappears in the presence of 18C6. The kobsd values for the reactions with EtOK have been dissected into fEtO- and kEtOK, i.e., the second-order rate constants for the reactions with dissociated EtO- and ion-paired EtOK, respectively. The Hammett plots correlated with σ- and σ-0 constants exhibit highly scattered points, while the Yukawa-Tsuno plots result in an excellent linear correlation with p = 2.11 and r = 0.21 for kEtO-, and P = 1.62 and r = 0.26 for kEtOK, implying that the reaction proceeds through a concerted mechanism. The catalytic effect (i.e., the kEtOK/kEtOr ratio) is independent of the electronic nature of the substituent Y. Thus, it has been concluded that K+ ion catalyzes the reaction by increasing the electrophilicity of the reaction center.
