Kinetics and Mechanism of Alkaline Hydrolysis of Y-Substituted Phenyl Phenyl Carbonates
摘要:
已通过光谱法测量了Y取代的苯基苯甲酸酯(2a-j)碱性水解的二级速率常数< T പി >$(k_{OH^-})$,并与先前报告的Y取代的苯基苯甲酸酯(1a-j)相应反应的< T പി >$k_{OH^-}$数值进行了比较。碳酸酯2a-j的反应性比苯酸酯1a-j高出8~16倍。Hammett图与< T Π >$\sigma^-$和< T Π >$\sigma^o$常数相关,但显示出许多散点,而Yukawa-Tsuno图则表现出良好的线性相关性,< T Π >$\rho$ = 1.21,< T Π >$\gamma$ = 0.33。因此,可以得出结论,该反应是通过一个协同机制进行的,其中脱离基团的排除仅稍微提前。然而,不能排除当前反应通过一个强迫协同机制及一个高度不稳定的中间体进行的可能性。
Kinetics and Mechanism of Alkaline Hydrolysis of Y-Substituted Phenyl Phenyl Carbonates
摘要:
已通过光谱法测量了Y取代的苯基苯甲酸酯(2a-j)碱性水解的二级速率常数< T പി >$(k_{OH^-})$,并与先前报告的Y取代的苯基苯甲酸酯(1a-j)相应反应的< T പി >$k_{OH^-}$数值进行了比较。碳酸酯2a-j的反应性比苯酸酯1a-j高出8~16倍。Hammett图与< T Π >$\sigma^-$和< T Π >$\sigma^o$常数相关,但显示出许多散点,而Yukawa-Tsuno图则表现出良好的线性相关性,< T Π >$\rho$ = 1.21,< T Π >$\gamma$ = 0.33。因此,可以得出结论,该反应是通过一个协同机制进行的,其中脱离基团的排除仅稍微提前。然而,不能排除当前反应通过一个强迫协同机制及一个高度不稳定的中间体进行的可能性。
Leaving-Group Substituent Controls Reactivity and Reaction Mechanism in Aminolysis of Phenyl Y-Substituted-Phenyl Carbonates
作者:Ji-Sun Kang、Yoon-Ju Song、Ik-Hwan Um
DOI:10.5012/bkcs.2013.34.7.2023
日期:2013.7.20
reported for the nucleophilicsubstitution reactions of phenyl Y-substituted-phenyl carbonates (5a-5k) with piperidine in 80 mol % /20 mol % DMSO at . The plots of vs. [piperidine] for the reactions of substrates possessing a strong electron-withdrawing group (EWG) in the leaving group (i.e., 5a-5i) are linear and pass through the origin. In contrast, the plots for the reactions of substrates bearing a weak
A Kinetic Study on Ethylaminolysis of Phenyl Y-Substituted-Phenyl Carbonates: Effect of Leaving-Group Substituents on Reactivity and Reaction Mechanism
作者:Yoon-Ju Song、Min-Young Kim、Ik-Hwan Um
DOI:10.5012/bkcs.2013.34.6.1722
日期:2013.6.20
A kinetic study on nucleophilicsubstitution reactions of phenyl Y-substituted-phenyl carbonates (5a-5j) with ethylamine in 80 mol % /20 mol % DMSO at is reported. The plots of vs. [amine] are linear for the reactions of substrates possessing a strong electron-withdrawing group (EWG) but curve upward for those of substrates bearing a weak EWG, indicating that the electronic nature of the substituent
报道了在 80 mol % /20 mol % DMSO 中,苯基 Y 取代的碳酸苯酯 (5a-5j) 与乙胺的亲核取代反应的动力学研究。对于具有强吸电子基团 (EWG) 的底物的反应,与 [胺] 的关系图是线性的,但对于具有弱 EWG 的底物的反应,曲线向上,表明离去基团中取代基 Y 的电子性质支配反应机理。根据取代基 Y 的性质,反应通过一种或两种中间体(两性离子四面体中间体及其去质子化形式)通过逐步机制进行。布朗斯特型图的分析和微观速率常数的剖析表明具有强 EWG 的底物的反应(例如,
Nucleophilic Substitution Reactions of Phenyl Y-Substituted-Phenyl Carbonates with Butane-2,3-dione Monoximate and 4-Chlorophenoxide: Origin of the α-Effect
作者:Min-Young Kim、Se-Won Min、Ik-Hwan Um
DOI:10.5012/bkcs.2013.34.1.49
日期:2013.1.20
Second-order rate constants have been measured spectrophotometrically for the reactions of phenyl Y-substituted-phenyl carbonates 7a-g with butane-2,3-dione monoximate ($Ox^-$) in 80 mol % $H_2O$/20 mol % DMSO at $25.0\pm}0.1^\circ}C$. The $\alpha}$-nucleophile $Ox^-$ is 53-95 times more reactive than the corresponding normal-nucleophile 4-$ClPhO^-$ toward 7a-g, indicating that the $\alpha}$-effect is operative. The magnitude of the $\alpha}$-effect (e.g., the $k_Ox^-}/k_4-ClPhO^-}$ ratio) is independent of the electronic nature of the substituent Y. The cause of the $\alpha}$-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 Br$\o}$nsted-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 $\alpha}$-effect exerted by $Ox^-$.
Alkaline Hydrolysis of Y-Substituted Phenyl Phenyl Thionocarbonates: Effect of Changing Electrophilic Center from C=O to C=S on Reactivity and Mechanism
作者:Song-I Kim、Hey-Ran Park、Ik-Hwan Um
DOI:10.5012/bkcs.2011.32.1.179
日期:2011.1.20
not advanced in the RDS. Thus, alkaline hydrolysis of 4a-i has been concluded to proceed through a stepwise mechanism with formation of an intermediate being RDS, which is in contrast to the forced concerted mechanism reported for the corresponding reactions of 3a-i. Enhanced stability of the intermediate upon modification of the electrophilic center from C=O to C=S has been concluded to be responsible