Modification of Both the Electrophilic Center and Substituents on the Nonleaving Group in Pyridinolysis of <i>O</i>-4-Nitrophenyl Benzoate and Thionobenzoates
作者:Ik-Hwan Um、So-Jeong Hwang、Mi-Hwa Baek、Eun Ji Park
DOI:10.1021/jo061682x
日期:2006.11.1
[GRAPHICS]A kinetic study is reported for reactions of 4-nitrophenyl benzoate (1c) and O-4-nitrophenyl X-substituted thionobenzoates (2a-e) with a series of pyridines in 80 mol % H2O/20 mol % dimethyl sulfoxide ( DMSO) at 25.0 +/- 0.1 degrees C. O-4-Nitrophenyl thionobenzoate (2c) is more reactive than its oxygen analogue 1c toward all the pyridines studied. The Bronsted-type plot is linear with beta(nuc) = 1.06 for reactions of 1c but curved for the corresponding reactions of 2c with beta(nuc) decreasing from 1.38 to 0.38 as the pyridine basicity increases, indicating that the reaction mechanism is also influenced on changing the electrophilic center from C=O to C=S. The curvature center of the curved Bronsted-type plots (defined as pK(a)(o)) occurs at pK(a) = 9.3 regardless of the electronic nature of the substituent X in the nonleaving group. The Hammett plot for reactions of 2a-e with 4-aminopyridine is nonlinear, i.e., the substrates having an electron-donating substituent exhibit negative deviations from the Hammett plot. However, the Yukawa-Tsuno plot for the same reactions exhibits good linear correlation, indicating that the negative deviations shown by these substrates arise from stabilization of the ground state through resonance interaction between the electron-donating substituent X and the C=S bond.
Nonlinear Broensted-type plot in the pyridinolysis of 2,4-dinitrophenyl benzoate in aqueous ethanol
作者:Enrique A. Castro、Carlos L. Santander
DOI:10.1021/jo00219a029
日期:1985.9
Effect of Changing Electrophilic Center from CO to CS on Rates and Mechanism: Pyridinolyses of <i>O</i>-2,4-Dinitrophenyl Thionobenzoate and Its Oxygen Analogue
rate constants have been measured spectrophotometrically for the reactions of O-2,4-dinitrophenyl thionobenzoate (1) and 2,4-dinitrophenylbenzoate (2) with a series of substituted pyridines in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 °C. The Brønsted-type plots obtained are nonlinear with β1 = 0.26, β2 = 1.07, and pKa° = 7.5 for the reactions of 1 and β1 = 0.40, β2 = 0.90, and pKa° = 9.5 for the reactions
已分光光度法测定了O -2,4-二硝基苯基硫代苯甲酸酯(1)和2,4-二硝基苯基苯甲酸酯(2)与一系列取代吡啶在80 mol%H 2 O / 20 mol中的反应的二级速率常数在25.0±0.1°C下的%DMSO。得到的布朗斯台德型曲线是非线性的β 1 = 0.26,β 2 = 1.07,且p ķ一个°= 7.5的反应1和β 1 = 0.40,β 2 = 0.90,且p ķ一个°= 9.5 2的反应,表明1和图2所示的流程通过两性离子四面体中间体T ±进行,其中速率确定步骤的变化分别在p K a °= 7.5和9.5处进行。除了与所研究的最强碱性吡啶的反应(p K a = 11.30)以外,硫代磺酸酯1比其氧类似物2具有更高的反应性。所述ķ 1值是用于的反应中较大的1比那些的2在低p- ķ一个区域,但在差ķ 1值变得可忽略随吡啶的碱性。另一方面,1在低p K a区域中,K 2 / k -