Kinetics of the pH-independent hydrolyses of 4-nitrophenyl chloroformate and 4-nitrophenyl heptafluorobutyrate in water-acetonitrile mixtures: consequences of solvent composition and ester hydrophobicity
作者:Omar A. El Seoud、Fábio Siviero
DOI:10.1002/poc.1081
日期:2006.11
The pH-independent hydrolyses of 4-nitrophenyl chloroformate, NPCF and 4-nitrophenyl heptafluorobutyrate, NPFB in aqueous acetonitrile were studied spectrophotometrically from 15 to 45 °C. The binary solvent composition covers water concentrations from 2.349 to 53.207 and from 2.745 to 53.333 mol L−1 for NPCF and NPFB, respectively. For both esters, the dependence of log (kobs), the observed rate constant
在15-45°C范围内用分光光度法研究了氯甲酸4-硝基苯酯,NPCF和4-硝基苯基七氟丁酸酯,NPFB在pH中的非依赖性水解。对于NPCF和NPFB,二元溶剂组成分别覆盖了2.349至53.207和2.745至53.333mol L -1的水浓度。对于两种酯,log(k obs),观察到的速率常数对log [水]的依赖性是S形的。对于NPCF和NPFB,发现相对于水的近似动力学阶数分别为2和3。Δ ģ ≠作为增加[水],由于Δ的复合物,准镜图像补偿的函数逐渐减小ħ ≠和Δ小号≠; 两个参数都增加。对于NPCF和NPFB,在存在0.190、0.540、0.890和0.180、0.529、0.890的L 2 O摩尔分数(L = H或D)的情况下,通过质子清单研究探索了过渡态的结构,分别。观察到的速率常数与氘在溶剂中的原子分数的关系曲线向下。循环跃迁状态模型适合动力学数据。这些模型包含酯和两个水