Kinetic Study of the Phenolysis of Bis(4-nitrophenyl) Carbonate, Bis(4-nitrophenyl) Thionocarbonate, and Methyl 4-Nitrophenyl Thionocarbonate
作者:Enrique A. Castro、Mauricio Angel、David Arellano、José G. Santos
DOI:10.1021/jo0101252
日期:2001.10.1
The reactions of a homogeneous series of phenols with bis(4-nitrophenyl) carbonate (BNPC), bis(4-nitrophenyl) thionocarbonate (BNPTOC), and methyl 4-nitrophenyl thionocarbonate (MNPTOC) are subjected to a kinetic investigation in water, at 25.0 degrees C and ionic strength of 0.2 M (KCl). Under excess of phenol over the substrate, all the reactions obey pseudo-first-order kinetics and are first order
均相系列苯酚与碳酸双(4-硝基苯酯),双(4-硝基苯基)硫代碳酸酯(BNPTOC)和4-硝基苯基硫代碳酸甲酯(MNPTOC)的反应在水中进行25.0摄氏度,离子强度为0.2 M(KCl)。在底物上过量的苯酚下,所有反应均遵循拟一级反应动力学,并且在酚盐阴离子中为一级反应。BNPC的反应显示出线性的Bönsted型图,斜率β= 0.66,与一致的机理一致(一个步骤)。相比之下,BNPTOC和MNPTOC的双相布朗斯台德图在高pK(a)时斜率分别为β= 0.30和0.44,在低pK(a)时斜率分别为β= 1.25和1.60,与逐步一致机制。对于两种硫代碳酸酯的反应,布朗斯台德图中心(pK(a)(0))的pK(a)值为7.1,它对应于4-硝基苯酚的pK(a)。这证实了硫代碳酸酯的酚类是逐步过程,形成了阴离子四面体中间体。通过比较标题反应和相似反应的动力学和机理,可以得出以下结论:(i)在阴离子四