作者:Stefano Salvestrini、Paola Di Cerbo、Sante Capasso
DOI:10.1039/b205850b
日期:2002.10.30
The hydrolysis of phenylureas has been found to be affected by temperature, pH and buffer concentration. Kinetic evidence suggests that the formation of phenylisocyanate, the initial product in the title reaction, occurs via an intermediate zwitterion. Depending on pH and buffer concentrations, the zwitterion can be produced through three parallel routes: at low pH, specific acid–general base catalysis, followed by slow deprotonation of a nitrogen atom by a general base; at high pH, specific basic–general acid catalysis, followed by slow protonation of a N atom by a general acid; at intermediate pH the reaction proceeds through a proton switch promoted by buffers. Bifunctional acid–base buffers such as HCO3−/CO32−, H2PO4−/HPO42− and CH3COOH/CH3COO− are very efficient catalysts. At high buffer concentration, as well as at pH < 3 or > 12, the breakdown of the zwitterion is rate-determining. The results are discussed in relation to recently published papers reporting different pathways.
苯脲的水解受到温度、pH值和缓冲液浓度的影响。动力学证据表明,标题反应的初始产物苯异氰酸酯是通过一个两性离子中间体形成的。根据pH值和缓冲液浓度,两性离子可以通过三条平行路径产生:在低pH值下,特定酸–广义碱催化作用,随后通过广义碱缓慢地去质子化一个氮原子;在高pH值下,特定碱–广义酸催化作用,随后通过广义酸缓慢地质子化一个氮原子;在中等pH值下,反应通过缓冲液促进的质子开关进行。具有双功能的酸–碱缓冲液如HCO3−/CO32−、H2PO4−/HPO42−和CH3COOH/CH3COO−是非常高效的催化剂。在高缓冲液浓度以及pH值<3或>12时,两性离子的分解是速率决定步骤。这些结果与最近发表的不同途径的论文中讨论的结果相关联。