Chlorination of 2-Phenoxypropanoic Acid with NCP in Aqueous Acetic Acid: Using a Novel Ortho−Para Relationship and the Para/Meta Ratio of Substituent Effects for Mechanism Elucidation
作者:Manuel A. P. Segurado、João Carlos R. Reis、Jaime D. Gomes de Oliveira、Senthamaraikannan Kabilan、Manohar Shanthi
DOI:10.1021/jo0706224
日期:2007.7.1
beyond the aromatic ring. Activation enthalpies and entropies were estimated for substrates bearing the isoselective substituent in either ortho and para positions, being demonstrated that they are much different from the values for the parent substrate. The electrophilic attack on the phenolic oxygen atom by the protonated chlorinating agent is proposed as the rate-determining step, this step being followed
对的(氧化chlorodehydrogenation测定速率常数[R ,小号)-2- phenoxypropanoic酸和九个邻- ,对- 10和五个间位取代的衍生物,使用(- [R ,小号)-1-氯-3-甲基-2,6-二苯基哌啶-4-酮(NCP)作为氯化剂。动力学是在伪一级反应条件下,相对于NCP,在5K(v / v)50%(v / v)的乙酸水溶液中,在高氯酸酸化的条件下,在298至318 K之间的5 K的温度间隔下进行的,衍生品。根据等动力学关系(IKR)分析了速率常数对温度的依赖性。对于在五个不同温度下研究的20个反应,等动力学温度估计为382 K,这表明水分子优先参与速率确定步骤。使用Hammett方程的四线性扩展分析了速率常数对间位和对位取代的依赖性。极性取代基效应的对位/间位比的参数λ估计为0.926,其静电模型表明在靠近苯氧基的氧原子附近带有电荷的活化络合物的形成。引入了一