Comparative kinetic studies on the alkaline hydrolysis of halogen substituted isocoumarins
作者:HAFIZ BADARUDDIN AHMAD、MUHAMMAD ASLAM MALANA、MUHAMMAD YOUSAF、MUHAMMAD REHAN、MAZHAR ABBAS
DOI:10.3906/kim-0906-75
日期:——
Kinetics of the hydrolysis of 3-(2'-chloro-6'-fluorobenzyl) isocoumarin (1), 3-(4'-fluorophenyl)isocoumarin (3), 3-(2'- fluorophenyl)isocoumarin (5), 3-(2'-chlorophenyl)isocoumarin (7), and 3-(4'-chlorophenyl)isocoumarin (9) were studied spectrophotometrically in the presence of aqueous solution of potassium hydroxide. The rates of hydrolyses for these isocoumarins were compared. The data for isocoumarin (1) were further investigated to probe the reaction mechanism. The dependence of pseudo-first order rate constant k_obs} on hydroxide ion concentration is fitted by the expression k_obs} = k_o + k_1[OH] + k_2 [OH]^2, showing the formation of monoanionic and dianionic tetrahedral intermediates during the course of reaction. The magnitude of k_o shows significant participation of solvent in the reaction mechanism.
3-(2'-氯-6'-氟苄基)异香豆素 (1)、3-(4'-氟苯基)异香豆素 (3)、3-(2'-氟苯基)异香豆素 (5)、3 的水解动力学在氢氧化钾水溶液存在下,通过分光光度法研究了 -(2'-氯苯基)异香豆素 (7) 和 3-(4'-氯苯基)异香豆素 (9)。 比较这些异香豆素的水解速率。 进一步研究异香豆素 (1) 的数据以探讨反应机理。 伪一级速率常数 k_obs} 对氢氧根离子浓度的依赖性通过表达式 k_obs} = k_o + k_1[OH] + k_2 [OH]^2 拟合,显示单阴离子和双阴离子四面体中间体的形成反应过程中。 k_o 的大小表明溶剂在反应机理中的重要参与。