Aminolysis of Isatin and N-Acetyl Isatin in Acetonitrile and Mixed Acetonitrile-Water Solvents
作者:Mahmoud F. Ibrahim、Asma A.A. Al-Karewi、Sherine N. Khattab、Ezzat A. Hamed、Ayman El-Faham
DOI:10.14233/ajchem.2014.16968
日期:——
The reactions of N-acetyl isatin and N-propionyl isatin with morpholine, piperazine and diethylamine in acetonitrile underwent nucleophilic substitution reactions at the amide linkage with ring opening process to give N-[2-(2-amino-2-oxo-acetyl)phenyl]acetamide derivatives and N-[2-(2-amino-2-oxoacetyl)phenyl]propionamide derivatives, respectively. The rate constants of the titled reactions were studied spectrophotometerically in pure acetonitrile and acetonitrile-water mixed solvent. The reactions in pure acetonitrile obeyed third order kinetics. The activation parameters suggest that the mechanism of the reaction proceeds by parallel specific base and dimer mechanisms depending on temperature and the nature of amine. The reaction of isatin with piperazine in acetonitrile-water mixed solvent passes through formation of solvated intermediate which in turn gives zwitterionic ion intermediate that leads to the final product in a slow step. The nonlinear plots of log kN versus 1/D of the binary solvent as well as the plot of log kN versus XH2O, indicate a specific solvation. The plot of log kN versus log [H2O] gives the number of water molecules (n) contaminated in the transition state. The inversely proportional correlation between ENT and log kA values agrees with the formation of solvated zwitterionic (tetrahedral) intermediates in the rate determined step. The application of multiparameter approach of a, b and p* indicates that the rate of the reaction is influenced by both specific and nonspecific solute-solvent interactions.
N-乙酰异靛酮和N-丙酰异靛酮与吗啉、哌嗪和二乙胺在乙腈中发生了核亲电取代反应,在酰胺键处伴随着环打开的过程,分别生成N-[2-(2-氨基-2-氧-乙酰基)苯基]乙酰胺衍生物和N-[2-(2-氨基-2-氧-乙酰基)苯基]丙酰胺衍生物。这些反应的速率常数在纯乙腈和乙腈-水混合溶剂中进行了光度计研究。纯乙腈中的反应遵循三阶动力学。活化参数表明反应机制取决于温度和胺的性质,经过平行的特定碱和二聚体机制。异靛酮与哌嗪在乙腈-水混合溶剂中的反应经历了溶剂化中间体的形成,进而生成带有两性离子的中间体,这一步骤较慢,最终产物的形成也较慢。log kN与二元溶剂的1/D的非线性图以及log kN与XH2O的图都表明了特定的溶剂化现象。log kN与log [H2O]的图给出了在过渡态中涉及的水分子数量(n)。ENT与log kA值之间的反比相关性支持了在速率决定步骤中形成溶剂化的两性离子(四面体)中间体。多参数方法(a, b和p*)的应用表明反应速率受特定和非特定溶质-溶剂相互作用的影响。