Synthesis, Characterization and Solvent Effects on the Electronic Absorption Spectra of Aminopyridine Schiff Bases
作者:Cordelia U. Dueke-Eze、Tolulope M. Fasina、Malose J. Mphahlele
DOI:10.14233/ajchem.2013.14805
日期:——
Six Schiff bases, namely, N-(2-hydroxylbenzylidene)pyridine-4-amine (IA), N-(2-hydroxylbenzylidene)pyridine-2-amine (IB), N-(5-nitro-2-hydroxylbenzylidene)pyridin-4-amine (IIA), N-(5-nitro-2-hydroxylbenzylidene)pyridin-2-amine (IIB), N-(5-bromo-2-hydroxylbenzylidene)pyridin-4-amine (IIIA) and N-(5-bromo-2-hydroxylbenzylidene)pyridin-2-amine (IIIB) derived from condensation reactions of 4-aminopyridine or 2-aminopyridine with salicylaldehye, 5-nitrosalicylaldehye and 5-bromosalicylaldehye were synthesized and characterized using elemental analysis, IR, NMR and Raman spectroscopic techniques. The effect of solvent on the electronic absorption spectra was examined in five solvents of different polarities, namely, 1,4-dioxane, chloroform, ethanol, acetonitrile and N,N-dimethyl formamide. The bands involving different electronic transitions were interpreted and regression coefficients calculated for the absorption band involving intermolecular charge transfer transition within the whole Schiff base molecule using an equation that relates the absorption maxima to empirical solvent parameters that depend on the dielectric constant, refractive index and hydrogen bonding ability of the solvents.
合成并表征了六种Schiff碱,分别为N-(2-羟基苯甲亚胺)pyridine-4-amine(IA)、N-(2-羟基苯甲亚胺)pyridine-2-amine(IB)、N-(5-硝基-2-羟基苯甲亚胺)pyridin-4-amine(IIA)、N-(5-硝基-2-羟基苯甲亚胺)pyridin-2-amine(IIB)、N-(5-溴-2-羟基苯甲亚胺)pyridin-4-amine(IIIA)和N-(5-溴-2-羟基苯甲亚胺)pyridin-2-amine(IIIB),这些化合物通过4-氨基吡啶或2-氨基吡啶与水杨醛、5-硝基水杨醛和5-溴水杨醛的缩合反应合成。采用元素分析、红外光谱、核磁共振和拉曼光谱技术对其进行了表征。研究了溶剂对电子吸收光谱的影响,使用了五种不同极性的溶剂,分别为1,4-二氧六环、氯仿、乙醇、乙腈和N,N-二甲基甲酰胺。对涉及不同电子跃迁的谱带进行了分析,并计算了吸收带中涉及分子间电荷转移跃迁的回归系数,使用的方程将吸收峰值与依赖于溶剂介电常数、折射率和氢键能力的经验溶剂参数关联起来。