Nabavizadeh S Masoud, Akbari Alireza, Rashidi Mehdi
Department of Chemistry, College of Sciences, Shiraz University, Shiraz, Iran 71454.
Dalton Trans. 2005 Jul 21(14):2423-7. doi: 10.1039/b503870g. Epub 2005 Jun 15.
1:1 adduct formation between methyltrioxorhenium (MTO) and pyridine in different solvents (n-hexane, benzene, chloroform, ethyl acetate, dichloromethane and acetone) was studied using spectrophotometric techniques. The formation constants were determined from the absorbance change of the adduct versus pyridine concentration. The values of the formation constants vary from 114.5 to 752.5 L mol(-1) at T= 20 degrees C depending on the dielectric constant of the solvent (epsilon(r) = 1.89-20.7). Enthalpy and entropy changes during the adduct formation reactions were determined from van't Hoff plots. The measured enthalpy change of -37.0 to -22.2 kJ mol(-1) depends on epsilon(r), which is explained by Onsager's reaction field theory. The measured entropy change ranges from -71.2 to -36.6 J K(-1) mol(-1), and the dependence on the solvent is discussed in terms of the solvation effect.
采用分光光度技术研究了甲基三氧化铼（MTO）与吡啶在不同溶剂（正己烷、苯、氯仿、乙酸乙酯、二氯甲烷和丙酮）中1:1加合物的形成。根据加合物吸光度随吡啶浓度的变化确定形成常数。在T = 20℃时，形成常数的值在114.5至752.5 L mol⁻¹之间变化，这取决于溶剂的介电常数（εr = 1.89 - 20.7）。通过范特霍夫图确定加合物形成反应过程中的焓变和熵变。测得的焓变为-37.0至-22.2 kJ mol⁻¹，取决于εr，这可以用昂萨格反应场理论来解释。测得的熵变范围为-71.2至-36.6 J K⁻¹ mol⁻¹，并根据溶剂化效应讨论了其对溶剂的依赖性。
