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首页> 外文期刊>Der Pharma Chemica: journal for medicinal chemistry, pharmaceutical chemistry and computational chemistry >Spectrophotometric Method for Determination of Dissociation Constant of weak acid like 2, 4-Dinitrophenol in 1-Propanol-Water Mixtures at 24.5 ?± 0.5?oC
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Spectrophotometric Method for Determination of Dissociation Constant of weak acid like 2, 4-Dinitrophenol in 1-Propanol-Water Mixtures at 24.5 ?± 0.5?oC

机译：分光光度法测定2-丙醇-水混合物中弱酸如2，4-二硝基苯酚在24.5？±0.5？oC下的解离常数

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摘要

Spectrophotometrically dissociation constant (pKa) of the indicator acid, 2,4-Dinitrophenol in 5,10,20,30 and 40 wt. % 1-propanol – water mixtures at 24.5±0.5ºC were determined. The experimental values of Ð??In- potassium salt of indicator acid and the derived values of intercept of Ð??In- values using Ion-pair intermediate model equation shows a good consistency ,suggesting the ion-pair intermediate model is applicable in the present instance. The maximum drop in pka was found to occur around 20 wt. % 1-propanol- water mixtures. This has been explained as due to increase in solvation energy for anion of the acid by London- dispersion force mechanism. The drastic increase in pka values above 20 wt% propanol has been assumed to be due to decrease in dielectric constant of the medium. This method is suitable for determination of dissociation constant for weak acid and this method will be helpful for determination of dissociation constant for drugs are weak acid in nature.
机译：指示剂酸2,4-二硝基苯酚在5、10、20、30和40 wt。％中的分光光度解离常数（pKa）。测定了24.5±0.5ºC下的％1-丙醇-水混合物。指示剂酸的?? In-钾盐的实验值和使用离子对中间模型方程式得出的?? In-值的截距的推导值显示出良好的一致性，建议离子对中间模型适用于当前实例。发现pka的最大下降发生在约20wt。％。 ％1-丙醇-水混合物。可以解释这是由于通过伦敦分散力机理增加了酸阴离子的溶剂化能。超过20 wt％的丙醇，pka值急剧增加被认为是由于介质介电常数的降低所致。该方法适用于测定弱酸的解离常数，有助于测定本质上为弱酸的药物的解离常数。

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