Department of Chemistry, Lanzhou University, Lanzhou, Gansu, 730000, China.
J Phys Chem A. 2011 Jun 9;115(22):5560-7. doi: 10.1021/jp202223b. Epub 2011 May 16.
The reactions of the alkaline fading of phenolphthalein (PN) have been studied in water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane microemulsions by monitoring the absorbance changes of PN in the system with the time and the results compared with those found for the same reactions in aqueous solutions. It was found that the values of the equilibrium constants and the forward reaction rate constants in the microemulsions were significantly larger than that in aqueous solutions and decreased with increasing the molar ratio of water to AOT (ω), except for that with low ω. The temperature dependence of the reaction rate constant was analyzed to obtain the values of free energy, enthalpy, and entropy of activation, which suggests the existence of an isokinetic relationship and a common mechanism for the reactions occurring in the microemulsions with different ω. It was also observed that the competition between the reactions of the alkaline fading of PN and the hydrolyzation of AOT in water/AOT/isooctane microemulsions when the reaction time was sufficiently long.
在水/双（2-乙基己基）磺基琥珀酸钠（AOT）/异辛烷微乳液中，通过监测体系中酚酞（PN）的吸光度随时间的变化，研究了碱性褪色反应的反应。将结果与相同反应在水溶液中的结果进行了比较。结果发现，平衡常数和正向反应速率常数的值在微乳液中明显大于水溶液中的值，并且随着水与 AOT 的摩尔比（ω）的增加而减小，除了 ω 较低的情况。通过分析反应速率常数的温度依赖性，获得了自由能、焓和活化熵的值，这表明在不同 ω 的微乳液中发生的反应存在等动力学关系和共同的机制。还观察到，当反应时间足够长时，PN 的碱性褪色反应和 AOT 在水/AOT/异辛烷微乳液中的水解反应之间存在竞争。
