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首页> 外文期刊>The journal of physical chemistry, B. Condensed matter, materials, surfaces, interfaces & biophysical >Probing the Acidity of Car boxylic Acids in Protic Ionic Liquids, Water, and Their Binary Mixtures: Activation Energy of Proton Transfer
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Probing the Acidity of Car boxylic Acids in Protic Ionic Liquids, Water, and Their Binary Mixtures: Activation Energy of Proton Transfer

机译：质子离子液体，水及其二元混合物中羧酸的酸性的探测：质子转移的活化能

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摘要

Acidity functions were used to express the ability of a solvent/solution to donate/accept a proton to a solute. The present work accounts for the acidity determination of HCOOH, CH3COOH, and CH3CH2COOH in the alkylimidazolium-based protic ionic liquids (PILs), incorporated with carboxylate anion, water, and in a binary mixture of PIL and water using the Hammett acidity function, H0. A reversal in the acidity trend was observed, when organic acids were transferred from water to PIL. It was emphasized that an increased stabilization offered by PIL cation toward the more basic conjugate anion of organic acid was responsible for this anomalous change in acidity order in PILs, which was absent in water. The greater stabilization of a basic organic anion by PIL cation is discussed in terms of the stable hard-soft acid base (HSAB) pairing. A change in the H0 values of these acids was observed with a change in temperature, and a linear correlation between the ln H0 and 1/T was noted. This relationship points toward the activation energy of proton transfer (E_(a,H~+))>a barrier provided by the medium during the proton transfer from Bronsted acid to indicator. The H0 function in binary mixtures points to the involvement of pseudosolvent, the behavior of which changes with the nature and concentration of acid. The presence of the maxima/minima in the H0 function is discussed in terms of the synergetic behavior of the pseudosolvent composed of the mixtures of aqueous PILs.
机译：使用酸度函数来表示溶剂/溶液将质子捐赠/接受质子的能力。本工作说明了使用Hammett酸度函数H0测定烷基咪唑基质子离子液体（PIL）中HCOOH，CH3COOH和CH3CH2COOH的酸度，该溶液与羧酸根阴离子，水以及PIL和水的二元混合物结合在一起。当有机酸从水转移到PIL时，酸度趋势发生了逆转。需要强调的是，PIL阳离子对更基本的有机酸共轭阴离子提供的增强的稳定性是造成PILs酸度顺序异常变化的原因，而这种变化在水中是不存在的。通过稳定的硬-软酸碱（HSAB）配对，讨论了PIL阳离子对碱性有机阴离子的更大稳定性。观察到这些酸的H0值随温度变化而变化，并且注意到ln H0与1 / T之间存在线性关系。这种关系指向质子转移的活化能（E_（a，H〜+））>质子从布朗斯台德酸转移到指示剂过程中介质提供的屏障。二元混合物中的H0函数表明假溶剂的参与，其行为随酸的性质和浓度而变化。根据由水性PIL混合物组成的假溶剂的协同行为，讨论了H0函数中最大值/最小值的存在。

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