Calculation of Water-E thanol Mixtures Autoprotoly sis Constants using ab initio methods

The a queous organic solvent mixtures such as water- ethanol, ha s proven ap propriate re action media in different fields of c hemistry due to specific properties and better a bility to dissolve more compounds than pure solvents. Among the thermodyn amics prope rties of solvent, autopr otolysis co nstant (pKap ) is one of the most important prop erties and k nowledge of this parameter is considered as fundamental concept in a pplication of the solvent. The smaller the autopr otolysis co nstant, the greater the range of acid or base strengths that can exist in a solven t and the greater the likelihood that it will be a differentiating solvent. Hence, acid-base titratio ns are best carried out in solvents with small autoprotolysis constant values [۱]. In mixtures of water and a mis cible organic solvent su ch as ethanol, the diel ectric const ant of mixed solvent co nsiderably changes with the proportion of ethanol. In repect of electrostatic intera ctions, the i nfluence of dielectric constant of solvent ca n be used for elucidation of solven t composition effect on chemical eq uilibrium s uch as autoprotolysis constant [۱].Different methods were empl oyed for the determination of pKap [۲]. On the other hand, during the last two decades there has been mu ch interest in developing a meth odology ena bling theoretical prediction of pK values, emp loying various quantu m theoretica l techniques [۳].Therefore, the o bjective of this study is the dete rmination of autoprotolysis constant of differ ent water-ethanol mixtures involving ۱۰-۹۰ volume percent of ethanol using DFT method, the deter mination of relationship between th e calculated autoprotolysis constants with experimental autoprotolysis c onstants and dielectric constant of m ixtures.

کلیدواژه ها:

Autop rotolysis constant ، Water-ethanol m ixture ، DFT Method