Mechanism of the Azeotropy Phenomenon in Aqueous Formic Acid Solutions
- PDF / 533,707 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 36 Downloads / 283 Views
ICAL CHEMISTRY OF SOLUTIONS
Mechanism of the Azeotropy Phenomenon in Aqueous Formic Acid Solutions E. G. Tarakanovaa, * and I. A. Kirilenkoa aKurnakov
Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia *e-mail: [email protected] Received March 24, 2020; revised April 27, 2020; accepted April 30, 2020
Abstract—The mechanism of the azeotropy phenomenon has been established at a molecular level for the first time on the example of the HCOOH–H2O system, which has an azeotropic region. The studies are based on the regularities of the formation of heteroassociates with strong hydrogen bonds in binary systems and on the assumption that both phases of a boiling azeotropic mixture are composed of the same heteroassociates. It has been established that an aqueous formic acid solution is azeotropic if the heteroassociates composing this solution at room temperature are converted under heating into the most stable of possible heteroassociates 2НСООН ∙ 2Н2О and 2НСООН ∙ Н2О, which are retained at boiling temperature. Such restructuring in the solution leads to the maximum strengthening of intermolecular interactions and occurs with minimum energy expenditures. Keywords: azeotropy, hydrogen bond, association of molecules, heteroassociates DOI: 10.1134/S0036023620100204
INTRODUCTION After the azeotropy phenomenon was discovered by J. Dalton in 1810, researchers strived to understand the causes of this phenomenon at a molecular level. Initially, it was explained by the formation of a chemical compound between the components of an azeotropic mixture, but this hypothesis was refuted by H. Roscoe in 1859 by demonstrating that the composition of a mixture depends on the external pressure. Afterwards, some qualitative descriptions assuming that azeotropy is caused by “different character of molecular interaction between dissimilar molecules” appeared with no explanation for the nature of this phenomenon [1]. The currently existing methods for the study of azeotropic mixtures and the modeling of their properties are based on extensive experimental data [1–9] and various thermodynamic equations and models [9–17]. The mass-spectrometric analysis of molecular associates formed upon the fragmentation of drops of aqueous alcohol solutions has demonstrated that the vaporization of molecules is associated with the presence of cluster structures in these solutions [18]. According to [18], azeotropy is caused by the fact that in the solutions of different concentrations different clusters are formed, that determine the capability of molecules for vaporization. The experimental results [1–9, 19, 20] and quantum chemistry methods make possible a deeper study for the azeotropy mechanism, and the contemporary data on the structure of solu-
tions [21–25] allow us to presume that both phases of a boiling azeotropic mixture are composed of the same molecular heteroassociates (HAs) retained at a high temperature due to strong hydrogen bonds. In the present work, the azeotropy phenomenon was studied for th
Data Loading...
