Thermodynamic parameters of intermolecular interaction in strongly associated solvents and their mixtures with dimethylformamide

Abstract

The specific and nonspecific constituents of the total energy of intermolecular interasction in ethylene glycol, diethylene glycol, and formamide were determined for the range 288.153323.15 K using a simulation approach. Diethylene glycol, like formamide and ethylene glycol, forms networks of hydrogen bonds. In ethylene glycol and formamide, the hydrogen bonds make a predominant contribution to the total interaction energy. The specific and nonspecific contributions in mixtures of the above solvents with dimethylformamide were calculated, and the results were discussed in combination with the data for aqueous dimethylformamide solutions.Owing to the presence of three-dimensional networks of hydrogen bonds in certain nonaqueous solvents, solvation of atomic and molecular species in them has a number of characteristic features [1]. In ethylene glycol and formamide, both of which contain two proton-acceptor and two proton-donor sites in the molecule, formation of the network structures has been reliably proved [2, 3], whereas with diethylene glycol this is still the matter of discussion [4]. Search for correlations between the structure and properties of strongly associated solvents and thermodynamic characteristics of their nonelectrolyte mixtures reflecting the specific features of intermolecular interaction of the components is an urgent problem of the modern chemistry of solutions [5]. This work is a part of studies of the structural and thermodynamic properties of mixtures of carboxylic acid amides with compounds forming a network of hydrogen bonds. Previously we studied the thermochemical characteristics of mixtures of formamide and ethylene glycol with N,N-disubstituted amides [6,7]. One of the main goals of this work was to estimate the contribution of specific and nonspecific interactions to the intermolecular interaction of strongly associated nonelectrolytes (ethylene glycol, diethylene glycol, formamide) and their binary systems with DMF, a typical aprotic polar solvent capable of formation of hydrogen-bonded heteroassociates. Important information on the structure and properties of nonaqueous solutions with hydrogen bond networks is furnished by computer simulation methods. Formamide and its mixtures with dimethylformamide were studied by this method in [3,8,9]. However, the thermodynamic characteristics of formamide and its mixtures with DMF, calculated by these methods, are poorly consistent with the results of a physicochemical experiment [3,9], which is most probably caused by inadequacy of the existing interaction potentials. Computer simulation of glycols and their solutions is hindered by the lack of data on the intermolecular interaction potentials. Analysis of the excess thermodynamic functions of mixing in nonelectrolyte solutions with hydrogen bonding, usually performed within the framework of associative models [10], is inadequate for these systems, because it is principally impossible to single out the associative formations. Therefore, it seems reasonable to consider nonaqueous solvents an...