INFLUENCE OF HEXAMETHYLPHOSPHOTRIAMIDE MOLECULES ON WATER STRUCTURE
Abstract
The volume-manometric method was used to measure the solubility of noble gases: helium, argon, and krypton in mixtures of water with HMPA in the region of small additions of the organic component at temperatures of 283.15; 298.15 and 313.15 K. The maximum on the solubility curves is explained by the competing effect of the hydrophobic and hydrophilic hydration of the corresponding fragments of HMPA molecules. The "bond-breaking" model of water was used in the present work. According to this model the possible deformations of the hydrogen bonds are neglected. It makes possible to calculate the fractions of water molecules participating in any number of hydrogen bonds at the specified temperature. The phenomenological model of the structure of HMPA aqueous solutions is presented. On the base of experimental solubility of gases and the permittivity of solutions, it is possible to calculate the structural characteristics of diluted aqueous solutions. In the frame of the model one can determine the contribution of the effects of hydrophobic hydration to the total energy of interactions in the water-non-electrolyte system and describe the changes in water structure in aqueous solutions. It was found that at x = 0.0035 mole fraction of HMPA, there is an increase in the number of water molecules participating in four hydrogen bonds without changing the average number of hydrogen bonds per water molecule. At x = 0.005 the properties of the system are already largely determined by the influence of the polar group (P = O) of the HMPA molecule. At x = 0.0101 additions of the organic component to water lead to the redistribution of H-bonds and have to the same consequences as the increase in temperature from 298.15 to 313.15 K.
Forcitation:
Zheleznyak N.I. Influence of hexamethylphosphotriamide molecules on water structure. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 10. P. 36-41
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