M. Yu. Nikiforov

The viscosity and density of the methanol + n-nonane, ethanol + n-nonane, and ethanol + n-decane systems

This work presents the results obtained in measurements of the kinematic viscosity and density of the methanol-n-nonane, ethanol-n-nonane, and ethanol-n-decane systems at various temperatures and low n-alkane concentrations (within the concentration range of miscibility). The dynamic viscosities of these systems at 298.15 K were calculated according to free volume theory. The results substantiated the existence of an anomaly in the behavior of viscosity of the methanol-n-nonane system (positive Δlnη values) and its absence for the ethanol-n-alkane systems.

Solubility of porphyrin macrocycles in mixed solvents

A method based on the statements of molecular association theory and a simple lattice model (ASL = Associated Solution + Lattice) is used to calculate the solubility of a series of porphyrin macrocycles (blood porphyrins) in binary solvents (tetrachloromethane-ethyl acetate, tetrachloromethane-methanol). Separate contributions to solubility are identified and the relative role of different factors determining the solubility dependence on the mixed solvent composition is analyzed. The calculated solubility values are in good agreement with the experimental data obtained for the studied systems by the isothermal saturation method with a spectrophotometric control of concentrations.

Solubility of caffeine in the supercritical CO2–methanol binary solvent

The caffeine–methanol association constant at 313 K has been determined by 1H NMR spectroscopy. The caffeine solubility in the supercritical carbon dioxide (SC-CO2)–methanol mixed solvent has been calculated using the association constant experimentally measured by NMR in the framework of the associated solution + lattice (ASL) model, which is based on the theory of molecular association and a simple lattice model. Individual contributions to the solubility have been determined, and the relative role of various factors determining the solubility of caffeine in the mixed solvent has been analyzed. The caffeine solubility as a function of the methanol content of the SC-CO2–methanol system is predicted to pass through a maximum.

Influence of molecular association on the solubility of methylxanthines in supercritical solvent CO2–methanol

Analysis of the experimental data on the solubility of methylxanthines (theophylline and theobromine) in supercritical (SC) solvent CO2–methanol at various concentrations of methanol within the framework of the ASL model (Associated Solution + Lattice) based on molecular association theory and the simple lattice model is presented. Hetero-association of methylxanthines with the molecules of methanol is studied by means of 1H NMR spectroscopy at 313 K. The contribution of molecular association to the solubility of methylxanthines in the mixed SC solvent CO2–methanol is analyzed. It is shown that the presence of NH group in the molecule of methylxanthine, when passing from caffeine to theophylline or theobromine, leads to an increase of the contribution of the component related to molecular association to solubility.

Calculations of the Solubility of Gases in Mixed Nonaqueous Solvents within the Framework of the Theory of Molecular Association

A method for calculating the solubility of gases in mixed nonaqueous solvents was suggested. The method was based on the theory of molecular association and the simple lattice model. It allowed the solubility of gases in mixed nonaqueous solvents to be calculated only using molecular association parameters and the mutual exchange energy ωAB determined from the data on phase equilibria in mixed solvents.

Viscosity of the Systems Methanol-n-Octane and Ethanol-n-Octane

The kinematic viscosity of binary solutions methanol-n-octane at 293.15-313.15 K and ethanol-n-octane at 263.15-298.15 K in the miscibility range (low concentrations of n-octane) was measured. In the methanol-octane system, the viscosity shows an abnormal behavior. As shown by molecular-dynamic calculations, this effect is due to formation of a specific type of associates, which results in a decrease in the molecular mobility as the n-octane concentration is increased (up to the phase separation point).

Self-diffusion and molecular association of acetylsalicylic acid and methyl salicylate in methanol-d4 in the temperature range 278–318 K

The effect of concentration on the self-diffusion coefficients of acetylsalicylic acid and methyl salicylate in methanol-d4 is investigated in the temperature range of 278–318 K using NMR. It is found that the self-diffusion coefficients increase along with temperature and fall as concentration rises. Within the limit of an infinitely dilute solution, the effective radii of solute molecules, calculated using the Stokes–Einstein equation shrink as the temperature grows. It is shown that the observed reduction of effective radii is associated with an increase in the fraction of solute monomers as the temperature rises. The physicochemical parameters of heteroassociation of acetylsalicylic acid and methyl salicylate with methanol are determined.

The viscosity of the methanol-n-decane system in the region of low n-decane concentrations

The kinematic viscosity and density of the methanol-n-decane system were measured at various temperatures at low n-decane concentrations (over the miscibility range). The theory of free volume with taking into account molecular association was used to calculate the dynamic viscosity of this system at 298.15 K. The results substantiated the presence of an anomaly in this system (positive Δlnη values).

Calculations of the enthalpy of solution of nonelectrolytes in mixed solvents within the framework of molecular association theory

The enthalpies of solution of nonelectrolytes in mixed solvents were calculated using the Associated Solution + Lattice thermodynamic model, whose parameters are equilibrium constants, the enthalpies of formation of associates, and the energy of mutual exchange of mixed solvent components. The method of calculations used provided close agreement between calculation results and experimental data on nonassociated solutions and systems with a complex molecular association character.

Comparative Analysis of the Methods for Calculating the Viscosity of Binary Nonelectrolyte Mixtures

The results of calculating the viscosity of binary nonelectrolyte systems by methods obviating fitting parameters were compared. A method was proposed for calculating the viscosity of n-alkanol-n-alkane solutions with account of the molecular association by the free-volume theory accurately to within 7.9%.