SPECIFICS OF ESTABLISHING TETRAALKYLAMONIUM IONS NEAR SOLVATION’ IN SOLVENTS WITH A SPATIAL NETWORK OF H-BONDS

Abstract

Diffusion coefficient and diffusion displacement length () of 5 tetraalkylammonium (TAA) ions (from Me 4 N + to Pe 4 N + ) in water, ethylene glycol (EG), formamide (F), and monoethanolamine (MEA) are calculated from literature data on the limiting molar electrical conductivity of these ions at 298.15 К. The sign of deviation from the Stokes-Einstein law in the form (–  r i ), where r i is ion structural radius as a criterion for solvation of ions  is used. In these solvents type of near solvation for TAA cations was established: positive if the parameter It is shown that adequate values of the degree of hydrophobic hydration of TAA ions in water> 0 can be obtained for the hydrodynamic boundary slip condition>0 ; negative - for values (–  r i ) 0 can be obtained for the hydrodynamic boundary “slip” condition. The last depend on the scale of TAA ions structural radii. We analysed experimental results of studying solvophobic solvation of TAA ions in water, formamide, ethylene glycol and monoethanolamine and concluded that the van der Waals Marcus radius scale is the most physically reasonable. Parameter  has maximum value in water and minimum one in monoethanolamine for the first five symmetric TAA ions in these solvents. In the series of H 2 O - F - EG - MEA value  decreases. This is consistent with the increase in viscosity in this range of solvents. In order to eliminate ambiguities in calculating the quantitative characteristics of near solvation, a general approach was developed. This approach based on the use of a specific scale of radii and  hydrodynamic condition of ion "slip" when setting the Stokes-Einstein law.