Does Synergism in Microscopic Polarity Correlate with Extrema in Macroscopic Properties for Aqueous Mixtures of Dipolar Aprotic Solvents?

Abstract

Aqueous mixtures of dipolar aprotic solvents (acetonitrile, γ-valerolactone, γ-butyrolactone, tetrahydrofuran, 1,4-dioxane, acetone, pyridine, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide) show synergism in microscopic polarity and extrema in macroscopic viscosity (η) and molar excess enthalpy (H) in water-rich compositions that correlate with solvent functional group electrostatic basicity (β). Microscopic polarities of aqueous solvent mixtures were estimated by measuring the spectral shift (λ) of 4-nitroaniline with UV-vis spectroscopy at 25 °C. Dynamic viscosities (η) and densities were measured for eight aqueous dipolar aprotic mixtures over the full range of compositions at (25 to 45) °C. The λ, η, and H values of the aqueous mixtures showed a linear trend with increasing electrostatic basicity of the solvent functional groups that is attributed to the size and strength of the hydration shell of water. Density functional theory (DFT) calculations were performed for 1:3 complexes (solvent: (HO)) and it was found that aqueous mixtures with high basicity have high binding energies and short hydrogen bonding distances implying that the size and strength of the hydration shell of water is proportional to functional group basicity. Consideration of functional group basicity of dipolar aprotic solvents allows one to relate synergism in microscopic polarity to extrema in macroscopic properties for a wide range of aqueous dipolar aprotic solvent mixtures.

Correspondence between Spectral-Derived and Viscosity-Derived Local Composition in Binary Liquid Mixtures Having Specific Interactions with Preferential Solvation Theory

“…Hunter basicity values of the dipolar aprotic molecule functional groups are also shown in Table . For mixtures of water with a dipolar aprotic solvent, an increase in β 2 H causes an increase in the strength of the hydration shell, and this is reflected in the trend of the viscosity values with β 2 H .…”

“… a The viscosity data (η, mPa s) and UV–vis data (λ max , nm) of 4-nitroaniline indicator were taken from a previous work, except for viscosity data of acetonitrile and dimethyl sulfoxide, which were obtained from the literature. Component 2 is acetonitrile (ACN), γ-butyrolactone (GBL), γ-valerolactone (GVL), tetrahydrofuran (THF), acetone (Ace), pyridine (Pyr), N , N -dimethylformamide (DMF), N , N -dimethylacetamide (DMA), N -methyl-2-pyrrolidone (NMP), or dimethyl sulfoxide (DMSO).…”

“…According to a previous work, maximum absorption wavelength in the UV–vis spectra of aqueous solutions of dipolar aprotic solvents with solvatochromic indicators correlates with functional group Hunter basicity. For aqueous systems, the spectral maxima and viscosity maxima are related to functional group Hunter basicity of the dipolar aprotic solvent .…”

“…According to a previous work, maximum absorption wavelength in the UV–vis spectra of aqueous solutions of dipolar aprotic solvents with solvatochromic indicators correlates with functional group Hunter basicity. For aqueous systems, the spectral maxima and viscosity maxima are related to functional group Hunter basicity of the dipolar aprotic solvent . However, one issue in the determination of spectral-derived local compositions is that they refer to the cybotactic region of the spectroscopic indicator, and they are biased according to the chemical characteristics of the indicator. , In determining Kamlet–Taft (KT) parameters for general solvent mixtures, techniques are available that correct for differences in solute–solvent interactions and local compositions with indicators. , However, although these approaches can be used to estimate solute–complex molecule interactions, they do not provide local composition of the complex molecules in the absence of the indicator or solute molecule.…”

“…Lines: correlation of data with preferential solvation (PS) models (Table ) with η data ( m = 2.5) and with λ max data ( m = 2.0). The η and λ max data were taken from previous work, except for viscosity data for the water–acetonitrile and water–dimethyl sulfoxide systems.…”