Solution Thermophysics of l-Ascorbic Acid in Aqueous Tetrabutylammonium Hydrogen Sulfate

Abstract

The densities and viscosities of l-ascorbic acid (vitamin C) in aqueous tetrabutylammonium hydrogen sulfate (Bu₄NHSO₄) solutions at several different concentrations of Bu₄NHSO₄ ($m_{{{\text{Bu}}_{4} {\text{NHSO}}_{4} }}$ = 0.000, 0.005, 0.010, 0.015 and 0.020 mol·kg⁻¹) were determined at T = (298.15–318.15) K under atmospheric pressure. Using these experimental data, values of the apparent molar volume ($\phi_{V}$), standard partial molar volume ($\phi_{V}^{ 0}$), the slope ($S_{V}^{ *}$), standard isobaric partial molar expansibility ($\phi_{E}^{ 0}$) and its temperature derivative $({{\partial \phi_{E}^{ 0} } \mathord{\left/ {\vphantom {{\partial \phi_{E}^{ 0} } {\partial T}}} \right. \kern-0pt} {\partial T}})_{p}$, the viscosity B-coefficient and solvation number ($S_{\text{n}}$), etc., were determined. Viscosity B-coefficients were further utilized to obtain the Gibbs energies of activation of viscous flow per mole of the solvents ($\Delta \mu_{ 1}^{ 0\ne }$) and of the solute ($\Delta \mu_{ 2}^{ 0\ne }$). The effects of molality, solute structure and temperature on all these parameters were analyzed in term of ion–ion and ion–solvent interactions, which revealed that the solutions are characterized predominantly by ion–solvent interactions and l-ascorbic acid behaves as a long-range structure maker.