Preferential Solvation of Vitamin C in Binary Solvent Mixtures Formed by Methanol, Ethanol, n-Propanol, Isopropanol and Water

The present work is an investigation of the preferential solvation of vitamin C in five solvent mixtures: ethanol (1) + methanol (2), isopropanol (1) + methanol (2), ethanol (1) + water (2), n-propanol (1) + water (2) and isopropanol (1) + water (2) from the reported solubility data by employing the method of inverse Kirkwood–Buff integrals. In the ethanol (1) + water (2) mixtures with compositions 0.25 < x1 < 1.00, and isopropanol (1) + water (2) and n-propanol (1) + water (2) mixtures with compositions 0.20 < x1 < 1.00, the local mole fractions of ethanol, isopropanol or n-propanol are smaller than those of the bulk solutions. Consequently, the values of preferential solvation parameter (δx1,3) are negative, which shows that vitamin C is preferentially solvated by water. Perhaps the structuring of water molecules near the vitamin C molecule contributes to lowering of the δx1,3 from the neat solvent water to negative values in the three solvent mixtures. Vitamin C acts as a Lewis base that interacts with the acidic hydrogen atoms of water. Nevertheless, in the ethanol (1) + methanol (2) and isopropanol (1) + methanol (2) mixtures, vitamin C is preferentially solvated neither by methanol nor by ethanol nor isopropanol.