Solution properties of vanillin and diacetyl in aqueous-ethanol solutions

Abstract

The apparent specific volumes and the spin-spin relaxation times ( T 2 values) of diacetyl and vanillin, in ethanol-water binary solvent mixtures were determined in the concentration range 1–50% ( w w ) for solute and 0–100% ( sol v v ) for ethanol in the binary mixture. The apparent specific volumes of diacetyl and vanillin showed a decrease with increasing concentration of solute and an increase with increasing concentration of ethanol in the binary solvent mixture. The former of these trends might be attributable to a hydrophobic stacking of the solute and to the effect of the formation of new solute-solvent intermolecular hydrogen bonds. The latter trend is marked only for low concentrations of solute, showing that the disturbance of water structure either by solute or by ethanol has an important effect on the apparent specific volume. Spin-spin relaxation times ( T 2 values) decreased with increasing concentration of solutes, as the proportion of ordered protons in solution increased (between solutions) and showed a minimum for the different concentrations of binary mixture (within solutions) which is attributed to the presence of ethanol in the binary mixture. The results for apparent specific volumes of diacetyl and vanillin, for the same range of concentrations, seem to be similar, reflecting similar packing characteristics of the two solutes. However, the slightly shorter T 2 values of vanillin are an indication of the faster relaxation of the ring (unexchangeable) protons of this solute. These results are important for taste and flavour research.