Abstract: The dielectric constants (D) for aqueous solutions of D-(-)-fructose, D-(+)-glucose, D-(+)-galactose, D-(+)-xylose, and D-(-)-ribose were measured at 278.15, 283.15, 288.15, 293.15, 298.15, 303.15, 308.15, and 313.15 K. Molalities of saccharides are at 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 mol·kg -1. The results indicated that the logarithmic values of dielectric constants for these saccharide-water solutions decreased with increasing molalities of saccharides and decreased also as the temperature rising. At given molalities, the relationship between dielectric constants and temperatures can be expressed by lgD=A1-B1(T-298.15) for fructose-water, glucose-water, galactose-water, and xylose-water solutions, and by lgD=A2-B2(T-298.15)+C2(T-298.15)2 for ribose-water solution. At given temperatures, dependence of the dielectric constants on the mole fraction (x) can be described by lg(D/D0)=-B3x for all five saccharide-water solutions. At given temperatures and molalities, the dielectric constants are mostly in the order: water>galactose-water>fructose-water>glucose-water≥xylose-water (there is not the order for ribose).

Key words: Dielectric constant, D-(-)-fructose, D-(+)-glucose, D-(+)-galactose, D-(+)-xylose, D-(-)-ribose