Studies on Glass. XVIII. The Heats of Solution of Crystalline and Glassy Glucose; the Heat of Mutarotation of α-Glucose

Abstract

A calorimeter has been developed for the rapid solution of a powdered solid in a suitable solvent and the accurate determination of the heat of solution during the process. This calorimeter has now been used to determine the heats of solution of two preparations of crystalline α‐d‐glucose in water, both with and without mutarotation, and also the heats of solution of two preparations of glucose glass. Relatively accurate thermodynamic data for the crystal‐to‐glass transformation have been computed from these solution heats. Also small, but significant, differences per mole in enthalpy (ΔH₂₉₈=102±18 cal.), in entropy (ΔS₂₉₈=0.24±0.06 cal./deg.), and in free energy (ΔF₂₉₈°=31±10 cal.) have been found for these two glass preparations. A value of ΔH₂₉₈=−175 (±5) calories has been obtained for the mutarotation of a mole of α‐glucose, dissolved in water, to yield the equilibrium mixture of the alpha‐ and beta‐forms.