CALORIMETRIC AND DTA STUDIES OF 1,3-DIOXOLANE HYDRATE AND (1,3-DIOXOLANE)(1-X)(TETRAHYDROFURAN)(X) MIXED HYDRATES

The heat capacities of 1,3-dioxolane clathrate hydrates (DXL . 17H(2)O ) doped with potassium hydroxide (x = 1.8 x 10(-4) and 1.8 x 10(-3) to water) were measured with an adiabatic calorimeter in the temperature range between 13 and 300 K. A glass transition due to freezing of the water reorientation appeared at 43 K in both samples. The relaxation time of the reorientational motion of the water molecule was obtained from the enthalpy relaxation data and the corresponding activation ent halpy was determined to be about 8 kJ mol(-1) for both samples. A eute ctic melting between DXL hydrate and KOH hydrate occurred at 216 K in the sample richer in KOH (x = 1.8 x 10(-3)), indicating that the solub ility limit of KOH to DXL hydrate is around x = 1.8 x 10(-4). Differen tial thermal analyses of (1,3-dioxolane)(1-x)(tetrahydrofuran)(x) mixe d hydrates doped with KOH (x = 1.8 x 10(-4)) were performed in the tem perature range between 20 and 100 K. The transition temperature report ed in tetrahydrofuran hydrate (T-trs = 62 K) decreased with increase i n x and the transition did not occur for x < 0.6 owing to the slowing down of the transition rate. This result indicates that the ordering t ransition of the water and guest molecules did not occur in DXL hydrat e because the hypothetical transition temperature is lower than the fr eezing temperature of the water reorientation.