DEUTERIOHYDRATES OF CYCLOPROPANE

The thermochemical constants of the two clathrate deuteriohydrates of the cyclopropane-D2O system have been determined by pressure vs. temperature measurements. The deuteriohydrate formulas are C3H6·7.8D2O and C3H6·17.2D2O, corresponding to the structure I 12-Å and structure II 17-Å hydrates, respectively. Below 0°, the deuteriohydrate dissociation pressures are higher than the hydrate dissociation pressures, but above 0° the deuteriohydrate dissociation pressures are lower than the hydrate dissociation pressures. The structure I deuteriohydrate is less dense than liquid D2O, but the structure I hydrate is more dense than liquid H2O. An explanation is offered for this anomaly. A comparison of the free energies of empty clathrate lattice formation from H2O and D2O ice shows that the deuteriohydrate lattice is only slightly more unstable than the hydrate lattice.