Aqueous nonelectrolyte solutions. Part V. Water – ethylene oxide ice freezing points, molar volumes, and proton magnetic resonance chemical shifts

Abstract

Densities at 10 °C and proton magnetic resonance (p.m.r.) chemical shifts at 0 °C have been measured for aqueous ethylene oxide over the whole solution composition range. Ice freezing points have been determined for solutions containing up to 2 mole % ethylene oxide in water and in deuterium oxide. The deuterium oxide freezing point is 3.809 ± 0.003 °C and its freezing enthalpy is −1510 ± 8 cal. The freezing point measurements show water and deuterium oxide having unexpected negative deviations from Raoult's law. A maximum thermodynamic stabilization of water is found for solutions containing 4 mole % ethylene oxide. Partial molar volume evaluation shows a water volume maximum at 3.2 mole % ethylene oxide and a minimum at about 89%. Proton magnetic resonance measurements indicate weak H-bonding of water to ethylene oxide involving only one lone pair per ethylene oxide molecule. An abnormal shoulder in the direction of lower magnetic field for the water chemical shift is found, with the anomaly maximum at 4 to 6 mole % ethylene oxide.Correlating with the 20 and 24 water molecules encaging ethylene oxide in its clathrate hydrate, these new solution measurements show that when 20 to 30 water molecules are associated with each ethylene oxide at lower temperature, the water solvent exhibits a free energy minimum, a volume maximum, and an anomalous increase of water H-bond strength. At these compositions each ethylene oxide molecule is apparently surrounded by its own H-bonded water coordination shell to which it is weakly H bonded.