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Dimethylsulfoxide usually boils at 189 °C. Under a vacuum, it distills off into the connected receiver at only 70 °C.

Vacuum distillation is a method of distillation whereby the pressure above the liquid mixture to be distilled is reduced to less than its vapor pressure (usually less than atmospheric) causing evaporation of the least volatile liquid(s) (those with the highest boiling points). Vacuum distillation is used with or without heating the solution.

Vacuum distillation works on the principle that boiling occurs when the vapor pressure of a liquid exceeds the ambient pressure. Ambient pressure refers to the atmospheric pressure for an open system, or to the pressure in the distillation apparatus, for a closed system.

The process is used when liquids to be distilled have high atmospheric boiling points or chemically change at temperatures near their atmospheric boiling points. Temperature sensitive materials (such as beta carotene) also require vacuum distillation to remove solvents from the mixture without damaging the product. Another reason vacuum distillation is used is that compared to atmospheric distillation there is a lower level of residue build up. This is important in commercial applications where temperature transfer is produced using heat exchangers.

Vacuum distillation is sometimes referred to as low temperature distillation. Typical industrial applications utilize the heat pump cycle to maximize efficiency. Common standards for oil industry are ASTM D1160, D2892, D5236. These standards describe typical applications of vacuum distillation at pressures ~1-100 mbar. Pilot plants up to 200 L can be built in accordance with these standards.

Short path vacuum distillation apparatus

Perkin triangle - for air-sensitive vacuum distillation