(β-propiolactone), an internal cyclic ether of β-hydroxypropionic acid with the structure

Propiolactone is a colorless liquid with a pungent odor, a melting point of –33.4°C, a boiling point of 155°C, and a density of 1.146 g/cm³ (20°C). It is obtained by catalytic interaction of formaldehyde (CH₂O) with ketene (CH₂=C=O). Solutions and vapors of propiolactone have strong bactericidal effects. Propiolactone is used in medicine for sterilizing blood, vaccines, enzymes, and other biological preparations; it is also used as a fumigant.