β-Propiolactone, often simply called propiolactone, is an organic compound with the formula CH2CH2CO2.

It is a colorless liquid with a slightly sweet odor, highly soluble in water and organic solvents.

[4] β-Propiolactone is prepared industrially by the reaction of formaldehyde and ethenone in the presence of aluminium- or zinc chloride as catalyst:[5]

[5] Propiolactone was once widely produced as an intermediate in the production of acrylic acid and its esters.

That application has been largely displaced in favor of safer and less expensive alternatives.