colourless liquid of disagreeable taste and pungent odour used in medicine as a sedative–hypnotic drug and in chemistry in the manufacture of organic chemicals. When administered as a medicine, it is largely excreted by the lungs and gives an unpleasant odour to the breath. It is most useful for recalcitrant cases and is an older drug for treatment of acute alcoholic dementia.

Paraldehyde is produced for commerce by polymerizing acetaldehyde with a trace of sulfuric acid; the resulting liquid is then neutralized with calcium carbonate and purified by fractional distillation. Paraldehyde boils at 124° C (255° F) and melts at a temperature of 12.5° C (54.5° F).