What is "lactide"

Lactide \Lac"tide\, n. [Lactic + anhydride.] (Chem.) A white, crystalline substance, obtained from lactic acid by distillation, and regarded as an anhydride; also, by extension, any similar substance.

n. 1 (context organic chemistry English) Any of a class of heterocyclic compounds, formally acid anhydrides, formed by heating α-lactones 2 (context organic compound English) The anhydride of lactic acid.

Lactide is the cyclic di- ester of lactic acid, i.e., 2-hydroxypropionic acid. Lactic acid cannot form a lactone as other hydroxy acids do because the hydroxy group is too close to the carboxylic group. Instead, lactic acid first forms a dimer, which is similar to a 5-hydroxyacid. The dimer contains a hydroxy group at a convenient distance from the carboxylic group for the formation of a lactone. Indeed, the dimer readily forms a six-membered cyclic diester known as lactide. Lactides may be prepared by heating lactic acid in the presence of an acid catalyst.

In general, a lactide is the cyclic diester, i.e., the di- lactone of two molecules of any 2-hydroxycarboxylic acid.