LACTONE

any of a class of cyclic organic esters, usually formed by reaction of a carboxylic acid group with a hydroxyl group or halogen atom present in the same molecule. Commercially important lactones include diketene and b-propiolactone used in the synthesis of acetoacetic acid derivatives and b-substituted propionic acids, respectively; the perfume ingredients pentadecanolide and ambrettolide; vitamin C; and the antibiotics methymycin, erythromycin, and carbomycin. The g- and d-lactones, containing five- and six-membered rings, respectively, are the most common. They are formed by loss of water from the corresponding hydroxy acids, a process that often occurs spontaneously even in aqueous solution. Diketene and b-propiolactone are made by the reaction of ketene with itself or with formaldehyde, respectively. Lactones with 7 to 24 atoms in the ring are prepared by slow distillation of the appropriate hydroxy acids under greatly reduced pressure.