ε-Caprolactone or simply caprolactone is a lactone (a cyclic ester) possessing a seven-membered ring. Its name is derived from caproic acid. This colorless liquid is miscible with most organic solvents and water.

Uses

ε-Caprolactone is a lactone building block used for the preparation of titanium alkoxides based on benzotriazole phenoxide ligands. It is also a monomer used in the production of highly specialised polymers. Ring-opening polymerization, for example, gives polycaprolactone.Another polymer is polyglecaprone, used as suture material in surgery.

Chemical reaction

Caprolactone was once produced as a precursor to caprolactam. Caprolactone is treated with ammonia at elevated temperatures to give the lactam: (CH2)5CO2 + NH3 → (CH2)5C(O)NH + H2O Carbonylation of caprolactone gives, after hydrolysis, pimelic acid. The lactone ring is easily opened with nucleophiles including alcohols and water to give polylactones and eventually the 6-hydroxyadipic acid.

Related compounds

Several other caprolactones are known. These isomers include α-, β-, γ-, and δ-caprolactones. All are chiral. (R)-γ-caprolactone is a component of floral scents and of the aromas of some fruits and vegetables, and is also produced by the Khapra beetle as a pheromone.δ-caprolactone is found in heated milk fat. An ether of caprolactone is used as a binder for AP/AN/Al rocket propellant HTCE: Hydroxy-Terminated Caprolactone Ether.

Safety

Caprolactone hydrolyses rapidly and the resulting hydroxycarboxylic acid displays unexceptional toxicity, as is common for the other hydroxycarboxylic acids.It is known to cause severe eye irritation. Exposure may result in corneal injury.