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. It was once produced on a large scale as a precursor to caprolactam.
Caprolactone is prepared industrially by Baeyer-Villiger oxidation of cyclohexanone with peracetic acid.
Caprolactone is a monomer used in the production of highly specialised polymers. Ring-opening polymerization, for example, gives polycaprolactone.[1] Another polymer is polyglecaprone, used as suture material in surgery.[2]
Although no longer economical, 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.
Several other caprolactones are known, including 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,[3] and is also produced by the Khapra beetle as a pheromone.[4] δ-caprolactone is found in heated milk fat.[5]
An ether of caprolactone is used as a binder for AP/AN/Al rocket propellant HTCE: Hydroxy-Terminated Caprolactone Ether [6]
Caprolactone hydrolyses rapidly and the resulting hydroxycarboxylic acid displays unexceptional toxicity, as is common for the other hydroxycarboxylic acids.[7] It is known to cause severe eye irritation. Exposure may result in corneal injury.