Caprolactone Explained

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.

Production and uses

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]

Reactions

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.

Related compounds

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]

Safety

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.

Notes and References

  1. Encyclopedia: Köpnick. Horst. Schmidt. Manfred. Brügging. Wilhelm. Rüter. Jörn. Kaminsky. Walter. Polyesters. Ullmann's Encyclopedia of Industrial Chemistry. 6th. 2002. Wiley-VCH. Weinheim. 10.1002/14356007.a21_227.
  2. Web site: glycolide E-caprolactone copolymer Summary Report. CureHunter. 2017-10-11.
  3. Mosandl. A.. Günther. C.. Stereoisomeric flavor compounds: structure and properties of gamma-lactone enantiomers. Journal of Agricultural and Food Chemistry. 37. 413–418. 1989. 10.1021/jf00086a031.
  4. Nunez. M. Teresa. Martin. Victor S.. 1990. Efficient oxidation of phenyl groups to carboxylic acids with ruthenium tetraoxide. A simple synthesis of (R)-gamma-caprolactone, the pheromone of Trogoderma granarium. Journal of Organic Chemistry. 55. 6. 1928–1932. 10.1021/jo00293a044.
  5. Parliament. Thomas H.. Nawar. Wassef W.. Fagerson. Irving S.. 1965. Delta-Caprolactone in Heated Milk Fat. Journal of Dairy Science. 48. 5. 615–616. 10.3168/jds.S0022-0302(65)88298-4. free.
  6. https://www.acronymfinder.com/Hydroxy_Terminated-Caprolactone-Ether-(solid-rocket-propellant)-(HTCE).html HTCE
  7. Encyclopedia: Miltenberger. Karlheinz. Hydroxycarboxylic Acids, Aliphatic. Ullmann's Encyclopedia of Industrial Chemistry. 6th. 2002. Wiley-VCH. Weinheim. 10.1002/14356007.a13_507.