Caprolactone

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.[3]

Caprolactone
Skeletal formula of caprolactone
Ball-and-stick model of the caprolactone molecule
Names
Preferred IUPAC name
2-oxepanone
Systematic IUPAC name
Hexano-6-lactone
Other names
Caprolactone
ε-Caprolactone
Epsilon-caprolactone
6-Hexanolactone
Hexan-6-olide
1-Oxa-2-oxocycloheptane
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.007.217
KEGG
UNII
Properties
C6H10O2
Molar mass 114.14 g/mol
Density 1.030 g/cm3
Melting point −1 °C (30 °F; 272 K)
Boiling point 241 °C (466 °F; 514 K)[1]
Miscible [2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.[3] Another polymer is polyglecaprone, used as suture material in surgery.[4]

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.

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,[5] and is also produced by the Khapra beetle as a pheromone.[6] δ-caprolactone is found in heated milk fat.[7]

An ether of caprolactone is used as a binder for AP/AN/Al rocket propellant HTCE: Hydroxy-Terminated Caprolactone Ether [8]

Safety

Caprolactone hydrolyses rapidly and the resulting hydroxycarboxylic acid displays unexceptional toxicity, as is common for the other hydroxycarboxylic acids.[9] It is known to cause severe eye irritation. Exposure may result in corneal injury.[2]

References
  1. "Capa Monomer product data sheet" (PDF). Perstorp. 2015-02-27. Archived from the original (PDF) on 2017-02-02. Retrieved 2017-10-11.
  2. "ε-caprolactone SIDS Initial Assessment Report" (PDF). OECD. Archived from the original (PDF) on 2011-08-15. Retrieved 2017-10-12.
  3. Köpnick, Horst; Schmidt, Manfred; Brügging, Wilhelm; Rüter, Jörn; Kaminsky, Walter (2002). "Polyesters". Ullmann's Encyclopedia of Industrial Chemistry (6th ed.). Weinheim: Wiley-VCH. doi:10.1002/14356007.a21_227.
  4. "glycolide E-caprolactone copolymer Summary Report". CureHunter. Retrieved 2017-10-11.
  5. Mosandl, A.; Günther, C. (1989). "Stereoisomeric flavor compounds: structure and properties of gamma-lactone enantiomers". Journal of Agricultural and Food Chemistry. 37: 413–418. doi:10.1021/jf00086a031.
  6. 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. doi:10.1021/jo00293a044.
  7. Parliament, Thomas H.; Nawar, Wassef W.; Fagerson, Irving S. (1965). "Delta-Caprolactone in Heated Milk Fat". Journal of Dairy Science. 48 (5): 615–616. doi:10.3168/jds.S0022-0302(65)88298-4.
  8. HTCE
  9. Miltenberger, Karlheinz (2002). "Hydroxycarboxylic Acids, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry (6th ed.). Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_507.
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