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IUPAC name
Other names epsilon-caprolactone
CAS number 502-44-3 Yes check.svgY
Molecular formula C6H10O2
Molar mass 114.14 g/mol
Density 1.030 g/cm3
Melting point

-1 °C

Boiling point

253 °C [1]

 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

ε-Caprolactone or simply caprolactone is a cyclic ester, a member of the lactone family, with a seven-membered ring with the formula (CH2)5CO2. This colorless liquid is miscible with most organic solvents. It is produced on a very large scale as a precursor to caprolactam.


Production and uses

The great majority of caprolactone is consumed, often in situ, as a precursor to caprolactam.[2] It is also a monomer used in the manufacture of highly specialised polymers. Ring-opening polymerization, for example, gives polycaprolactone.[3]

Caprolactone is prepared industrially by Baeyer-Villiger oxidation of cyclohexanone with peracetic acid. The three main manufacturers are BASF in the USA, Daicel in Japan and the largest Solvay in the UK. Solvay announced in October 2007 that its production unit has been acquired by Perstorp AB of Sweden.


The dominant reaction for caprolactone is its conversion to caprolactam, billions of kilograms of which are produced annually. 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, although none approaches the technological importance of ε-caprolactone. These isomers include alpha-, beta-, gamma-, delta-caprolactones. All are chiral. Gamma-caprolactone is component of flower aromas and an insect pheromone.[4] delta-Caprolactone is found in heated milk fat.[5]


Caprolactone hydrolyses rapidly and the resulting hydroxycarboxylic acid displays unexceptional toxicity, as is common for the other hydroxycarboxylic acids.[6] It is known to cause severe eye irritation. Exposure may result in corneal injury.


  1. ^ OECD SIDS [ 502443 - epsilon-caprolactone]
  2. ^ Josef Ritz, Hugo Fuchs, Heinz Kieczka, William C. Moran "Caprolactam" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a05_031
  3. ^ Horst Köpnick, Manfred Schmidt, Wilhelm Brügging, Jörn Rüter, Walter Kaminsky "Polyesters" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a21_227
  4. ^ Leading reference: M. Teresa Nunez, Victor S. Martin (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, 1990, Volume 55, Issue 6, pp 1928–1932. doi:10.1021/jo00293a044
  5. ^ Thomas H. Parliament, Wassef W. Nawar and Irving S. Fagerson (1965), Delta-Caprolactone in Heated Milk Fat Journal of Dairy Science Vol. 48 No. 5 pages 615-616.
  6. ^ Karlheinz Miltenberger "Hydroxycarboxylic Acids, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. doi:10.1002/14356007.a13_507


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