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

Names
Preferred IUPAC name Oxepan-2-one
Other names Caprolactone ε-Caprolactone Hexano-6-lactone 6-Hexanolactone Hexan-6-olide 1-Oxa-2-oxocycloheptane
Identifiers
CAS Number	502-44-3 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:17915 Y
ChEMBL	ChEMBL373123 Y
ChemSpider	9972 Y
ECHA InfoCard	100.007.217
KEGG	C01880 Y
PubChem CID	10401
UNII	56RE988L1R Y
CompTox Dashboard (EPA)	DTXSID4027159
InChI InChI=1S/C6H10O2/c7-6-4-2-1-3-5-8-6/h1-5H2 Y Key: PAPBSGBWRJIAAV-UHFFFAOYSA-N Y InChI=1/C6H10O2/c7-6-4-2-1-3-5-8-6/h1-5H2 Key: PAPBSGBWRJIAAV-UHFFFAOYAG
SMILES C1CCC(=O)OCC1
Properties
Chemical formula	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]
Solubility in water	Miscible [2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) 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.

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,^[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]