ε-Caprolactone or simply caprolactone is a

lactone Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...

(a cyclic

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

) possessing a seven-membered ring. Its name is derived from

caproic acid Caproic acid, also known as hexanoic acid, is the carboxylic acid derived from hexane with the chemical formula . It is a colorless oily liquid with an odor that is fatty, cheesy, waxy, and like that of goats or other barnyard animals. It is a f ...

. This colorless liquid is miscible with most organic solvents and water. It was once produced on a large scale as a precursor to

caprolactam Caprolactam (CPL) is an organic compound with the formula (CH2)5C(O)NH. This colourless solid is a lactam (a cyclic amide) of caproic acid. Global demand for this compound is approximately five million tons per year, and the vast majority is use ...

Production and uses

Caprolactone is prepared industrially by Baeyer-Villiger oxidation of cyclohexanone with

peracetic acid Peracetic acid (also known as peroxyacetic acid, or PAA) is an organic compound with the chemical formula, formula CH3CO3H. This peroxy acid is a colorless liquid with a characteristic acrid odor reminiscent of acetic acid. It can be highly corros ...

. Caprolactone is a monomer used in the production of highly specialised

polymer A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...

Ring-opening polymerization In polymer chemistry, ring-opening polymerization (ROP) is a form of chain-growth polymerization, in which the terminus of a polymer chain attacks cyclic monomers to form a longer polymer (see figure). The reactive center can be radical, anion ...

, for example, gives

polycaprolactone Polycaprolactone (PCL) is a biodegradable polyester with a low melting point of around 60 °C and a glass transition temperature of about −60 °C. The most common use of polycaprolactone is in the production of speciality polyureth ...

. Another polymer is polyglecaprone, used as suture material in surgery.

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 Carbonylation refers to reactions that introduce carbon monoxide into organic and inorganic substrates. Carbon monoxide is abundantly available and conveniently reactive, so it is widely used as a reactant in industrial chemistry. The term carbony ...

of caprolactone gives, after hydrolysis,

pimelic acid Pimelic acid is the organic compound with the formula HO2C(CH2)5CO2H. Pimelic acid is one unit longer than a related dicarboxylic acid, adipic acid, a precursor to many polyesters and polyamides. However compared to adipic acid, pimelic acid i ...

. 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. These isomers include α-, β-, γ-, and δ-caprolactones. All are chiral. (''R'')-γ-caprolactone is a component of

floral scent Floral scent, or flower scent, is composed of all the volatile organic compounds (VOCs), or aroma compounds, emitted by floral tissue (e.g. flower petals). Other names for floral scent include, aroma, fragrance, floral odour or perfume. Flower scen ...

s and of the aromas of some fruits and vegetables, and is also produced by the Khapra beetle as a

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

. δ-caprolactone is found in heated milk fat. An ether of caprolactone is used as a binder for AP/ AN/ Al rocket propellant HTCE: Hydroxy-Terminated Caprolactone Ether HTCE
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Safety

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

References

{{Authority control Epsilon-lactones Monomers Oxepanes