Epsilonlactone

Epsilonlactone, or epsilon-lactone, is a seven-membered cyclic ester (a lactone). In lactone nomenclature, the Greek letters indicate ring size, with gamma-, delta-, and epsilon-lactones corresponding to five-, six-, and seven-membered rings, respectively. The best-known member is epsilon-caprolactone, commonly called caprolactone, which serves as a monomer for biodegradable polyesters.

Structure and basic properties: The seven-membered ring comprises six carbon atoms and one oxygen atom; the carbonyl carbon is part of the ring, giving a lactone functional group with two oxygens (one carbonyl, one ether). Its molecular formula is C6H10O2. Epsilon-caprolactone is a key precursor in polymer chemistry and participates readily in ring-opening polymerization under appropriate catalysts and conditions.

Synthesis: Epsilon-lactones are typically prepared by intramolecular esterification (lactonization) of omega-hydroxycarboxylic acids (HO-(CH2)n-CO2H) under dehydrating conditions. Industrially, epsilon-caprolactone is commonly prepared by Baeyer–Villiger oxidation of cyclohexanone, which inserts an oxygen to yield caprolactone, followed by purification.

Applications and reactivity: Epsilon-lactones readily undergo ring-opening polymerization, yielding polyesters such as polycaprolactone, which is used in biodegradable plastics, drug delivery, and tissue engineering. They can copolymerize with other lactones and comonomers. The ring’s relatively low strain compared with smaller lactones influences reactivity and hydrolytic stability. Safety follows standard chemical handling guidelines.