epsilonlactones

Epsilon-lactones are seven-membered cyclic esters formed by intramolecular esterification of omega-hydroxy carboxylic acids. In lactone nomenclature, the prefix epsilon (ε) denotes a seven-membered ring, distinguishing them from smaller gamma- and delta-lactones. The most notable example is ε-caprolactone, a commercial monomer used to make polycaprolactone (PCL), a biodegradable polyester.

Preparation typically involves the cyclization of ω-hydroxy acids under dehydrating or activating conditions. Common methods employ coupling reagents such as DCC or EDC in the presence of catalytic acid or base, or traditional acid-catalyzed lactonization at elevated temperature. Alternative routes include ring-closing metathesis of dicarboxylate precursors or enzymatic lactonization in biological systems.

Properties and applications: Seven-membered rings have reduced strain compared with smaller lactones, which influences reactivity and polymerizability. ε-Caprolactone readily undergoes ring-opening polymerization to yield polycaprolactone, a biodegradable and biocompatible polyester used in medical implants, controlled drug delivery systems, and packaging. Other ε-lactones are explored as monomers for specialty polymers and as intermediates in the synthesis of natural products.

See also: lactone, gamma-lactone, delta-lactone, polycaprolactone.