diester

Diester is a general term in organic chemistry for a compound that contains two ester functional groups. An ester consists of a carbonyl group bonded to an alkoxy group (R-C(=O)-O-R'). A diester thus has two such ester linkages within a single molecule, which may be the same or different. Diesters are typically formed by condensation of a diacid (or its derivative) with two equivalents of an alcohol, or by transesterification of an existing ester with a second alcohol.

Common examples include dialkyl diesters of dicarboxylic acids, such as diethyl phthalate and dibutyl phthalate, used as plasticizers, and diesters of adipic or sebacic acids. A distinct class is phosphate diesters, where a phosphate group forms two ester bonds to alcohol moieties. In biology, phosphate diesters connect sugar units in nucleic acids; the phosphodiester linkages between nucleotides are ester bonds between a phosphate and two sugar hydroxyl groups.

Properties and reactions: Diesters undergo typical ester chemistry. They hydrolyze under acidic or basic conditions, yielding the corresponding diacid (or monoester and acid, depending on hydrolysis) and alcohols. They can undergo transesterification and, for dialkyl esters, saponification is a common route to acids and alcohols. They are often less reactive than acid chlorides but can be stable under standard conditions.

Applications: Diesters serve as plasticizers, solvents, and intermediates in organic synthesis. In polymer science, repeating diester linkages form polyesters such as PET and poly(ethylene terephthalate).