estér

Estér is the term used in French and some other languages for the class of organic compounds known in English as esters. Esters are derived from carboxylic acids and alcohols and share the characteristic functional group R-CO-O-R'. They are typically formed by a condensation reaction that removes water, and they occur widely in nature and industry, contributing to fragrances, flavors, and various materials.

Structure and naming: The general formula of an ester is R-CO-O-R'. Naming traditions vary, but common names combine the alkyl (or aryl) group from the alcohol with the name of the acid, often ending in -ate (for example, ethyl acetate, methyl benzoate). IUPAC naming uses the corresponding alkyl ester of the carboxylic acid, such as ethyl ethanoate or methyl benzoate.

Synthesis: The primary laboratory method is Fischer esterification, where a carboxylic acid and an alcohol react in the presence of an acid catalyst (often sulfuric acid) with water removal to shift the equilibrium toward ester formation. Other methods include reaction of acid chlorides with alcohols and transesterification, where one ester is converted to another in the presence of an alcohol.

Properties and uses: Esters are often colorless liquids or low-melting solids with characteristic, sometimes fruity, odors. They are widely used as solvents, plasticizers, fragrances, and flavorings. In industry, esters form polymers (polyesters) such as PET, and fatty acid esters are central to biodiesel production through transesterification of fats or oils.

Safety and environmental aspects: Esters generally have low to moderate toxicity and hydrolyze to alcohols and carboxylic acids. They can be flammable and may cause irritation; appropriate handling and disposal practices are advised.