The product of a condensation reaction (esterification) in which a molecule of an acid unites with a molecule of alcohol with elimination of a molecule of water as shown in the following reaction.

At one time it was thought that esterification was analogous to neutralization, and esters are still named as though they are “alkyl salts” of carboxylic acids.
Esters are generally insoluble in water and have boiling points slightly higher than hydrocarbons of similar molecular weight.
Ethyl and butyl acetates are volatile industrial solvents, used particularly in the formulation of lacquers. Higher-boiling esters such as butyl phthalate are used as softening agents (plasticizers) in the compounding of plastics. The natural waxes of biological origin are largely simple esters. For example, a principal component of beeswax is myricyl palmitate. See also Solvent.
Esters of cellulose (cellulose triacetate) are used in photographic film, as a textile fiber (acetate rayon), and several have become important as thermoplastic materials. Cellulose nitrate, called celluloid pyroxylin, forms celluloid, dynamite cotton, and gun cotton. Cordite and ballistite are made from gun cotton. Dimethyl and diethyl sulfates (esters of sulfuric acid) are excellent agents for alkylating organic molecules that contain labile hydrogen atoms, for example, starch and cellulose.
Esters of unsaturated acids, for example, acrylic or methacrylic acid, are reactive and polymerize rapidly, yielding resins; thus, methyl methacrylate yields a polymethyl methacrylate resin (Lucite). Analogously, esters of unsaturated alcohols are reactive and readily react with themselves; thus, vinyl acetate polymerizes to polyvinyl acetate.
Many low-molecular-weight esters have characteristic, fruit-like odors: banana (isoamyl acetate), rum (isobutyl propionate), and pineapple (butyl butyrate). These esters are used to some extent in compounding synthetic flavors and perfumes. See also Alcohol; Carboxylic acid; Fat and oil; Polyester resins.