CH3CHCHCOOH

Crotonic acid, systematically known as (E)-but-2-enoic acid and with the chemical formula CH3CHCHCOOH, is a monocarboxylic acid. It is one of the isomers of butenoic acid, specifically the trans isomer. The cis isomer is known as isocrotonic acid. Crotonic acid is a white crystalline solid at room temperature with a pungent odor. It is sparingly soluble in water but readily soluble in organic solvents like ethanol and ether.

This compound is found naturally in some plants and is produced industrially through various chemical synthesis routes. Historically, it was obtained from the distillation of rotenone. Crotonic acid can be polymerized to form polycrotonic acid, which has potential applications. It is also used as an intermediate in the synthesis of other organic compounds, including pharmaceuticals and agrochemicals. In some contexts, it is used as a food additive, although its use is regulated. Its unsaturated nature makes it reactive in addition reactions, characteristic of alkenes, as well as reactions involving the carboxylic acid group.