transbutenedioic

Transbutenedioic acid, commonly called trans-butenedioic acid or fumaric acid, is an organic dicarboxylic acid with the formula C4H4O4. It is the trans (E) isomer of butenedioic acid; the cis isomer is maleic acid. Its structure features a carbon–carbon double bond conjugated with two carboxyl groups, giving it acidic properties and the ability to form fumarate salts and esters.

In biology, fumarate is a key intermediate in cellular respiration. It is formed from succinate by succinate dehydrogenase and is subsequently converted to malate by fumarase in the citric acid cycle. This metabolic role reflects the compound’s natural occurrence in organisms.

Industrial production of fumaric acid is primarily from maleic anhydride, which is produced by catalytic oxidation of hydrocarbons such as benzene or butane. The anhydride is hydrolyzed to the corresponding dicarboxylic acid, and, through heat-driven isomerization, the trans (fumaric) form is obtained. Because the trans isomer is thermodynamically favored under these conditions, the process yields predominantly trans-butenedioic acid.

Applications include use as an acidity regulator in foods (E297) and as a monomer or co-monomer in the production of unsaturated polyester resins and alkyd resins. It is also employed in various cosmetic and pharmaceutical formulations as an excipient or intermediary. Fumaric acid is a widely used industrial chemical due to its reactivity and the stability of its fumarate salts.

Safety considerations are typical of organic acids: fumaric acid can be irritating to skin and eyes and should be handled with appropriate protective equipment. It is regulated for food use in many jurisdictions and should be stored away from reactive materials.