Crystallographic analysis shows that the intramolecular hydrogen bond is little affected in the monopotassium salt.

Maleic acid is also used as an adhesion promoter for different substrates, such as nylon and zinc coated metals e.g galvanized steel, in methyl methacrylate based adhesives.

This conversion, an isomerization, is catalysed by a variety of reagents, such as mineral acids and thiourea.

Again, the large difference in water solubility makes fumaric acid purification easy.

Reversible addition (of H+) leads to free rotation about the central C-C bond and formation of the more stable and less soluble fumaric acid.

Maleic acid, being electrophilic, participates as a dienophile in many Diels-Alder reactions.

Many drugs that contain amines are provided as the maleate acid salt, e.g. carfenazine, chlorpheniramine, pyrilamine, methylergonovine, and thiethylperazine.