Many derivatives are known, some of which exist in two structural forms, exhibiting geometrical isomerism after the mode of fumaric and maleic acids.
It forms deliquescent crystals, which are readily soluble in alcohol and melt at ioo° C. When heated for some time at 130° C. it yields fumaric acid (q.v.), and on rapid heating at 180° C. gives maleic anhydride and fumaric acid.
It is decomposed by boiling water and yields fumaric ester.
Pechmann, Ber., 1898, 31, p. 2950) and, with fumaric methyl ester it forms pyrazolin dicarboxylic ester.
Consequently, of each pair of isomers we may establish beforehand which is the more stable; either in particular circumstances, a direct change taking place, as, for instance, with maleic acid, which when exposed to sunlight in presence of a trace of bromine, yields the isomeric fumaric acid almost at once, or, indirectly, one may conclude that the isomer which forms under greater heat-development is the more stable, at least at lower temperatures.