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Maleic acid and fumaric acid are cis-trans isomers of each other.
1. Maleic anhydride is hydrated. This produces maleic acid.
2. Maleic acid is isomerised in the presence of a catalyst.
3. Fumaric acid is produced.
Easy as that! (Except the temperature and pressure have to be kept controlled throughout)
It's illegal.
Fuhk youu
An acid found in grapes is called maleic acid