Bromine‐Catalyzed Isomerization of Maleic Acid to Fumaric Acid

The presence of small amounts of ceric and bromide ions in the aqueous sulfuric acid solution of maleic acid can catalyze the isomerization of maleic acid to fumaric acid rapidly and quantitatively at room temperature. A qualitative kinetic study was carried out to see how the rate and the yield of this reaction depend on the relative amounts of maleic acid, ceric ion, and bromide ion. In general, the rate increases asymptotically to a limiting value as the concentration of maleic acid, ceric or bromide ion increases. Sulfuric acid has both the chemical and physical effects on the rate of isomerization. If the relative amounts of the reactants is in the order of [maleic acid]≥[Br−]≥[Ce(IV)], a very high yield up to 98% can easily be obtained. Sulfuric acid does not have major effect on the yield. A mechanism was proposed to rationalize the experimental results.