Question

We did an experiment in my organic chemistry lab. We converted maleic acid into a fumaric acid via an acid catalyzed, HCl, cis-trans alkene isomerization reaction. One of the post lab questions was:

Fumaric acid is much less soluble in water than maleic acid. Could this be a driving

force for the isomerization? Explain using LeChatelier’s principle.

Answer 1

Because of the low solubility of fumaric acid in water it is almost completely precipitated from the aqueous reaction solution as a crystal. Hence the solubilty factor is a driving force for the isomerisation of maleic to fumaric acid.

This can be explained as follows: Maleic acid is soluble in water whereas the solubility of fumaric acid in this solvent is very limited. This is based the intramolecular hydrogen bonding. Maleic acid have a stronger net dipole moment than fumaric acid. They are polar and are easily hydrated by the polar water molecules. Fumaric acid is non-polar and has dipole moments that cancel out each other, giving the molecule a zero net dipole moment. Also the tightly and efficiently packing of the molecules in the solid state is partly responsible for the low solubility of fumaric acid in water.