Question

Why can we not use water as a solvent for the reaction of cyclopentadiene and maleic anhydride? Is it possible to convert between the two products without using the corresponding precursor ( ethyl acetate) ? How?

Answer 1

Generally water should not be present in the reaction of cyclopentadiene and maleic anhydride. The reaction is carried out in nonpolar solvent dur to Hydrophobicity interaction. Hydrophobic effects are assumed to stabilize the more compact endo transition state more than the extended exo transition state. This difference in compactness of both states is evident from the well-known smaller activation volume for the endo cycloaddition.

SPECIAL EFFECTS OF WATER ON DIELS–ALDER REACTIONS
For a long time water was not a popular solvent for the Diels-Alder reaction. Before 1980 its use had been reported only incidentally. Diels and Alder themselves performed the reaction between furan and maleic acid in an aqueous medium in 1931, an experiment which was repeated by Woodward and Baer in 1948. These authors noticed a change in endo–exo selectivity when comparing the reaction
in water with that in ether. Also, in two patents the Diels–Alder reaction is mentioned in connection with water. In 1973 Eggelte, de Koning, and Huisman studied the reaction of maleic acid with furan in several solvents. These authors noticed, for the first time, a beneficial rate effect of water on the Diels–Alder reaction. Still, it was not until the work of Breslow et al. that it became common knowledge that water was a unique medium for Diels–Alder reactions.

Effect of ethyl acetate

It will dissolve maleic anhydride to make homogeneous solution of maleic anhydride for the reaction.