That is because, as in the case of the Diels-Alder reaction, it is usually possible to design an ionic solvent that dissolves the reactants easily but is reluctant to give house room to the resultant product.

ECONOMIST: Ionic solvent

In the past year, for example, Dr Seddon and Tom Welton, a chemist at Imperial College London, have shown that one of the most important and difficult processes in industrial organic chemistry, the Diels-Alder reaction (which links carbon atoms together and thus allows big molecules to be assembled) can work better in ionic than in conventional solvents.

ECONOMIST: Ionic solvent