Solvophobic acceleration of Diels-Alder reactions in supercritical carbon dioxide

The kinetics of the Diels-Alder reaction of dienophile N-ethylmaleimide and 9-ydroxymethylanthracene was studied. The Diels-Alder reaction of dienophile N-ethylmaleimide with 9-hydroxymethylanthracene proceeded at rates in scCO ₂ that are much faster than in traditional organic solvents, e.g., acetonitrile, methanol, etc. The transformation of reactants to transition state was concurrent with a decrease in the exposed surface area of the solutes, which decreased the molecular interaction between the solute (reactants or transition state) and the solvent. This decrease in solute-solvent interaction accelerated the reaction. The results indicated negative pressure and density dependencies of the rate constant, which was consistent with the solvophobic mechanism due to the direct positive relationship between fluid density and solute solubility. This is an abstract of a paper presented at the 6th Annual Green Chemistry and Engineering Conference (Washington, D.C. 6/24-27/2003).