Solvent Effects during Acid-Catalyzed Esterification Reactions

The combined use of chemical and biological catalysis will potentially allow for the sustainable production of high value chemicals that are traditionally sourced from petroleum. Acid catalyzed esterification is one reaction that is important for the production of these higher value chemicals. This study explored the solvation effects of a polar solvent (THF) versus those of a nonpolar solvent (toluene) on esterification reactions catalyzed with Amberlyst-15 and beta zeolite.

The reaction was fractional order with respect to butanol concentration, and first-order with respect to butyric acid concentration, when using toluene as a solvent. In contrast, the reaction in tetrahydrofuran was first order with respect to both butanol and butyric acid. This discrepancy can be explained based on solvation of abundant surface intermediates leading to the appearance of a site blocking term in the rate expression for toluene. Accompanying the change in the reaction order, the reaction rate was increased by approximately an order of magnitude when using toluene as a solvent. These observations can be explained in the context of transition state theory applied to thermodynamically nonideal systems.