FACTORS INFLUENCING THE K10 MONTMORILLONITE-CATALYZED DIELS-ALDER REACTION BETWEEN METHYL ACRYLATE AND CYCLOPENTADIENE

Experimental factorial design has been used to study several factors that are assumed to affect the results of the K10-catalyzed Die] s-Alder reaction between methyl acrylate and cyclopentadiene. The results obtained were complemented by physical characterization of the solid catalysts using X-ray diffraction, FTIR studies of adsorption of pyridine, methyl acrylate, and solvents, and BET measurements. Among the factors studied, the nature of the solvent is the most important one influencing the reaction results. Complementary studies have shown that solvents miscible with water give rise to low yields and endo/exo selectivities, very close to those obtained without clay in the same solvent. In these solvents the clay does not play any catalytic role and the reaction takes place in the bulk of the solvent. In general, excellent results are obtained with solvents nonmiscible with water, but a close relationship exists between the nature of the solvent and the cation exchanged into the K10 montmorillonite. In particular, anisole is the best solvent for Zn2+-doped K10 montmorillonite-catalyzed reaction, but it is not so good when the exchanged cation is Fe3+ In this case a radical-promoted Friedel-Crafts reaction of cyclopentadiene with anisole and oligomerization of cyclopentadiene take place. The presence of radicals has been confirmed by ESR experiments. Furthermore, in methylene chloride as solvent, catalytic activity is related to strength of Lewis acidity, and Zn2+-K10 is a better catalyst than Fe3+-K10. © 1992.