Mono- and bifunctional heterogeneous catalytic transformation of terpenes and terpenoids

Selective reactions of terpenes, catalyzed by different heterogeneous systems, are reported. alpha-pinene and limonene epoxides can be effectively isomerized to carbonyl compounds (selectivity >70%) over silica aluminas that appear to be good alternatives to homogeneous ZnBr2. The different reactivity of geometric isomers can be used to separate them. Unsaturated ketones can be converted through a two-step one-pot reaction in cyclic or bicyclic ethers through a bifunctional process involving a hydrogenation and an acid-catalyzed step. However, the choice of the solvent allows to inhibit the acidic sites, thus obtaining a selective hydrogenation reaction. On the other hand, the acidic reaction alone can be useful for alcohol epimerization and epimer separation. Grafting of Ti in a siliceous matrix gives rise to a material with both redox and acidic properties. Solids obtained in this way are active and selective in the epoxidation of terpenic alcohols but can also promote bifunctional reactions.