Tuning Selectivity in Terpene Chemistry: Selective Hydrogenation versus Cascade Reactions over Copper Catalysts

Abstract

The selectivity of Cu/Al 2 O 3 under very mild catalytic hydrogenation conditions can be tuned only by switching the solvent. Geraniol can be converted in a one-pot one-step process into a mixture of citronellol and menthol in hydrocarbon solvents or reduced to citronellol with 98% selectivity in 2-propanol without any additive. Both reactions can be applied to essential oils or synthetic mixtures containing geraniol, citronellal and nerol.

Synthetic Scope of Alcohol Transfer Dehydrogenation Catalyzed by Cu/Al2O3: A New Metallic Catalyst with Unusual Selectivity

“…On the contrary, allylic alcohols react very fast, much faster than their saturated analogues, as shown by the comparison between mirtenol and mirtanol (entry 18 versus 19) and of carveol and dihydrocarveol (entry 16 versus 17) although in this last case steric effects may also play a role. Selectivity is not high when secondary reactions can take place, as in the case of geraniol, which under these conditions gives citronellol and isopulegol,28 but anaerobic conditions avoid formation of the corresponding carboxylic acid which are often observed when using gold catalysts 12a. 29…”

New generation biofuels: γ-valerolactone into valeric esters in one pot

“…Previous work showed that the size of the metallic particles catalysts prepared by the chemisorption hydrolysis technique does not change very much going from 5 to 8% loading, 23b whereas the hydrogenation activity increases according to the higher Cu content. 28 On the other hand, the catalyst obtained using a zeolite support gave a messy product distribution where the desired product was present in a low amount.…”

Regioselective Hydrogenations

“…Recently was reported (Scheme 8) [18]. It was demonstrated how the selectivity of the reaction with respect to citronellol and menthol could be switched based on the basicity of the solvent used, which is due to the complex reaction mechanism in the liquid phase.…”