Study on selectivity of β-myrcene hydrogenation in high-pressure carbon dioxide catalysed by noble metal catalysts

Abstract

Hydrogenation of monoterpenes, such as b-myrcene, in high-density carbon dioxide over 0.5 wt.% Pd, or Rh, or Ru supported on alumina was investigated. Hydrogenation catalysed by Rh and Ru is generally faster in a single supercritical (sc) phase (gaseous reagents and solid catalyst) than in a biphasic system (liquid + gas reactants + solid catalyst). The reaction catalysed by Pd occurs faster in two phases. The final composition of the reaction mixture is strongly dependent on the noble metal catalyst used for the reaction. Palladium gives mainly 2,6-dimethyloctane (ª95%), rhodium produces 2,6-dimethyloctane with a yield higher than 40%, and around 40% of 2,6-dimethyloct-2-ene, while ruthenium gives around 10% of 2,6-dimethyloctane and 50% of 2,6-dimethyloct-2-ene leaving the highest amount of unreacted b-myrcene. The Pd catalyst is highly active with an excellent selectivity in enabling the one-pot synthesis of 2,6-dimethyloctane through b-myrcene hydrogenation in the presence of scCO 2 . The overall activity of the noble metal catalysts decreased in the order Pd > Rh > Ru. The problem of leaching of the active metal from the catalyst rod was also investigated.

Continuous catalyst-free aromatization of γ-terpinene using air as an oxidant

“…Terpenes are obtained by fractional distillation of turpentine 1 and can be modified by catalytic methods 2 such as hydrogenation, [3][4][5] dehydrogenation, 6-14 rearrangement, [15][16][17] and oxidation reactions. Terpenes are obtained by fractional distillation of turpentine 1 and can be modified by catalytic methods 2 such as hydrogenation, [3][4][5] dehydrogenation, 6-14 rearrangement, [15][16][17] and oxidation reactions.…”

Influence of pretreatments for extraction of lipids from yeast by using supercritical carbon dioxide and ethanol as cosolvent

“…Carbon dioxide (CO 2 ) is an inert, inexpensive, easily available, odorless, tasteless, environment-friendly, and GRAS (Generally Recognized As Safe) solvent. The supercritical technology is a green sustainable process [6,7] in which the solvent power and selectivity can be tuned according to the operating conditions.…”

Environmentally Benign Transformations of Monoterpenes and Monoterpenoids in Supercritical Fluids

“…In the case of Pd, the reaction performed in the supercritical phase was slightly slower than that under biphasic conditions. Pd/Al 2 O 3 was the most active catalyst and yielded the completely saturated product 2,6-dimethyloctane 80 [78]. The Rh/Al 2 O 3 catalyst led to monounsaturated 2,6-dimethyloct-2-ene 78 in only slightly smaller amounts than 2,6-dimethyloctane 80, whereas 2,6-dimethyloct-1-ene 79 was formed in minor quantities.…”

“…Hydrogenation of b-myrcene 7 over Pd, Rh, and Ru supported on Al 2 O 3 in high-pressure CO 2 was carried out [78] (Scheme 23). A comparison of the reactions under biphasic conditions (118 atm) and in the supercritical phase (158 atm) demonstrated that the reactions over Rh and Ru catalysts performed in a single supercritical phase attained equilibrium faster than hydrogenation carried out in biphasic conditions.…”