Vapour phase catalytic transformations of terpene hydrocarbons in the C₁₀H₁₆ series. III. Dehydrogenation of Δ³-carene over modified chromia and chromia–alumina catalysts

Abstract

The vapour phase dehydrogenation of 3-carene has been studied over chromia, chromia–alumina, chromia doped with potassium, and chromia–alumina doped with potassium and fluoride ions. Addition of potassium to chromia and chromia–alumina up to 1% by weight does not significantly affect the overall conversion of 3-carene whereas it increases its dehydrogenation to p- and m-cymenes. Potassium ions above 1% lower both the total conversion and dehydrogenation of 3-carene to cymenes. The ratio of p- to m-cymene over chromia–alumina is enhanced by added potassium ions up to 2%, but over chromia it remains unaffected. Addition of potassium to chromia decreases the formation of menthanes and menthadienes but its addition to chromia–alumina reduces the formation of menthanes and increases that of menthadienes. Impregnation of chromia–alumina with hydrofluoric acid suppresses the formation of menthadienes and increases that of menthanes. All these are explained in terms of the effect of added potassium and fluoride ions on the acidity of the catalysts.

Dehydrogenation of Δ3-carene over chromia and chromia–alumina catalysts

“…The high heat over reduced chromia may be explained if we assume that the exposed Cr(I1) ions, being d4 systems, favour Jahn-Teller distortion of their surroundings so that there are empty coordination sites on which strong adsorption of pyridine can take place. Similar reduction in the activity of reduced chro~nia by carbon monoxide is also reported (12).…”

“…Reduced chromia when pretreated with CO, and also when CO is passed along with 3-carene si~nultaneously, the cymene ratio is found to be reduced (12). Clark et 01.…”

Design, Synthesis, and Biological Investigation of Novel Classes of 3-Carene-Derived Potent Inhibitors of TDP1

“…Interestingly, 2-carene 9 is widely found in nature albeit in small concentrations. The isolation of 9 from essential oils, or from reaction mixtures after 3-carene 8 isomerization, is difficult, making 9 expensive and therefore not attractive for use in organic synthesis [ 25 , 26 , 27 , 28 , 29 ]. Recently, we developed a method for the isomerization of readily available 3-carene 8 to 2-carene 9 using montmorillonite clays as a catalyst [ 30 ].…”

Vapour phase catalytic transformations of terpene hydrocarbons in the C10H16 series. IV. Effect of nitrogen, hydrogen, and pyridine on the dehydrogenation of Δ3-carene over chromia and chromia-alumina catalysts

“…Hydrogen over chromium oxide is easily desorbed (10) and therefore its presence on the surface of the catalyst does not seriously affect the conversion of 3-carene. It is presumed that hydrogen reduces the unsaturated compounds that precede the formation of polymers and of coke which would deposit on the active centers of the catalyst as in an earlier scheme (5). On suppressing the formation of polymers and coke, the formation of cymenes goes up.…”