Vapor Phase Catalytic Transformations of Terpene Hydrocarbons in the C₁₀H₁₆ Series. II. Aromatization of α-Pinene over Chromia–Alumina

Abstract

The aromatization of a-pinene in the vapor phase over chromia gel and chromia-alumina catalysts prepared from aluminas of different acidity has been studied. The acidity of alumina support has a remarkable influence on the composition of the aromatics resulting from the dehydrogenation of a-pinene. Over weakly acidic chromia-alumina doped with 1% sodium catalyst, a-pinene is aromatized to p-cymene, 1,2,4-and 1,2,3-trimethylbenzenes with traces of toluene and xylenes, whereas over the strongly acidic chromia -pure alumina and chromia-alumina containing 5% H F catalysts it gives considerable amount of m-cymene, toluene, and tetramethylbenzenes. A satisfactory mechanism to explain the formation of these compounds is offered.

Ring-Opening Reactions of α- and β-Pinenes in Pressurized Hot Water in the Absence of Any Additive

“…p -Cymene is formed from α-pinene when heated with various catalysts. , Mesoporous silica-supported 12-tungstenophosphoric acid is also effective in these reactions . Since the presence of air was suggested to be responsible for the present dehydrogenative aromatization reaction (Scheme ), it was hoped that limonene and p -cymene might be selectively synthesized from the reaction of α-pinene in hot pressurized water by controlling the amount of oxygen.…”

“…9,10 Mesoporous silica-supported 12-tungstenophosphoric acid is also effective in these reactions. 34 Since the presence of air was suggested to be responsible for the present dehydrogenative aromatization reaction (Scheme 3), it was hoped that limonene and p-cymene might be selectively synthesized from the reaction of α-pinene in hot pressurized water by controlling the amount of oxygen. However, saturation of water with oxygen and filling the empty space of the reactor with oxygen gas did not improve the yield of pcymene (yield 23 ± 2%) and the vessel was soot-blackened after 60 min.…”

Dehydroisomerisation of α-Pinene and Limonene to p-Cymene over Silica-Supported ZnO in the Gas Phase

“…Usually, the synthesis of p-Cymene from α-pinene is carried out in the gas phase at ambient pressure. A range of heterogenous catalysts have been reported for this reaction giving 100% α-pinene conversion at 300-460 • C [1, [16][17][18][19]. These include Cr 2 O 3 /Al 2 O 3 (390-460 • C, 53% p-Cymene yield) [16], zeolite Y (300 • C, 54% yield) [17], Pd/SiO 2 (300 • C, 67% yield) [1], Pd-Zn/Al-SBA-15 (300 • C, 77% yield) [18] and bulk Zn(II)-Cr(III) mixed oxide (350 • C, 78% yield) [19].…”

“…A range of heterogenous catalysts have been reported for this reaction giving 100% α-pinene conversion at 300-460 • C [1, [16][17][18][19]. These include Cr 2 O 3 /Al 2 O 3 (390-460 • C, 53% p-Cymene yield) [16], zeolite Y (300 • C, 54% yield) [17], Pd/SiO 2 (300 • C, 67% yield) [1], Pd-Zn/Al-SBA-15 (300 • C, 77% yield) [18] and bulk Zn(II)-Cr(III) mixed oxide (350 • C, 78% yield) [19]. The supported Pd catalysts exhibit high activity at 300 • C, but require continuous hydrogen supply to reduce catalyst coking causing catalyst deactivation [1].…”

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

“…have been employed in this laboratory for the vapour-phase catalytic transformation of terpene hydrocarbons from Indian turpentine, with a view to convert them into stable useful intermediates. Isomerization and aromatization of p-and a-pinenes were already reported (1)(2)(3)(4). Recently, the dehydrogenation of 3-carene over chromia and chromiaalumina catalysts, impregnated with potassium and fluoride ions, has been reported (5) with special reference to the ratio of p-cymene to mcymene formed from 3-carene.…”