Vapor Phase Catalytic Transformations of Terpene Hydrocarbons in the C₁₀H₁₆ Series. I. Isomerization of α-Pinene over Alumina

Abstract

The isomerization of α-pinene in the vapor phase over alumina catalysts of varying acid strength has been studied. The isomerization proceeds via two parallel paths, one giving bi- and tricyclic products such as camphene, β-pinene, tricyclene, and bornylene and the other giving rise to monocyclic compounds such as dipentene, terpinolene, α-terpinene, γ-terpinene, p-cymene, and p-menthene. Dependence of the distribution of reaction products on space time reveals that camphene, β-pinene, tricyclene, dipentene, and terpinolene are the primary products. The acid strength of alumina catalysts has a remarkable influence on the selectivity ratio of bi- and tricyclic to monocyclic products, the strong acid sites favoring the formation of monocyclic products. From the study of the reactions of camphene and tricyclene over the same catalysts under similar conditions it has been concluded that the decrease in the selectivity ratio with increasing acid strength of the catalysts is mainly due to the further isomerization of the bi- and tricyclic compounds to monocyclic products which takes place only on the strong acid sites.

Isomerization of limonene over natural zeolite-clinoptilolite

“…Based on the results of this work and previous reports (Stanislaus & Yeddanalpalli, 1972; Detrekoy et al , 1973; Grau et al , 1999), the following mechanism of formation of terpinolene, α-terpinene, γ-terpinene and p-cymene may be proposed. In the first step, a proton derived from a strongly acidic site (Brønsted acidic site) attaches to the double bond in position 8–9 of the limonene molecule and simultaneously a carbonium ion at the C8 atom is formed.…”

Support enhanced α-pinene isomerization over HPW/SBA-15

“…[7,[9][10][11] α-Pinene isomerization offers routes to two important product families: monocyclic compounds such as limonene, terpinene, and terpinolene, and polycyclic compounds including camphene, β-pinene and tricyclene. [12][13][14][15][16] Camphene is a widely employed fragrance and solvent and a precursor to camphor, and additive in the formulation of insect repellents, explosives and plastics. [1,7,13] Limonene finds large scale application in the perfume and pharmaceutical industries of around 50,000 tons annually.…”

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.…”