Comprehensive Kinetic and Mechanistic Considerations for the Gas‐Phase Behaviour of Pinane‐Type Compounds

Abstract

The thermal behaviour of selected pinane‐type compounds, α‐pinene (1), β‐pinene (2), pinane (3) and nopinone (4), has been investigated. The conversion of the bicyclic starting materials to their acyclic and monocyclic isomers as well as the consecutive reactions of the acyclic main isomerisation products are discussed. The conversion of 1–4 in a reaction network is presented and the experimental evidence for the formation of pyrolysis products by a biradical pathway is discussed. In addition to these results a kinetic model describing the isomerisation of the bicyclic compounds to their acyclic and monocyclic isomers is presented. A good correlation between kinetic simulations and experimental data is revealed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Thermal Isomerization of (+)‐cis‐ and (−)‐trans‐Pinane Leading to (−)‐β‐Citronellene and (+)‐Isocitronellene

“…The thermal isomerization of bicyclic terpenes with the pinane skeleton (1; Scheme 1) yields acyclic isomers and p-menthane-type monocyclic terpenes. [4][5][6][7] The rearrangement of a-pinene leads to the formation of limonene and alloocimene. [4,8] Linalool, an important building block in the synthesis of vitamin E and flavor compounds, is formed by thermal isomerization of 2-pinanol.…”

“…[4][5][6][7] The rearrangement of a-pinene leads to the formation of limonene and alloocimene. [4,8] Linalool, an important building block in the synthesis of vitamin E and flavor compounds, is formed by thermal isomerization of 2-pinanol. [9] All of these isomerization reactions of bicyclic pinane-type compounds yield at least one acyclic Abstract: Catalyzed and uncatalyzed rearrangement reactions of terpenoids play a major role in laboratory and industrial-scale synthesis of fine chemicals.…”

“…limonene from a-or b-pinene). [4,5,[8][9][10][11] The use of compounds without p-bonds in the reactive part of the bicyclic molecule (carbon atoms C 1 , C 2 of 1; Scheme 1) [12] leads to the formation of acyclic products only (e.g. 2 from 1 or linalool from 2-pinanol) by opening of the cyclobutane ring.…”

“…4, 5 in Scheme 1). [4,5,9,[13][14][15] The products from the reaction network for the thermal rearrangement based on 1 are shown in Scheme 1. According to their general structure, they can be classified into three groups assigned by three reaction pathways.…”

“…According to their general structure, they can be classified into three groups assigned by three reaction pathways. Two major reaction pathways (I and II) lead to the formation of b-citronellene (2) [4,5,13,[16][17][18][19][20] and isocitronellene (3) [5,20] as the main products. Whereas the formation of 2 from 1 (path I) is thoroughly investigated, the formation of 3 (path III) is mentioned in only two references.…”