Kinetic and mechanistic aspects of myrcene production via thermal-induced β-pinene rearrangement

Thermal Rearrangements of Monoterpenes and Monoterpenoids

“…In contrast to the biradical formed in the case of 4, 74 is still chiral, and, therefore, the initial optical purity is maintained. Separation of the enantiomers of 40 on a bcyclodextrin GC column revealed similar enantiomer ratios as found for recovered 5 [57] [90]. A [1,3]-C shift would form the anti-Bredt hydrocarbon 75, and, since such compounds are thermally instable, they either form consecutive products or the activation energies needed for their formation are extremely high.…”

“…Since 72 is an important substrate for the synthesis of various fine chemicals (flavors, fragrances), its production by thermal cleavage of the cyclobutane ring in 5 is not only important from an academic point of view but also for industrial chemists [3a,b,g,h]. Many protocols have been developed to increase the yields: passage through a capillary reactor [51], carrier-gas-assisted pyrolysis [29] [82] [87] [90], flash vacuum pyrolysis at 0.07 mbar and 9008 [11], or thermal cleavage carried out in a flow system using supercritical alcohols as a fluid [57] [58]. The results all have in common that performing the reaction at high temperatures (> 6008) and low contact times (< 0.1 s) is advantageous for the yield of 72.…”

Kinetic study of the thermal rearrangement of cis- and trans-2-pinanol

“…The reaction mechanism for the thermal isomerization of pinane-and pinene-type compounds has been extensively discussed in literature and it is generally agreed upon that the fragmentation of the four-membered ring is the initial step in the thermal isomerization of bicyclic monoterpenes consisting of a bicyclo[3.1.1]heptane system [26][27][28][29][30][31][32][33][34][35][36]. Two types of cyclobutane rupture mechanisms were proposed to explain the formation of the different primary acyclic and monocyclic pyrolysis products: a concerted mechanism of the cyclobutane fragmentation containing a 4--electron anti-aromatic transition state and a stepwise mechanism with biradical intermediates.…”

Myrcene as a Natural Base Chemical in Sustainable Chemistry: A Critical Review

“…[47] Later, Ondruschka delivered detailed insight into the reaction course. [45] Experiments revealed that the pyrolysis temperature and the residence time have the highest influence. The formation of myrcene is similar to a stepwise fragmentation of a cyclobu- www.chemsuschem.org tane ring, whereas the other cyclic by-products yield from [1,n]-H-shifts (Scheme 3).…”

“…Products within the reaction based on b-pinene according to Ondruschka. [45] Table 3. Overview of catalyst systems used in the dimerization of isoprene to myrcene.…”