Abstract
Linalool is an important intermediate for syntheses of isoprenoid fragrance compounds and vitamins A and E. One process option for its production is the thermal gas-phase isomerization of cis- and trans-pinan-2-ol. Investigations of this reaction were performed in a flow-type apparatus in a temperature range from 350–600 °C and a residence time range of 0.6–0.8 s. Rearrangement of the bicyclic alcohol led to linalool, plinols arising from consecutive reactions of linalool and other side products. Effects of residence time, temperature, surface-to-volume-ratio, carrier gas, and the presence of additives on yield and selectivity were studied. Furthermore, the effects of such parameters on ene-cyclization of linalool affording plinols were investigated. Results indicate that manipulation of the reaction in order to affect selectivity is difficult due to the large free path length to other molecules in the gas phase. However, conditions have been identified allowing one to increase the selectivity and the yield of linalool throughout pyrolysis of pinan-2-ol.
Highlights
Terpenoids are a large class of natural occurring compounds
Terpenoids are oligomers or polymers of isoprene. They offer an access to complex molecular structures and in some cases they are part of Nature’s pool of chiral compounds. Those facts make them interesting starting materials for the synthesis of chiral ligands or auxiliaries used in enantioselective catalytic syntheses [3,4,5]
Rearrangement reactions of monoterpenoids play a major role in the industrial synthesis of fine chemicals, flavors, and fragrances
Summary
Terpenoids are a large class of natural occurring compounds. Besides being important in Nature, for example as pheromones or antioxidants, they are valuable fine chemicals used in the fragrance, flavor, Molecules 2013, 18 and pharmaceutical industry [1,2]. Terpenoids are oligomers or polymers of isoprene They offer an access to complex molecular structures and in some cases they are part of Nature’s pool of chiral compounds. Those facts make them interesting starting materials for the synthesis of chiral ligands or auxiliaries used in enantioselective catalytic syntheses [3,4,5]. In this context, rearrangement reactions of monoterpenoids play a major role in the industrial synthesis of fine chemicals, flavors, and fragrances. The gas-phase isomerization of the monoterpenoid pinan-2-ol (1) results in the formation of the acyclic allylic alcohol linalool (2) [6,7]
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