Transition-Metal Catalyzed Autoxidation of cis- and trans-Pinane to a Mixture of Diastereoisomeric Pinanols

Abstract

Autoxidations of the pinanes, obtained after hydrogenation of naturally occurring Pinus elliottii oil, were performed with or without solvent, using the catalytic system Co(OAc)2/Mn(OAc)2/NH4Br in a 9:1:5 molar ratio, and dioxygen as the oxidant. The best selectivity for the pinanols was 71% (cis:trans ratio, 3:1) with 17% conversion. Autoxidations were also carried out in the absence of catalyst. The hydroperoxides formed with 17% conversion were decomposed with Na2SO3 and PPh3, resulting in 62% pinanols (cis:trans ratio, 5:1). The pyrolysis of the pinanols at 600 °C and a contact time of 1.15 × 10-2 s/mol yielded 54% of linalool. The side products were mainly due to an “ene” reaction, giving diastereoisomeric 1,2-dimethyl-3-isopropenylcyclopentanols. Keywords: Catalytic oxidation; pinane; pinanol; pyrolysis; linalool

Synthesis and characterization of triglyceride‐based polyols and tack‐free coatings via the air oxidation of soy oil

“…Cobalt catalysts are widely used in the oxidation of unsaturated compounds due to their activity with hydroperoxides 47–49. To expedite the onset of the third regime of oxidation, cobalt(II) ethyl hexanoate (65 wt % in mineral oil) was used as a catalyst in a 5 wt %/vol % mixture with raw soybean oil.…”

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

“…This thermal isomerization is industrially relevant due to the high linalool selectivity, up to 90% [10]. The main undesired side-products of this thermal rearrangement is plinol [11]. Besides plinol, Ohloff and Klein [9] identified ␤-terpineol (<3%) and a methyl-ketone (<5%) as byproducts of the pyrolysis of cis-and trans-2-pinanol at 873 K. The structure of the methyl-ketone was later elucidated as 5,7-dimethyloct-6-ene-2-one by Coxon et al [12], Erman and Kane [13] reported isolinalool as a minor product during the pyrolysis of pinanols.…”

Thermal Behavior of Pinan-2-ol and Linalool

“…Commercially available cis -pinan-2-ol ( cis - 1 ; 85–90 wt% cis ) was used in the pyrolysis experiments. For comparison, samples of trans- pinan-2-ol ( trans - 1 ; 81–89 wt% trans ) were prepared by synthesis and subsequent chromatographic separation of cis / trans mixtures according to literature procedures [14,15,16,24], as depicted in Scheme 1. The structures of some bicyclic terpenes are shown in Figure 1.…”

“…The corresponding four step synthesis starts with the Pd-catalyzed reduction of α-pinene ( 3 ) which leads to cis - and trans -pinane ( 4 ) (Scheme 1). The subsequent oxidation affords cis - and trans -pinan-2-hydroperoxide ( 5 ) which is reduced over Pd/carbon catalysts to cis - and trans - 1 [14,15,16]. The last step is the pyrolysis of 1 to 2 with the by- and side-products mentioned below [9,13,14].…”

“…, result in differences in linalool selectivity and yield. Side reactions can also be influenced or even suppressed by using short reaction times or additives [14,15,22]. For example, Semikolenov et al added small amounts of pyridine to a solution of pinan-2-ol to suppress side reactions and increase linalool selectivity [22].…”