A-Terpinolene

The only commonly occurring bicyclic monoterpene with the carane skeleton is car-3-ene (61) which is believed to be formed by a 1,3-elimination from the a-terpinyl ion intermediate (62) . The coexistence in many plants of car-3-ene (61) and a-terpinolene (63), thought to be derived from the same intermediate (62) as well via a 1,2-elimination, seems to support this hypothesis. However, degradation studies of a-car-3-ene (61) derived from... 

It is known that the presence in the oil composition of cyclic monoterpene hydrocarbons having two double bonds in the cycle, i.e. a- and y-terpinene, a-terpinolene, sabinene, and also eugenol, thymol and carvacrol [15] is responsible for the antioxidant properties of the essential oils. However the oil composition is not a constant, depends on taxonomic variety of plants [16], time and conditions of oil storage [17], It was shown that the essential oils of sage [18], savory [19], clove and cardamom [20], coriander [21] and maijoran [22] noticeably varied during a storage and the main process was autooxidation. 

Figure 2. Black pepper 1 - a-pinene, 2 - sabinene, 3 - P-pinene, 4 - limonene + 1,8-cineole, 5 - y-terpinene, 6 - a-terpinolene, 7 - P-caryophellene, 8 - myristicine.

In the present work, geraniol (1) predominantly afforded the monoterpene alcohols a-terpineol (4) and linalool (3), along with lesser amounts of each of the hydrocarbons, myrcene (5), a-terpinene (6), limonene (7), y-terpinene (8), the ocimenes (9), a-terpinolene (10) and alloocimenes (11). The cyclic oxide, 2,6,6-trimethyl-2-vinyltetrahydropyran (12) was also present as a trace component. Nerol... 

Geraniol, nerol, and linalool are almost insoluble in water at ambient temperature. Although acid-labile, they do not readily react in water at moderate temperature and neutral pH. In unacidified water at 220 °C in the MBR, they reacted within minutes. Geraniol rearranged to a-terpineol (18%) and linalool (16%), predominantly. Smaller amounts of the monoterpene hydrocarbons were also obtained, including myrcene, a-terpinene (10%), limonene (11%), y-terpinene, the ocimenes, a-terpinolene, and alloocimenes (Scheme 3.13) [31]. 

The reference standards of different monoterpenes, sesquiterpenes, and alkanes were obtained from Aldrich Chemical Co., Inc. (Milwaukee, WI, USA), Fluka Chemical Corporation (New York, NY, USA), Roth Co. Chemische Fabrik (Karlsruhe, Germany), Sigma Chemical Co. (St. Louis, MO, USA) and Varian Associated (Houston, TX, USA). These reference standards include tricyclene, a-pinene, sabinene, a-phellandrene, 1-decene, limonene, fenchone, a-terpineol, a-terpinolene, c/s-verbenol, cis- and trans-carveol, cA-dihydrocarveol, a-longipinene, a-cedrene, (-)-isolongifolol, a-humulene, valencene, cuparene, myristyl alcohol, citronellyl acetate, neryl acetate, geranyl acetate, camphene, alloaromadendrene, -eicosane, and n-heneicosane. Solutions were prepared in methanol at concentrations of 10 mg/mL. For GC/MS analysis each standard solution was diluted by mixing 0.1 mL of the standard solution with 0.9 mL of methanol. 

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