1,8-Cineol structure

Oxidation photocatalyzed by polyoxometalates [66k] has been applied to the fimctionalization of 1,8-cineole (structure IX-10) [661], widely distributed in the plant kingdom. The photooxygenation of IX-10 gave a mixture of ketones and alcohols which were transformed by the subsequent action of pyridinium chloro-chromate into 5- and 6-keto derivatives in the ratio IX-11 IX-12 = 2.5 1. A laser flash photolysis study of the mechanism has been carried out for the deca-tungstate anion catalyzed reaction [66m]. 

The bees must have some important role for these chemicals, for without them their lives are shorter. They possess remarkable structures for collecting and storing scents and devote enormous effort to the task. Why do they do this What do they do with the chemicals they collect Unfortunately, we know too little about euglossine bees to answer these questions definitively. It is easy to attract and trap male bees using synthetic fragrance chemicals such as cineole as bait, but females are considerably more difficult to find. As a result, several euglossine species are known only through male specimens, and much in these creatures lives remains hidden from our view. 

Cineole 42 as well as 1,4-cineole 43 are cyclic ethers (Structure 4.10). All including ascaridol 44 are bicyclic oxygenated monoterpenes. Their formation can be seen in Fig. 4.3. 

Chemical structure-activity relationships suggested that phenolic monoter-penes (thymol, methyleugenol) seemed to be the most active, followed by alcohols (terpineol) and other oxigenated monoterpenes (1,8-cineole) [225, 229, 230]. Within the monoterpenes, -pinene was more active than a-pinene [226], and a-pinene was more active than caryophyllene and myrcene [234]. 

The reaction that takes place is hydrogen halide-promoted ether cleavage. In such a reaction with excess hydrogen halide, the C—O—C unit is cleaved and two carbon-halogen bonds are formed. This suggests that cineole is a cyclic ether because the product contains both newly formed carbon-halogen bonds. A reasonable structure consistent with these facts is... 

Figure 1. Chemical structures of selected off-flavor notes of citrus juice products. (A) 4-vinyl guaiacol, (B) a-terpineol, (C) 1,8-cineole, (D) 1,4-cineole, (E)...

A large number of monoterpenes have been reported to be phytotoxic, and they have been proposed as potential starting structures for herbicides.44 Nevertheless, of the monoterpenes, we only know anything of significance about the mode of action of the cineoles. Early work showed that relataively high concentrations of 1,8-cineole (Fig. 10.1) inhibit mitochondrial respiration of isolated... 

The aroma differences in various sources of cardamom are attributed to the proportion of esters and 1,8-cineole (Wijesekera and Jayawardena, 1973 Korikanthimath et al., 1999). The flavour characteristics of some important volatile components of cardamom are given in Table 3.7 and the chemical structures of major aroma compounds are given in Fig. 3.1. 

The large cardamom pericarp (husk) yielded 0.18% volatile oil by the Clevenger hydrodistillation method. This oil was analysed for physical parameters, e.g. specific gravity (0.9148), refractive index (1.4733) and optical rotation (-7.700). The volatile oil was subjected to GC-MS analysis and 37 compounds were identified, constituting > 98% of the total oil. The major compounds characterized were 1,8-cineole (38.7%), [3-pinene (13.6%), a-terpineol (12.6%), spathulenol (8.3%), 4-terpineol (4.5%), ger-macrene D (3.0%), a-pinene (2.8%) and (3-selinene (2.7%). GC and GC-MS data revealed that 1,8-cineole content was less than 50% when compared with the seed oil. Table 4.5 shows the major constituents separated by GC-MS (Rout et al., 2003). Figure 4.1 gives the structures of the major chemical components in the volatile oil from seeds. 

Essential oil from A. annua is another active research interest as it could be potentially used in perfume, cosmetics, and aromatherapy. Depending on its geographical origin, the oil yield in A. annua ranges from 0.02% to 0.49% on a fresh weight basis and from 0.04% to 1.9% on a dry weight basis. The major components in the oil were reported to be artemisia ketone (80), isoartemisia ketone (81), 1,8-cineole (82), and camphor (83) (Structure 5-5). GC/MS was employed to analyze the chemical composition in the essential oil more than 70 constituents have been identified. For more detailed information on the oil composition of essential oil from A. annua, the readers are referred to Refs. 65, 66 and 72-81. 

Bondavalli et al. have found some stereoselectivity in the reduction of the oxime (180) derived from 1,8-cineol. With lithium aluminium hydride it mostly gives the endo-amine (181), but with sodium in Jcohol the exo-amine predominates. The bromination of pinol (182) —not naturally occurring—has been shown by Wolinsky to occur with rearrangement. Wallach s structure is incorrect the product is 6,7-dibromo-1,8-cineol (183). Treatment of this with hydrogen bromide leads to the ring-opened pinol tribromide (184). de Mayo... 

Figure 2. Structures of terpenoids chemically formed from linalool (1 ) at pH 3.5 (cf. Fig.1-4). (2) 2,4(8)-p-menthadiene (3) B-myrcene (4) a-phellandrene (5) cx-terpinene (6) limonene (7) B-phellandrene (8) (Z)-ocimene (9) y-terpinene (10) (E)-ocimene (11) p-cymene (12) terpinolene (13) (E,Z)-alloocimene (14) (E,E)-alloocimene (15) a-terpineol (16) 3,7-dimethyl-l-oct-ene-3,7-diol (17) 1,8-cineole (18) 2,2,6-trimethyl-2-vinyl-te-trahydropyran.

Maleic, succinic, citraconic, itaconic, phthalic, and naphthalic anhydrides have flat structures, and glutaric, diphenic, camphoric, and cineolic anhydrides geometrically specifiable non-planar ones... 

Cineole Ascaridole Limonene Oxide Pinene Oxide Figure 12.6 Structural formulas of some terpenes used as penetration enhancers. 

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