Monoterpenes reactions

The product distribution of the monoterpene reactions with ozone has not been fully elucidated. However, studies by Hatakeyama et al. (1989) indicate the formation of pinonaldehyde, nor-pinonaldehyde, formaldehyde, CO, and C02 from the reaction of a-pinene with ozone. The /3-pinene/ozone reaction led to the formation of 6,6-dimethylbicyclo-[3.1.1]heptane-2-one, formaldehyde, and C02. Aerosol accounted for approximately 14-18% of the overall reaction in each case. 

Alvarado, A., J. Arey, and R. Atkinson (1998), Kinetics of the gas-phase reactions of OH and NO3 radicals and O3 with the monoterpene reaction products pinonaldehyde, caronaldehyde, and sabinaketone, J. Atmos. Chem., 31, 281-297. 

Atkinson, R., and S.M. Aschmann (1993), Atmospheric chemistry of the monoterpene reaction products nopinone, camphenilone, and 4-acetyl-1-methylcyclohexene, J. Atmos. Chem., 16, 337-348. 

The product of this reaction is geranyl pyrophosphate Hydrolysis of the pyrophosphate ester group gives geramol a naturally occurring monoterpene found m rose oil... 

The enzyme catalyzed reactions that lead to geraniol and farnesol (as their pyrophosphate esters) are mechanistically related to the acid catalyzed dimerization of alkenes discussed m Section 6 21 The reaction of an allylic pyrophosphate or a carbo cation with a source of rr electrons is a recurring theme m terpene biosynthesis and is invoked to explain the origin of more complicated structural types Consider for exam pie the formation of cyclic monoterpenes Neryl pyrophosphate formed by an enzyme catalyzed isomerization of the E double bond m geranyl pyrophosphate has the proper geometry to form a six membered ring via intramolecular attack of the double bond on the allylic pyrophosphate unit... 

This bicychc carbocation then undergoes many reactions typical of carbocation inter mediates to provide a variety of bicychc monoterpenes as outlined m Figure 26 7... 

Experimental procedures have been described in which the desired reactions have been carried out either by whole microbial cells or by enzymes (1—3). These involve carbohydrates (qv) (4,5) steroids (qv), sterols, and bile acids (6—11) nonsteroid cycHc compounds (12) ahcycHc and alkane hydroxylations (13—16) alkaloids (7,17,18) various pharmaceuticals (qv) (19—21), including antibiotics (19—24) and miscellaneous natural products (25—27). Reviews of the microbial oxidation of aUphatic and aromatic hydrocarbons (qv) (28), monoterpenes (29,30), pesticides (qv) (31,32), lignin (qv) (33,34), flavors and fragrances (35), and other organic molecules (8,12,36,37) have been pubflshed (see Enzyp applications, industrial Enzyt s in organic synthesis Elavors AND spices). 

Chlorofonn is too non-polar to dissolve the phenolic compounds under study, but it dissolves many of the monoterpenes, at least to some extent. Because the solubility of some monoterpenes into chloroform was low, different solvent/ solid ratios were tested. These were 50,20,10 and 5 1/kg of dry phloem. The extracts were bright yellow and the strongest colour was with the smallest solvent/solid ratio (51/kg). The colour of the solvent indicated that the solubility of the extractable compounds was not restricting the reaction even with the smallest solvent volume. The taste of the dry samples was evaluated by comparing them to the original phloem sample. The results showed that the mildest taste was in the phloem extracted with a solvent/solid ratio of 50 1/kg and 20 1/kg also had some effect on the taste. The taste of the chloroform-extracted phloem was stabile and it was the same after a week. 

Gas-phase products from the reactions of ozone with the monoterpenes (-)-p-pinene and (+)-sabinene included the ketones formed by oxidative fission of the exocyclic C=C bonds as well as ozonides from the addition of ozone to this bond (Griesbaum et al. 1998). 

Atkinson R, SM Aschmann, AM Winer, JN Pitts (1985a) Kinetics and atmospheric implications of the gas-phase reactions of NOj radicals with a series of monoterpenes and related organics at 294 2 K. Environ Sci Technol 19 159-163. 

The above system has been used for the reaction of EtjNH with myrcene to give a mixture of hydroamination products (53% yield) containing 80% of N,N-diethylgeranylamine [208], a key intermediate for the synthesis of industrially important monoterpenes [208, 209-211], including (-)-menthol (Tagasako process) [212]. 

The activity of the FePeCli6-S/tert-butyl hydroperoxide (TBHP) catalytic system was studied under mild reaction conditions for the synthesis of three a,p-unsaturated ketones 2-cyclohexen-l-one, carvone and veibenone by allylic oxidation of cyclohexene, hmonene, and a-pinene, respectively. Substrate conversions were higher than 80% and ketone yields decreased in the following order cyclohexen-1-one (47%), verbenone (22%), and carvone (12%). The large amount of oxidized sites of monoterpenes, especially limonene, may be the reason for the lower ketone yield obtained with this substrate. Additional tests snggested that molecular oxygen can act as co-oxidant and alcohol oxidation is an intermediate step in ketone formation. 

Allylation of acyloyl-imidazoles and pyrazoles61 with allyl halide mediated by indium in aqueous media provides a facile regioselective synthesis of P, y-unsaturated ketones (Scheme 11.1), which has been applied to the synthesis of the monoterpene artemesia ketone. The same product can be obtained by indium-mediated allylation of acyl cyanide (Eq. 11.35).62 Samarium, gallium, and bismuth can be used as a mediator for the allylation of nitrones and hydrazones to give homoallylic hydroxylamine and hydrazides in aqueous media in the presence of Bu4NBr (Scheme 11.2).63 The reaction with gallium and bismuth can be increased dramatically under microwave activation. 

The vicinal diol of the monoterpene series, (15,2S,3/ ,5S)-(+)-2,6,6-trimethylbicyclo [3.1.1]heptane-2,3-diol (1), was converted upon reaction with methyl dichloro-phosphite into a tricyclic phosphite 2 showing a 95 5 ratio of epimers differing at the phosphorus stereocentre (Scheme 1). Its complexes with Rh(I) and Pd(II) were found to have the structures (u-Cl)2[Rh(CO)L, and ris-CL,PdL2 respectively [16]. 

Naturally occurring monoterpene alcohols were heated in water without prior deriva-tization with typical biological water-solubilizing groups such as phosphates or glyco-sidic units. Biomimetic reactions that normally would be acid-catalyzed, proceeded on the underivatized compounds in the absence of added acidulant. Cooling of the mixtures rendered the products insoluble, readily isolable and the aqueous phase did not require neutralization before workup. 

Winer, A.M., Lloyd, A.C., Damall, KR., Pitts, Jr., J.N. (1976) Relative rate constants for the reaction of the hydroxyl radical with selected ketones, chloroethenes, and monoterpene hydrocarbons. J. Phys. Chem. 80, 1635-1639. 

The selective diene hydrogenation of monoterpenes such as myrcene, which contain both isolated monoene and diene moieties, forms a particular challenge [84]. The catalyst [RhH(CO)(PPh3)3] (60) has been reported to perform remarkably well for such hydrogenation reactions, and the diene moiety was shown to be selectively reduced to the monoene, while the isolated double bond remained unaffected under the reaction conditions used (Scheme 14.20). The rates of reaction expressed as average TOF (determined at ca. 80% conversion) ranged from ca. 640 (in benzene, 20 atm H2 at 100 °C) to 7600 mol mol 1 h 1 (in cyclohexane, 20 atm H2 at 80 °C). The hydrogenation in benzene solution resulted in... 

Chrysanthemic acid (1) consists of ten carbons, suggesting that it is a monoterpene. The cyclopropane ring of the acid moiety is a feature of pyrethrins. Rivera et al. isolated chrysanthemyl pyrophosphate synthase (CPPase or alternatively referred to as chrysanthemyl diphosphate synthase) underlying the formation of chrysanthemyl pyrophosphate (16) containing a cyclopropane ring from two molecules of dimethylallyl pyrophosphate (15) (DMAPP) and the gene thereof [21]. They found that the reaction involves the cF-2-3 cyclopropanation of DMAPPs in a non-head-to-tail manner. 

Limonene, one of the most prominent natural monoterpenes (cf Section VII), represents a particular derivative of 4-vinylcyclohexene since it has been studied with respect to the pronounced energy dependence of its fragmentation behaviour (Scheme 7). Counterintuitively, and in contrast to 4-vinylcyclohexene, the radical cations of limonene (27) do not undergo the retro-Diels-Alder reaction if the internal energy of the ions is low. As... 

The gas-phase reactivity of various terpenes has been measured. Stephens and Scott were the first to include two terpenes (pinene and a-phel-landrene) with their study of the relative reactivity of various hydrocar ns. Both monoterpenes showed the high reactivity predicted by their olefinic structure. Conversion of nitric oxide to nitrogen dioxide in e presence of isoprene is at a rate intermediate between those for ethylene and trans-2-butene, and Japar et al, reported rate constants for the a-pinene and terpinolene-ozone reactions. Grimsrud et a/. measured the rate con-... 

Yokouchi, Y. and Ambe, Y. Aerosols formed from the chemical reaction of monoterpenes and ozone, Atmos. Environ., 19(8) 1271 1276,1985. 

The second reaction that we wish to describe is that of the aerobic oxidation of a-pinene, which is a bicyclic monoterpene with an oxidizable double bond. The use of such a renewable feedstock in the production of chemicals is considered as the first step towards greening the life cycle of chemical products. In this context, oxidation a-pinene, which occurs widely in the plant kingdom, may be viewed as an important reaction because its oxidation products... 

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