Limonene, sources

In this chapter, properties and stability of limonene, sources and recovery methods as well as the reported toxicity and health properties are described. 

Uses ndReactions. Some of the principal uses for P-pinene are for manufacturing terpene resins and for thermal isomerization (pyrolysis) to myrcene. The resins are made by Lewis acid (usuaUy AlCl ) polymerization of P-pinene, either as a homopolymer or as a copolymer with other terpenes such as limonene. P-Pinene polymerizes much easier than a-pinene and the resins are usehil in pressure-sensitive adhesives, hot-melt adhesives and coatings, and elastomeric sealants. One of the first syntheses of a new fragrance chemical from turpentine sources used formaldehyde with P-pinene in a Prins reaction to produce the alcohol, Nopol (26) (59). 

Myrcene Manufacture. An important commercial source for mycene is its manufacture by pyrolysis of p-piaene at 550—600°C (87). The thermal isomerization produces a mixture of about 75—77 wt % myrcene, 9% limonene, a small amount of T -limonene [499-97-8] and some decomposition products and dimers. The cmde mixture is usually used without purification for the production of the important alcohols nerol and geraniol. Myrcene may be purified by distillation but every precaution must be taken to prevent polymerization. The use of inhibitors and distillation at reduced pressures and moderate temperatures is recommended. Storage or shipment of myrcene in any purity should also include the addition of a polymerization inhibitor. 

Hydrocarbon resins comprise a range of low-molecular-weight products (M < 3000) used as adhesives, hot-melt coatings, tackifying agents, inks, and additives in rubber. These include products based on monomers derived from petroleum as well as plant sources. The petroleum-derived products include polymers produced from various alkenes, isoprene, piperylene, styrene, a-methylstyrene, vinyltuolene, and dicyclopentadiene. The plant-derived products include polyterpenes obtained by the polymerization of dipentene, limonene,... 

In 1977, a Pseudomonad was isolated from soil by enrichment culture technique with linalool as the sole source of carbon and energy [36]. The bacterial strain was later identified as Pseudomonas incognita and given the name linalool strain . It was also capable of growing on geraniol, nerol and limonene. The biotransformation of geraniol by this... 

Limonene (92) is the most widely distributed terpene in nature after a-pinene [68]. The (+)-isomer is present in Citrus peel oils at a concentration of over 90% a low concentration of the (-)-isomer is found in oils from the Mentha species and conifers [26]. The first data on the microbial transformation of limonene date back to the sixties. A soil Pseudomonad was isolated by enrichment culture technique on limonene as the sole source of carbon [69]. This Pseudomonad was also capable of growing on a-pinene, / -pinene, 1-p-menthene and p-cymene. The optimal level of limonene for growth was 0.3-0.6% (v/v) although no toxicity was observed at 2% levels. Fermentation of limonene by this bacterium in a mineral-salts medium resulted in the formation of a large number of neutral and acidic products. Dihydrocarvone, carvone, carveol, 8-p-menthene-1,2-cw-diol, 8-p-menthen-1 -ol-2-one, 8-p-menthene-1,2-trans-diol and 1 -p-menthene-6,9-diol were among the neutral products isolated and identified. The acidic compounds isolated and identified were perillic acid, /Msopropenyl pimelic acid, 2-hydroxy-8-p-menthen-7-oic acid and... 

The same group has also isolated a strain of Pseudomonas putida-arvilla (PL-strain) from limonene and (+)-a-pinene as the sole carbon source that was capable of growing on (+)-limonene, (+)-a-pinene, (-)-a-pinene, / -pinene, 1-p-menthene, 3-p-menthene and p-cymene as substrates [75]. Limonene was degraded to perillyl alcohol, perillaldehyde and perillic acid. 

More recently the biotransformation of limonene by another Pseudomonad strain, P. gladioli was reported [76,77]. P. gladioli was isolated by an enrichment culture technique from pine bark and sap using a mineral salts broth with limonene as the sole source of carbon. Fermentations were performed during 4-10 days in shake flasks at 25°C using a pH 6.5 mineral salts medium and 1.0% (+)-limonene. Major conversion products were identified as (+)-a-terpineol and (+)-perillic acid. This was the first time that the microbial conversion of limonene to (+)-a-terpineol was reported, see pathway 4. The conversion of limonene to a-terpineol was achieved with an enzyme, a-terpineol dehydratase (a TD), by the same group [78]. The enzyme, purified more than tenfold after cell-disruption of Pseudomonas gladioli, stereospecifically converted (4 )-(+)-limonene to (4/ )-(+)-a-terpineol or (4S)-(+)-limonene to (4S)-(+)-a-terpineol. a-Terpineol is widely distributed in nature and is one of the most commonly used perfume chemicals [27]. 

TERPENELESS OIL. An essential oil from which the teqoene components have been removed by extraction and fractionation, either alone or in combination. The optical activity of the oil is thus reduced. The terpene-less grades are much more highly concentrated than the original oil (15—30 times). Removal of terpenes is necessary to inhibit spoilage, particularly of oils derived from citrus sources. O11 atmospheric oxidation the specific terpenes form compounds that impair the value of the oil for example, d-limonene oxidazes to carvone and y-terpinene to p-cymene. Terpeneless grades of citrus oils are commercially available. 

Exposure to VOCs in public beauty shops can also be high. Many cosmetic products contain VOCs such as 2-phenoxyethanol, 2-butanone, acetone, terpenes, 2-hydroxy-4-methoxy-benzophenone or phenylmethanol. In particular, hair sprays are potential sources of indoor pollutants. To estimate VOC concentrations associated with the use of beauty products, a female subject was placed in the model room described earlier and sprayed with 16.1 g hair lacquer. Propellant gases (butane, pentane), ethanol, limonene and tripropyleneglycol (isomers) were subsequently monitored in the room. Thirty minutes after the application of this product, the highest VOC concentrations were measured for ethanol (>100pg/m3)... 

Disposal bins have been studied for the VOCs associated with them by Stathero-poulos, Agapiou and Pallis (2005). The most prominent classes of compounds emitted are generally aliphatic and aromatic hydrocarbons, esters, terpenes and alcohols. The highest median concentrations for a single compound was 649.9 tg/ m 1 for decane while median concentrations of several other compounds such as limonene, undecane, nonane, ethanol, acetic acid ethyl ester and 1, 2,4-trimethylbenzene are in the range 159.1-353.1 pg/nf3. Therefore, waste bins are not only sources of odorants but sources of VOC as well. 

The degree of chemical and optical purities of limonenes, again, depends on the exact source of the oil. Bulk rf-limonene currently available in the United States has optical purities in the range... 

There are four diastereomeric menthols according to the relative orientations of the methyl, isopropyl, and hydroxyl groups. They are known as menthol, isomenthol, neomenthol, and neoisomenthol, each of which exists in two enantiomeric forms. The most abundant and readily available is /-menthol, or (/A 2.S, 5iZ)-(-)-menthol (23), whereas other stereoisomers, although available from nature, are more economically produced through chemical derivatizations from menthone, limonene, and a-pinene. Commercial (-)-menthol from natural sources can be as pure as 99% in both chemical and optical purities. Synthetic menthol is currently made by an asymmetric isomerization (see Chapters 12 and 31).34... 

Depending on the source, the essential oil of nutmeg contains mainly sabinene (15-50%), a-pinene (10-22%) and (3-pinene (7-18%), with myrcene (0.7-3%), 1,8-cineole (1.5-3.5%), myristicin (0.5-13.5%), limonene (2.7-4.1%), safrole (0.1-3.2%) and terpinen-4-ol (0-11%). The contents depend on whether the oil is of West Indian, Indian or Sri Lankan origin (http //www.chem.uwimona. edu.jm 1104/lectures/nutmeg.html). 

Isolated aroma chemicals are aroma-active substances isolated from natural sources mainly by means of crystallization, distillation, and adduct formation/decomposition. Although synthetic materials are in many cases convenient to use, isolated aroma chemicals continue to be advantageous, especially when chirality is the issue. Even if chirality is not a problem, in some cases (eg., 1,8-cineole (1), eugenol (2), and limonene (3)), isolated natural chemicals serve better than their synthetic counterpart (Table 3). 3 Isolated aroma chemicals can be useful as such for the industry, and they are also utilized as starting materials for further synthetic manipulations.34,35... 

The substituted limonene cannabidiol (334) is a psychotomimetically inactive constituents of Cannabis, and its irradiation has been studied using various light sources. In methanol, the main product is a 1-methoxy-compound formed by addition of methanol, but in cyclohexane a mixture containing A THC, A iso-THC (335), a photoreduction product (8,9-dihydrocannabidiol), and 3 -cyclo-hexylcannabidiol (336) is obtained. ... 

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