Benzene natural sources

It should be emphasized that mankind has come and still comes into contact with fullerene in everyday life. Pristine fullerene C60 itself can be found in our environment, e.g., in the soot produced by free burning of hydrocarbons like benzene and cyclohexane, as well as in charcoal, though in very small amounts (Shibuya et al., 1999) and in the kitchen (in natural gas combustion streams) (Bang et al., 2004 Murr and Soto, 2005). The impact of these natural sources is rather negligible though with the growth of production of fullerenes it could lead to much more serious environment pollution and be (or could not ) of a hazard to some extent. 

In 1989, the same authors reported the isolation of murrayazolinol (166) from the same natural source as a minor carbazole alkaloid (155). In 1995, this alkaloid was also obtained by Ahmad as a minor carbazole alkaloid from the benzene extract of... 

In the early days of organic chemistry, the word aromatic was used to describe certain fragrant substances from fruits, trees, and other natural sources. Chemists soon realized, however, that substances grouped as aromatic behaved in a chemically different manner from most other organic compounds. Today, the term aromatic refers to the class of compounds that can be represented as having a six-membered ring with three double bonds. Benzene is the simplest aromatic compound, but aspirin, the steroid sex hormone estradiol, and many other important compounds also contain aromatic rings. 

Beside methanol and formaldehyde, the oxidation of methane may be directed to another route, leading to the formation of its condensation products, for example, ethane, ethylene and benzene. This route may provide an alternative way for the chemical use of natural sources of methane. Here, various catalysts were also tested using both 02 and N20 as the oxidants [22], The general picture observed by most authors was similar to that with methane oxidation to oxygenates. The conversion of methane was always higher with 02 than with N20. However, the selectivity to the coupling products showed an opposite trend. 

Benzene found in the environment is from both human activities and natural processes. Benzene was first discovered and isolated from coal tar in the 1800s. Today, benzene is made mostly from petroleum sources. Because of its wide use, benzene ranks in the top 20 in production volume for chemicals produced in the United States. Various industries use benzene to make other chemicals, such as styrene (for Styrofoam and other plastics), cumene (for various resins), and cyclohexane (for nylon and synthetic fibers). Benzene is also used for the manufacturing of some types of rubbers, lubricants, dyes, detergents, drugs, and pesticides. Natural sources of benzene, which include volcanoes and forest fires, also contribute to the presence of benzene in the environment. Benzene is also a part of crude oil and gasoline and cigarette smoke. For more information on the nature and uses of benzene, see Chapters 3 and 4. 

Coal tar is the main natural source of benzene and other aromatic hydrocarbons. Coal tar contains benzene, toluene, xylene, phenol, naphthalene and anthracene. 

Table I compares calculated concentrations of benzene, toluene, and ethylbenzene at several locations near the refinery with reported values for typical urban, rural, and remote settings from past EPA studies (Shah and Heyerdahl, 1988). For benzene, refinery impacts at the fenceline were similar to those observed in a rural environment. At the nearby residence, benzene concentrations were similar to those observed in a remote pristine setting. Ethylbenzene impacts were similar to benzene. Toluene impacts were somewhat higher, falling between typical rural and urban air quality. No comparable data were available for xylene. Automobiles and an adjacent power plant contribute some of these chemicals to the air. Biogenic (natural) sources also contribute. In the entire middle Atlantic region, natural sources provide about 40% of airborne hydrocarbons, with a higher percentage in more rural areas like Yorktown (Placet and Streets, 1989).

In the nineteenth century, many other compounds having properties similar to those of benzene were isolated from natural sources. Because these compounds possessed strong and characteristic odors, they were called aromatic compounds. It is their chemical properties, though, not their odor that make these compounds special. 

Commercial Preparation.—The most important method for preparing phenol on a commercial scale is the potash fusion of benzene sul-phonate (p. 520), though it may also be prepared by the diazo synthesis (p. 597). Its chief natural source is coal tar, from which it is obtained in the fractions of coal tar distillation, boiling below 210°, i.e., in the light and middle oils (p. 497). The process of isolating it has been described (p. 498), the purest product being in the form of the hydrate, m.p. 16°. The yield from coal tar is 0.4 to 0.5 per cent, it being one of the five most important coal tar distillation products. 

Many compounds isolated from natural sources are aromatic in part. In addition to benzene, benzaldehyde, and toluene, such compounds as the steroidal hormone estrone and the well-known analgesic morphine have aromatic rings. Many synthetic drugs are also aromatic in part the tranquilizer diazepam (Valium) is an example. 

Tocopherols and tocotrienols form pale yellow and viscous liquids at room temperature that are soluble in lipids and lipophilic solvents but are insoluble in water. In agreement with the substitution pattern, the hydrophobic properties of tocopherols decrease in the order of a- > 0- > y- > 8-tocopherol (Sliwiok and Kocjan, 1992). The melting point of RRR-a-tocopherol is ca 3°C, while that of RRR-y-tocopherol is at -3° to -2°C (Schudel et al., 1972). The ultraviolet absorption spectra of tocopherols and tocotrienols in ethanol show maxima in the range of 290-298 nm (Schudel et al., 1972 Diplock, 1985). The pure tocopherols isolated from natural sources exhibit relatively small optical rotations tocopherols are dextrorotatory in ethanol, while they are levorotatory in benzene. The free phenolic hydroxyl group of tocopherol molecules mainly determines their chemical properties (Schudel et al., 1972). 

Benzene (which is the name that was given to the aromatic compound CeUe) is probably the most common and industrially important aromatic compound in wide use today. It was discovered in 1825 by Michael Faraday, and its commercial production from coal tar (and, later on, other natural sources) began in earnest about twenty-five years later. The structure ofbenzene emerged during the 1860s, the result of contributions from several chemists, most famously that of Kekule. 

Cyclohexane is a large volume petrochemical used mainly in nylon manufacture. In 1965 the free-world consumption was 1.1 million tons, and this is expected to double substantially by 1970 (5). Methods for manufacturing cyclohexane are thus of considerable interest. While presently most cyclohexane is made by hydrogenating benzene (I), some is derived from natural sources. A potential method for manufacturing cyclohexane is by the selective hydrodealkylation of methylcyclohexane. Such a process is considerably more direct than the demethanation of toluene, followed by hydrogenation of the resulting benzene. 

When mixtures of hydrocarbons from natural sources, such as petroleum or coal, are separated, certain of the compounds that emerge have pleasant odors and are thus known as aromatic hydrocarbons. When these substances, which include wintergreen, cinnamon, and vanillin, are examined, they are all found to contain a common feature a six-membered ring of carbon atoms called the benzene ring. Benzene has the formula and a planar (flat) structure in which all of the bond angles are 120°. H... 

It is difficult to synthesise aromatic compounds in the laboratory from scratch and most aromatic compounds are prepared from benzene or other simple aromatic compounds (e.g. toluene and naphthalene). These in turn are isolated from natural sources like coal or petroleum. 

Many extracts are based chemically on the benzene ring, a class of often fragrant compounds which have come to be called aromatics as a consequence. They include benzaldehyde, which smells like almonds, and vanillin, the basis of vanilla. Camphor oil (8008-51-3) is the essential oil removed from the camphor tree. It contains camphor, as well as many other compounds. Camphor may also be extracted from other natural sources, but usually in smaller quantities. Vegetable extracts usually contain terpenes (CjoHig), a class of flammable hydrocarbons based on the isoprene unit (C5H8). 

Early in the development of organic chemistry, organic compounds were arbitrarily classified as aliphatic or aromatic. Aliphatic compounds have open-chain structure. In addition to aliphatic compounds, there was a large number of compounds which were obtained from natural sources e.g., resins, balsams, aromatic oils etc., all of which had a pleasant odour. These compounds had higher percentage of carbon content than the corresponding aliphatic hydrocarbons and most of the simple compounds contained atleast six carbon atoms. These compounds were known as aromatic compounds. Further more, when these aromatic compounds were subjected to various methods of treatment, they often produced benzene or derivatives of benzene. 

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