Benzene sources

Until 1960, coal was the source material for almost all benzene produced in Europe. Petroleum benzene was first produced in Europe by the United Kingdom in 1952, by Erance in 1958, by the Eederal Republic of Germany in 1961, and by Italy in 1962. Coal has continued to decline as a benzene source in Europe, and this is evident with the closure of coke ovens in Germany (73). Most of the benzene produced in Europe is now derived from petroleum or pyrolysis gasoline. In Europe, pyrolysis gasoline is a popular source of benzene because European steam crackers mn on heavier feedstocks than those in the United States (73). 

EPA has recently found the maximum individual risks and total population risks from a number of radionuclide and benzene sources to be too low to be properly described as "significant". Specifically, benzene emissions from maleic anhydride process vents created maximum individual risks of 7.6 in 100,000 and an aggregrate yearly cancer incidence of twenty-nine thousandths of... 

Loschmidt s possible diallene (hexatetraene) structure for benzene. Source Loschmidt, Chemische Stud/en (1861), 30 (58), Schema 181. 

Loschmidt s two other possible representations for benzene. Source Loschmidt,... 

Kekule s open-chain and closed-chain sausage formulas for benzene. Source Kekul, Bulletin de la Societe Chimique [2] 3 (1865) 108. 

Kekule s new graphic formula for benzene. Source Kekul, Lehrbuch der organischen Chemie 0866), 2 496. 

Kekule s tetrahedral carbon atom model his new model for benzene. Source Museum for the History of Sciences, University of Ghent. 

Figure 25.29 Phase diagram for mixtures (a) Water -1-triethylamine, (b) water -1- 2-methyl-piperidine, (c) sulfur + benzene. Source WE Acree Jr, Thermodynamic Properties of Nonelectrolyte Solutions, Academic Press, Orlando, 1 984. From (a) F Kohler and OK Rice, J Chem Phys 26, 1614 (1 957) (b) O Flaschner and B Marewen, J Chem Soc 93, 1000 (1908).

FIGURE 16.8 High efficiency analysis of a test sample using five coupled Acquity 1.7-pm columns at near ambient temperature (40 C). Analysis conditions Total column length, 450 mm flow rate, 0.17 ml/min (system) pressure, 999 bar temperature, 40°C (Polaratherm) detection, 210 nm (20 Hz). Mobile phase 30/70 acetonitrile/water. Peak identification 1 = uracil, 2 = caffeine, 3 — pyridine, 4 — aniline, 5 — phenol, 6 — acetophenone, 7 = benzene. Source Reproduced with permission from 2006 Elsevier B.V. 

A further potential source of environmental pollution is the burning of wood, garbage and organic wastes - such as gardening refuse (where about 1.4 kg benzene are obtained from one tonne) and rice waste [13, 29, 30]. Since the combustion gases from wood total only about 400,000 t hydrocarbons [13] per annum in the USA, this benzene source is of minor significance in relation to the 26-30 million t consumed as raw material or in gasoline. 

An example of where recycling can be effective in improving selectivity is in the production of benzene from toluene. The series reaction is reversible. Hence recycling diphenyl to the reactor can be used to suppress its formation at the source. 

The second source of sulfonic acid uses the following reaction scheme alkylation of benzene by a propylene oligomer then sulfonation of the alkylbenzene. 

Dewar and his co-workers, as mentioned above, investigated the reactivities of a number of polycyclic aromatic compounds because such compounds could provide data especially suitable for comparison with theoretical predictions ( 7.2.3). This work was extended to include some compounds related to biphenyl. The results were obtained by successively compounding pairs of results from competitive nitrations to obtain a scale of reactivities relative to that of benzene. Because the compounds studied were very reactive, the concentrations of nitric acid used were relatively small, being o-i8 mol 1 in the comparison of benzene with naphthalene, 5 x io mol 1 when naphthalene and anthanthrene were compared, and 3 x io mol 1 in the experiments with diphenylamine and carbazole. The observed partial rate factors are collected in table 5.3. Use of the competitive method in these experiments makes them of little value as sources of information about the mechanisms of the substitutions which occurred this shortcoming is important because in the experiments fuming nitric acid was used, rather than nitric acid free of nitrous acid, and with the most reactive compounds this leads to a... 

Benzene was prepared from coal tar by August W von Hofmann m 1845 Coal tar remained the primary source for the industrial production of benzene for many years until petroleum based technologies became competitive about 1950 Current production IS about 6 million tons per year m the United States A substantial portion of this ben zene is converted to styrene for use m the preparation of polystyrene plastics and films... 

The article A History of the Structural Theory of Benzene—The Aromatic Sex tet and Huckel s Rule in the February 1997 issue of the Journal of Chemical Educa tion (pp 194-201) IS a rich source of additional informa tion about this topic... 

Carboxylic acid anhydrides compounds of the type RCOCR can also serve as sources of acyl cations and m the presence of aluminum chloride acylate benzene One acyl unit of an acid anhydride becomes attached to the benzene ring and the other becomes part of a carboxylic acid... 

Using benzene acetic anhydride and 1 propanethiol as the source of all the carbon atoms along with any necessary inorganic reagents outline a synthesis of the compound shown... 

From about 1970, but before the availability of suitable lasers, Parmenter and others obtained SVLF spectra, particularly of benzene, using radiation from an intense high-pressure xenon arc source (see Section 3.4.4) and passing it through a monochromator to select a narrow band ca 20 cm wide) of radiation to excite the sample within a particular absorption band. 

In a polluted or urban atmosphere, O formation by the CH oxidation mechanism is overshadowed by the oxidation of other VOCs. Seed OH can be produced from reactions 4 and 5, but the photodisassociation of carbonyls and nitrous acid [7782-77-6] HNO2, (formed from the reaction of OH + NO and other reactions) are also important sources of OH ia polluted environments. An imperfect, but useful, measure of the rate of O formation by VOC oxidation is the rate of the initial OH-VOC reaction, shown ia Table 4 relative to the OH-CH rate for some commonly occurring VOCs. Also given are the median VOC concentrations. Shown for comparison are the relative reaction rates for two VOC species that are emitted by vegetation isoprene and a-piuene. In general, internally bonded olefins are the most reactive, followed ia decreasiag order by terminally bonded olefins, multi alkyl aromatics, monoalkyl aromatics, C and higher paraffins, C2—C paraffins, benzene, acetylene, and ethane. 

The Clean Air Act Amendments of 1990 limit the amount of benzene in gasoline in the United States to 1% (7). Initially there was some concern that this would dismpt the benzene supply and demand balance in the chemical industry because at that time gasoline contained benzene above 1%. If refiners had to extract all of the benzene above 1%, substantial additional benzene would be produced. However, only modest increases in the quantity of benzene produced from reformer sources is expected as most refiners can adjust the composition of reformer feed and reformer severity to produce less benzene. 

Friedel-Crafts alkylation using alkenes has important industrial appHcations. The ethylation of benzene with ethylene to ethylbenzene used in the manufacture of styrene, is one of the largest scale industrial processes. The reaction is done under the catalysis of AlCl in the presence of a proton source, ie, H2O, HCl, etc, although other catalysts have also gained significance. 

Capacities of maleic anhydride faciUties worldwide are presented in Table 7. The switch of feedstock from benzene to butane was completed in the United States in 1985, being driven by the lower unit cost and lower usage of butane in addition to the environmental pressures on the use of benzene. Worldwide, the switch to butane is continuing with 58% of the total world maleic anhydride capacity based on butane feedstock in 1992. This capacity percentage for butane has increased from only 6% in 1978. In 1992, 38% of the total world maleic anhydride capacity was based on benzene feedstock and 4% was derived from other sources, primarily phthaUc anhydride by-product streams. 

MPa (15—20 atm), 300—400 kg benzene per kg catalyst per h, and a benzene ethylene feed ratio of about 30. ZSM-5 inhibits formation of polyalkjlated benzenes produced with nonshape-selective catalysts. With both ethylene sources, raw material efficiency exceeds 99%, and heat recovery efficiency is high (see Xylenes and ethylbenzene). 

Gycloaliphatics and Aromatics. Cychc compounds (cyclohexane and benzene) are also important sources of petrochemical products (Fig. 14). Aromatics are ia high concentration ia the product streams from a catalytic reformer. When aromatics are needed for petrochemical manufacture, they are extracted from the reformer s product usiag solvents such as glycols (eg, the Udex process) and sulfolane. 

The earliest reported reference describing the synthesis of phenylene sulfide stmctures is that of Friedel and Crafts in 1888 (6). The electrophilic reactions studied were based on reactions of benzene and various sulfur sources. These electrophilic substitution reactions were characterized by low yields (50—80%) of rather poorly characterized products by the standards of 1990s. Products contained many by-products, such as thianthrene. Results of self-condensation of thiophenol, catalyzed by aluminum chloride and sulfuric acid (7), were analogous to those of Friedel and Crafts. 

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