Compounds monoaromatic

Haggblom M (1990) Mechanisms of bacterial degradation and transformation of chlorinated monoaromatic compounds. J Basic Microbiol 30 115-141. 

The monoaromatic compounds benzene, toluene, ethylbenzene and xylene, commonly found in crude oil, are often jointly called BTEX compounds. The most harmful of these compounds is benzene, which is a known carcinogen. BTEX compounds occur naturally near natural gas and petroleum deposits and are detected in the fumes of forest fires. Most of the highly volatile BTEX compounds released by human activity originate from fuel use and end up as pollutants in the air. Inhaling BTEX-polluted air is also the greatest hazard to humans by these compounds. BTEX compounds are water-soluble, and therefore, improper handling can also cause groundwater contamination. 

The chemical objectives of naphtha and gasoline hydrotreatment are essentially the removal of S and N, and up to whether possible, to saturate the monoaromatic rings. One collateral requirement has to do with achieving the objective with no octane losses. The chemistry of the HDN of nitrogen compounds, commonly found in gasoline, has been the subject of studies, some of which are considered in this section. 

There are several chemical compounds found in the waste waters of a wide variety of industries that must be removed because of the danger they represent to human health. Among the major classes of contaminants, several aromatic molecules, including phenols and aromatic amines, have been reported. Enzymatic treatment has been proposed by many researchers as an alternative to conventional methods. In this respect, PX has the ability to coprecipitate certain difficult-to-remove contaminants by inducing the formation of mixed polymers that behave similarly to the polymeric products of easily removable contaminants. Thus, several types of PX, including HRP C, LiP, and a number of other PXs from different sources, have been used for treatment of aqueous aromatic contaminants and decolorization of dyes. Thus, LiP was shown to mineralize a variety of recalcitrant aromatic compounds and to oxidize a number of polycyclic aromatic and phenolic compounds. Furthermore, MnP and a microbial PX from Coprinus macrorhizus have also been observed to catalyze the oxidation of several monoaromatic phenols and aromatic dyes (Hamid and Khalil-ur-Rehman 2009). 

Together with singly charged ions doubly and multiply charged ions may also arise in the ionization process. However, the number of doubly charged and especially of multiply charged species is much lower. The yield of these ions depends on the structure of a molecule and on the experimental conditions. For example, polycyclic aromatic hydrocarbons give more ions of these types compared to aliphatic or monoaromatic compounds. 

TCDD may be in a state of flux, resulting from dechlorination of octa-and hepta-CDD and being further dechlorinated to 2-mono-CDD [54]. Beside dechlorination reactions in sediments [4],dioxin dechlorination reactions have been demonstrated in the presence of microorganisms ([5, 12, 13, 431-433], dihydroxylated monoaromatic compounds [433], vitamin B12, and zero valent metals [3]. 

Chemical/Physical. Incomplete combustion of propane in the presence of excess hydrogen chloride resulted in a high number of different chlorinated compounds including, but not limited to alkanes, alkenes, monoaromatics, alicyclic hydrocarbons, and polynuclear aromatic hydrocarbons. Without hydrogen chloride, 13 nonchlorinated polynuclear aromatic hydrocarbons were formed (Eklund et al, 1987). 

Cycle Oil. Heavier, distillate range compounds formed during FCC processing can accumulate within the FCC fractionator. The primary fraction is called light cycle oil (LCO) and contains high percentages of monoaromatic and diaromatic compounds plus olefins and heavier branched paraffins. Unhydrotreated LCO is often quite unstable and has a very low cetane number. For this reason, it is blended into diesel fuel in controlled amounts. Heavy cycle oil and heavy naphtha are additional side cuts that can be produced. These streams can be pumped around to remove heat from the fractionator, used to supply heat to other refinery units, or used as low-quality blendstock component. 

Aromatic compounds are typically no more than 15% of the total weight of most crude oil. The branched or alkylated aromatic derivatives are more prevalent than the nonalkylated aromatics. For example, toluene and xylene are found in higher percentages than benzene. Also, monoaromatic compounds such as toluene and xylene are some of the most common of the aromatics in crude. 

Monoaromatic, diaromatic and polycyclic aromatic compounds can all be found in fuels. Although concentrations vary in different fuels, the presence of these aromatics can have both desirable and undesirable consequences. Examples include the following ... 

High content of aromatic compounds including monoaromatics, diaromatics, and polyaromatics... 

The di- + triaromatic subfraction analyzes as 54% monoaromatics and 47% diaromatics by proton NMR. The average molecule also contains many short alkyl substituents, more than one aromatic ring, and one naphthene ring. The average molecular weight calculated from NMR is lower than that obtained by VPO. These data indicate that non-condensed di- and triaromatics are present in this subfraction. Compounds such as ... 

Longoria A, Tinoco R, Vazquez-Duhalt R (2008) Chloroperoxidase-Mediated Transformation of Highly Halogenated Monoaromatic Compounds. Chemosphere 72 485... 

Mackay, D., W.-Y. Shiu, and K.C. Ma. 1992a. Illustrated Handbook of Physical - Chemical Properties and Environmental Fate of Organic Compounds. I. Monoaromatic Hydrocarbons, Chlorobenzenes and Polychlorinated Biphenyls. Lewis Publishers, Boca Raton, Florida, 697 pages. 

The kinetics associated with catalytic reactions are complex however, some general trends can be determined. Reactions are often first order with respect to the reactant, and the rates of hydrodechlorination are faster than hydrogenation. Polyaromatic compounds react faster than monoaromatic compounds, and chlorinated alkenes react faster than their corresponding alkanes. Finally, the reaction rate often increases with increasing degree of chlorination, though this does not hold true for the chlorinated ethylenes. 

Nanny, M. A. (1999). Deuterium NMR characterization of noncovalent interactions between monoaromatic compounds and fulvic acids. Org. Geochem. 30, 901-909. 

Figure 17.5 Illustration that salicylate, or an analogous carbon-substituted monoaromatic ring, cannot be derived from an unsubstituted monoaromatic compound. 

Acid-II fraction is mainly composed of alkyl substituted monoaromatic phenols. As for Base-II (G) fraction, proton signals are much more widely spread than that of Fraction K particularly at lower magnetic field, as shown in Figure 11. This may suggest that the fraction is composed of heteroaromatic compounds involving nitrogen atom in the ring structure (18). 

The results in Figure 1 can be interpreted in terms of general ring structures with the hydrocarbon classes. The peak for the polypolar aromatic fraction at 160° C probably is caused by polar-monocyclic compounds and the peak at 240° C is probably the result of polar dicyclic compounds. The broad curve in the monoaromatics centering at 275°C is probably mainly caused by alkyl-substituted tetralins while the peaks... 

The extracts were fractionated by a Preparative Liquid Chromatography method - PLC-8 [2], in eight distinct chemical classes FI-saturated hydrocarbons (HC), F2-monoaromatics, F3-diaromatics, F4-triaromatics, F5-polynuclear aromatics, F6-resins, F7-asphaltenes and F8-asphaltols. This method, proposed by Karam et al. as an extension of SARA method [4], was especially developed for coal-derived liquids. It combines solubility and chromatographic fractionation, affording discrete, well-defined classes of compounds which are readable for direct chromatographic and spectroscopic analysis. 

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