Polynuclear aromatic compounds aromaticity

Plcel, K. C. Stamoudls, V. C. Simmons, M S. Photolytlc and Partitioning Behavior of Polynuclear Aromatic Compounds, Aromatic Amines, and Phenols In Aqueous Coal Oil," U.S. Dept, of Energy Report DOE/MC/49533-1837 (ANL/SER-4), 1985. 

The composition of coal tar varies with the carbonization method but consists, largely, of mononuclear and polynuclear aromatic compounds and their derivatives. Coke oven tars are relatively low in aliphatic and phenolic content while low-temperature tars have much higher contents of both. 

Outside of carbon monoxide for which the toxicity is already well-known, five types of organic chemical compounds capable of being emitted by vehicles will be the focus of our particular attention these are benzene, 1-3 butadiene, formaldehyde, acetaldehyde and polynuclear aromatic hydrocarbons, PNA, taken as a whole. Among the latter, two, like benzo [a] pyrene, are viewed as carcinogens. Benzene is considered here not as a motor fuel component emitted by evaporation, but because of its presence in exhaust gas (see Figure 5.25). 

The aromatic extracts are black materials, composed essentially of condensed polynuclear aromatics and of heterocyclic nitrogen and/or sulfur compounds. Because of this highly aromatic structure, the extracts have good solvent power. 

The most notable studies are those of Ingold, on the orienting and activating properties of substituents in the benzene nucleus, and of Dewar on the reactivities of an extensive series of polynuclear aromatic and related compounds ( 5.3.2). The former work was seminal in the foundation of the qualitative electronic theory of the relationship between structure and reactivity, and the latter is the most celebrated example of the more quantitative approaches to the same relationship ( 7.2.3). Both of the series of investigations employed the competitive method, and were not concerned with the kinetics of reaction. 

This qualification must be applied to the results of Dewar and his co-workers relating to the reaction of a series of polynuclear aromatic compounds with solutions of nitric acid in acetic anhydride at o °C... 

Whenever unvented combustion occurs iadoors or when venting systems attached to combustion units malfunction, a variety of combustion products win be released to the iadoor environment. Iadoor combustioa units include nonelectric stoves and ovens, furnaces, hot water heaters, space heaters, and wood-burning fireplaces or stoves. Products of combustion include CO, NO, NO2, fine particles, aldehydes, polynuclear aromatics, and other organic compounds. Especially dangerous sources are unvented gas and kerosene [8008-20-6] space heaters which discharge pollutants directly into the living space. The best way to prevent the accumulation of combustion products indoors is to make sure all units are properly vented and properly maintained. 

The endoperoxides of polynuclear aromatic compounds are crystalline soHds that extmde singlet oxygen when heated, thus forming the patent aromatic hydrocarbon (44,66,80,81). Thus 9,10-diphenyl-9,10-epidioxyanthrancene [15257-17-7] yields singlet oxygen and 9,10-diphenylanthracene. 

The fused 3+ ring aromatics in petroleum include both cata- and peri-condensed stmctures (see Table 4, Fig. 8). The cata-condensed species are those stmctures where only one face is shared between rings, the peri-condensed molecules are those that share more than one face. The fused ring aromatics form the class of compounds known as polynuclear aromatic hydrocarbons (PAH) which includes a number of recognized carcinogens in the 4+ ring family (33). Because of the potential health and environmental impact of PAH, these compounds have been studied extensively in petroleum. 

Rubbers. Plasticizers have been used in mbber processing and formulations for many years (8), although phthaHc and adipic esters have found Htde use since cheaper alternatives, eg, heavy petroleum oils, coal tars, and other predominandy hydrocarbon products, are available for many types of mbber. Esters, eg, DOA, DOP, and DOS, can be used with latex mbber to produce large reductions in T. It has been noted (9) that the more polar elastomers such as nitrile mbber and chloroprene are insufficiendy compatible with hydrocarbons and requite a more specialized type of plasticizer, eg, a phthalate or adipate ester. Approximately 50% of nitrile mbber used in Western Europe is plasticized at 10—15 phr (a total of 5000—6000 t/yr), and 25% of chloroprene at ca 10 phr (ca 2000 t/yr) is plasticized. Usage in other elastomers is very low although may increase due to toxicological concerns over polynuclear aromatic compounds (9). 

The petroleum oils are of three basic types aromatic, naphthemic, and paraffinic. Aromatic oils contain hazardous materials that require special handling precautions. Naphthenic oil does not contain hazardous levels of polynuclear aromatics (PNAs) and is less hysteretic. Because of these considerations the naphthenic oil is gaining in usage at the expense of more utilized aromatics. Paraffinic oil is only used modestly in tire compounds. The... 

Aerobic, Anaerobic, and Combined Systems. The vast majority of in situ bioremediations ate conducted under aerobic conditions because most organics can be degraded aerobically and more rapidly than under anaerobic conditions. Some synthetic chemicals are highly resistant to aerobic biodegradation, such as highly oxidized, chlorinated hydrocarbons and polynuclear aromatic hydrocarbons (PAHs). Examples of such compounds are tetrachloroethylene, TCE, benzo(a)pyrene [50-32-8] PCBs, and pesticides. 

Polynuclear aromatic hydrocarbons. These consist of a variety of complex structures made up of aromatic rings alone, or combinations of aliphatic rings, aromatic rings, and aliphatic chains, etc. One such class of compounds is biphenyl and its derivatives, in which two benzene rings are connected by a single C — C linkage. The structural formula of biphenyl (or phenylbenzene) is... 

Other polynuclear hydrocarbons may include bridged hydrocarbons, spiro hydrocarbons, mixed systems containing alicyclic and aromatic rings, and aliphatic chains, etc. Examples may be found in the CRC Handbook [63, Section C]. Physical properties of selected polynuclear aromatic compounds are given in [49, p. 967]. 

Sulfur Compounds. All crude oils contain sulfur in one of several forms including elemental sulfur, hydrogen sulfide, carbonyl sulfide (COS), and in aliphatic and aromatic compounds. The amount of sulfur-containing compounds increases progressively with an increase in the boiling point of the fraction. A majority of these compounds have one sulfur atom per molecule, but certain aromatic and polynuclear aromatic molecules found in low concentrations in crude oil contain two and even three sulfur atoms. Identification of the individual sulfur compounds in the heavy fractions poses a considerable challenge to the analytical chemist. 

Binuclear aromatic hydrocarbons are found in heavier fractions than naphtha. Trinuclear and polynuclear aromatic hydrocarbons, in combination with heterocyclic compounds, are major constituents of heavy crudes and crude residues. Asphaltenes are a complex mixture of aromatic and heterocyclic compounds. The nature and structure of some of these compounds have been investigated. The following are representative examples of some aromatic compounds found in crude oils ... 

The constituents of residual fuels are more complex than those of gas oils. A major part of the polynuclear aromatic compounds, asphaltenes, and heavy metals found in crude oils is concentrated in the residue. 

During the cracking process, fragmentation of complex polynuclear cyclic compounds may occur, leading to formation of simple cycloparaffins. These compounds can he a source of Ce, C7, and Cg aromatics through isomerization and hydrogen transfer reactions. 

A higher steam/hydrocarhon ratio favors olefin formation. Steam reduces the partial pressure of the hydrocarbon mixture and increases the yield of olefins. Heavier hydrocarbon feeds require more steam than gaseous feeds to additionally reduce coke deposition in the furnace tubes. Liquid feeds such as gas oils and petroleum residues have complex polynuclear aromatic compounds, which are coke precursors. Steam to hydrocarbon weight ratios range between 0.2-1 for ethane and approximately 1-1.2 for liquid feeds. 

Phenanthrene, anthracene, and other polynuclear aromatic compounds. 

M - 2 Aromatic isocyanates Aromatic phenols Certain butenols Certain fluorinated amines e.g., C8F17CH2CHICH2NH2 or CF3(CF2)7CH2CH2CH2NH2 Possible Precursor Compounds Polynuclear aromatics (e.g., dihydroxyphenanthrene) Ethylsilanes (dimers to heptamers)... 

In summary, examples of the successful use of silica gel as a conventional stationary phase are in the analysis of mixtures containing polarizable and relatively low polarity solutes typified by mixtures of aromatic hydrocarbons, polynuclear aromatics, nitro compounds, carotenes and vitamin A formulas. 

Standardization. Standardization in analytical chemistry, in which standards are used to relate the instrument signal to compound concentration, is the critical function for determining the relative concentrations of species In a wide variety of matrices. Environmental Standard Reference Materials (SRM s) have been developed for various polynuclear aromatic hydrocarbons (PAH s). Information on SRM s can be obtained from the Office of Standard Reference Materials, National Bureau of Standards, Gaithersburg, MD 20899. Summarized in Table VII, these SRM s range from "pure compounds" in aqueous and organic solvents to "natural" matrices such as shale oil and urban and diesel particulate materials. 

The dosimeter can detect various polynuclear aromatics at the pph level after 1 hour of exposure. It has been shown that the RTF of aza-arenes can he enhanced by using mercury(II) chloride as a heavy atom (21). Also, sensitized fluorescence spectrometry with a solid organic substrate can be used to detect trace amounts of polynuclear aromatic compounds (22). 

The theory and development of a solvent-extraction scheme for polynuclear aromatic hydrocarbons (PAHs) is described. The use of y-cyclodextrin (CDx) as an aqueous phase modifier makes this scheme unique since it allows for the extraction of PAHs from ether to the aqueous phase. Generally, the extraction of PAHS into water is not feasible due to the low solubility of these compounds in aqueous media. Water-soluble cyclodextrins, which act as hosts in the formation of inclusion complexes, promote this type of extraction by partitioning PAHs into the aqueous phase through the formation of complexes. The stereoselective nature of CDx inclusion-complex formation enhances the separation of different sized PAH molecules present in a mixture. For example, perylene is extracted into the aqueous phase from an organic phase anthracene-perylene mixture in the presence of CDx modifier. Extraction results for a variety of PAHs are presented, and the potential of this method for separation of more complex mixtures is discussed. 

Wise SA, Chesisr SN, Hertz HS, Hilpert LR, and May WE (1977) A chemically bonded amino-silane stationary phase for the high-performance liquid chromatographic separation of polynuclear aromatic compounds. Anal Chem 49 2306-2310. 

About 100 gal of process wastewater is typically generated from 1 t of coke produced.15 These wastewaters from byproduct coke making contain high levels of oil and grease, ammonia nitrogen, sulfides, cyanides, thiocyanates, phenols, benzenes, toluene, xylene, other aromatic volatile components, and polynuclear aromatic compounds. They may also contain toxic metals such as antimony, arsenic, selenium, and zinc. Water-to-air transfer of pollutants may take place due to the escape of volatile pollutants from open equalization and storage tanks and other wastewater treatment systems in the plant. 

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