Distillation of coal-tar

Coal tar is the condensation product obtained by cooling to approximately ambient temperature, the gas evolved in the destmctive distillation of coal. It is a black viscous Hquid denser than water and composed primarily of a complex mixture of condensed ring aromatic hydrocarbons. It may contain phenoHc compounds, aromatic nitrogen bases and their alkyl derivatives, and paraffinic and olefinic hydrocarbons. Coal-tar pitch is the residue from the distillation of coal tar. It is a black soHd having a softening point of 30—180°C (86—359°F). 

The principal binder material, coal-tar pitch, is produced by the distillation of coal tar. Coal tar is obtained primarily as a by-product of the destmctive distillation of bituminous coal in coke ovens during the production of metallurgical coke. Petroleum pitch is used to a much lesser extent as a binder in carbon and graphite manufacture. Because of its low sohds content, petroleum pitch is used as an impregnant to strengthen carbon artifacts prior to graphitization. 

Sources of Raw Materials. Coal tar results from the pyrolysis of coal (qv) and is obtained chiefly as a by-product in the manufacture of coke for the steel industry (see Coal, carbonization). Products recovered from the fractional distillation of coal tar have been the traditional organic raw material for the dye industry. Among the most important are ben2ene (qv), toluene (qv), xylene naphthalene (qv), anthracene, acenaphthene, pyrene, pyridine (qv), carba2ole, phenol (qv), and cresol (see also Alkylphenols Anthraquinone Xylenes and ethylbenzenes). 

The economics of this process are to some extent dependent on the value of the acetone which is formed with the phenol. The process is, however, generally considered to be competitive with the modified Raschig process in which there is no by-product of reaction. In all of the above processes benzene is an essential starting ingredient. At one time this was obtained exclusively by distillation of coal tar but today it is commonly produced from petroleum. 

Naphthalene is obtained from the middle oil in the distillation of coal-tar. It crystallises in colourless, glistening plates, which have a characteristic smell. 

Simple aromatic hydrocarbons come from two main sources coal and petroleum. Coal is an enormously complex mixture made up primarily of large arrays of benzene-like rings joined together. Thermal breakdown of coal occurs when it is heated to 1000 °C in the absence of air, and a mixture of volatile products called coal for boils off. Fractional distillation of coal tar yields benzene, toluene, xylene (dimethylbenzene), naphthalene, and a host of other aromatic compounds (Figure 15.1). 

In a phenol, a hydroxyl group is attached directly to an aromatic ring. The parent compound, phenol itself, Cr,HsOH (4), is a white, crystalline, molecular solid. It was once obtained from the distillation of coal tar, but now it is mainly synthesized from benzene. Many substituted phenols occur naturally, some being responsible for the fragrances of plants. They are often components of essential oils, the oils that can be distilled from flowers and leaves. Thymol (5), for instance, is the active ingredient of oil of thyme, and eugenol (6) provides most of the scent and flavor of oil of cloves. 

Bitumens occur naturally or are formed as the residue in the distillation of coal tar, petroleum, etc. Industrially, the two most important bitumens are asphalt and coal tar. Asphalt is a brown to black tarlike variety of bitumen that again occurs naturally or is the residue of distillation. Coal tar is the black, thick liquid obtained as the residue from the distillation of bituminous coal. 

Thiophene is present in the benzene fraction from the distillation of coal tar. As with pyrrole and furan, the same type of resonance forms contribute to its overall molecular constitution, and the compound is aromatic in character. There is a difference between thiophene and furan, however, because sulfur is less electronegative than oxygen. Thus, the chemistry of thiophene tends to be closer to that of pyrrole than to that of furan. For example, thiophene does not enter easily into [4 + 2] cycloaddition reactions and quite severe conditions, high pressure (15 bar) and a temperature of 100 C, are necessary in order to force a cycloaddition between it and maleic anhydride. 

Other important expls obtd on nitration of products of distillation of coal tar were Di- and Tri nitrobenzene (Vol 2 of Encycl, pp B46ff and Nitronaphthalenes, which will be described under Naphthalene and Derivatives... 

Among the methods available for the synthesis of the pyridine system, Hantzsch synthesis is probably the most important and widely used synthetic route. However, the pyridine ring can be synthesized from the reaction between pentan-2,4-dione and ammonium acetate. Cyclization of 1,5-diketones is also considered as a convenient method for the synthesis of corresponding pyridine derivatives. Commercially, pyridine is obtained from distillation of coal tar. 

Phenol was prepared before World War I through the distillation of coal tar. The first synthetic process involved the sulfonation of benzene followed by desulfonation with a base. In this process, benzene sulfonic acid is prepared from the reaction of benzene and sulfuric acid ... 

Ammoniaeal Liquor or Gas Liquor. Impure ammonia water obtained as a by-product in the distillation of coal, tar, bones, etc... 

NapMhalin is readily procured by the distillation of coal-tar, but its quantity is considerably enlarged if chlorine be transmitted into ho menstruum, or if the latter be treated with bleaching powder, water, and sulphuric acid. Naphthalin always passes over last in the distillation of tar, mixed, however, with paranaplr-thalin, from whjch it is separated by treatment with alcohol, in which menstruum the latter is insoluble ... 

Distillation of coal tar yields light oil (contg benzene, toluene 8c xylene), middle oil (contg phenol, cresol naphthalene), heavy oil (contg impure cresol other phenols) and green oil (contg anthracene) (Refs 4,9,11 13)... 

Thomas Hancock (1786-1865) and Charles Macintosh (1766-1845) a chemist dissolved natural rubber in naphtha obtained by the fractional distillation of coal tar. They, then dipped ordinary cloth in this rubber solution to produce waterproof cloth for making coats. This waterproof coat came to be known as Mackintosh . 

The simplest member of the quinoline family is quinoline itself. It is a hygroscopic, yellowish oily liquid that is slightly soluble in water, soluble in alcohol, ether, carbon disulfide, and readily soluble in many other organic solvents. It can be obtained through the distillation of coal tar [2]. Quinoline can be prepared from aniline with acrolein under heated sulfuric acid (the Skraup synthesis [3-6], shown in Scheme 1) [ 1]. Isoquinoline was also isolated from coal tar in 1885 [2]. Both of these bases have been known about for a long time. 

Some aromatic hydrocarbons are obtained from distillation of coal tar. 

Toluene (Figure 3.2a) is the principle intoxicant in many inhaled products and is one of the most frequently abused chemicals. Its chemical formula is C Hg, and it is a colorless, flammable liquid with a sweet, pungent odor. It occurs naturally in the tolu tree, in crude oil fuels, and from the distillation of coal tar. Toluene is used to boost the amount of octane in... 

Fractional Distillation of Coal Tar.—The distillation of the coal tar is carried out in iron retorts, and fractions distilling at certain temperatures are obtained. These fractions vary somewhat in different works and with different tars, but the following may be given as a general result. 

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