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BENZENE, C6H6
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See also:BENZENE, See also:C6H6 , a See also:hydrocarbon discovered in 1825 by See also:Faraday in the liquid produced in the See also:compression of the See also:illuminating See also:gas obtained by distilling certain See also:oils and fats. E. See also:Mitscherlich prepared it in 1834 by distilling benzoic See also:acid with See also:lime; and in 1845 See also:Hofmann discovered it in See also:coal-See also:tar. It was named " benzin" or " benzine " by Mitscherlich in 1833, but in the following See also:year See also:Liebig proposed "benzol" (the termination of being suggested by the See also:Lat. oleum, oil); the See also:form " benzene " was due to A. W. Hofmann. The word "benzine " is sometimes used in See also:commerce for the coal-tar product, but also for the See also:light See also:petroleum better known as petroleum-benzine; a similar See also:ambiguity is presented by the word " benzoline," which is applied to the same substances as the word "benzine." "Benzene" is the See also:term used by See also:English chemists, "benzol" is used in See also:Germany, and " benzole " in See also:France. Benzene is manufactured from the See also:low-boiling fractions of the coal-tar distillate (see COAL-TAR). The first successful fractionation of coal-tar See also:naphtha was devised by C. B. See also:Mansfield (1819-1855), who separated a benzol distilling below loo° from a less volatile naphtha by using a See also:simple dephlegmator. At first, the oil was manufactured principally for See also:combustion in the Read-Holliday See also:lamp and for dissolving See also:rubber, but the development of the coal-tar See also:colour See also:industry occasioned a demand for benzols of definite purity. In the earlier stages 30 %, 50 % and 90 % benzols were required, the 30 % being mainly used for the755 manufacture of "See also:aniline for red," and the 90 o fcr "aniline for See also:blue." (The term "30 % benzol" means that 30 % by See also:volume distils below roo°.) A purer benzol was subsequently required for the manufacture of aniline See also:black and other dye-stuffs. The See also:process originally suggested by Mansfield is generally followed, the success of the operation being principally conditioned by the efficiency of the dephlegmator, in which various improvements have been made. The light oil fraction of the coal-tar distillate, which comes over below 140° and consists principally of benzene, See also:toluene and the xylenes, yields on fractionation (1) various volatile impurities such as See also:carbon disulphide, (2) the benzene fraction boiling at about 8o° C., (3) the toluene fraction boiling at See also:rod', (4) the See also:xylene fraction boiling at 140°O. The fractions are agitated with strong sulphuric acid, and then washed with a See also:caustic soda See also:solution. The washed products are then refractionated. The toluene fraction requires a more thorough washing with sulphuric acid in See also:order to eliminate the thiotolene, which is sulphonated much less readily than thiophene. Benzene is a colourless, limpid, highly refracting liquid, having a pleasing and characteristic odour. It may be solidified to rhombic crystals which melt at 5.40 C. (Mansfield obtained perfectly pure benzene by freezing a carefully fractionated See also:sample.) It boils a t 8o•4°, and the vapour is highly inflammable, the See also:flame being extremely smoky. Its specific gravity is o•899 at o° C. It is very slightly soluble in See also:water, more soluble in See also:alcohol, and completely miscible with See also:ether, acetic acid and carbon disulphide. It is an excellent solvent for gums, resins, fats, &c.; See also:sulphur, See also:phosphorus and See also:iodine also dissolve in it. It sometimes separates with crystals of a solute as "benzene of See also:crystallization," as for example with See also:triphenylmethane, thio-p-tolyl See also:urea, See also:tropine, &c.
Benzene is of exceptional importance commercially on See also:account of the many compounds derivable from it, which are exceedingly valuable in the arts. Chemically it is one of the most interesting substances known, since it is the See also:parent of the enormous number of compounds styled the " aromatic " or " benzenoid " compounds. The constitution of the benzene See also:ring, the See also:isomerism of its derivatives, and their syntheses from aliphatic or open-See also:chain compounds, are treated in the See also:article See also:CHEMISTRY. A See also:summary of its chemical transformations may be given here, and reference should be made to the articles on the See also:separate compounds for further details.
Passed through a red-hot See also:tube, benzene vapour yields See also:hydrogen, See also:diphenyl, diphenylbenzenes and See also:acetylene; the formation of the last See also:compound is an instance of a reversible reaction, since See also:Berthelot found that acetylene passed through a red-hot tube gave some benzene. Benzene is very See also:stable to oxidants, in fact resistance to oxidation is a strong characteristic of the benzene ring. See also:Manganese dioxide and sulphuric acid oxidize it to benzoic and o-See also:phthalic acid; See also:potassium chlorate and sulphuric acid breaks the ring; and See also:ozone oxidizes it to the highly explosive See also: Additional information and CommentsThere are no comments yet for this article.
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