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MODERN GASWORKS PRACTICE
marked unsaturated character. The aromatics, in faet, resemble the paraffins rather than the olefines, in that they give rise to substitution products more readily than to addition compounds. It should be noted that an aromatic hydrocarbon never contains fewer than six carbon atoms, and whereas this series is readily attacked by nitric and sulphuric acids the paraffins are unattacked, while the olefines yield addition compounds. Other aromatic hydrocarbons of importance in the study of carbonization are those which contain more than one benzene nucleus in the molecule. They are of two classes, namely:—
(a) Multinuclear hydrocarbons, e.g. diphenyl (C12H10), in which the benzene nuclei are linked together directly, or they are united by one or more carbon bonds. Thus
Diphenyl, C12H10.
(&) Condensed benzenoid hydrocarbons, e.g. naphthalene (Ci0Hs) and anthracene (C14H12),iii which. case two or more benzene nuclei are united through one or more carbon atoms. In other words, the benzene nuclei are, so to speak, fused together so that certain of the carbon atoms are common to both rings. Hence the term “ condensed-ring ” compounds. Thus :—
Of the remaining hydrocarbons commonly met with in the products of carboni-zation phenol is of importance. This is an aromatic body containing a hydroxyl group directly attached to the benzene ring. While substances having the hydroxyl directly attacher! in this way are known as phenols, those which have the hydroxyl in the side chain are known as aromatic alcohols. The phenols of toluene are known as cresols. Thus :—
Phenol, CeHs.0H. Benzyl alcohol, (jgjHs.CH2.OH.
Ortho-cresol, C6H4.CH3.OH.