SOME DERIVATIVES OF BENZENE
Attention has been called to the complex nature of coal tar. Among the compounds present are the hydrocarbons, benzene, toluene, naphthalene, and anthracene. These compounds are not only useful in themselves but serve for the preparation of many other important compounds known under the general name of coal-tar products.
Nitrobenzene (oil of myrbane) (C6H5NO2). When benzene is treated with nitric acid a reaction takes place which is expressed by the following equation:
C6H6 + HNO3 = C6H5NO2 + H2O.
The product C6H5NO2 is called nitrobenzene. It is a slightly yellowish poisonous liquid, with a characteristic odor. Its main use is in the manufacture of aniline.
Aniline (C6H5NH2). When nitrobenzene is heated with iron and hydrochloric acid the hydrogen evolved by the action of the iron upon the acid reduces the nitrobenzene in accordance with the following equation:
C6H5NO2 + 6H = C6H5NH2 + 2H2O.
The resulting compound is known as aniline, a liquid boiling at 182°. When first prepared it is colorless, but darkens on standing. Large quantities of it are used in the manufacture of the aniline or coal-tar dyes, which include many important compounds.
Carbolic acid (C6H5OH). This compound, sometimes known as phenol, occurs in coal tar, and is also prepared from benzene. It forms colorless crystals which are very soluble in water. It is strongly corrosive and very poisonous.
Naphthalene and anthracene. These are hydrocarbons occurring along with benzene in coal tar. They are white solids, insoluble in water. The well-known moth balls are made of naphthalene. Large quantities of naphthalene are used in the preparation of indigo, a dye formerly obtained from the indigo plant, but now largely prepared by laboratory methods. Similarly anthracene is used in the preparation of the dye alizarin, which was formerly obtained from the madder root.