Aromatic hydrocarbons (also called arenes) are organic bio compounds whose molecules contain one or more cycles with six Carbon atoms. The benzene ring is characterized by special physical and chemical properties. The name "arena" entered organic and general chemistry in the late 18th - early 19th century. These included substances that consisted of two chemical compounds - Carbon and Hydrogen and had a pleasant smell (resins, balms, essential oils, frankincense). Over time, the name "aromatic hydrocarbons" has lost its meaning, since aromatic substances were found among other classes of organic substances, and most aromatic compounds have an unpleasant or specific smell. For the first time, benzene was isolated at the beginning of the 19th century from light gas. A little later (1845) A.F. Hoffmann releases aromatic hydrocarbons (benzene) from coal tar. Nowadays, the class of arenes (according to the IUPAC classification) combines compounds based on benzene nuclei. So, such compounds are divided into single and multi-core arenas, as well as to aromatic hydrocarbons with condensed nuclei.
Mononuclear arenas are organic compounds that contain one benzene ring. The structure of the benzene molecule, a typical representative of the arenes, is most often demonstrated by the Kekule formula in the form of a cycle of six Carbon atoms, which are alternately connected by simple C — C and double C = C bonds. This structure is confirmed by the data of modern physicochemical analysis.
The main ideas of Kekule about the structure of benzene are as follows: 1) benzene has the structure of a hexagonal ring; 2) in the benzene ring there are three simple and three double bonds; 3) all six Carbon atoms in the benzene ring are equivalent to each other. The formula displays the elemental composition of benzene, the ratio of Carbon and Hydrogen atoms in the molecule, the absence of isomers for monosubstituted benzene derivatives.
Aromatic hydrocarbons are quite common in nature. They are an integral part of coal tar, which is obtained after dry distillation of coal. Arenas are part of many varieties of oil and other natural products (resins, balms, etc.). In the process of dry distillation of coal, on average, about three percent of coal tar or coal tar is obtained. And from fractional distillation of coal tar, a number of fractions are obtained: light oil (contains xylene, toluene, benzene, thiophene), carbolic oil (contains cresols, phenols and naphthalene), creosote oil (contains naphthalene), anthracene oil (contains phenanthrene, anthracene and other higher arenas) and pitch used for paving roads and as building material.
The use of aromatic hydrocarbons. Benzene is characterized by a specific odor, practically insoluble in water. It is a good solvent for organic bio compounds. Synthesized from coal tar. Benzene is a valuable raw material for the production of dyes, medicines, explosives, plant growth stimulants, herbicides, insecticides, etc.
Toluene is highly soluble in organic solvents. Obtained from coal tar, as well as from certain grades of oil. Benzene alcohol, benzaldehyde, benzoic acid, dyes, medicines, saccharin, and trinitrotoluene are synthesized from toluene.
Xylene are good organic solvents. Obtained from coal oil, as well as by fractional distillation of coal tar. From xylene, phthalic anhydride, xylene, and artificial lavsan are synthesized. Xylene is sometimes added to gasoline.