Benzene, fundamental structures in organic chemistry.

frankjavier (54)in #steemstem • 7 years ago

Benzene

The term benzene is used to refer to an aromatic hydrocarbon that has six carbon atoms and has a ring structure. It is a flammable and colorless liquid that is used as a reagent and as a solvent. It should be remembered that a hydrocarbon is an organic compound that combines carbon and hydrogen atoms. Its molecular form, therefore, is based on the bonding of carbon atoms and hydrogen atoms in chains that can be branched or linear and closed or open. Benzene has six carbon atoms and six hydrogen atoms that make up a hexagon. At the vertices of this figure, the carbon atoms appear, with three simple bonds and three double bonds that are placed in alternate positions.

Source, Wikimedia Public Domain

History

The discoverer of benzene was the British chemist and physicist Michael Faraday (1791-1867), when he managed to isolate lighting gas in 1825 when the owners of the gas factory for the London lighting asked him to find a solution to the problem that during the winter, with the cold, the gas lost its ability to produce a flame. At that time, the gas for lighting was obtained from the fat of marine animals such as seals and stored in iron bottles. Faraday, who at that time was the director of the laboratory of the Royal Society of London, realized that with the cold the gas condensed and accumulated in the bottom of the bottles in the form of transparent and aromatic liquid. So it was that Faraday, whose effigy appeared on the 20-pound sterling banknotes, discovered a new hydrocarbon: benzene. Although currently the properties of benzene are best known among all organic compounds, its chemical structure was not determined until 1931. At the beginning of organic chemistry, chemists divided organic compounds into aromatic (fragrant) and aliphatic (fatty).

The German August Kekulé (1829-1896), Between 1857 and 1858 Friedrich August Kekulé, who at that time was 28-29 years old, developed a theory about organic chemical structure based on two notions: the tetravalence of carbon (carbon atoms have four electrons in their last layer, thus they can form four bonds with other atoms) and the ability of their atoms to form bonds between them.

This new theory on the structure of carbon atoms allowed better understanding of organic molecules and their reactions, facilitating research on chemical synthesis and the production of organic compounds after 1860. This caused that, years later, after Kekulé himself proposed a circular atomic structure of benzene, the mass production of carbon by-products and the appearance of plastics.

August Kekulé 1829-1896, Wikimedia Public Domain

Hoffmann, in 1845, found it in coal tar, which is still the main source of benzene and its derivatives. It was soon observed that benzene behaves like the compound from which a huge number of compounds derived, which had been isolated in nature or had been prepared in the laboratory, with the famous tar dyes. As we already pointed out, its molecular formula was known (C6H6), but the problem was in knowing how atoms were arranged in the structure. Later in 1865 he proposed to solve the problem of benzene, that these carbon chains can sometimes be closed forming rings.

Later, the American Linus Pauling (1901-1994) postulated the mesomerism or resonance of benzene: a tool that allows the representation of a molecular structure through the linear combination of theoretical structures that do not coincide with the real structures. A ton of coal transformed into coke in an oven produces about 7.6 liters of benzene.

Naturally, benzene is found in petroleum

Nowadays, large quantities of benzene are obtained from oil, either by extracting it directly from certain types of crude oil or by chemical treatment of it. It is one of the most widely used chemicals in the world. It is used for the manufacture of nylon, resins, plastics, lubricants, gums, detergents and dyes. Even benzene is used to produce pesticides and certain medications.

What happens to benzene when it enters the environment

Benzene is commonly found in the environment. The main sources of benzene in the environment are industrial processes. Benzene levels in the air can be increased by emissions generated by the combustion of coal and oil, operations involving waste or storage of benzene, automobile exhaust and evaporation of gasoline in service stations. Tobacco smoke is another source of benzene in the air, especially inside homes. Industrial discharges, the disposal of products containing benzene, and leakage of gasoline from underground tanks release benzene into water and soil. Benzene can pass into the air from the surface of water and soil. Once in the air, benzene reacts with other chemicals and degrades in a few days. Benzene in the air can be dragged to the ground by rain or snow. Benzene degrades more slowly in water and soil. Benzene is poorly soluble in water and can pass through the soil into groundwater. Benzene does not accumulate in plants or animals.