Benzene is a colorless, fragrant, volatile liquid that burns with a yellow flame with soot and is used in the industrial production of a group of materials such as polystyrene, synthetic rubber, and nylon. This liquid is also used in the preparation of detergents and dyes.
Benzene belongs to the family of hydrocarbons, each molecule of which has 6 carbon atoms and 6 hydrogen atoms, which form a cyclic arrangement. This arrangement is called the benzene ring, which is also present in many compounds, including aspirin and the explosive trinitrotoluene. Benzene is toxic and carcinogenic.
Adding gasoline to gasoline increases the octane number of gasoline and reduces the chance of engine crash. For this reason, until the 1950s, most gasoline contained several percent benzene, but then tetraethyl lead became more common than benzene. The obsolescence of leaded gasoline has led to the return of benzene to the gasoline of some countries, but due to the negative effects of this article on health, strict regulations have been imposed on the amount of gasoline, which is usually limited to less than one percent.
History Benzene was discovered by Michael Faraday in 1825. Faraday first isolated benzene from a glowing compressed gas made from pyrolysis of whale oil, and called it hydrogen bicarbonate for the first time. Then, in 1834, a man named Ail Hart Miterlish synthesized benzene by heating benzoic acid with calcium oxide, and by measuring its vapor density, it showed that benzene had the molecular formula C6H6. In the past, benzene was obtained by heating coal tar and then converting its vapor into liquid, but today benzene is extracted in large quantities from crude oil.
molecular structure According to the molecular formula of benzene, different structures are imagined for this molecule. Organic chemists in the nineteenth century made various speculations about the structure of this molecule, some of which were rejected due to the number of isomeric products derived from benzene, and others accepted until the original structure of benzene by Friedrich August Kokole in 1865. AD was identified.
According to the cochlear description, benzene is a ring molecule in which six carbon atoms form a regular hexagonal structure, each attached to a hydrogen atom. He stated that covalent bonds between carbon atoms are one-way, simple, and dual. Of course, he believed that the place of simple and double bonds changes quickly, and this makes the length of carbon-carbon bonds the same. (In fact, he described for benzene something similar to the modern concept of resonance).
Orbital description Based on the orbital description of quantum mechanics, each carbon can be considered to have sp2 hybridization, with each of these orbitals used to form a covalent bond of the sigma with the hydrogen atom and two neighboring carbon atoms. Finally, a p-orbital remains perpendicular to the plane of the molecule, capable of laterally overlapping with similar orbitals on adjacent carbon; Therefore, the electron cloud of Pie (∏) is formed by the overlap of six p orbitals on the base of six ring carbon atoms.
Attributes The colorless, fragrant, and perhaps fragrant liquid evaporates quickly and is extremely flammable. It is found in plastics, resins, nylon, lubricating oils, paints, detergents, pesticides, and more.
Benzene derivatives All benzene derivatives can be considered as aromatic organic substances.
The permissible amount of benzene in gasoline Equivalent to the standard 228 EN and 1319 ASTM D, the maximum permissible amount of benzene in gasoline is 1% by volume. For 2011, the United States has reduced the permitted level of benzene in gasoline to 62.0%. In Iran, although the amount of benzene in gasoline has been reduced with the use of Euro 4 gasoline, but there is a difference between the responsible organizations regarding the observance of the standard limit.
The European standard for airborne benzene pollutants is 5 mg / m3 (PPB) and in Japan it is 3 mg / m3, while in the five polluted areas of Tehran the highest airborne benzene is 150 mg / m3 and the lowest is 50 mg / m3. Is a cube; Therefore, the amount of benzene in the air of the capital of Iran in the late 1380s has been at least more than 12 times the international standards and sometimes at the time of air pollution has reached 300 PPB and in some areas 1000 PPB. With the distribution of Euro 4 gasoline in metropolitan areas, in the middle of the 1390s, the amount of gasoline has reached 30 PPB.
Dangers of benzene Benzene is known to be a carcinogenic compound. All work procedures including benzene should be done under the hood and laboratory gloves should be used. Benzene has been used as a common solvent in laboratories in the past, but after scientists discovered its carcinogenic identity, its use as a solvent was severely curtailed and similar solvents such as acetone and acetone were used.
Prolonged exposure to benzene has destructive effects on the tissues that make up blood cells, especially bone marrow cells. Complications of chronic exposure to benzene, decreased body hematopoiesis, impaired immune system as well as leukemia, leukemia, respiratory disorders, chronic amnesia, delayed ossification of the human fetus, damage to the human reproductive system, infertility, production of glandular tumors Lymphatic and liver damage. Several institutes, including the World Cancer Research Association, the American Environmental Protection Agency, and the US Department of Health and Human Services, have identified benzene as the cause of leukemia. The latent period of leukemia typically occurs 5 to 15 years after the first contact.