Benzene is a liquid organic compound with a characteristic aromatic odor. The compound with the molecular formula C6H6 is an aromatic hydrocarbon and the simplest and at the same time classic example of the aromaticity of certain compounds. Benzene is miscible with almost all organic solvents, but hardly with water.
Benzene is used in the production of important industrial chemicals such as ethylbenzene, cumene, cyclohexane and nitrobenzene.
Benzene is contained in motor gasoline. In Germany and the EU, according to EN 228, only a maximum of one percent is permitted, as is the case in the USA.
Occurrence and emissions
Smaller amounts of benzene are found in petroleum. When cigarettes are smoked, small amounts of benzene vapour (10-100 µg per cigarette) are released. In the atmosphere, after two to five days, half of the benzene present is broken down because it reacts with hydroxyl radicals (free OH groups). Benzene is mainly released by exhaust gases from petrol engines. 75 percent of emissions are caused by motor vehicles.
Due to the serious dangers, benzene and preparations containing benzene may not be placed on the market in Germany with more than 0.1 percent. Larger quantities may only be used in closed systems and for industrial or research purposes.
Benzene increases the knock resistance of petrol, which is why it plays an important role in the development of petrol.
In the past, benzene was used as a good solvent and cleaning agent in many areas. As a solvent for waxes, resins and oils, benzene is increasingly being replaced by less toxic substances such as non-carcinogenic toluene.
Benzene vapours are toxic when inhaled. Slight poisoning results in dizziness, nausea, drowsiness and apathy. Severe poisoning can lead to fever, visual disturbances, temporary blindness and unconsciousness. Benzene addiction, which can occur when benzene is inhaled, leads to feelings of drunkenness and euphoria. Benzene can lead to death if it is exposed to the organism for a long time.
The toxic effect as well as the carcinogenic effect can be attributed to the formation of a carcinogenic metabolite. In the body, benzene is oxidized enzymatically on the ring. The resulting highly reactive epoxide (arene oxide) reacts with numerous biological compounds and can also damage the genetic material. Long-term absorption of small amounts of benzene leads above all to damage to the internal organs and the bone marrow. The latter results in a decrease in the number of red blood cells (anemia), which manifests itself in palpitations, flickering eyes, fatigue, dizziness, pallor and headaches. Benzene is stored in the brain, bone marrow and fatty tissue. It is excreted slowly through the kidneys.