Lexikon

a colorless liquid with a sweet odor. It belongs to hydrocarbons, the simplest representative of aromatics with chemical formula of C₆H₆. Its boiling temperature is 80,5 °C, melting temperature 6 °C, specific gravity 0.880 g/cm³ at 20 °C. It evaporates into the air very quickly and dissolves slightly in water. It is highly flammable and is formed from both natural processes and human activities. Natural sources of benzene include emissions from volcanoes and forest fires. benzene is also a natural part of crude oil, gasoline, and cigarette smoke.benzene is widely used to make other chemicals which are applied to make plastics, resins, and nylon and other synthetic fibers. benzene is also used to make some types of rubbers, lubricants, dyes, detergents, drugs, and pesticides. It breaks down slowly in water and soil, and can pass through the soil into underground water. benzene does not build up in plants or animals. Breathing very high levels of benzene can result in death, while high levels can cause drowsiness, dizziness, rapid heart rate, headaches, tremors, confusion, and unconsciousness. Eating or drinking foods containing high levels of benzene can cause vomiting, irritation of the stomach, dizziness, sleepiness, convulsions, rapid heart rate, and death. The major effect of benzene from long-term exposure is on the blood. benzene causes harmful effects on the bone marrow and can cause a decrease in red blood cells leading to anemia. It can also cause excessive bleeding and can affect the immune system, increasing the chance for infection. Long-term exposure to high levels of benzene in the air can cause leukemia, particularly acute myelogenous leukemia, often referred to as AML. This is a cancer of the bloodforming organs. The Department of Health and Human Services (DHHS) in the USA has determined that benzene is a known carcinogen. The International Agency for Research on Cancer (IARC) and the EPA have determined that benzene is carcinogenic to humans. (Source: Agency for Toxic Substances and Deseas Registry, ATSDR, www.atsdr.cdc.gov)

benzene, or benzol, is an aromatic ring with the molecular formula C₆H₆. benzene is a colorless and flammable liquid with a strong smell and a relatively high melting point. Because it is a known carcinogen, its use as in gasoline is now limited, but it is an important industrialsolvent and precursor in the production of drugs and plastics. benzene is a natural constituent of mineral oil.

Alkylbenzenes are organic compounds that has an alkyl group bound to a benzene ring. Two well known alkylbenzenes are methylbenzene and toluene, both are colorless flammable liquids obtained from petroleum or coal tar, used as a solvent for gums and lacquers and in high-octane fuels. See also BTEX.

chlorobenzenes are a group of cyclic aromatic compounds in which one or more hydrogen atoms of the benzene ring have been replaced by a chlorine atom. The generic molecular formula is C₆H_6–nCl_n, where n = 1–6. There are 12 different chlorinated benzenes: monochlorobenzene (MCB), dichlorobenzene (DCB) (three isomers), trichlorobenzene (TCB) (three isomers), tetrachlorobenzene (TeCB) (three isomers), pentachlorobenzene (PeCB), and hexachlorobenzene. MCB, 1,2-DCB, 1,3-DCB, and 1,2,4-TCB are colourless liquids, while all other congeners are white crystalline solids at room temperature. The solubility of chlorobenzenes in water is low (decreasing with increasing chlorination), flammability is low, the octanol/water partition coefficients are moderate to high (increasing with increasing chlorination), and vapour pressures are low to moderate (decreasing with increasing chlorination).
They are used mainly as intermediates in the synthesis of pesticides and other chemicals; 1,4-dichlorobenzene is used in space deodorants and as a moth repellent. The higher chlorinated benzenes have been used as components of dielectric fluids.
Clorobenzenes other than hexachlorobenzene have low or moderate toxicity to human, and the risk of chlorinated benzenes causing harm to aquatic and terrestrial organisms is considered to be low too.
Their physicochemical properties suggest that chlorobenzenes released to the environment are likely to be volatilized to the atmosphere. The Henry’s law constants measured for chlorobenzenes suggest that they are readily volatilized, especially from aquatic systems with long residence times, such as large lakes and oceans. However, chlorobenzenes released to water may also be adsorbed onto sediment, especially if it is rich in organic matter. Volatilization from soil is also likely, although, depending on the characteristics of the soil, there may also be sorption to soil. The most important factor affecting the behaviour and fate of chlorobenzenes in soil is sorption. adsorption–desorption processes in soil affect the rate of volatilization and leaching and the availability of chemicals to microbial and chemical degradation or uptake by plants or other organisms. The soil sorption coefficients for chlorobenzenes range from 466 to 58 700 and generally increase with increasing chlorination. sorption of chlorobenzenes to soil is affected by many parameters, and it increases with increasing organic matter content.
chlorobenzenes in soil, sediment, and sewage sludge can be degraded by microorganisms. The major mechanism of aerobic degradation is via oxidative dechlorination, usually initiated by dioxygenative hydroxylation, leading to the formation of hydroxylated aromatic compounds (mainly catechols), which undergo ring fission and subsequent mineralization to carbon dioxide and water. The less chlorinated benzenes are more readily degraded than the higher chlorinated ones. biodegradation under anerobic conditions has also been reported, although this occurs at a slower rate than aerobic biodegradation.
They are accumulated by water and terrestrial organisms, mainly in the fat tissue or in the liver of higher organisms.

nitrobenzene is a water-insoluble pale yellow oil with an almond-like odor. It is produced on a large scale as a precursor to aniline. Although occasionally used as a flavoring or perfume additive, nitrobenzene is highly toxic in large quantities. In the laboratory, it is occasionally used as a solvent.

Nitrobenzene is highly toxic, mainly for blood cells and kidney, as well as for the brain. It is readily absorbed through the lung and

The summary of the UK Health Protection Agency says:

Fire hazard:

• Flammable
• Violently reacts with strong oxidants, acids and nitrogen oxides
• Emits toxic fumes of nitrogen oxides when heated to decomposition
• In the event of a fire involving nitrobenzene, use fine water and liquid tight chemical protective clothing with breathing apparatus

Health hazard:

• Toxic by inhalation, ingestion and skin absorption
• Possibly carcinogenic in humans
• May cause reproductive toxicity
• The onset of symptoms may be delayed 1-4 hours after exposure to nitrobenzene
• Inhalation can cause irritation of the respiratory tract, nausea, headache, dizziness, shortness of breath and in extreme cases could lead to coma and death
• Ingestion of nitrobenzene may cause gastrointestinal irritation with nausea, vomiting and diarrhoea, as well as symptoms similar to those for inhalation
• Inhalation and ingestion may also cause vertigo and bluish colouration of the skin due to a condition called methaemoglobinaemia, with drowsiness, high blood pressure, convulsions, anaemia, jaundice and kidney failure
• Skin contact with nitrobenzene may result in mild skin irritation and eye contact may lead to mild eye irritation

Environmental hazard::

• Dangerous for the environment
• Inform Environment Agency of substantial incidents

Prolonged exposure may cause serious damage to the central nervous system, impair vision, cause liver or kidney damage, anemia and lung irritation. Inhalation of fumes may induce headache, nausea, fatigue, dizziness, cyanosis, weakness in the arms and legs, and in rare cases may be fatal. The oil is readily absorbed through the skin and may increase heart rate, cause convulsions or rarely death. Ingestion may similarly cause headaches, dizziness, nausea, vomiting and gastrointestinal irritation, loss of limbs and also causes internal bleeding.

Nitrobenzene is considered a likely human carcinogen by the United States Environmental Protection Agency too.

Sources and further information:

http://whqlibdoc.who.int/ehc/WHO_EHC_230.pdf

http://www.hpa.org.uk/Topics/ChemicalsAndPoisons/CompendiumOfChemicalHazards/Nitrobenzene/

http://en.wikipedia.org/wiki/Nitrobenzene