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Nitrobenzene
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Nitrobenzene, also known as nitrobenzol or oil of mirbane, is an organic compound with the chemical formula C6H5NO2. Nitrobenzene is a water-insoluble oil which exhibits a pale yellow to yellow-brown coloration in liquid form (at room temperature and pressure) with an almond-like odor. When frozen it appears as a greenish-yellow crystal. Although occasionally used as a flavoring or perfume additive, nitrobenzene is highly toxic in large quantities and is mainly produced as a precursor to aniline.
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Encyclopedia
Nitrobenzene, also known as nitrobenzol or oil of mirbane, is an organic compound with the chemical formula C6H5NO2. Nitrobenzene is a water-insoluble oil which exhibits a pale yellow to yellow-brown coloration in liquid form (at room temperature and pressure) with an almond-like odor. When frozen it appears as a greenish-yellow crystal. Although occasionally used as a flavoring or perfume additive, nitrobenzene is highly toxic in large quantities and is mainly produced as a precursor to aniline. In the laboratory it finds occasional use as a solvent, especially for electrophilic reagents.
Production
Nitrobenzene is prepared by nitration of benzene with a mixture of concentrated sulfuric acid, water, and nitric acid, called "mixed acid." Its production is one of the most dangerous processes conducted in the chemical industry due to the exothermicity of the reaction (?H = -117 kJ/mol).
There were four producers of nitrobenzene in the United States in 1991: First Chemicals Corporation, Mobay, DuPont Chemicals, and Rubicon Inc. World capacity for nitrobenzene in 1985 was ca. 1.7×106 tonnes.
Mechanism of nitration
The reaction pathway entails formation of an adduct between the Lewis acidic nitronium ion, NO2+, and benzene. The nitronium ion is generated in situ via the reaction of nitric acid and an acidic dehydration agent, typically sulfuric acid:
- HNO3 + H+ NO2+ + H2O
Uses
Approximately 95% of nitrobenzene is consumed in the production of aniline.
Specialized applications
More specialized applications include the use of nitrobenzene as a precursor to rubber chemicals, pesticides, dyes, and pharmaceuticals. Nitrobenzene is also used in shoe and floor polishes, leather dressings, paint solvents, and other materials to mask unpleasant odors. Redistilled, as oil of mirbane, nitrobenzene has been used as an inexpensive perfume for soaps. A significant merchant market for nitrobenzene is its use in the production of the analgesic paracetamol (also known as acetaminophen) (Mannsville 1991). Nitrobenzene is also used in Kerr cells, as it has an unusually large Kerr constant.
Organic reactions
Aside from its conversion to aniline, nitrobenzene is readily converted to related derivatives such as azobenzene, nitrosobenzene, and phenylhydroxylamine. The nitro- group is deactivating, thus substitution tends to occur at the meta-position.
Safety
Nitrobenzene is highly toxic (TLV 5 mg/m3) and readily absorbed through the skin.
Although nitrobenzene is not currently known to be a carcinogen, 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.
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