Nitrobenzene


 * Nitrobenzene ** is an [|organic compound] with the [|chemical formula] [|C6H5][|NO2] . It is a water-insoluble pale yellow oil with an [|almond] -like odor. It freezes to give greenish-yellow crystals. 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], especially for [|electrophilic] [|reagents].

Production
Nitrobenzene is prepared by [|nitration] of benzene with a mixture of concentrated [|sulfuric acid], [|water] , and [|nitric acid]. This mixture is sometimes called "mixed acid." The production of nitrobenzene is one of the more dangerous processes conducted in the chemical industry because of the exothermicity of the reaction (Δ//H// = −117 kJ/mol). [|[1]] World capacity for nitrobenzene in 1985 was about 1.7×106 [|tonnes]. [|[1]]

Mechanism of nitration
Main article: [|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 by 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], [|[1]] which is a precursor to [|rubber] chemicals, [|pesticides] , [|dyes] , [|explosives] , and [|pharmaceuticals].

Specialized applications
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). [|[2]] 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], [|[3]] [|nitrosobenzene] , [|[4]] and [|phenylhydroxylamine]. [|[5]] The nitro- group is deactivating, thus substitution tends to occur at the //meta//-position.

Safety
Nitrobenzene is highly toxic ( [|Threshold Limit Value] 5 mg/m3) and readily absorbed through the skin. 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, [|[6]] and is classified by the [|IARC] as a [|Group 2B carcinogen] which is "possibly carcinogenic to humans". [|[7]] It has been shown to cause liver, kidney, and thyroid adenomas and carcinomas in rats. [|[8]]