Nitrobenzene (Properties, Uses)

Nitrobenzene has the molecular formula C6H5NO2 and is a yellowish, sticky, aromatic nitro-compound. It is a pale-yellow oil with an almond-like odor that is water-insoluble. It freezes to make the crystals greenish-yellow. For the production of aniline, which is an important industrial precursor, the most important application of nitrobenzene (consuming 95 percent). Nitrobenzene with the odor of bitter almonds is a colorless to light yellow, sticky, highly toxic liquid. It was first prepared in 1834 by Eilhardt Mitscherlich, a German chemist, who treated benzene with smoky nitric acid. It is made from benzene as a precursor to aniline on a large scale. It is sometimes used in the laboratory as a solvent, especially for electrophilic reagents.

Nitrobenzene is an industrial chemical; it is an almond-like sticky yellow liquid with an odor. It is only partially dissolved in water (1.9 g/l at 20°C) and evaporates into the air. It is manufactured for use in industry in large quantities. Nitrobenzene is prepared with a mixture of concentrated sulfuric acid, water, and nitric acid by benzene nitration. This mixture is often referred to as “mixed acid.” Due to the exothermicity of the reaction (ΔH = −117 kJ/mol), the processing of nitrobenzene is one of the most hazardous processes performed in the chemical industry. It has an explosive threshold of 1.8% in air volume, representing a fire threat.

Nitrobenzene

To produce a chemical called aniline, much of the nitrobenzene manufactured in the United States is used. Lubricating oils such as those used in engines and machinery are also made using nitrobenzene. In the manufacture of dyes, medicines, pesticides, and synthetic rubber, a limited amount of nitrobenzene is used. In 1985, the world’s nitrobenzene potential was around 1.7 to 106 tonnes. The method of nitration involves the formation of the nitronium ion (NO2+), followed by its electrophilic aromatic replacement reaction with benzene. The nitronium ion is formed by a nitric acid reaction and by an acid dehydration agent, usually sulfuric acid:

HNO3 + H+ NO2+ + H2O

Nitrobenzene can also be used to produce associated derivatives such as azobenzene, nitrosobenzene and phenylhydroxylamine in addition to aniline. In addition, it can be used to produce lubricating oils, colorants, medicines, pesticides and synthetic rubber. Masking harmful odors emitting from shoes, floor polisher, and leather as well as paint solvents is another special application of this. In the processing of aniline, approximately 95% of nitrobenzene is consumed:

C6H5NO2 + 3 H2 → C6H5NH2 + 2 H2O

Furthermore, it can sometimes be used as a solvent, especially for laboratory electrophilic reagents. Nitrobenzene undergoes much slower nitration, halogenation, and sulfonation than benzene does. It appears as a liquid that is light yellow to dark brown, and its flash point is 190°F. Quite slightly soluble in water; toxic to the skin by inhalation and absorption; combustion creates toxic nitrogen oxides. As a flavoring agent for soaps and as a solvent for shoe dyes, small quantities of nitrobenzene are used. In the organic synthesis of colorants, pesticides and synthetic solvents, dinitrobenzene isomers (1, 2-, 1, 3-, and 1, 4-) are used. Chemicals used in the manufacture of explosives are 1,3-Dinitrobenzene and 1,3,5-trinitrobenzene.

In the processing of lubricating oils, dyes, medicines, pesticides, and synthetic rubber, nitrobenzene is also used. Nitrobenzene exposure irritates the skin, eyes and respiratory tract and can lead to fatigue, dyspnea, dizziness, disturbed vision, shortness of breath, collapse and even death due to methemoglobinemia. The liver, spleen, kidneys and central nervous system are also damaged by nitrobenzene. This material is a potential mutagen and is fairly expected to be a carcinogen in humans. In Kerr cells, nitrobenzene is also used, since it has an extremely broad Kerr constant. Evidence suggests its use as a plant growth/flowering stimulant in farming.

Nitrobenzene is an organic compound that has been used as a standard for identification and analysis as well as environmental removal. The cytotoxic effects of the compound have been studied in cell lines of hepatocarcinoma. Nitrobenzene can be selectively reduced to azoxybenzene, azobenzene, nitrosobenzene, hydrazobenzene, and phenylhydroxylamine in addition to its conversion to aniline. In reactions like the Skraup quinoline synthesis, it has been used as a mild oxidant. Nitrobenzene is produced commercially in the presence of a sulfuric acid catalyst at 50 to 65°C by exothermic nitration of benzene with smoked nitric acid. To remove residual acid, the crude nitrobenzene is passed through washer-separators and is then purified to remove benzene and water.

Nitrobenzene metabolism in mammals requires both oxidation and reduction reactions. Evidence for this comes from the discovery of possible nitrobenzene oxidation products and the reduction of urinary reactions in humans and animals exposed to the compound. The conversion of hemoglobin to methemoglobin is influenced by nitrobenzene. Around 30 percent of it is metabolized to aminophenols and nitrophenols, which are excreted.

Information Sources:

  1. chemicalbook.com
  2. pubchem.ncbi.nlm.nih.gov
  3. wikipedia