Nitrobenzene is an
organic compoundAn organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
with the
chemical formulaA chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
C
6H
5NO2Nitro compounds are organic compounds that contain one or more nitro functional groups . They are often highly explosive, especially when the compound contains more than one nitro group and is impure. The nitro group is one of the most common explosophores used globally...
. It is a water-insoluble pale yellow oil with an
almondThe almond , is a species of tree native to the Middle East and South Asia. Almond is also the name of the edible and widely cultivated seed of this tree...
-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale as a precursor to
anilineAniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...
. 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
solventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
, especially for electrophilic
reagentA reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
s.
Production
Nitrobenzene is prepared by
nitrationNitration is a general chemical process for the introduction of a nitro group into a chemical compound. The dominant application of nitration is for the production of nitrobenzene, the precursor to methylene diphenyl diisocyanate...
of benzene with a mixture of concentrated
sulfuric acidSulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
,
waterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, and
nitric acidNitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
. 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).
World capacity for nitrobenzene in 1985 was about 1.7×10
6 tonnes.
Mechanism of nitration
The reaction pathway entails formation of an adduct between the
Lewis acid]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
ic nitronium ion (NO
2+) 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
anilineAniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...
, which is a precursor to
rubberNatural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
chemicals,
pesticidePesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s,
dyeA dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s, explosives, and pharmaceuticals.
Specialized applications
Nitrobenzene is also used in shoe and floor polishes, leather dressings, paint
solventA solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s, and other materials to mask unpleasant odors. Redistilled, as oil of mirbane, nitrobenzene has been used as an inexpensive perfume for
soapIn chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...
s. A significant merchant market for nitrobenzene is its use in the production of the
analgesicAn analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....
paracetamolParacetamol INN , or acetaminophen USAN , is a widely used over-the-counter analgesic and antipyretic . It is commonly used for the relief of headaches and other minor aches and pains and is a major ingredient in numerous cold and flu remedies...
(also known as acetaminophen) (Mannsville 1991). Nitrobenzene is also used in Kerr cells, as it has an unusually large
Kerr constantThe Kerr effect, also called the quadratic electro-optic effect , is a change in the refractive index of a material in response to an applied electric field. The Kerr effect is distinct from the Pockels effect in that the induced index change is directly proportional to the square of the electric...
.
Organic reactions
Aside from its conversion to aniline, nitrobenzene is readily converted to related derivatives such as
azobenzeneAzobenzene is a chemical compound composed of two phenyl rings linked by a N=N double bond. It is the best known example of an azo compound. The term 'azobenzene' or simply 'azo' is often used to refer to a wide class of molecules that share the core azobenzene structure, with different chemical...
,
nitrosobenzeneNitrosobenzene is the organic compound with the formula C6H5NO. The compound can be viewed as hybrid of singlet O2 and azobenzene. This diamagnetic species exists in equilibrium with its dimer.-Preparation:...
, and
phenylhydroxylaminePhenylhydroxylamine is the organic compound with the formula C6H5NHOH. It is an intermediate in the redox-related pair C6H5NH2 and C6H5NO. Phenylhydroxylamine should not be confused with its isomer α-phenylhydroxylamine or O-phenylhydroxylamine, is C6H5ONH2.-Preparation and derivatives:This...
. The nitro- group is deactivating, thus substitution tends to occur at the
meta-position.
Safety
Nitrobenzene is highly toxic (
Threshold Limit ValueThe threshold limit value of a chemical substance is a level to which it is believed a worker can be exposed day after day for a working lifetime without adverse health effects. Strictly speaking, TLV is a reserved term of the American Conference of Governmental Industrial Hygienists...
5 mg/m
3) 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,
cyanosisCyanosis is the appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen. The onset of cyanosis is 2.5 g/dL of deoxyhemoglobin. The bluish color is more readily apparent in those with high hemoglobin counts than it is...
, 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, and is classified by the
IARCThe International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
as a
Group 2B carcinogen which is "possibly carcinogenic to humans". It has been shown to cause liver, kidney, and thyroid adenomas and carcinomas in rats.
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