Aniline, phenylamine or aminobenzene is an organic compound An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic. The distinction between "organic" and " with the formula A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound C₆H₅NH₂. Consisting of a phenyl group Benzene, or benzol, is an organic chemical compound with the molecular formula C6H6. It is sometimes abbreviated Ph–H. Benzene is a colorless and highly flammable liquid with a sweet smell and a relatively high melting point. Because it is a known carcinogen, its use as an additive in gasoline is now limited, but it is an important industrial attached to an amino group Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines, trimethylamine and aniline; see Category:Amines for, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane A polyurethane is any polymer consisting of a chain of organic units joined by urethane (carbamate) links. Polyurethane polymers are formed through step-growth polymerization by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two hydroxyl (alcohol) groups in the presence of a. Like most volatile amines, it possesses the somewhat unpleasant odour of rotten fish. It ignites readily, burning with a smoky flame characteristic of aromatic compounds. Aniline is colorless, but it slowly oxidizes Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. In organic chemistry oxidations and reductions are different from ordinary redox reactions because many reactions carry the name but do not actually involve electron transfer in the electrochemical sense of the word and resinifies in air, giving a red-brown tint to aged samples.

Production

Aniline is mainly produced in industry in two steps from benzene Benzene is an organic chemical compound with the molecular formula C6H6. It is sometimes abbreviated Ph–H. Benzene is a colorless and highly flammable liquid with a sweet smell and a relatively high melting point. Because it is a known carcinogen, its use as an additive in gasoline is now limited, but it is an important industrial solvent and. First, benzene is nitrated Nitration is a general chemical process for the introduction of a nitro group into a chemical compound. Examples of nitrations are the conversion of glycerin to nitroglycerin and the conversion of toluene to trinitrotoluene. Both of these conversions use nitric acid and sulfuric acid using a concentrated mixture of nitric 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 nitric acid. Fuming nitric acid is characterized as white fuming nitric acid and red fuming nitric acid, depending on the amount of nitrogen dioxide present and sulfuric acid Sulfuric acid is a strong mineral acid with the molecular formula H2SO4(aq). It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion. Principal uses include lead-acid at 50 to 60 °C, which gives nitrobenzene Nitrobenzene is an organic compound with the chemical formula C6H5N . In the second step, the nitrobenzene is hydrogenated Hydrogenation, a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, generally an, typically at 200-300 °C in presence of various metal catalysts Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive:

C₆H₅NO₂ + 3 H₂ → C₆H₅NH₂ + 2 H₂O

Originally, the reduction was effected with a mixture of ferrous chloride and iron metal via the Bechamp reduction.

As an alternative, aniline is also prepared from phenol Phenol, also known as carbolic acid, is an organic compound with the chemical formula C6H5OH. It is a white, crystalline solid. This functional group consists of a phenyl, bonded to a hydroxyl . It is produced on a large scale (about 7 billion kg/year) as a precursor to many materials and useful compounds. It is a mildly acidic compound that and ammonia, the phenol being derived from the cumene process Cumene process is an industrial process for developing phenol and acetone from benzene and propylene. The term stems from cumene , the intermediate material during the process.^[2]

In commerce, three brands of aniline are distinguished: aniline oil for blue, which is pure aniline; aniline oil for red, a mixture of equimolecular quantities of aniline and ortho- and para-toluidines; and aniline oil for safranine, which contains aniline and ortho-toluidine There are three isomers of toluidine, which are organic compounds. These isomers are o-toluidine, m-toluidine, and p-toluidine. The o- stands for ortho- , m- stands for meta- , and p- stands for para- . All three are aryl amines whose chemical structures are similar to aniline except that a methyl group is substituted onto the aromatic ring. The, and is obtained from the distillate Distillation is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction (échappés) of the fuchsine Fuchsine or rosaniline hydrochloride is a magenta dye with chemical formula C20H19N3·HCl. There are other similar chemical formulations of products sold as fuchsine, and several dozen other synonyms of this molecule fusion.^{[citation needed]}

Related aniline derivatives

Many derivatives of aniline can be prepared in similar fashion from nitrated aromatic compounds. Nitration followed by reduction of toluene Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. Chemically it is a mono-substituted benzene derivative, i.e. one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3 affords toluidines There are three isomers of toluidine, which are organic compounds. These isomers are o-toluidine, m-toluidine, and p-toluidine. The o- stands for ortho- , m- stands for meta- , and p- stands for para- . All three are aryl amines whose chemical structures are similar to aniline except that a methyl group is substituted onto the aromatic ring. The. Nitration of chlorobenzene and related derivatives gives aniline derivatives, e.g. 4-chloroaniline.

Reactions

The chemistry of aniline is extremely rich because the compound has been cheaply available for many years. Below are some classes of its reactions.

Oxidation

The oxidation of aniline has been heavily investigated, and can result in reactions localized at nitrogen or more commonly results in the formation of new C-N bonds. In alkaline solution, azobenzene Azobenzene is a chemical compound composed of two phenyl rings linked by a N=N double bond. 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 functional groups extending from the phenyl rings. These compounds should be formally referred to as ' results, whereas arsenic acid Arsenic acid is the chemical compound with the formula H3AsO4. More descriptively written as AsO3, this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic acid as such has not been isolated, but only found in solution where it is largely ionized. Its hemihydrate form (H3AsO4·½H2 produces the violet-coloring matter violaniline. Chromic acid Chromic acid generally refers to a collection of compounds generated by the acidification of solutions containing chromate and dichromate anions or the dissolving of chromium trioxide in sulfuric acid. Often the species are assigned the formulas H2CrO4 and H2Cr2O7. The anhydride of these "chromic acids" is chromium trioxide, also called converts it into quinone Benzoquinone, sometimes referred to simply as "quinone", is one of the two isomers of cyclohexadienedione. These compounds have the molecular formula C6H4O2. Orthobenzoquinone is the 1,2-dione, whereas parabenzoquinone is the 1,4-dione. Orthobenzoquinone is the oxidized form of catechol , while parabenzoquinone is the oxidized form of, whereas chlorates, in the presence of certain metallic salts (especially of vanadium Vanadium is the chemical element with the symbol V and atomic number 23. It is a soft, silvery gray, ductile transition metal. The formation of an oxide layer stabilizes the metal against oxidation. Andrés Manuel del Río discovered vanadium in 1801 by analyzing the mineral vanadinite, and named it erythronium. Four years later, however, he was), give "aniline black". Hydrochloric acid and potassium chlorate give chloranil. Potassium permanganate Potassium permanganate is the inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4– ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intense purple solutions, the evaporation of which gives prismatic purplish-black glistening in neutral solution oxidizes it to nitrobenzene Nitrobenzene is an organic compound with the chemical formula C6H5N , in alkaline solution to azobenzene Azobenzene is a chemical compound composed of two phenyl rings linked by a N=N double bond. 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 functional groups extending from the phenyl rings. These compounds should be formally referred to as ', ammonia and oxalic acid Oxalic acid is the chemical compound with the formula that can be written in a number of equivalent ways, C2O4H2, C2O22, and as HOOCCOOH. This colourless solid is a dicarboxylic acid. In terms of acid strength, it is about 3,000 times stronger than acetic acid. Its conjugate base, known as oxalate (C2O42-), is a reducing agent as well as a, in acid solution to aniline black. Hypochlorous acid Hypochlorous acid is a weak acid with the chemical formula HClO. In the swimming pool industry, hypochlorous acid is referred to as HOCl. It forms when chlorine dissolves in water. It cannot be isolated in pure form due to rapid equilibration with its precursor . HClO is used as a bleach, an oxidizer, a deodorant, and a disinfectant gives 4-aminophenol 4-Aminophenol is the organic compound with the formula H2NC6H4OH. Typically available as a white powder, it is commonly used as a developer in black and white film, marketed under the name Rodinal and para-amino diphenylamine Diphenylamine is the organic compound with the formula 2NH. It is a colourless solid, but samples are often yellow due to oxidized impurities. Oxidation with persulfate affords a variety of polyanilines Polyaniline is a conducting polymer of the semi-flexible rod polymer family. Although it was discovered over 150 years ago, only recently has polyaniline captured the attention of the scientific community due to the discovery of its high electrical conductivity. Amongst the family of conducting polymers and organic semiconductors, polyaniline is compounds. These polymers exhibit rich redox and acid-base properties.

Electrophilic reactions at carbon

Like phenols Phenol, also known as carbolic acid, is an organic compound with the chemical formula C6H5OH. It is a white, crystalline solid. This functional group consists of a phenyl, bonded to a hydroxyl . It is produced on a large scale (about 7 billion kg/year) as a precursor to many materials and useful compounds. It is a mildly acidic compound that, aniline derivatives are highly susceptible to electrophilic substitution reactions. Its high reactivity reflects that it is an enamine An enamine is an unsaturated compound derived by the reaction of an aldehyde or ketone with a secondary amine followed by loss of H2O, which enhances the electron-donating ability of the ring. For example, reaction of aniline with sulfuric acid Sulfuric acid is a strong mineral acid with the molecular formula H2SO4(aq). It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion. Principal uses include lead-acid at 180 °C produces sulfanilic acid, H₂NC₆H₄SO₃H, which can be converted to sulfanilamide Sulfanilamide is a sulfonamide antibacterial. Chemically, it is a molecule containing the sulfonamide functional group attached to an aniline. As an antibiotic, it functions by competitively inhibiting enzymatic reactions involving para-aminobenzoic acid (PABA). PABA is needed in enzymatic reactions that produce folic acid which acts as a coenzyme. Sulfanilamide is one of the sulfa drugs Sulfonamide is the basis of several groups of drugs. The original antibacterial sulfonamides are synthetic antimicrobial agents that contain the sulfonamide group. Some sulfonamides are also devoid of antibacterial activity, e.g., the anticonvulsant sultiame. The sulfonylureas and thiazide diuretics are newer drug groups based on the antibacterial, which were widely used as antibacterials Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction. Antiseptics are generally distinguished from antibiotics by the latter's ability to be transported through the lymphatic system to destroy bacteria within the body, and from disinfectants, which destroy in the early 20th century. The largest scale industrial reaction of aniline involves its alkylation with formaldehyde Formaldehyde is an organic compound with the formula CH2O. As the simplest aldehyde, it is an important precursor to many other chemical compounds, especially for polymers. In 2005, annual world production of formaldehyde was estimated to be 21 million tonnes (46 billion pounds). In view of its widespread use, toxicity and volatility, exposure to:

2 C₆H₅NH₂ + CH₂O → CH₂(C₆H₄NH₂)₂ + H₂O

The resulting diamine is the precursor to 4,4'-MDI and related diisocyanates.

Reactions at nitrogen

Basicity

Aniline is a weak base In chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. Bases are also the oxides or hydroxides of metals. A soluble base is also often referred to as an alkali if hydroxide ions are involved. This refers to the Brønsted-Lowry theory of acids and bases. Alternative definitions of bases include. Aromatic amines An aromatic amine is an amine with an aromatic substituent - that is -N such as aniline are, in general, much weaker bases than aliphatic In organic chemistry, compounds composed of carbon and hydrogen are divided into two classes: aromatic compounds, which contain benzene rings or similar rings of atoms, and aliphatic compounds , which do not contain aromatic rings amines because of the electron-withdrawing effect of the phenyl group. Aniline reacts with strong acids to form anilinium Categories: Aromatic amines | Aromatic compounds | Amines | (or phenylammonium) ion (C₆H₅-NH₃⁺).^[3] The sulfate In inorganic chemistry, a sulfate is a salt of sulfuric acid forms beautiful white plates. Although aniline is weakly basic, it precipitates Precipitation is the formation of a solid in a solution or inside another solid during a chemical reaction or by diffusion in a solid. When the reaction occurs in a liquid, the solid formed is called the precipitate, and the liquid remaining above the solid is called the supernate. Powders derived from precipitation have also historically been zinc Zinc , also known as spelter, is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2. Zinc is the 24th most abundant element in the, aluminium Aluminium (UK: /ˌæljʉˈmɪniəm/ AL-yew-MIN-ee-əm) or aluminum (US: /əˈluːmɨnəm/ ( listen) ə-LOO-mi-nəm) is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth', and ferric Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron(II) or Fe2+. Iron(III) is usually the most stable form of iron in air, as illustrated by the pervasiveness salts, and, on warming, expels ammonia Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of from its salts. The weak basicity is due to a negative inductive effect as the lone pair on the nitrogen is partially delocalised into the pi system of the benzene ring.

Acylation

Aniline reacts with carboxylic acids^[4] or more readily with acyl chlorides such as acetyl chloride to give amides. The amides formed from aniline are sometimes called anilides, for example CH₃-CO-NH-C₆H₅ is acetanilide. Antifebrin (acetanilide), an anti-pyretic and analgesic, is obtained by the reaction of acetic acid and aniline.

N-Alkylation

N-methylation of aniline with methanol at elevated temperatures over acid catalsts gives N-methylaniline and dimethylaniline:

C₆H₅NH₂ + 2 CH₃OH → C₆H₄N(CH₃)₂ + H₂O

Methyl and dimethylaniline are colourless liquids with b.p. of 193-195 °C and 192 °C, respectively. These derivatives are of importance in the colour industry. Aniline combines directly with alkyl iodides to form secondary and tertiary amines.

Carbon disulfide derivatives

Boiled with carbon disulfide, it gives sulfocarbanilide (diphenylthiourea) (CS(NHC₆H₅)₂), which may be decomposed into phenyl isothiocyanate(C₆H₅CNS), and triphenyl guanidine (C₆H₅N=C(NHC₆H₅)₂).

Diazotization

Aniline and its ring-substituted derivatives react with nitrous acid to form diazonium salts. Through these intermediates, aniline can be conveniently converted to -OH, -CN, or a halide via Sandmeyer reactions.

Other reactions

It reacts with nitrobenzene to produce phenazine in the Wohl-Aue reaction. Hydrogenation gives cyclohexylamine.

Being a standard reagent in laboratories, aniline is used for many niche reactions. Its acetate is used in the Aniline acetate test for carbohydrates, identifying pentoses by conversion to furfural. It is used to stain neural RNA blue in the Nissl stain.^{[citation needed]}

Uses

The largest application of aniline is for the preparation of methylene diphenyl diisocyanate (MDI). The majority of aniline serves this market. Other uses include rubber processing chemicals (9%), herbicides (2%), and dyes and pigments (2%).^[5] As additives to rubber, aniline derivatives such as phenylenediamine and diphenylamine, are antioxidants. Illustrative of the drugs prepared from aniline is paracetamol (acetaminophen, Tylenol). The principal use of aniline in the dye industry is as a precursor to indigo, the blue of blue jeans.^[2]

History

Aniline was first isolated from the destructive distillation of indigo in 1826 by Otto Unverdorben^[6] , who named it crystalline. In 1834, Friedrich Runge (Pogg. Ann., 1834, 31, p. 65; 32, p. 331) isolated from coal tar a substance that produced a beautiful blue colour on treatment with chloride of lime, which he named kyanol or cyanol. In 1841, C. J. Fritzsche showed that, by treating indigo with caustic potash, it yielded an oil, which he named aniline, from the specific name of one of the indigo-yielding plants, from Portuguese anil "the indigo shrub" from Arabic an-nil "the indigo" assimilated from al-nil, from Persian nila, from nili "indigo" with Indigofera anil, anil being derived from the Sanskrit नीली nīla, dark-blue, and nīlā,^[7] the indigo plant. About the same time N. N. Zinin found that, on reducing nitrobenzene, a base was formed, which he named benzidam. August Wilhelm von Hofmann investigated these variously-prepared substances, and proved them to be identical (1855), and thenceforth they took their place as one body, under the name aniline or phenylamine.

The great commercial value of aniline was due to the readiness with which it yields, directly or indirectly, dyestuffs. The discovery of mauve in 1856 by William Henry Perkin was the first of a series of an enormous range of dyestuffs, such as fuchsine, safranine and induline. Its first industrial-scale use was in the manufacture of mauveine, a purple dye discovered in 1856 by Hofmann's student William Henry Perkin. At the time of mauveine's discovery, aniline was an expensive laboratory compound, but it was soon prepared "by the ton" using a process previously discovered by Antoine Béchamp.^[8] The synthetic dye industry grew rapidly as new aniline-based dyes were discovered in the late 1850s and 1860s.

Toxicology

Aniline is toxic by inhalation of the vapour.^[9] The IARC lists it in Group 3 (not classifiable as to its carcinogenicity to humans) due to the limited and contradictory data available. The early manufacture of aniline resulted in increased incidents of bladder cancer, but these effects are now attributed to naphthylamines, not anilines.^[2]

References

1. ^ Solubility of aniline in methanol
2. ^ ^{a b c} Thomas Kahl, Kai-Wilfrid Schröder, F. R. Lawrence, W. J. Marshall, Hartmut Höke, Rudolf Jäckh "Aniline" in Ullmann's Encyclopedia of Industrial Chemistry 2007; John Wiley & Sons: New York.doi:10.1002/14356007.a02_303
3. ^ McMurry, John E. (1992), Organic Chemistry (3rd ed.), Belmont: Wadsworth, ISBN 0-534-16218-5
4. ^ Carl N. Webb (1941), "Benzanilide", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0082 ; Coll. Vol. 1: 82
5. ^ "Aniline". The Chemical Market Reporter. http://www.the-innovation-group.com/ChemProfiles/Aniline.htm. Retrieved 2007-12-21.
6. ^ Otto Unverdorben (1826). "Ueber das Verhalten der organischen Körper in höheren Temperaturen". Annalen der Physik 84 (11): 397–410. doi:10.1002/andp.18260841109.
7. ^ http://www.etymonline.com/index.php?term=aniline
8. ^ Perkin, William Henry. 1861-06-08. "Proceedings of Chemical Societies: Chemical Society, Thursday, May 16, 1861." The Chemical News and Journal of Industrial Science. Retrieved on 2007-09-24.
9. ^ Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.

External links

• International Chemical Safety Card 0011
• Aniline electropolymerisation
• U.S. National Library of Medicine: ChemIDplus - Aniline

This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.

Categories: Aromatic amines | Dyes | Enamines | Hazardous air pollutants | IARC Group 3 carcinogens | Arabic words and phrases

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