Aniline
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| Names | |||
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| IUPAC name
Phenylamine
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| Other names
Aminobenzene
Benzenamine | |||
| Identifiers | |||
3D model (JSmol)
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| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| DrugBank | |||
| ECHA InfoCard | 100.000.491 | ||
| KEGG | |||
| UNII | |||
CompTox Dashboard (EPA)
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| Properties | |||
| C6H5NH2 | |||
| Molar mass | 93.13 g/mol | ||
| Appearance | colorless liquid | ||
| Density | 1.0217 g/mL, liquid | ||
| Melting point | −6.3 °C (20.7 °F; 266.8 K) | ||
| Boiling point | 184.13 °C (363.43 °F; 457.28 K) | ||
| 3.6 g/100 mL at 20°C | |||
| Basicity (pKb) | 9.3 | ||
| Viscosity | 3.71 cP (3.71 mPa·s at 25 °C | ||
| Thermochemistry | |||
Std enthalpy of
combustion (ΔcH⦵298) |
-3394 kJ/mol | ||
| Hazards | |||
| NFPA 704 (fire diamond) | |||
| Related compounds | |||
| Supplementary data page | |||
| Aniline (data page) | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Aniline, 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. 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 and resinifies in air, giving a red-brown tint to aged samples.
Production
Aniline is mainly produced in industry in two steps from benzene. First, benzene is nitrated using a concentrated mixture of nitric acid and sulfuric acid at 50 to 60°C, which gives nitrobenzene. In the second step, the nitrobenzene is hydrogenated, typically at 200-300 °C in presence of various metal catalysts:
- 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 and ammonia, the phenol being derived from the cumene process.[1]
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, and is obtained from the distillate (échappés) of the fuchsine 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 affords toluidines. Nitration of chlorobenzene and related derivatives and reduction of the nitration products 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 results, whereas arsenic acid produces the violet-coloring matter violaniline. Chromic acid converts it into quinone, whereas chlorates, in the presence of certain metallic salts (especially of vanadium), give aniline black. Hydrochloric acid and potassium chlorate give chloranil. Potassium permanganate in neutral solution oxidizes it to nitrobenzene, in alkaline solution to azobenzene, ammonia and oxalic acid, in acid solution to aniline black. Hypochlorous acid gives 4-aminophenol and para-amino diphenylamine. Oxidation with persulfate affords a variety of polyanilines compounds. These polymers exhibit rich redox and acid-base properties.
Electrophilic reactions at carbon
Like phenols, aniline derivatives are highly susceptible to electrophilic substitution reactions. Its high reactivity reflects that it is an enamine, which enhances the electron-donating ability of the ring. For example, reaction of aniline with sulfuric acid at 180 °C produces sulfanilic acid, H2NC6H4SO3H, which can be converted to sulfanilamide. Sulfanilamide is one of the sulfa drugs, which were widely used as antibacterials in the early 20th century. The largest scale industrial reaction of aniline involves its alkylation with formaldehyde:
- 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. Aromatic amines such as aniline are, in general, much weaker bases than aliphatic amines because of the electron-withdrawing effect of the phenyl group. Aniline reacts with strong acids to form anilinium (or phenylammonium) ion (C6H5-NH3+).[2] The sulfate forms white plates. Although aniline is weakly basic, it precipitates zinc, aluminium, and ferric salts, and, on warming, expels ammonia from its salts. The weak basicity is due to a negative inductive effect as the lone pair on the nitrogen is partially delocalized into the pi system of the benzene ring.
Acylation
Aniline reacts with carboxylic acids[3] 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 catalysts gives N-methylaniline and dimethylaniline:
- C6H5NH2 + 2 CH3OH → C6H4N(CH3)2 + H2O
N-methylaniline and dimethylaniline are colorless 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. This diazonium salt can also be reacted with NaNO2 and phenol which produces a dye which is benzeneazophenol, this process is called coupling.
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%).[4] As additives to rubber, aniline derivatives such as phenylenediamine[disambiguation needed] 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.[1]
Aniline is also used at a smaller scale in the production of the intrinsically conducting polymer polyaniline.
History
Aniline was first isolated from the destructive distillation of indigo in 1826 by Otto Unverdorben,[5] who named it crystalline. In 1834, Friedlieb 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 name of one of the indigo-yielding plants, Añil (Indigofera suffruticosa, syn. I. anil, ultimately from Sanskrit "nīla", dark-blue[6]). 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.[7] The synthetic dye industry grew rapidly as new aniline-based dyes were discovered in the late 1850s and 1860s, an echo of the importance of the compound being found in the name of one of the world's largest chemical companies, BASF, originally the Badische Anilin- und Soda-Fabrik.
"Analin" was used as an analgesic drug in the 18th century. Its cardiac suppressing side-effects were countered with caffeine.[8] Gelsemium was preferred and administered until slight ptosis (drooping eyelids) appeared.
Market
The aniline industry worldwide experienced a wave of renewed facilities operations during the last years. The years of 2010 and 2011 brought around high-scale operation rates compared to the levels during the recession period. The future 5 years are forecast to lead to a large scale aniline market growth – average annual tempo is said to mount 5%. Moreover according to the market projections the trend is to persist on the Asian markets in the coming decade.[9]
Toxicology
Aniline is toxic by inhalation of the vapour.[10] 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.[1]
References
- This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.
{{cite encyclopedia}}: Missing or empty|title=(help)
- ^ 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
- ^ McMurry, John E. (1992), Organic Chemistry (3rd ed.), Belmont: Wadsworth, ISBN 0-534-16218-5
- ^ Carl N. Webb (1941). "Benzanilide". Organic Syntheses; Collected Volumes, vol. 1, p. 82.
- ^ "Aniline". The Chemical Market Reporter. Retrieved 2007-12-21.
- ^ Otto Unverdorben (1826). "Ueber das Verhalten der organischen Körper in höheren Temperaturen". Annalen der Physik. 84 (11): 397–410. doi:10.1002/andp.18260841109.
- ^ http://www.etymonline.com/index.php?term=aniline
- ^ 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.
- ^ http://books.google.com/books?id=jAdYAAAAMAAJ&pg=PA932&lpg=PA932&dq=beef+extract+analgesic&source=bl&ots=k5pOMentfU&sig=l7b8SwqhcMM35QPpPDVeq-llbxk&hl=en&ei=g7-oTpmREuyDsgKd-qzODw&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCUQ6AEwAA#v=onepage&q=beef%20extract%20analgesic&f=false
- ^ "Forecasts Signify Large Scale Aniline Market Growth".
- ^ Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.
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