Aniline, phenylamine or aminobenzene is an organic compound with the formula C₆H₅N H₂ (or C₆H₇N). It is an organic chemical compound, specifically a primary aromatic amine. It consists of a benzene ring attached to an amino group. The chemical structure of aniline is shown at the right.

Synthesis

See also Industrial production of aniline

Aniline can be produced from benzene in two steps. First, benzene is nitrated (reacted with nitric acid, a form of electrophilic substitution reaction) to give nitrobenzene. Second, the nitrobenzene is reduced to give aniline. A variety of reducing agents are effective for the reduction, including H₂ (with a catalyst), hydrogen sulfide, iron, zinc, or tin.

Many derivatives of aniline can be prepared similarly. In commerce three brands of aniline are distinguishedâ€"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 (Ã©chappÃ©s) of the fuchsine fusion. Monomethyl and dimethyl aniline are colourless liquids prepared by heating aniline, aniline hydro-chloride and methyl alcohol in an autoclave at 220Â°C. They are of great importance in the colour industry. Monomethyl aniline boils at 193-195Â°C; dimethyl aniline at 192Â°C.

Properties

Aniline is oily and, although colourless, it can be slowly oxidized and resinified in air to form impurities which can give it a red-brown tint. Its boiling point is 184 Â°C and its melting point is -6 Â°C. It is a liquid at room temperature.

Like most volatile amines, it possesses a somewhat unpleasant odour of rotten fish, and also has a burning aromatic taste; it is a highly acrid poison. It ignites readily, burning with a large smoky flame.

Chemically, aniline is a weak base. Aromatic amines such as aniline are generally much weaker bases than aliphatic amines. Aniline reacts with strong acids to form salts containing the anilinium (or phenylammonium) ion (C₆H₅-NH₃⁺), and reacts with acyl halides (such as acetyl chloride (ethanoyl chloride), CH₃COCl) to form amides. The amides formed from aniline are sometimes called anilides, for example CH₃-CO-NH-C₆H₅ is acetanilide, for which the modern name is N-phenyl ethanamide.

The sulphate forms beautiful white plates. Although aniline is but feebly basic, it precipitates zinc, aluminium and ferric salts, and on warming expels ammonia from its salts. Aniline combines directly with alkyl iodides to form secondary and tertiary amines; boiled with carbon disulphide it gives sulphocarbanilide (diphenyl thio-urea), CS(NHC₆H₅)₂, which may be decomposed into phenyl mustard-oil, C₆H₅CNS, and triphenyl guanidine, C₆H₅N: C(NHC₆H₅)₂. Sulphuric acid at 180Â° C gives sulphanilic acid, NH₂.C₆H₄.SO₃H. Anilides, compounds in which the amino group is substituted by an acid radical, are prepared by heating aniline with certain acids; antifebrin or acetanilide is thus obtained from acetic acid and aniline. The oxidation of aniline has been carefully investigated. In alkaline solution azobenzene results, while arsenic acid produces theviolet-colouring matter violaniline. Chromic acid converts it into quinone, while 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 para-amino phenol and para-amino diphenylamine.

Like phenols, aniline derivatives are highly reactive in electrophilic substitution reactions. For example, sulfonation of aniline produces sulfanilic acid, which can be converted to sulfanilamide. Sulfanilamide is one of the sulfa drugs which were widely used as antibacterials in the early 20th century.

Aniline and its ring-substituted derivatives react with nitrous acid to form diazonium salts. Through these, the -NH₂ group of aniline can be conveniently converted to -OH, -CN, or a halide.

Uses

Originally the great commercial value of aniline was due to the readiness with which it yields, directly or indirectly, valuable dyestuffs. The discovery of mauve in 1856 by William Perkin was the first of a series of dyestuffs which are now to be numbered by hundreds. Reference should be made to the articles dyeing, fuchsine, safranine, indulines, for more details on this subject. In addition to dyestuffs, it is a starting-product for the manufacture of many drugs such as Acetaminophen/Paracetamol (Tylenol).

Currently the largest market for aniline is preparation of methylene diphenyl diisocyanate (MDI), some 85% of aniline serving this market. Other uses include rubber processing chemicals (9%), herbicides (2%), and dyes and pigments (2%). Aniline producers price capacity market demand consumption production growth uses outlook n.d., The Chemical Market Reporter, Schnell Publishing Company. Retrieved January 12, 2002 from http://www.the-innovation-group.com/ChemProfiles/Aniline.htm

History

Aniline was first isolated from the destructive distillation of indigo in 1826 by Otto Unverdorben (Pogg. Ann., 1826, 8, p. 397), who named it crystalline. In 1834, Friedrich Runge (Pogg. Ann., 1834, 31, p. 65; 32, p. 331) isolated from coal tar a substance which produced a beautiful blue colour on treatment with chloride of lime; this 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, Indigofera anil, anil being derived from the Sanskrit nÄ«la, dark-blue, and nÄ«lÄ, 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.

Its first industrial-scale use was in the manufacture of mauveine, a purple dye discovered in 1856 by William Henry Perkin.

p-toluidine, an aniline derivative, can be used in qualitative analysis to prepare carboxylic acid derivitives.

Toxicology

Aniline is toxic by inhalation of the vapour, absorption through the skin or swallowing. It causes headache, drowsiness, cyanosis, mental confusion and in severe cases can cause convulsions. Prolonged exposure to the vapour or slight skin exposure over a period of time affects the nervous system and the blood, causing tiredness, loss of appetite, headache and dizziness.Muir, GD (ed.) 1971, Hazards in the Chemical Laboratory, The Royal Institute of Chemistry, London.

Oil mixtures containing rapeseed oil denatured with aniline have been clearly linked by epidemiological and analytic chemical studies to the toxic oil syndrome that hit Spain in the spring and summer of 1981, in which 20,000 became acutely ill, 12,000 were hospitalized, and more than 350 died in the first year of the epidemic. The precise etiology though remains unknown.

Some authorities class aniline as a carcinogen, although the IARC lists it in Group 3 (not classifiable as to its carcinogenicity to humans) due to the limited and contradictary data available.

Safety Data

See also [1], [2] and references included at end of article

The majority of the below data was taken from:# 2004 Emergency Response Guidebook ERG2004, 2004.# Hazardous Chemicals Data NFPA 49, PC-49-94, 1994.# Canadian WHMIS - Workplace Hazardous Materials Information System.# U.S.C.G CHRIS database.# U.S. EPA Cameo database.# NIOSH/OSHA exposure limit data

Exposure limit(s): TLV: 2 ppm; 7.6 mg/m3 (as TWA) (skin) (ACGIH 1992-1993). OSHA PEL: TWA 5 ppm (19 mg/m3) skin NIOSH REL: Ca See Appendix A NIOSH IDLH: Potential occupational carcinogen 100 ppm

Carcinogin: G-A3, CP65

Poison_Class: 1

Exposure effects: May cause liver and kidney damage. May cause fetal effects. Repeated exposure may cause sensitization dermatitis. Chronic exposure may cause hemolysis of the red blood cells followed by stimulation of the bone marrow. Laboratory experiments have resulted in mutagenic effects. May cause cyanosis - a blue-gray coloring of the skin and lips caused by a lack of oxygen. Animal studies have reported the development of tumors.

Ingestion: Harmful if swallowed. Aniline acts through an intermediate to change hemoglobin to methemoglobin. In one subject, 65 mg of aniline increased the methemoglobin level by 16% within 2 hours. Intense methemoglobinemia may lead to asphyxia severe enough to injure the cells of the central nervous system. Pathologic findings in acute fatalities from aniline include chocolate color of the blood; injury to the kidney, liver and spleen; and hemolysis. Alcohol can intensify the ability of aniline to induce methemoglobinemia.

Inhalation: Harmful if inhaled. Causes respiratory tract irritation. Methemoglobinemia is characterized by dizziness, drowsiness, headache, shortness of breath, cyanosis (bluish discoloration of skin due to deficient oxygenation of the blood), rapid heart rate and chocolate-brown blood. Inhalation of aniline causes anoxia due to the formation of methemoglobin.

Skin: Causes skin irritation. Harmful if absorbed through the skin. May cause skin sensitization, an allergic reaction, which becomes evident upon re-exposure to this material. Vapors are readily absorbed through the skin.

Eyes: Causes severe eye irritation. May cause lacrimation (tearing), blurred vision, and photophobia. May cause chemical conjunctivitis and corneal damage.

First aid

Ingestion: Do NOT induce vomiting. If victim is conscious and alert, give 2-4 cupfuls of milk or water. Never give anything by mouth to an unconscious person. Get medical aid immediately.

Inhalation: Get medical aid immediately. Remove from exposure to fresh air immediately. If breathing is difficult, give oxygen. DO NOT use mouth-to-mouth respiration. If breathing has ceased apply artificial respiration using oxygen and a suitable mechanical device such as a bag and a mask.

Skin: Get medical aid immediately. Immediately flush skin with plenty of soap and water for at least 15 minutes while removing contaminated clothing and shoes. Wash clothing before reuse. Destroy contaminated shoes.

Eyes: Immediately flush eyes with plenty of water for at least 15 minutes, occasionally lifting the upper and lower eyelids. Get medical aid. Do NOT allow victim to rub or keep eyes closed.

References

External links

*International Chemical Safety Card 0011
* National Pollutant Inventory - Aniline
*NIOSH Pocket Guide to Chemical Hazards
*IARC Monograph "Aniline"
*Computational Chemistry Wiki entry
*Aniline electropolymerisation

Aniline: Encyclopedia BETA

Contents

Aniline