Aniline is the simplest primary aromatic amine and a compound formed by the substitution of a hydrogen atom in the benzene molecule with an amino group. It is colorless oil like flammable liquid with strong odor. When heated to 370 C, it is slightly soluble in water and soluble in ethanol, ether, chloroform and other organic solvents. It becomes brown in the air or under the sun. It can be distilled by steam. A small amount of zinc powder is added to prevent oxidation when it is distilled. The purified aniline can be added 10 ~ 15ppm NaBH4 to prevent oxidation deterioration. The solution of aniline is alkaline.
It is easy to produce salt when it reacts with acid. The hydrogen atoms on its amino groups can be substituted by alkyl or acyl groups to produce second or third grade aniline and acyl aniline. When substitution reaction occurs, the products of ortho and para substituted products are mainly produced. It reacts with nitrite to form diazonium salts, which can be used to produce a series of benzene derivatives and azo compounds.
Many industrial feedstocks including N-alkylaniline, alkylaniline, o-nitroaniline, O-benzyl two amine, phenyl hydrazine, cyclohexanamine, etc is derived from Aniline. It can be used as the intermediates of the fungicide sodium p-aminobenzenesulfonate, SSEED, methyl sterilamine, sterilized amine, carbendazim, pyrazinyl, Benzalin, insecticide, pyrazino, pyrazino, pyrazino, pyrazinophos, herbicide methamidine, acetochlor, butachlor, cyclohexanone, imidazolinic acid etc.
Aniline is hygroscopic. It can be dried with KOH or CaH2, and distilled under reduced pressure. Treatment with stannous chloride removes sulfur-containing impurities, reducing the tendency to become coloured by aerial oxidation. It can be crystallised from Et2O at low temperatures. More extensive purifications involve preparation of derivatives, such as the double salt of aniline hydrochloride and cuprous chloride or zinc chloride, or N-acetylaniline (m 114o) which can be recrystallised from water. Redistilled aniline is dropped slowly into a strong aqueous solution ofrecrystallised oxalic acid. Aniline oxalate (m 174-175o) is filtered off, washed several times with water and recrystallised three times from 95% EtOH. Treatment with saturated Na2CO3 solution regenerated aniline which was distilled from the solution, dried and redistilled under reduced pressure [Knowles Ind Eng Chem 12 881 1920]. After refluxing with 10% acetone for 10hours, aniline is acidified with HCl (Congo Red as indicator) and extracted with Et2O until colourless. The hydrochloride is purified by repeated crystallisation before aniline is liberated by addition of alkali, then dried with solid KOH, and distilled. The product is sulfur-free and remains colourless in air [Hantzsch & Freese Chem Ber 27 2529, 2966 1894]. Non-basic materials, including nitro compounds, are removed from aniline in 40% H2SO4 by passing steam through the solution for 1hour. Pellets of KOH are then added to liberate the aniline which is steam distilled, dried with KOH, distilled twice from zinc dust at 20mm, dried with freshly prepared BaO, and finally distilled from BaO in an all-glass apparatus [Few & Smith J Chem Soc 753 1949]. Aniline is absorbed through skin and is TOXIC.[Beilstein 12 IV 223.]
A yellowish to brownish oily liquid with a musty fishy odor. Melting point -6°C; boiling point 184°C; flash point 158°F. Denser than water (8.5 lb / gal) and slightly soluble in water. Vapors heavier than air. Toxic by skin absorption and inhalation. Produces toxic oxides of nitrogen during combustion. Used to manufacture other chemicals, especially dyes, photographic chemicals, agricultural chemicals and others.
Aniline is a heat sensitive base. Combines with acids to form salts. Dissolves alkali metals or alkaline earth metals with evolution of hydrogen. Incompatible with albumin, solutions of iron, zinc and aluminum, and acids. Couples readily with phenols and aromatic amines. Easily acylated and alkylated. Corrosive to copper and copper alloys. Can react vigorously with oxidizing materials (including perchloric acid, fuming nitric acid, sodium peroxide and ozone). Reacts violently with BCl3. Mixtures with toluene diisocyanate may ignite. Undergoes explosive reactions with benzenediazonium-2-carboxylate, dibenzoyl peroxide, fluorine nitrate, nitrosyl perchlorate, peroxodisulfuric acid and tetranitromethane. Violent reactions may occur with peroxyformic acid, diisopropyl peroxydicarbonate, fluorine, trichloronitromethane (293° F), acetic anhydride, chlorosulfonic acid, hexachloromelamine, (HNO3 + N2O4 + H2SO4), (nitrobenzene + glycerin), oleum, (HCHO + HClO4), perchromates, K2O2, beta-propiolactone, AgClO4, Na2O2, H2SO4, trichloromelamine, acids, FO3Cl, diisopropyl peroxy-dicarbonate, n-haloimides and trichloronitromethane. Ignites on contact with sodium peroxide + water. Forms heat or shock sensitive explosive mixtures with anilinium chloride (detonates at 464° F/7.6 bar), nitromethane, hydrogen peroxide, 1-chloro-2,3-epoxypropane and peroxomonosulfuric acid. Reacts with perchloryl fluoride form explosive products. .
Combustion can produce toxic fumes including nitrogen oxides and carbon monoxide. Aniline vapor forms explosive mixtures with air. Aniline is incompatible with strong oxidizers and strong acids and a number of other materials. Avoid heating. Hazardous polymerization may occur. Polymerizes to a resinous mass.
Reduction of nitrobenzene with hydrogen
Aniline is currently obtained by catalytic hydrogenation of nitrobenzene. The catalyst usually used is Cu-SiO2, which has good selectivity and can successfully reduce nitrobenzene to aniline. It is not easy to produce hydrogenation on benzene core. The reaction is carried out in a fluidized bed reactor. After purification, the hydrogen is heated by the heater to 350~400℃.
And then it is ushered in the evaporator, while nitrobenzene enters the evaporator from the upper trough, and contacts with the hot hydrogen to be gasified and overheat to 180~223 ℃.
The mixed gas enters from the bottom of the fluidized bed and contacts with the copper catalyst loaded on the silica gel in the fluidized bed. The generated crude aniline and water vapor are discharged from the top of the bed. Crude benzylamine is cooled and separated by a condenser, and then finished aniline is rectified.
Air & Water Reactions
Darkens on exposure to air and light. Polymerizes slowly to a resinous mass on exposure to air and light. Slightly soluble in water.
A primary aromatic amine, aniline is a weak base and forms salts with mineral acids such as aniline hydrochloride. PKb = 9.30, 0.2mol aqueous solution PH value 8.1. In acidic solution, nitrous acid converts aniline into a diazonium salt that is an intermediate in the preparation of a great number of dyes and other organic compounds of commercial interest. When aniline is heated with organic acids, it gives amides, called anilides, such as acetanilide from aniline and acetic acid. Monomethylaniline and dimethylaniline can be prepared from aniline and methyl alcohol. Catalytic reduction of aniline yields cyclohexylamine.
Various oxidizing agents convert aniline to quinone, azobenzene, nitrosobenzene, p-aminophenol, and the phenazine dye aniline black. Amino groups can undergo acylation, halogenation, alkylation and diazotization, and the presence of amino groups makes it nucleophiles capable of many nucleophilic reactions, and at the same time activates the electrophilic substitution on aromatic rings.
The toxicity of Aniline is LD50500mg/kg (dog oral administration), and is a common pollutant in the environment. Aniline has strong toxicity to blood and nerves. It can be absorbed by skin or by respiratory tract to cause toxicity.
The acute (short-term) and chronic (long-term) effects of aniline in humans consist mainly of effects on the lung, such as upper respiratory tract irritation and congestion. Chronic exposure may also result in effects on the blood. Human cancer data are insufficient to conclude that aniline is a cause of bladder tumors while animal studies indicate that aniline causes tumors of the spleen. EPA has classified aniline as a Group B2, probable human carcinogen.
Evidence reported by the National Institute for Occupational Safety and Health (NIOSH) clearly associates the occupational exposure to o-toluidine and aniline with an increased risk of bladder cancer among workers. The risk of bladder cancer is greatest among workers with possible and definite exposures to o-toluidine and aniline, and the risk increases with the duration of exposure.
Aniline is classified as very toxic. Probable oral lethal dose in humans is 50-500 mg/kg for a 150 lb. person. Aniline poisoning is characterized by methemoglobin formation in the blood and resulting cyanosis or blue skin. The formation of methemoglobin interferes with the oxygen-carrying capacity of the blood. The approximate minimum lethal dose for a 150 lb. human is 10 grams. Serious poisoning may result from ingestion of 0.25 mL. People at special risk include individuals with glucose-6-phosphate-dehydrogenase deficiency and those with liver and kidney disorders, blood diseases, or a history of alcoholism.
Aniline,C6H5NH2, is slightly soluble in water,miscible in alcohol and ether,and turns yellow to brown in air. Aniline may be made(1) by the reduction, with iron or tin in HCI, of nitrobenzene, and(2) by the amination of chlorobenzene by heating with ammonia to a high temperature corresponding to a pressure of over 200 atmospheres in the presence of a catalyst(a mixture of cuprous chlorideandoxide).Aniline is the end point of reduction of most mononitrogen substituted benzene nuclei,as nitro benzene beta-phenyl hydroxylamine, azoxybenzene, azobenzene, hydrazobenzene. Aniline is detected by the violet coloration produced by a small amountof sodium hypochlorite. Aniline is used as a solvent, in the preparation of compound in the manufacture of dyes and their intermediates, and in the manufacture of medicinal chemicals.
Aniline is predominantly used as a chemical intermediate for dyes, drugs, explosives, plastics, and photographic and rubber chemicals. Many chemicals can be made from Aniline, including:
- Isocyanaates for the urethane industry
- Antioxidants, activators, accelerators, and other chemicals for the rubber industry
- Indigo, acetoacetanilide, and other dyes and pigments for a variety of applications
- Diphenylamine for the rubber, petroleum, plastics, agricultural, explosives, and chemical industries
- Various fungacides and herbicides for the agricultural industry
- Pharmaceutical, organic chemical, and other products
ChEBI: A primary arylamine in which an amino functional group is substituted for one of the benzene hydrogens.
Aniline was first obtained in 1826 by the destructive distillation of indigo. It is named because of the specific indigo-yielding plant “Indigofera anil” (Indigofera suffruticosa); In 1857, W.H.Jr. Perkin made aniline from reduction of nitrobenzene with iron filings using hydrochloric acid as catalyst which is still being used. At present, the methods of aniline production include catalytic vapor phase reduction of nitrobenzene with hydrogen, catalytic reaction of chlorobenzene and ammonolysis of phenol (Japan).
Before 1960s, aniline production was based on coal tar benzene, and now petroleum benzene has been used. At the end of 1990s, the world's aniline production capacity was above 2.5 million t. 50% of the aniline is used in the production of dye intermediates. About 25% aniline is used to produce isocyanate and its copolymers. The remaining (25%) is used for pesticides, gasoline antiknock agents, and photographic materials etc.