Aniline is an organic compound containing an aromatic nucleus and an amino group attached to it. It is also sometimes called phenylamine or aminobenzene. It is an oily liquid, colorless, but with a characteristic odor. Highly poisonous.
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Aniline is a very useful intermediate, so it is produced on a relatively large scale. Industrial synthesis starts with benzene. It is nitrated at 60°C with a mixture of concentrated sulfuric and nitric acids. Next, the resulting nitrobenzene is reduced with hydrogen at a temperature of about 250 °C using catalysts. High blood pressure may also be applied.
In the laboratory, reduction can be done with hydrogen at the time of its release. To do this, in the reaction mixture, metallic zinc or iron is reacted with an acid. The resulting atomic hydrogen reacts with nitrobenzene.
It is possible to obtain aniline in one stage if benzene is reacted with a mixture of sodium azide and aluminum chloride. The reaction lasts12 hours. The yield of this reaction is 63%.
Physical properties
As noted above, aniline is a colorless oily liquid. At a temperature of -5.9 °C, it freezes. Boils at 184.4 °C. Almost as dense as water (1.02 g/cm3). Aniline is soluble in water, although rather slightly. But it is miscible in any ratio with various organic solvents: benzene, toluene, acetone, diethyl ether, ethanol and many others.
Chemical properties
The chemical properties of aniline are quite diverse. For example, it exhibits both acidic and basic properties. The latter are due to the fact that the amino group can attach a hydrogen ion (proton) to itself. Hence the name of this process - protonation. Due to this, aniline can interact with acids, forming s alts:
C6H5NH2 + HCl → [C6 H5NH3]+Cl-
Acidic properties are explained by the fact that the hydrogen atoms in the amino group are easily split off and replaced by other atoms. So, aniline can interact with alkali metals. The reaction with potassium proceeds without catalysts, with sodium the presence of catalysts is necessary: copper, nickel, cob alt or s alts of these metals. This reaction can also go with calcium, but in this case, heating to 200 °C is necessary.
Replaced by hydrogen and radicals. This occurs when aniline reacts with alcohols. The reaction is carried out in an acidic medium, as it is necessaryprotonation of the amino group. The temperature of the reaction mixture must be maintained at about 220 °C. Sometimes high pressure is applied. The final product contains mono-, di- and trisubstituted aniline derivatives. Therefore, to obtain a pure substance, it is necessary to use purification, such as distillation.
Alkylation can also be carried out using alkyl halides. Multiple products can also be obtained here.
Aniline can also react on the aromatic nucleus. Usually these are electrophilic substitution reactions (nitration, sulfonation, alkylation, acylation). The amino group activates the benzene core, so the new groups get into the para position. Halogenation is very easy. In this case, all hydrogen atoms in the nucleus are replaced.
As can be seen from the reaction equations, the chemical properties of aniline are quite diverse. Not all are listed here.
Application
Because of its physical and chemical properties, pure aniline is used only in laboratories as a reagent or organic solvent. In industry, all aniline is spent on the synthesis of more complex and useful compounds. For example, aniline phosphate is used as an inhibitor (retarder) of carbon steel corrosion.
A large share of aniline goes to the production of polyisocyanates, from which, in turn, polyurethanes are obtained. It is an organic polymer that is used in many industries to make flexible molds,protective coatings, varnishes, sealants.
7% aniline is used as an additive for polymers. It can be either pure aniline or compounds derived from it. They play the role of initiators, stabilizers, plasticizers, blowing agents, vulcanizers or polymerization accelerators. This diversity is achieved due to the specific chemical properties of aniline.
Nitrogen-containing organic substances are often used in the production of dyes. Aniline is no exception. More than 150 different dyes are directly synthesized from it, and even more from its derivatives. The most important of these are aniline black, deep black pigment, nigrosines, indulins and azo dyes.
Toxicity
Aniline is a toxic substance. Once in the blood, it forms compounds that cause oxygen starvation. It can also enter the body in the form of vapors, through the skin or mucous membranes. Signs of aniline poisoning are weakness, dizziness, headache. With more severe poisoning, nausea, vomiting, and increased heart rate occur.
This substance has a detrimental effect on the nervous system. In chronic poisoning, memory loss, sleep disorders, and mental disorders can occur.
First aid for intoxication is to remove the source of poisoning and wash the victim with warm water. This will help dissolve the aniline that has settled on the victim's skin. There are also special antidotes. They are injected into the body in severe cases.
