Aniline is an organic compound containing an aromatic nucleus and an amino group connected to it. It is also sometimes called phenylamine or aminobenzene. It is an oily liquid that has no color, but with a characteristic odor. Very poisonous.
Getting
Aniline is a very useful intermediate, so it is produced on a relatively large scale. Industrial synthesis begins with benzene. It is nitrated at a temperature of 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 used.
In the laboratory, reduction can be performed with hydrogen at the time of its evolution. To do this, in the reaction mixture, zinc metal or iron is reacted with acid. The resulting atomic hydrogen interacts with nitrobenzene.
Aniline can be obtained in one step if benzene is reacted with a mixture of sodium azide and aluminum chloride. The reaction lasts 12 hours. The yield of such a 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. The density is almost like that of water (1.02 g / cm 3 ). Aniline is soluble in water, although rather slightly. But it is mixed 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 to itself a hydrogen ion (proton). Hence the name of this process is protonation. Due to this, aniline can interact with acids, forming salts:
C 6 H 5 NH 2 + HCl → [C 6 H 5 NH 3 ] + 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 occurs without catalysts; with sodium, the presence of catalysts is necessary: copper, nickel, cobalt or salts of these metals. This reaction can occur 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 environment, since protonation of the amino group is necessary. The temperature of the reaction mixture should be maintained at about 220 ° C. Sometimes high blood pressure is applied. The final product contains mono-, di- and trisubstituted derivatives of aniline. Therefore, to obtain a pure substance, it is necessary to use purification, for example distillation.
Alkylation can also be carried out using alkyl halides. Several products can also be obtained here.
Aniline can also react in the aromatic nucleus. Usually these are electrophilic substitution reactions (nitration, sulfonation, alkylation, acylation). The amino group activates the benzene core, so the new groups stand in 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
Due to its physical and chemical properties, aniline in its pure form 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 proportion of aniline goes to the production of polyisocyanates, from which, in turn, polyurethanes are obtained. This is an organic polymer that is used in many industries for the manufacture of elastic forms, protective coatings, varnishes, sealants.
7% aniline is used as an additive for polymers. This can be either pure aniline or compounds derived from it. They play the role of initiators, stabilizers, plasticizers, pore formers, 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 manufacture of dyes. Anilin was no exception. More than 150 different dyes are directly synthesized from it, and even more - from its derivatives. The most important of them are aniline black, a deep black pigment, nigrosines, inlins and azo dyes.
Toxicity
Aniline is a toxic substance. Once in the blood, it forms compounds that cause oxygen starvation. It can also penetrate 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, as well as increased heart rate occurs.
This substance has a detrimental effect on the nervous system. In chronic poisoning, a decrease in memory, sleep disorders, as well as 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, which is a donkey on the skin of the victim. There are special antidotes. They are introduced into the body in severe cases.