Amines are ... Structure, properties, classes of amines

Amines entered our life completely unexpectedly. Until recently, these were poisonous substances, a collision with which could lead to death. And now, after a century and a half, we are actively using synthetic fibers, fabrics, building materials, dyes based on amines. No, they did not become safer, just people could "tame" them and subordinate them, gaining some benefit for themselves. About which one, and we will talk further.

Definition

Amines are organic compounds that are derivatives of ammonia, in the molecules of which hydrogen is replaced by hydrocarbon radicals. They can be up to four at a time. The configuration of molecules and the number of radicals determine the physical and chemical properties of the amines. In addition to hydrocarbons, such compounds may contain aromatic or aliphatic radicals, or a combination thereof. A distinctive feature of this class is the presence of an RN fragment in which R is an organic group.

Classification

All amines can be divided into three large groups:

1. By the nature of the hydrocarbon radical.
2. The number of radicals bound to a nitrogen atom.
3. By the number of amino groups (mono-, di-, tri-, etc.).

The first group includes aliphatic, or limiting amines, of which representatives are methylamine and methylethylamine. And also aromatic - for example, aniline or phenylamine. The names of representatives of the second group are directly related to the number of hydrocarbon radicals. Thus, primary amines (containing one nitrogen group), secondary (having two nitrogen groups in combination with different organic groups) and tertiary (correspondingly having three nitrogen groups) are isolated. The names of the tertiary group speak for themselves.

Nomenclature (name formation)

To form the name of the compound, an attachment "amine" is added to the name of the organic group that binds to nitrogen, and the groups themselves are listed in alphabetical order, for example: methylprotylamine or methyldiphenylamine (in this case "di" indicates that there are two radicals in the compound Phenyl). It is possible to form a name based on carbon, and the amino group is represented as a substituent. Then its position is determined by the subscript under the element designation, for example, CH ₃ CH ₂ CH (NH ₂ ) CH ₂ CH ₃ . Sometimes in the upper right-hand corner the figure indicates the carbon sequential number.

Some compounds still retain trivial, well-known simplified names, such as aniline, for example. In addition, among them may be found such that they have incorrectly composed names that are used on a par with systematic ones, because scientists and people who are far from science are so much easier and more convenient to communicate and understand each other

Physical properties

The secondary amine, like the primary amine, is capable of forming hydrogen bonds between molecules, although slightly weaker than usual. This fact explains the higher boiling point (above one hundred degrees) inherent in amines, compared to other compounds having a similar molecular weight. The tertiary amine, because of the absence of the NH group, is not capable of forming hydrogen bonds, therefore it begins to boil already at eighty-nine degrees Celsius.

At room temperature (eighteen to twenty degrees Celsius), only the lower aliphatic amines are in the form of vapor. The middle ones are in a liquid state, while the higher ones are in a solid state. All classes of amines have a specific odor. The smaller the organic radicals in a molecule, the more distinct it is: from the practically odorless higher compounds to the smelling fish, the middle and stinking ammonia lower.

Amines can form strong hydrogen bonds with water, that is, they are highly soluble in it. The more hydrocarbon radicals present in the molecule, the less soluble it is.

Chemical properties

As it is logical to assume, amines are derivatives of ammonia, and therefore, they have similar properties. Conventionally, we can distinguish three types of chemical interaction, which are possible for these compounds.

1. First, we consider the properties of amines as bases. Lower (aliphatic), connecting with water molecules, give an alkaline reaction. The bond is formed by the donor-acceptor mechanism, due to the fact that the nitrogen atom has an unpaired electron. When interacting with acids, all the amines form salts. These are solid, highly soluble in water substances. Aromatic amines exhibit weaker base properties, since their unshared electron pair is shifted to the benzene ring and interacts with its electrons.
2. Oxidation. The tertiary amine is easily oxidized by combining with oxygen in the ambient air. In addition, all amines are able to ignite from an open flame (unlike ammonia).
3. Interaction with nitrous acid is used in chemistry in order to distinguish amines among themselves, since the products of this reaction depend on the amount of organic groups present in the molecule:

• Lower primary amines form alcohols as a result of the reaction;
• Aromatic primary under similar conditions give phenols;
• Secondary are converted into nitroso compounds (as evidenced by a characteristic smell);
• Tertiary salts form salts that quickly break down, so the value of such a reaction is not.

Special properties of aniline

Aniline is a compound having the properties inherent in both the amino group and the benzene group. This is explained by the mutual influence of atoms inside the molecule. On the one hand, the benzene ring weakens the main (i.e., alkaline) manifestations in the aniline molecule. They are lower than that of aliphatic amines and ammonia. But on the other hand, when the amino group affects the benzene ring, it becomes, on the contrary, more active and enters substitution reactions.

For the qualitative and quantitative determination of aniline in solutions or compounds, a reaction with bromine water is used, at the end of which a white precipitate appears in the form of 2,4,6-tribromoaniline at the bottom of the tube.

Amines in nature

Amines are found in nature everywhere in the form of vitamins, hormones, intermediate products of metabolism, they are in the body of animals and plants. In addition, when decaying living organisms, medium amines are also produced, which in the liquid state spread the unpleasant smell of the herring brine. Widely described in the literature "cadaveric poison" appeared precisely because of the specific ambergris amines.

For a long time, the substances we examined were confused with ammonia due to a similar odor. But in the mid-nineteenth century, the French chemist Würz was able to synthesize methylamine and ethylamine and prove that when they burn, they release a hydrocarbon. This was a fundamental difference between the mentioned compounds and ammonia.

Amine production under industrial conditions

Since the nitrogen atom in the amines is in the lowest oxidation state, the reduction of the nitrogen-containing compounds is the simplest and most accessible way of their preparation. It is widely used in industrial practice because of its cheapness.

The first method is the reduction of nitro compounds. The reaction, during which aniline is formed, is called the scientist Zinin and was performed for the first time in the middle of the nineteenth century. The second method consists in the reduction of amides with lithium aluminum hydride. Of the nitriles, it is also possible to recover the primary amines. The third option is alkylation reactions, that is, the introduction of alkyl groups into ammonia molecules.

The use of amines

In themselves, in the form of pure substances, amines are used little. One of the rare examples is polyethylene polyamine (PEPA), which, under household conditions, facilitates the hardening of epoxy resin. In general, the primary, tertiary or secondary amine is an intermediate product in the production of various organic substances. The most popular is aniline. It is the basis of a large palette of aniline dyes. The color that will be obtained at the end depends directly on the selected raw material. Pure aniline gives a blue color, and the mixture of aniline, ortho- and para-toluidine will be red.

Aliphatic amines are needed to produce polyamides, such as nylon and other synthetic fibers. They are used in engineering, as well as in the production of ropes, fabrics and films. In addition, aliphatic diisocyanates are used in the manufacture of polyurethanes. Due to its exceptional properties (lightness, strength, elasticity and ability to attach to any surfaces), they are in demand in construction (assembly foam, glue) and in the footwear industry (anti-skid sole).

Medicine is another area where amines are used. Chemistry helps to synthesize antibiotics from a group of sulfonamides, which are successfully used as second line drugs, that is, back-up. In case the bacteria develop resistance to basic medicines.

Harmful effects on the human body

It is known that amines are very toxic substances. Harm to health can cause any interaction with them: inhalation of vapors, contact with open skin or ingestion of compounds inside the body. Death comes from lack of oxygen, since amines (in particular aniline) bind to the hemoglobin of the blood and do not allow it to capture oxygen molecules. Distressing symptoms are shortness of breath, blueing of the nasolabial triangle and fingertips, tachypnea (rapid breathing), tachycardia, loss of consciousness.

In case of getting these substances on bare parts of the body, they should be quickly removed with cotton wool, previously moistened with alcohol. Do this as carefully as possible, so as not to increase the area of pollution. If symptoms of poisoning appear, you should always consult a doctor.

Aliphatic amines are a poison for the nervous and cardiovascular systems. They can cause depression of the liver, its dystrophy and even cancer of the bladder.