Amines entered our life completely unexpectedly. Until recently, these were toxic substances, the 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, which are based on amines. No, they did not become safer, just people were able to “tame” them and subjugate, deriving certain benefits for themselves. We will talk about which one later.
Definition
Amines are organic compounds that are derivatives of ammonia, in the molecules of which hydrogen is replaced by hydrocarbon radicals. There can be up to four at a time. The configuration of the molecules and the number of radicals determine the physical and chemical properties of 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:
- By the nature of the hydrocarbon radical.
- By the number of radicals bound to the nitrogen atom.
- By the number of amino groups (mono-, di-, three - and so on).
The first group includes aliphatic, or terminal amines, of which methylamine and methylethylamine are representatives. As well as aromatic ones - for example, aniline or phenylamine. The names of the representatives of the second group are directly related to the amount of hydrocarbon radicals. So, primary amines (containing one nitrogen group), secondary (having two nitrogen groups in combination with various organic groups) and tertiary (respectively, 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, the prefix “amine” is added to the name of the organic group that binds to nitrogen, and the groups are mentioned in alphabetical order, for example: methylprotylamine or methyldiphenylamine (in this case, “di” indicates that there are two radicals in the compound phenyl). It is allowed to make a name based on carbon, and to represent the amino group as a substituent. Then its position is determined by the index under the designation of the element, for example, CH 3 CH 2 CH (NH 2 ) CH 2 CH 3 . Sometimes in the upper right corner the number indicates the carbon number.
Some compounds still retain trivial, well-known simplified names, such as aniline, for example. In addition, among them there may be such that they have incorrectly composed names that are used on a par with systematic ones, because it is easier and more convenient for scientists and people far from science to communicate and understand each other
Physical properties
The secondary amine, like the primary amine, is capable of forming hydrogen bonds between the molecules, albeit slightly weaker than usual. This fact explains the higher boiling point (above one hundred degrees), inherent in amines, in comparison with other compounds having a similar molecular weight. The tertiary amine, due to the absence of the NH-group, is not able to form 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 steam. The middle ones are in a liquid state, and the higher ones are in a solid state. All classes of amines have a specific smell. The less organic radicals there are in the molecule, the more distinct it is: from practically odorless higher compounds to fish-smelling medium and stinky lower ammonia.
Amines can form strong hydrogen bonds with water, that is, they are highly soluble in it. The more hydrocarbon radicals are present in the molecule, the less soluble it is.
Chemical properties
It is logical to assume that amines are derivatives of ammonia, which means that their properties are similar. Conventionally, there are three types of chemical interaction that are possible for these compounds.
- First, consider the properties of amines as bases. Lower (aliphatic), when combined 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 amines form salts. These are solid, water-soluble substances. Aromatic amines exhibit weaker base properties, since their lone electron pair shifts to the benzene ring and interacts with its electrons.
- Oxidation. The tertiary amine is easily oxidized by combining with oxygen in atmospheric air. In addition, all amines are capable of igniting from an open flame (unlike ammonia).
- The interaction with nitrous acid is used in chemistry in order to distinguish between amines, 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 turn into nitroso compounds (as evidenced by a characteristic odor);
- tertiary form salts, which are rapidly destroyed, so this reaction is not valuable.
Special properties of aniline
Aniline is a compound having properties inherent to 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 the substitution reaction.
For 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 forms in the form of 2,4,6-tribromaniline at the bottom of the tube.
Amines in nature
Amines are found in nature everywhere in the form of vitamins, hormones, intermediate metabolic products, and they are found in animals and plants. In addition, when rotting living organisms, medium amines are also obtained, which in a liquid state spread an unpleasant odor of herring brine. Widely described in the literature, "cadaveric poison" appeared precisely due to the specific amber amber.
For a long time, the substances under consideration were confused with ammonia due to a similar smell. But in the mid-nineteenth century, the French chemist Würz was able to synthesize methylamine and ethylamine and prove that they emit hydrocarbon upon combustion. This was a fundamental difference between the compounds and ammonia.
Obtaining amines in an industrial environment
Since the nitrogen atom in amines is in the lowest oxidation state, the reduction of nitrogen-containing compounds is the simplest and most affordable way to obtain them. It is he who is widely distributed in industrial practice because of its cheapness.
The first method is the restoration of nitro compounds. The reaction during which aniline is formed is called the scientist Zinin and was carried out for the first time in the mid-nineteenth century. The second method is the reduction of amides with lithium aluminum hydride. Primary amines can also be reduced from nitriles. The third option is alkylation reactions, that is, the introduction of alkyl groups into ammonia molecules.
The use of amines
By themselves, in the form of pure substances, amines are used little. One of the rare examples is polyethylene polyamine (PEPA), which in domestic conditions facilitates the hardening of epoxy. Basically, a primary, tertiary or secondary amine is an intermediate 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 comes out at the end depends directly on the raw material chosen. Pure aniline gives a blue color, and a 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 mechanical engineering, as well as in the production of ropes, fabrics and films. In addition, aliphatic diisocinates are used in the manufacture of polyurethanes. Due to their exceptional properties (lightness, strength, elasticity and the ability to attach to any surface), they are in demand in construction (mounting foam, glue) and in the footwear industry (anti-slip soles).
Medicine is another area where amines are used. Chemistry helps to synthesize from them antibiotics of the sulfonamide group, which are successfully used as second-line drugs, that is, reserve. In case bacteria develops resistance to essential drugs.
Harmful effects on the human body
Amines are known to be highly toxic substances. Any interaction with them can cause harm to health: inhalation of vapors, contact with open skin or ingestion of compounds into the body. Death occurs due to a lack of oxygen, since amines (in particular, aniline) bind to the hemoglobin of the blood and prevent it from capturing oxygen molecules. The alarming symptoms are shortness of breath, blueness of the nasolabial triangle and fingertips, tachypnea (rapid breathing), tachycardia, loss of consciousness.
If these substances get on the exposed parts of the body, it is necessary to quickly remove them with cotton wool, previously moistened with alcohol. This should be done as carefully as possible so as not to increase the area of contamination. If symptoms of poisoning appear, you should definitely consult a doctor.
Aliphatic amines are a poison for the nervous and cardiovascular systems. They can cause inhibition of the liver, its degeneration and even cancer of the bladder.