Amines came into our lives quite 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, which are based on amines. No, they did not become safer, people were simply able to "tame" them and subdue them, deriving certain benefits for themselves. About which one, and we'll talk further.
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 the same time. The configuration of 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 R-N 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.
- According to the number of radicals associated withnitrogen atom.
- By the number of amino groups (mono-, di-, three-, etc.).
The first group includes aliphatic or limiting amines, representatives of which 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 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 name of the organic group that binds to nitrogen is added with the prefix "amine", and the groups themselves are mentioned in alphabetical order, for example: methylprotylamine or methyldiphenylamine (in this case, "di" indicates that the compound has two phenyl radicals). It is allowed to make a name, the basis of which will be carbon, and the amino group to be represented as a substituent. Then its position is determined by the index under the element designation, for example, CH3CH2CH(NH2) CH2CH3. Sometimes in the upper right corner the number indicates the serial number of carbon.
Some compounds still retain trivial, well-known simplified names, such as aniline, for example. In addition, among them there may be those that have incorrectly composed names usedon a par with systematic ones, because it is easier and more convenient for scientists and people who are far from science to communicate and understand each other
Physical properties
Secondary amine, like primary, is able to form hydrogen bonds between molecules, albeit 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, due to the absence of an N-H group, is not able to form hydrogen bonds, therefore it begins to boil already at eighty-nine degrees Celsius.
At room temperature (eighteen - twenty degrees Celsius), only lower aliphatic amines are in the form of a vapor. 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 fewer organic radicals in a molecule, the more distinct it is: from almost odorless higher compounds to middle ones smelling like fish and lower ones smelling like ammonia.
Amines can form strong hydrogen bonds with water, that is, they are highly soluble in it. The more hydrocarbon radicals present in a molecule, the less soluble it is.
Chemical properties
As it is logical to assume, amines are derivatives of ammonia, which means that their properties are similar. It is conditionally possible to distinguish three types of chemical interaction that are possible for these compounds.
- First consider propertiesamines as bases. The lower (aliphatic) ones, 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 reacting with acids, all amines form s alts. These are solid substances that are highly soluble in water. Aromatic amines exhibit weaker base properties as 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 the atmospheric air. In addition, all amines are flammable (unlike ammonia).
- Interaction with nitrous acid is used in chemistry to distinguish between amines, since the products of this reaction depend on the number of organic groups present in the molecule:
- lower primary amines form alcohols as a result of the reaction;
- aromatic primaries give phenols under similar conditions;
- secondary ones are converted into nitroso compounds (as evidenced by the characteristic smell);
- tertiary forms s alts that quickly break down, so this reaction is of no value.
Special properties of aniline
Aniline is a compound having properties inherent in both the amino group and the benzene group. This is explained by the mutual influence of atoms within the molecule. On the one hand, the benzene ring weakens the basic (i.e., alkaline) manifestations in the moleculeaniline. They are lower than those 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 into 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 in the form of 2, 4, 6-tribromaniline falls to the bottom of the tube.
Amines in nature
Amines are found in nature everywhere in the form of vitamins, hormones, metabolic intermediates, they are in the body of animals and plants. In addition, when living organisms rot, medium amines are also obtained, which, in a liquid state, spread an unpleasant smell of herring brine. The "cadaveric poison" widely described in the literature appeared precisely due to the specific ambergris of amines.
For a long time, the substances we are considering were confused with ammonia because of the similar smell. But in the mid-nineteenth century, the French chemist Wurtz was able to synthesize methylamine and ethylamine and prove that they release hydrocarbons when burned. This was the fundamental difference between the mentioned compounds and ammonia.
Obtaining amines in industrial conditions
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 used in industrial practice because of its cheapness.
The first method is the reduction of nitro compounds. The reaction that produces anilinebears the name of the scientist Zinin and was held for the first time in the middle of the nineteenth century. The second method is to reduce 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.
Use of amines
Themselves, in the form of pure substances, amines are used little. One rare example is polyethylenepolyamine (PEPA), which makes it easier to cure epoxy in the home. 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 will turn out at the end depends directly on the selected raw material. Pure aniline gives a blue color, while 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 diisocyanates 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 the construction industry (mounting foam, glue) and in the shoe 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 develop resistance to essential drugs.
Harmful effects on the human body
It is known that amines are very toxic substances. Harm to he alth can be caused by any interaction with them: inhalation of vapors, contact with open skin, or ingestion of compounds into the body. Death occurs from a lack of oxygen, since amines (in particular, aniline) bind to blood hemoglobin and prevent it from capturing oxygen molecules. Alarming symptoms are shortness of breath, blue nasolabial triangle and fingertips, tachypnea (rapid breathing), tachycardia, loss of consciousness.
If these substances get on bare areas of the body, you must quickly remove them with cotton wool previously moistened with alcohol. This must be done as carefully as possible so as not to increase the area of \u200b\u200bcontamination. 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 depression of liver function, its dystrophy, and even oncological diseases of the bladder.
