Aromatic amines exhibit. Amines

Since amines, being derivatives of ammonia, have a structure similar to it (i.e., they have an unshared pair of electrons in the nitrogen atom), they exhibit properties similar to it. Those. amines, like ammonia, are bases, since the nitrogen atom can provide an electron pair to form a bond with electron-deficient particles according to the donor-acceptor mechanism (corresponding to the definition of Lewis basicity).

I. Properties of amines as bases (proton acceptors)

1. Aqueous solutions of aliphatic amines show an alkaline reaction, because when they interact with water, alkylammonium hydroxides are formed, similar to ammonium hydroxide:

CH 3 NH 2 + H 2 O CH 3 NH 3 + + OH -

Aniline practically does not react with water.

Aqueous solutions are alkaline in nature:

The bond of a proton with an amine, as with ammonia, is formed according to the donor-acceptor mechanism due to the lone electron pair of the nitrogen atom.

Aliphatic amines are stronger bases than ammonia, because alkyl radicals increase the electron density on the nitrogen atom due to + I-effect. For this reason, the electron pair of the nitrogen atom is held less firmly and interacts more easily with the proton.

2. Interacting with acids, amines form salts:

C 6 H 5 NH 2 + HCl → (C 6 H 5 NH 3) Cl

phenylammonium chloride

2CH 3 NH 2 + H 2 SO 4 → (CH 3 NH 3) 2 SO 4

methyl ammonium sulfate

Amine salts are solids that are highly soluble in water and poorly soluble in non-polar liquids. When reacting with alkalis, free amines are released:

Aromatic amines are weaker bases than ammonia, since the lone electron pair of the nitrogen atom shifts towards the benzene ring, conjugating with the π-electrons of the aromatic nucleus, which reduces the electron density on the nitrogen atom (-M effect). On the contrary, the alkyl group is a good electron density donor (+I-effect).

or

A decrease in the electron density on the nitrogen atom leads to a decrease in the ability to split off protons from weak acids. Therefore, aniline interacts only with strong acids (HCl, H 2 SO 4), and its aqueous solution does not color litmus blue.

The nitrogen atom in amine molecules has an unshared pair of electrons, which can participate in the formation of a bond by the donor-acceptor mechanism.

aniline ammonia primary amine secondary amine tertiary amine

the electron density on the nitrogen atom increases.

Due to the presence of a lone pair of electrons in the molecules, amines, like ammonia, exhibit basic properties.

aniline ammonia primary amine secondary amine

the basic properties are enhanced, due to the influence of the type and number of radicals.

C6H5NH2< NH 3 < RNH 2 < R 2 NH < R 3 N (в газовой фазе)

II. Amine oxidation

Amines, especially aromatic ones, are easily oxidized in air. Unlike ammonia, they are capable of being ignited by an open flame. Aromatic amines spontaneously oxidize in air. Thus, aniline quickly turns brown in air due to oxidation.

4CH 3 NH 2 + 9O 2 → 4CO 2 + 10H 2 O + 2N 2

4C 6 H 5 NH 2 + 31O 2 → 24CO 2 + 14H 2 O + 2N 2

III. Interaction with nitrous acid

Nitrous acid HNO 2 is an unstable compound. Therefore, it is used only at the moment of selection. HNO 2 is formed, like all weak acids, by the action of a strong acid on its salt (nitrite):

KNO 2 + HCl → HNO 2 + KCl

or NO 2 - + H + → HNO 2

The structure of the reaction products with nitrous acid depends on the nature of the amine. Therefore, this reaction is used to distinguish between primary, secondary and tertiary amines.

Primary aliphatic amines with HNO 2 form alcohols:

R-NH 2 + HNO 2 → R-OH + N 2 + H 2 O

• Of great importance is the reaction of diazotization of primary aromatic amines under the action of nitrous acid obtained by the reaction of sodium nitrite with hydrochloric acid. And then phenol is formed:

Secondary amines (aliphatic and aromatic) under the action of HNO 2 are converted into N-nitroso derivatives (substances with a characteristic odor):

R 2 NH + H-O-N=O → R 2 N-N=O + H 2 O

alkylnitrosamine

· The reaction with tertiary amines leads to the formation of unstable salts and is of no practical importance.

IV. Special properties:

1. Formation of complex compounds with transition metals:

2. Addition of alkyl halides Amines add haloalkanes to form a salt:

By treating the resulting salt with alkali, you can get a free amine:

V. Aromatic electrophilic substitution in aromatic amines (reaction of aniline with bromine water or nitric acid):

In aromatic amines, the amino group facilitates substitution in the ortho and para positions of the benzene ring. Therefore, aniline halogenation occurs rapidly even in the absence of catalysts, and three hydrogen atoms of the benzene ring are replaced at once, and a white precipitate of 2,4,6-tribromaniline precipitates:

This reaction with bromine water is used as a qualitative reaction for aniline.

In these reactions (bromination and nitration) predominantly formed ortho- and pair-derivatives.

4. Methods for obtaining amines.

1. Hoffmann reaction. One of the first methods for obtaining primary amines is the alkylation of ammonia with alkyl halides:

This is not the best method, since the result is a mixture of amines of all degrees of substitution:

etc. Not only alkyl halides, but also alcohols can act as alkylating agents. To do this, a mixture of ammonia and alcohol is passed over aluminum oxide at high temperature.

2. Zinin's reaction- a convenient way to obtain aromatic amines in the reduction of aromatic nitro compounds. The following are used as reducing agents: H 2 (on a catalyst). Sometimes hydrogen is generated directly at the moment of the reaction, for which metals (zinc, iron) are treated with dilute acid.

2HCl + Fe (shavings) → FeCl 2 + 2H

C 6 H 5 NO 2 + 6 [H] C 6 H 5 NH 2 + 2H 2 O.

In industry, this reaction proceeds by heating nitrobenzene with water vapor in the presence of iron. In the laboratory, hydrogen "at the moment of isolation" is formed by the reaction of zinc with alkali or iron with hydrochloric acid. In the latter case, anilinium chloride is formed.

3. Recovery of nitriles. Use LiAlH 4:

4. Enzymatic decarboxylation of amino acids:

5. The use of amines.

Amines are used in the pharmaceutical industry and organic synthesis (CH 3 NH 2, (CH 3) 2 NH, (C 2 H 5) 2 NH, etc.); in the production of nylon (NH 2 - (CH 2) 6 -NH 2 - hexamethylenediamine); as a raw material for the production of dyes and plastics (aniline), as well as pesticides.

List of sources used:

1. O.S. Gabrielyan and others. Chemistry. Grade 10. Profile level: textbook for educational institutions; Bustard, Moscow, 2005;
2. "Tutor in Chemistry" edited by A. S. Egorov; "Phoenix", Rostov-on-Don, 2006;
3. G. E. Rudzitis, F. G. Feldman. Chemistry 10 cells. M., Education, 2001;
4. https://www.calc.ru/Aminy-Svoystva-Aminov.html
5. http://www.yaklass.ru/materiali?mode=lsntheme&themeid=144
6. http://www.chemel.ru/2008-05-24-19-21-00/2008-06-01-16-50-05/193-2008-06-30-20-47-29.html
7. http://cnit.ssau.ru/organics/chem5/n232.htm

Amines are organic derivatives of ammonia containing an amino group NH 2 and an organic radical. In general, the formula of an amine is the formula of ammonia in which the hydrogen atoms are replaced by a hydrocarbon radical.

Classification

• According to how many hydrogen atoms in ammonia are replaced by a radical, primary amines (one atom), secondary, tertiary are distinguished. Radicals can be the same or different types.
• An amine may contain more than one amino group, but several. According to this characteristic, they are divided into mono, di-, tri-, ... polyamines.
• According to the type of radicals associated with the nitrogen atom, there are aliphatic (not containing cyclic chains), aromatic (containing a cycle, the most famous is aniline with a benzene ring), mixed (fat-aromatic, containing cyclic and non-cyclic radicals).

Properties

Depending on the length of the chain of atoms in the organic radical, amines can be gaseous (tri-, di-, methylamine, ethylamine), liquid or solid substances. The longer the chain, the harder the substance. The simplest amines are water soluble, but as you move to more complex compounds, the water solubility decreases.

Gaseous and liquid amines are substances with a pronounced smell of ammonia. Solids are practically odorless.

Amines exhibit strong basic properties in chemical reactions; as a result of interaction with inorganic acids, alkylammonium salts are obtained. The reaction with nitrous acid is qualitative for this class of compounds. In the case of the primary amine, alcohol and gaseous nitrogen are obtained, with the secondary, an insoluble yellow precipitate with a pronounced smell of nitrosodimethylamine; with the tertiary reaction does not go.

They react with oxygen (burn in air), halogens, carboxylic acids and their derivatives, aldehydes, ketones.

Almost all amines, with rare exceptions, are toxic. So, the most famous representative of the class, aniline, easily penetrates the skin, oxidizes hemoglobin, depresses the central nervous system, disrupts metabolism, which can even lead to death. Toxic to humans and couples.

Signs of poisoning:

Dyspnea,
- cyanosis of the nose, lips, fingertips,
- rapid breathing and increased heartbeat, loss of consciousness.

First aid:

Wash off the chemical reagent with cotton wool and alcohol,
- provide access to clean air,
- call an ambulance.

Application

As a hardener for epoxy resins.

As a catalyst in the chemical industry and metallurgy.

Raw material for the production of polyamide artificial fibers, such as nylon.

For the manufacture of polyurethanes, polyurethane foams, polyurethane adhesives.

The initial product for the production of aniline is the basis for aniline dyes.

For the production of medicines.

For the manufacture of phenol-formaldehyde resins.

For the synthesis of repellents, fungicides, insecticides, pesticides, mineral fertilizers, rubber vulcanization accelerators, anti-corrosion reagents, buffer solutions.

As an additive to motor oils and fuels, dry fuel.

For obtaining photosensitive materials.

Urotropin is used as a food additive, as well as an ingredient in cosmetics.

In our online store you can buy reagents belonging to the class of amines.

methylamine

Primary aliphatic amine. It is in demand as a raw material for the production of medicines, dyes, pesticides.

diethylamine

secondary amine. It is used as an initial product in the production of pesticides, drugs (for example, novocaine), dyes, repellents, additives to fuel and motor oils. It is used to make reagents for corrosion protection, for beneficiation of ores, for curing epoxy resins, and for accelerating vulcanization processes.

Triethylamine

Tertiary amine. It is used in the chemical industry as a catalyst in the production of rubber, epoxy resins, polyurethane foams. In metallurgy - a hardening catalyst in non-firing processes. Raw material in the organic synthesis of medicines, mineral fertilizers, weed control agents, paints.

1-butylamine

Tert-butylamine, a compound in which a tert-butyl organic group is bonded to nitrogen. The substance is used in the synthesis of rubber vulcanization enhancers, drugs, dyes, tannins, weed and insect control preparations.

Urotropin (Hexamine)

polycyclic amine. A substance in demand in the economy. Used as a food additive, drug and drug component, ingredient in cosmetics, buffer solutions for analytical chemistry; as a dry fuel, polymer resin hardener, in the synthesis of phenol-formaldehyde resins, fungicides, explosives, corrosion protection agents.

Amines - these are derivatives of ammonia (NH 3), in the molecule of which one, two or three hydrogen atoms are replaced by hydrocarbon radicals.

According to the number of hydrocarbon radicals that replace hydrogen atoms in the NH 3 molecule, all amines can be divided into three types:

The group - NH 2 is called an amino group. There are also amines that contain two, three or more amino groups.

Nomenclature

The word "amine" is added to the name of organic residues associated with nitrogen, while the groups are mentioned in alphabetical order: CH3NC3H - methylpropylamine, CH3N(C6H5)2 - methyldiphenylamine. For higher amines, the name is compiled, taking the hydrocarbon as a basis, adding the prefix "amino", "diamino", "triamino", indicating the numerical index of the carbon atom. Trivial names are used for some amines: C6H5NH2 - aniline (systematic name - phenylamine).

For amines, chain isomerism, functional group position isomerism, isomerism between types of amines is possible

Physical Properties

Lower limiting primary amines - gaseous substances, have the smell of ammonia, dissolve well in water. Amines with a higher relative molecular weight are liquids or solids, their solubility in water decreases with increasing molecular weight.

Chemical properties

Amines are chemically similar to ammonia.

1. Interaction with water - the formation of substituted ammonium hydroxides. Ammonia solution in water has weak alkaline (basic) properties. The reason for the main properties of ammonia is the presence of a lone electron pair at the nitrogen atom, which is involved in the formation of a donor-acceptor bond with a hydrogen ion. For the same reason, amines are also weak bases. Amines are organic bases.

2. Interaction with acids - the formation of salts (neutralization reactions). As a base, ammonia forms ammonium salts with acids. Similarly, when amines react with acids, substituted ammonium salts are formed. Alkalis, as stronger bases, displace ammonia and amines from their salts.

3. Combustion of amines. Amines are combustible substances. The combustion products of amines, as well as other nitrogen-containing organic compounds, are carbon dioxide, water and free nitrogen.

Alkylation is the introduction of an alkyl substituent into the molecule of an organic compound. Typical alkylating agents are alkyl halides, alkenes, epoxy compounds, alcohols, less often aldehydes, ketones, ethers, sulfides, diazoalkanes. Alkylation catalysts are mineral acids, Lewis acids and zeolites.

Acylation. When heated with carboxylic acids, their anhydrides, acid chlorides or esters, primary and secondary amines are acylated to form N-substituted amides, compounds with a fragment -C (O) N<:

The reaction with anhydrides proceeds under mild conditions. Acid chlorides react even more easily, the reaction is carried out in the presence of a base to bind the HCl formed.

Primary and secondary amines interact with nitrous acid in different ways. With the help of nitrous acid, primary, secondary and tertiary amines are distinguished from each other. Primary alcohols are formed from primary amines:

C2H5NH2 + HNO2 → C2H5OH + N2 + H2O

This releases gas (nitrogen). This is a sign that there is primary amine in the flask.

Secondary amines form yellow, sparingly soluble nitrosamines with nitrous acid - compounds containing the >N-N=O fragment:

(C2H5)2NH + HNO2 → (C2H5)2N-N=O + H2O

Secondary amines are hard to miss, the characteristic smell of nitrosodimethylamine spreads throughout the laboratory.

Tertiary amines simply dissolve in nitrous acid at ordinary temperatures. When heated, a reaction with the elimination of alkyl radicals is possible.

How to get

1. Interaction of alcohols with ammonia during heating in the presence of Al 2 0 3 as a catalyst.

2. Interaction of alkyl halides (haloalkanes) with ammonia. The resulting primary amine can react with excess alkyl halide and ammonia to form a secondary amine. Tertiary amines can be prepared similarly

Amino acids. Classification, isomerism, nomenclature, obtaining. Physical and chemical properties. Amphoteric properties, bipolar structure, isoelectric point. Polypeptides. Individual representatives: glycine, alanine, cysteine, cystine, a-aminocaproic acid, lysine, glutamic acid.

Amino acids- these are derivatives of hydrocarbons containing amino groups (-NH 2) and carboxyl groups -COOH.

General formula: (NH 2) f R(COOH) n where m and n most often equal to 1 or 2. Thus, amino acids are compounds with mixed functions.

Classification

isomerism

The isomerism of amino acids, as well as hydroxy acids, depends on the isomerism of the carbon chain and on the position of the amino group in relation to the carboxyl (a-, β - and γ - amino acids, etc.). In addition, all natural amino acids, except aminoacetic, contain asymmetric carbon atoms, so they have optical isomers (antipodes). There are D- and L-series of amino acids. It should be noted that all amino acids that make up proteins belong to the L-series.

Nomenclature

Amino acids usually have trivial names (for example, aminoacetic acid is called differently glycocol or iicin, and aminopropionic acid alanine etc.). The name of an amino acid according to the systematic nomenclature consists of the name of the corresponding carboxylic acid, of which it is a derivative, with the addition of the word amino- as a prefix. The position of the amino group in the chain is indicated by numbers.

How to get

1. Interaction of α-halocarboxylic acids with an excess of ammonia. In the course of these reactions, the halogen atom in halocarboxylic acids (for their preparation, see § 10.4) is replaced by an amino group. The hydrogen chloride released at the same time is bound by an excess of ammonia into ammonium chloride.

2. Hydrolysis of proteins. Complex mixtures of amino acids are usually formed during the hydrolysis of proteins, however, using special methods, individual pure amino acids can be isolated from these mixtures.

Physical Properties

Amino acids are colorless crystalline substances, readily soluble in water, melting point 230-300°C. Many α-amino acids have a sweet taste.

Chemical properties

1. Interaction with bases and acids:

a) as an acid (carboxyl group is involved).

b) as a base (amino group is involved).

2. Interaction within the molecule - the formation of internal salts:

a) monoaminomonocarboxylic acids (neutral acids). Aqueous solutions of monoaminomonocarboxylic acids are neutral (pH = 7);

b) monoaminodicarboxylic acids (acidic amino acids). Aqueous solutions of monoaminodicarboxylic acids have pH< 7 (кислая среда), так как в результате образования внутренних солей этих кислот в растворе появляется избыток ионов водорода Н + ;

c) diaminomonocarboxylic acids (basic amino acids). Aqueous solutions of diaminomonocarboxylic acids have pH > 7 (alkaline), because as a result of the formation of internal salts of these acids, an excess of OH - hydroxide ions appears in the solution.

3. The interaction of amino acids with each other - the formation of peptides.

4. Interact with alcohols to form esters.

The isoelectric point of amino acids that do not contain additional NH2 or COOH groups is the arithmetic mean between the two pK values: respectively for alanine .

The isoelectric point of a number of other amino acids containing additional acidic or basic groups (aspartic and glutamic acids, lysine, arginine, tyrosine, etc.) also depends on the acidity or basicity of the radicals of these amino acids. For lysine, for example, pI should be calculated from half the sum of pK" values ​​for α- and ε-NH2 groups. Thus, in the pH range from 4.0 to 9.0, almost all amino acids exist predominantly in the form of zwitterions with a protonated amino group and a dissociated carboxyl group.

Polypeptides contain more than ten amino acid residues.

Glycine (aminoacetic acid, aminoethanoic acid) is the simplest aliphatic amino acid, the only amino acid that does not have optical isomers. Empirical formula C2H5NO2

Alanine (aminopropanoic acid) is an aliphatic amino acid. α-alanine is part of many proteins, β-alanine is part of a number of biologically active compounds. Chemical formula NH2 -CH -CH3 -COOH. Alanine is easily converted into glucose in the liver and vice versa. This process is called the glucose-alanine cycle and is one of the main pathways of gluconeogenesis in the liver.

Cysteine ​​(α-amino-β-thiopropionic acid; 2-amino-3-sulfanylpropanoic acid) is an aliphatic sulfur-containing amino acid. Optically active, exists in the form of L- and D-isomers. L-cysteine ​​is a component of proteins and peptides and plays an important role in the formation of skin tissues. It is important for detoxification processes. The empirical formula is C3H7NO2S.

Cystine (chem.) (3,3 "-dithio-bis-2-aminopropionic acid, dicysteine) is an aliphatic sulfur-containing amino acid, colorless crystals, soluble in water.

Cystine is a non-encoded amino acid that is a product of the oxidative dimerization of cysteine, during which two cysteine ​​thiol groups form a cystine disulfide bond. Cystine contains two amino groups and two carboxyl groups and is a dibasic diamino acid. Empirical formula C6H12N2O4S2

In the body, they are found mainly in the composition of proteins.

Aminocaproic acid (6-aminohexanoic acid or ε-aminocaproic acid) is a hemostatic drug that inhibits the conversion of profibrinolysin to fibrinolysin. Gross-

formula C6H13NO2.

Lysine (2,6-diaminohexanoic acid) is an aliphatic amino acid with pronounced base properties; essential amino acid. Chemical formula: C6H14N2O2

Lysine is part of proteins. Lysine is an essential amino acid that is part of almost any protein, it is necessary for growth, tissue repair, production of antibodies, hormones, enzymes, albumins.

Glutamic acid (2-aminopentanedioic acid) is an aliphatic amino acid. In living organisms, glutamic acid in the form of glutamate anion is present in proteins, a number of low molecular weight substances, and in free form. Glutamic acid plays an important role in nitrogen metabolism. Chemical formula C5H9N1O4

Glutamic acid is also a neurotransmitter amino acid, one of the important members of the excitatory amino acid class. The binding of glutamate to specific receptors of neurons leads to the excitation of the latter.

Simple and complex proteins. peptide bond. The concept of the primary, secondary, tertiary and quaternary structure of the protein molecule. Types of bonds that determine the spatial structure of the protein molecule (hydrogen, disulfide, ionic, hydrophobic interactions). Physical and chemical properties of proteins (precipitation, denaturation, color reactions). isoelectric point. The value of proteins.

Squirrels - these are natural high-molecular compounds (biopolymers), the structural basis of which is polypeptide chains built from α-amino acid residues.

Simple proteins (proteins) are high-molecular organic substances consisting of alpha-amino acids connected in a chain by a peptide bond.

Complex proteins (proteids) are two-component proteins that, in addition to peptide chains (a simple protein), contain a component of a non-amino acid nature - a prosthetic group.

Peptide bond - a type of amide bond that occurs during the formation of proteins and peptides as a result of the interaction of the α-amino group (-NH2) of one amino acid with the α-carboxyl group (-COOH) of another amino acid.

The primary structure is the sequence of amino acids in a polypeptide chain. Important features of the primary structure are conservative motifs - combinations of amino acids that play a key role in protein functions. Conservative motifs are preserved in the course of species evolution; they often make it possible to predict the function of an unknown protein.

Secondary structure - local ordering of a fragment of a polypeptide chain, stabilized by hydrogen bonds.

Tertiary structure - the spatial structure of the polypeptide chain (a set of spatial coordinates of the atoms that make up the protein). Structurally, it consists of secondary structure elements stabilized by various types of interactions, in which hydrophobic interactions play an important role. In the stabilization of the tertiary structure take part:

covalent bonds (between two cysteine ​​residues - disulfide bridges);

ionic bonds between oppositely charged side groups of amino acid residues;

hydrogen bonds;

hydrophilic-hydrophobic interactions. When interacting with surrounding water molecules, the protein molecule "tends" to curl up so that the non-polar side groups of amino acids are isolated from the aqueous solution; polar hydrophilic side groups appear on the surface of the molecule.

Quaternary structure (or subunit, domain) - the mutual arrangement of several polypeptide chains as part of a single protein complex. Protein molecules that make up a protein with a quaternary structure are formed separately on ribosomes and only after the end of synthesis form a common supramolecular structure. A protein with a quaternary structure can contain both identical and different polypeptide chains. The same types of interactions take part in the stabilization of the quaternary structure as in the stabilization of the tertiary. Supramolecular protein complexes can consist of dozens of molecules.

Physical Properties

The properties of proteins are as diverse as the functions they perform. Some proteins dissolve in water, forming, as a rule, colloidal solutions (for example, egg white); others dissolve in dilute salt solutions; others are insoluble (for example, proteins of integumentary tissues).

Chemical properties

In the radicals of amino acid residues, proteins contain various functional groups that are capable of entering into many reactions. Proteins enter into oxidation-reduction reactions, esterification, alkylation, nitration, they can form salts with both acids and bases (proteins are amphoteric).

For example, albumin - egg white - at a temperature of 60-70 ° is precipitated from a solution (coagulates), losing the ability to dissolve in water.

Amines entered 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

For the qualitative and quantitative determination of aniline in solutions or compounds, a reaction with is used at the end of which a white precipitate in the form of 2,4,6-tribromaniline falls on the bottom of the test tube.

Amines in nature

Amines are found in nature everywhere in the form of vitamins, hormones, metabolic intermediates, they are also found in 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 due to a 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 during which aniline is formed is named by the scientist Zinin and was carried out 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.

Application of amines

By themselves, in the form of pure substances, amines are used little. One rare example is polyethylenepolyamine (PEPA), which makes epoxy resin easier to cure in the home. Basically a primary, tertiary or secondary amine is an intermediate in the production of various organics. 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 obtain polyamides such as nylon and others. 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 construction (mounting foam, glue) and in the shoe industry (anti-slip soles).

Medicine is another area where amines are used. Chemistry helps to synthesize antibiotics of the sulfonamide group from them, which are successfully used as second-line drugs, that is, reserve ones. In case bacteria develop resistance to essential drugs.

Harmful effects on the human body

It is known that amines are very 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 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.

In case of contact with these substances on bare areas of the body, it is necessary to 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 degeneration and even oncological diseases of the bladder.

Due to the presence of lone pairs of electrons on nitrogen atoms. Thus, amines have basic properties similar to alcohols, ethers, and other organic compounds that belong to the group of Lewis bases. However, nitrogen atoms are less electronegative than oxygen atoms, so amines are much stronger Lewis bases relative to the proton than oxygen-containing bases, i.e. than alcohols and ethers and their substituted derivatives.

Picture 1.

Quantification of the basicity of amines

Amines have stronger basic properties than water; therefore, aqueous solutions of amines also exhibit basic properties. The equilibrium constants for the acid-base interaction of water and amines are designated $K_B$ and serve as a quantitative characteristic of the main properties of aqueous solutions of amines.

Figure 2.

The concentration of water itself is not included in these expressions for $K_B$, since water is present in solutions in a significant excess (in this case, measurements related to dilute amine solutions are considered) and the water concentration is considered constant (its change can be neglected). Instead of the $K_B$ values, it is more convenient to use the $K_a$ values, which characterize the acidity of conjugated alkylammonium ions:

Figure 3

In this case, the concept of the quantity $pK_a$ is generally similar to the concept of $pH$, and it can be easily measured. The values ​​of $pK_a$ (25 $^\circ$C) measured in aqueous solutions for a number of aliphatic amines are given in the table below:

Figure 4

The dependence of the basicity of amines on their structure

Analyzing the above $pK_a$ values, we can conclude that since all aliphatic amines have $pK_B$ values ​​lower than the $pK_B$ value of ammonia, their aqueous solutions will exhibit stronger basic properties than the corresponding ammonia solutions.

The basicity of aqueous solutions of amines decreases in the series:

$R_2NH > RNH_2 $~$ R_3N$

And such a change in properties is not consistent with the influence of the positive $I$-effect of alkyl groups, since solutions of tertiary amines show more basic than solutions of secondary amines. This is usually explained by the occurrence of steric hindrances in the transfer of protons and solvation in the case of solutions of tertiary amines.

In the gas phase, or in the case of individual substances, the basicity of amines changes in a sequence that is correct from the point of view of consideration of electronic effects:

$R_3N > RNH_2 > R_2NH > R_3N$

Basicity of arylamines

Aromatic amines are characterized by a significantly lower basicity compared to aliphatic analogues. So the value of $pK_B$ for aniline is 9.37, and the acidity of the aniline-derived cation $(C_6H_5NH_3)^+$ ($pK_a$ = 4.63) is correspondingly much higher than that of alkylammonium cations.

Figure 5

Such a significant decrease (by six orders of magnitude) in the basic properties of aniline relative to methylamine and other aliphatic amines is due to the negative $I$ effect of the aromatic nucleus and the positive $M$ effect of the amino group. The decisive role in the weakening of the basic properties of aniline is played by the delocalization of lone pairs of electrons of nitrogen atoms over benzene rings. Such delocalization generally reduces the ability of the amino group to bind protons or other acceptors.

Figure 6

As can be seen, lone electron pairs of nitrogen atoms in aniline molecules "shift" predominantly to the ortho and para positions of benzene rings, which causes the effect of ortho/para orientation upon substitution in aniline molecules.

In addition, in the case of the presence of substituents in the aromatic systems of arylamines, they have a significant effect on their basic properties. This influence can be assessed both qualitatively and quantitatively. Substituents with electron-donating properties cause an increase in the basic properties of amines, and electron-withdrawing substituents, on the contrary, lower the basicity of arylamines. So the value of $pK_a$ for various substituted aniline derivatives is given in the table below:

Figure 7

$N$-Methyl and $N,N$-dimethylanilines exhibit stronger basic properties than the original aniline itself. So for $C_5H_5N(CH_3)_2$ the value of $pK_a$ is 5.07, and for $C_5H_5N(C_2H_5)_2$ $pK_a$ is 6.57. Aniline is almost completely protonated (forms phenylammonium chloride) even in dilute acid solutions, for example, in 0.1 $H$ solution of $HCl$. 4-Nitroaniline is completely protonated only in solutions of concentrated acids - in 50% $H_2SO_4$, and 2,4-dinitroaniline ($pK_a$=-4.4) dissolves only in sulfuric acid with a concentration above 80%. Amine salts are generally readily soluble in water even when the parent amine is insoluble in water. This is widely used in the separation of amines from non-basic impurities. The amine is converted into a salt when the mixture is treated with an aqueous solution of a strong acid, the aqueous layer is separated, from which, after alkaline treatment, pure free amine is isolated.