Chemical properties of amines. Amines - concept, properties, application

Based on the nature of hydrocarbon substituents, amines are divided into

General structural features of amines

Just like in the ammonia molecule, in the molecule of any amine the nitrogen atom has a lone electron pair directed to one of the vertices of the distorted tetrahedron:

For this reason, amines, like ammonia, have significantly expressed basic properties.

Thus, amines, similar to ammonia, react reversibly with water, forming weak bases:

The bond between the hydrogen cation and the nitrogen atom in the amine molecule is realized using a donor-acceptor mechanism due to the lone electron pair of the nitrogen atom. Saturated amines are stronger bases compared to ammonia, because in such amines, hydrocarbon substituents have a positive inductive (+I) effect. In this regard, the electron density on the nitrogen atom increases, which facilitates its interaction with the H + cation.

Aromatic amines, if the amino group is directly connected to the aromatic ring, exhibit weaker basic properties compared to ammonia. This is due to the fact that the lone electron pair of the nitrogen atom is shifted towards the aromatic π-system of the benzene ring, as a result of which the electron density on the nitrogen atom decreases. In turn, this leads to a decrease in basic properties, in particular the ability to interact with water. For example, aniline reacts only with strong acids, but practically does not react with water.

Chemical properties of saturated amines

As already mentioned, amines react reversibly with water:

Aqueous solutions of amines have an alkaline reaction due to the dissociation of the resulting bases:

Saturated amines react with water better than ammonia due to their stronger basic properties.

The basic properties of saturated amines increase in the series.

Secondary saturated amines are stronger bases than primary saturated amines, which in turn are stronger bases than ammonia. As for the main properties of tertiary amines, then if we're talking about about reactions in aqueous solutions, the basic properties of tertiary amines are expressed much worse than those of secondary amines, and even slightly worse than those of primary ones. This is due to steric hindrances, which significantly affect the rate of amine protonation. In other words, three substituents “block” the nitrogen atom and interfere with its interaction with H + cations.

Interaction with acids

Both free saturated amines and their aqueous solutions react with acids. In this case, salts are formed:

Since the basic properties of saturated amines are more pronounced than those of ammonia, such amines react even with weak acids, such as carbonic acid:

Amine salts are solids that are highly soluble in water and poorly soluble in non-polar organic solvents. The interaction of amine salts with alkalis leads to the release of free amines, similar to the displacement of ammonia when alkalis act on ammonium salts:

2. Primary saturated amines react with nitrous acid to form the corresponding alcohols, nitrogen N2 and water. For example:

A characteristic feature of this reaction is the formation of nitrogen gas, and therefore it is qualitative for primary amines and is used to distinguish them from secondary and tertiary ones. It should be noted that most often this reaction is carried out by mixing the amine not with a solution of nitrous acid itself, but with a solution of a salt of nitrous acid (nitrite) and then adding a strong mineral acid to this mixture. When nitrites interact with strong mineral acids, nitrous acid is formed, which then reacts with the amine:

Secondary amines give, under similar conditions, oily liquids, the so-called N-nitrosamines, but this reaction in real Unified State Exam assignments not found in chemistry. Tertiary amines do not react with nitrous acid.

Complete combustion of any amines leads to the formation of carbon dioxide, water and nitrogen:

Interaction with haloalkanes

It is noteworthy that exactly the same salt is obtained by the action of hydrogen chloride on a more substituted amine. In our case, when hydrogen chloride reacts with dimethylamine:

Preparation of amines:

1) Alkylation of ammonia with haloalkanes:

In case of ammonia deficiency, its salt is obtained instead of amine:

2) Reduction by metals (to hydrogen in the activity series) in an acidic environment:

followed by treatment of the solution with alkali to release the free amine:

3) The reaction of ammonia with alcohols when passing their mixture through heated aluminum oxide. Depending on the alcohol/amine proportions, primary, secondary or tertiary amines are formed:

Chemical properties of aniline

Aniline - the trivial name for aminobenzene, having the formula:

As can be seen from the illustration, in the aniline molecule the amino group is directly connected to the aromatic ring. Such amines, as already mentioned, have much less pronounced basic properties than ammonia. Thus, in particular, aniline practically does not react with water and weak acids such as carbonic acid.

Reaction of aniline with acids

Aniline reacts with strong and medium strength inorganic acids. In this case, phenylammonium salts are formed:

Reaction of aniline with halogens

As was already said at the very beginning of this chapter, the amino group in aromatic amines is drawn into the aromatic ring, which in turn reduces the electron density on the nitrogen atom, and as a result increases it in the aromatic ring. An increase in electron density in the aromatic ring leads to the fact that electrophilic substitution reactions, in particular reactions with halogens, proceed much more easily, especially in the ortho and para positions relative to the amino group. Thus, aniline easily reacts with bromine water, forming a white precipitate of 2,4,6-tribromoaniline:

This reaction is qualitative for aniline and often makes it possible to identify it among others organic compounds.

Reaction of aniline with nitrous acid

Aniline reacts with nitrous acid, but due to the specificity and complexity of this reaction, it does not appear in the real Unified State Exam in chemistry.

Aniline alkylation reactions

Using sequential alkylation of aniline at the nitrogen atom with halogenated hydrocarbons, secondary and tertiary amines can be obtained:

Chemical properties of amino acids

Amino acids are compounds whose molecules contain two types of functional groups - amino (-NH 2) and carboxy- (-COOH) groups.

In other words, amino acids can be considered as derivatives of carboxylic acids, in the molecules of which one or more hydrogen atoms are replaced by amino groups.

Thus, general formula amino acids can be written as (NH 2) x R(COOH) y, where x and y are most often equal to one or two.

Since amino acid molecules contain both an amino group and a carboxyl group, they exhibit chemical properties similar to both amines and carboxylic acids.

Acidic properties of amino acids

Formation of salts with alkalis and alkali metal carbonates

Esterification of amino acids

Amino acids can react with esterification with alcohols:

NH 2 CH 2 COOH + CH 3 OH → NH 2 CH 2 COOCH 3 + H 2 O

Basic properties of amino acids

1. Formation of salts when interacting with acids

NH 2 CH 2 COOH + HCl → + Cl —

2. Interaction with nitrous acid

NH 2 -CH 2 -COOH + HNO 2 → HO-CH 2 -COOH + N 2 + H 2 O

Note: interaction with nitrous acid proceeds in the same way as with primary amines

3. Alkylation

NH 2 CH 2 COOH + CH 3 I → + I —

4. Interaction of amino acids with each other

Amino acids can react with each other to form peptides - compounds containing in their molecules the peptide bond –C(O)-NH-

At the same time, it should be noted that in the case of a reaction between two different amino acids, without observing some specific synthesis conditions, the formation of different dipeptides occurs simultaneously. So, for example, instead of the reaction of glycine with alanine above, leading to glycylananine, the reaction leading to alanylglycine can occur:

In addition, the glycine molecule does not necessarily react with the alanine molecule. Peptization reactions also occur between glycine molecules:

And alanine:

In addition, since the molecules of the resulting peptides, like the original amino acid molecules, contain amino groups and carboxyl groups, the peptides themselves can react with amino acids and other peptides due to the formation of new peptide bonds.

Individual amino acids are used to produce synthetic polypeptides or so-called polyamide fibers. Thus, in particular, using the polycondensation of 6-aminohexane (ε-aminocaproic) acid, nylon is synthesized in industry:

The nylon resin obtained as a result of this reaction is used for the production textile fibers and plastics.

Formation of internal salts of amino acids in aqueous solution

In aqueous solutions, amino acids exist predominantly in the form of internal salts - bipolar ions (zwitterions).

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

Classification

• Based on how many hydrogen atoms are replaced by a radical in ammonia, primary amines (one atom), secondary, and tertiary are distinguished. Radicals can be the same or different types.
• An amine may contain more than one amino group. According to this characteristic, they are divided into mono, di-, tri-, ... polyamines.
• Based on the type of radicals associated with the nitrogen atom, there are aliphatic (not containing cyclic chains), aromatic (containing a ring, the most famous is aniline with a benzene ring), mixed (fatty-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. How longer chain, the harder the substance. The simplest amines are water-soluble, but as we move to more complex compounds, water solubility decreases.

Gaseous and liquid amines are substances with a pronounced ammonia odor. Solid ones are practically odorless.

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

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

Almost all amines, with rare exceptions, are poisonous. Thus, 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 vapors.

Signs of poisoning:

- shortness of breath,
- blueness of the nose, lips, fingertips,
- rapid breathing and increased heart rate, 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 materials for the production of polyamide artificial fibers, for example, nylon.

— For the production of polyurethanes, polyurethane foams, polyurethane adhesives.

— The starting product for the production of aniline is the basis for aniline dyes.

- For production medicines.

— For the production 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.

— To obtain photosensitive materials.

— Hexamine is used as food supplement, 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, and pesticides.

Diethylamine

Secondary amine. It is used as a starting product in the production of pesticides, drugs (for example, novocaine), dyes, repellents, additives to fuel and motor oils. Reagents are made from it for corrosion protection, ore enrichment, curing epoxy resins, and accelerating vulcanization processes.

Triethylamine

Tertiary amine. Used in the chemical industry as a catalyst in the production of rubber, epoxy resins, polyurethane foams. In metallurgy, it is a hardening catalyst in non-firing processes. Raw materials 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 agents.

Hexamine (hexamine)

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

Amines are the only class of organic compounds that are noticeably basic. However, amines are weak bases. Now it will be useful to return to the table. 12-1 to recall the three definitions of acids and bases. According to the three definitions of basicity, three aspects of the chemical behavior of amines can be distinguished.

1. Amines react with acids, acting as proton acceptors:

Therefore, amines are Bronsted bases. 2. Amines are electron pair donors (Lewis bases):

3. Aqueous solutions of amines therefore, amines, when interacting with water, are capable of generating hydroxide anions

Therefore, amines are Arrhenius bases. Although all amines are weak bases, their basicity depends on the nature and number of hydrocarbon radicals attached to the nitrogen atom. Alkylamines are much more basic than aromatic amines. Among the alkylamines, the most basic are the secondary ones, the primary ones are somewhat less basic, followed by the tertiary amines and ammonia. In general, basicity decreases in the order:

A measure of the basicity of a substance is the basicity constant, which is the equilibrium constant of the interaction of an amine with water (see the Arrhenius definition of basicity above). Since water is present in large excess, its concentration does not appear in the expression of the basicity constant:

The stronger the base, the larger number protons will be torn away from water molecules and the higher will be the concentration of hydroxide ions in the solution. Thus, stronger bases are characterized

large K values ​​Values ​​for some amines are given below:

These values ​​illustrate the relationship between the basicity of amines and their structure, which was discussed above. The strongest base is secondary dimethylamine, and the weakest is the aromatic amine aniline.

Aromatic amines are very weak bases because the lone electron pair of the nitrogen atom (which determines the basic properties of amines) interacts with the -electron cloud of the aromatic nucleus and is therefore less accessible to a proton (or other acid). The higher basicity of secondary amines compared to primary ones is explained by the fact that alkyl groups, due to their positive inductive effect, supply electrons through -bonds to the nitrogen atom, which facilitates the sharing of a lone electron pair. Two alkyl groups contribute electrons to the nitrogen atom more strongly than one, so secondary amines are stronger bases. Based on this, one would expect that tertiary amines are even stronger bases than secondary ones. However, this assumption is justified only for the gas phase, and in aqueous solution the basicity of tertiary amines is not so high. This is probably due to solvation effects.

Amines are weak organic bases. Their basicity is determined by the number and nature of organic substituents connected to the nitrogen atom. The presence of an aromatic ring sharply reduces the basicity (the value of amines. Secondary amines are stronger bases than primary and tertiary ones.

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 replacing 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, and the groups are mentioned in alphabetical order: CH3NC3H - methylpropylamine, CH3N(C6H5)2 - methyldiphenylamine. For higher amines, the name is compiled using the hydrocarbon as a basis, adding the prefix “amino”, “diamino”, “triamino”, indicating the numerical index of the carbon atom. For some amines, trivial names are used: C6H5NH2 - aniline (systematic name - phenylamine).

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

Physical properties

Low-limit primary amines are gaseous substances, have an ammonia odor, and are highly soluble 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 have similar chemical properties to ammonia.

1. Interaction with water - the formation of substituted ammonium hydroxides. A solution of ammonia in water has weak alkaline (basic) properties. The reason for the basic properties of ammonia is the presence of a lone electron pair on 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 - 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. Alkalies, as stronger bases, displace ammonia and amines from their salts.

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

Alkylation is the introduction of an alkyl substituent into a molecule of an organic compound. Typical alkylating agents are alkyl halides, alkenes, epoxy compounds, alcohols, and less commonly aldehydes, ketones, ethers, sulfides, and diazoalkanes. Alkylation catalysts include 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 the -C(O)N moiety<:

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

Primary and secondary amines react with nitrous acid in different ways. Nitrous acid is used to distinguish primary, secondary and tertiary amines 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 a primary amine in the flask.

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

(C2H5)2NH + HNO2 → (C2H5)2N-N=O + H2O

Secondary amines are difficult 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.

Methods of obtaining

1. Interaction of alcohols with ammonia when heated 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, production. 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, like hydroxy acids, depends on the isomerism of the carbon chain and on the position of the amino group relative to the carboxyl (a-, β - and γ - amino acids, etc.). In addition, all natural amino acids, except aminoacetic acid, 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 glycol or icin, and aminopropionic acid - alanine etc.). The name of an amino acid according to 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.

Methods of obtaining

1. Interaction of α-halocarboxylic acids with excess ammonia. During these reactions, the halogen atom in halogenated carboxylic acids (for their preparation, see § 10.4) is replaced by an amino group. The resulting hydrogen chloride is bound by excess ammonia to form ammonium chloride.

2. Protein hydrolysis. The hydrolysis of proteins usually produces complex mixtures of amino acids, but 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 (a carboxyl group is involved).

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

2. Interaction inside 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 a 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 a pH > 7 (alkaline environment), since 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. React 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 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 part of proteins and peptides and plays important role in the processes of skin tissue formation. Important for detoxification processes. Empirical formula C3H7NO2S.

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

Cystine is a non-coded amino acid that is a product of the oxidative dimerization of cysteine, during which two thiol groups of cysteine ​​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 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, part of almost any protein, 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 the glutamate anion is present in proteins, a number of low-molecular 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 representatives of the class of “excitatory amino acids”. The binding of glutamate to specific neuronal receptors leads to the excitation of the latter.

Simple and complex proteins. Peptide bond. The concept of the primary, secondary, tertiary and quaternary structure of a 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 reactions, denaturation reactions, color reactions). Isoelectric point. The meaning of proteins.

Proteins - These are natural high-molecular compounds (biopolymers), the structural basis of which is made up of 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 (simple protein), contain a non-amino acid component - 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.

Primary structure is the sequence of amino acids in a polypeptide chain. Important features of the primary structure are conserved motifs - combinations of amino acids that play a key role in protein functions. Conserved motifs are conserved throughout the evolution of species and can often be used to predict the function of an unknown protein.

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

Tertiary structure is 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 a critical role. The following take part in stabilizing the tertiary structure:

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 fold so that the nonpolar 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) - mutual arrangement 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 completion 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 one. 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, usually forming colloidal solutions (for example, egg white); others dissolve in dilute salt solutions; still 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 participating in many reactions. Proteins undergo oxidation-reduction reactions, esterification, alkylation, nitration, and can form salts with both acids and bases (proteins are amphoteric).

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

Amines- organic derivatives of ammonia, in the molecule of which one, two or all three hydrogen atoms are replaced by a carbon residue.

There are usually three types of amines:

Amines in which the amino group is bonded directly to an aromatic ring are called aromatic amines.

The simplest representative of these compounds is aminobenzene, or aniline:

Basic distinctive feature The electronic structure of amines is the presence of a lone electron pair on the nitrogen atom included in the functional group. This causes amines to exhibit the properties of bases.

There are ions that are the product of the formal replacement of all hydrogen atoms in the ammonium ion by a hydrocarbon radical:

These ions are found in salts similar to ammonium salts. They are called quaternary ammonium salts.

Isomerism and nomenclature of amines

1. Amines are characterized by structural isomerism:

A) carbon skeleton isomerism:

b) isomerism of the position of the functional group:

2. Primary, secondary and tertiary amines are isomeric to each other (interclass isomerism):

As can be seen from the examples given, in order to name an amine, the substituents associated with the nitrogen atom are listed (in order of precedence) and the suffix is ​​added - amine.

Physical properties of amines

The simplest amines (methylamine, dimethylamine, trimethylamine) are gaseous substances. The remaining lower amines are liquids that dissolve well in water. They have a characteristic odor reminiscent of ammonia.

Primary and secondary amines are capable of forming hydrogen bonds. This leads to a noticeable increase in their boiling points compared to compounds that have the same molecular weight but are unable to form hydrogen bonds.

Aniline is an oily liquid, sparingly soluble in water, boiling at a temperature of 184 °C.

Chemical properties of amines

Chemical properties amines are determined mainly by the presence of a lone electron pair on the nitrogen atom.

Amines as bases. The nitrogen atom of the amino group, like the nitrogen atom in the ammonia molecule, due to a lone pair of electrons, can form a covalent bond according to the donor-acceptor mechanism, acting as a donor. In this regard, amines, like ammonia, are capable of attaching a hydrogen cation, i.e., acting as a base:

1. Reaction of amions with water leads to the formation of hydroxide ions:

2. Reaction with acids. Ammonia reacts with acids to form ammonium salts. Amines are also capable of reacting with acids:

The basic properties of aliphatic amines are more pronounced than those of ammonia. This is due to the presence of one or more donor alkyl substituents, the positive inductive effect of which increases the electron density on the nitrogen atom. An increase in electron density turns nitrogen into a stronger electron pair donor, which improves its basic properties:

Amion combustion. Amines burn in air to form carbon dioxide, water and nitrogen:

Application of amines

Amines are widely used to obtain drugs, polymer materials. Aniline is the most important compound of this class, which is used for the production of aniline dyes, drugs (sulfonamide drugs), and polymeric materials (aniline formaldehyde resins).