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, and 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, then 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 with the formation of 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 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. In such amines, as already mentioned, the basic properties are much less pronounced than in 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 aromatic core. 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:

Obtaining aniline

1. Reduction of nitrobenzene by metals in the presence of strong non-oxidizing acids:

C 6 H 5 -NO 2 + 3Fe + 7HCl = +Cl- + 3FeCl 2 + 2H 2 O

Cl - + NaOH = C 6 H 5 -NH 2 + NaCl + H 2 O

Any metals located before hydrogen in the activity series can be used as metals.

Reaction of chlorobenzene with ammonia:

C 6 H 5 −Cl + 2NH 3 → C 6 H 5 NH 2 + NH 4 Cl

Chemical properties of amino acids

Amino acids are compounds in which there are two types of molecules functional groups– amino (-NH 2) and carboxy (-COOH) groups.

In other words, amino acids can be considered as derivatives 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, a reaction may occur leading to alanylglycine:

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 resulting nylon resin is used to produce 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):

Obtaining amino acids

1) Reaction of chlorinated carboxylic acids with ammonia:

Cl-CH 2 -COOH + 2NH 3 = NH 2 -CH 2 -COOH + NH 4 Cl

2) Breakdown (hydrolysis) of proteins under the action of solutions of strong mineral acids and alkalis.

Amino acids are organic amphoteric compounds. They contain two functional groups of opposite nature in the molecule: an amino group with basic properties and a carboxyl group with acidic properties. Amino acids react with both acids and bases:

H 2 N -CH 2 -COOH + HCl → Cl [H 3 N-CH 2 -COOH],

H 2 N -CH 2 -COOH + NaOH → H 2 N-CH 2 -COONa + H 2 O.

When amino acids are dissolved in water, the carboxyl group removes a hydrogen ion, which can attach to the amino group. In this case, an internal salt is formed, the molecule of which is a bipolar ion:

H 2 N-CH 2 -COOH + H 3 N -CH 2 -COO - .

Acid-base transformations of amino acids into different environments can be represented by the following general diagram:

Aqueous solutions of amino acids have a neutral, alkaline or acidic environment depending on the number of functional groups. Thus, glutamic acid forms an acidic solution (two -COOH groups, one -NH 2), lysine forms an alkaline solution (one -COOH group, two -NH 2).

Like primary amines, amino acids react with nitrous acid, with the amino group converted to a hydroxo group and the amino acid to a hydroxy acid:

H 2 N-CH(R)-COOH + HNO 2 → HO-CH(R)-COOH + N 2 + H 2 O

Measuring the volume of nitrogen released allows us to determine the amount of amino acid ( Van Slyke method).

Amino acids can react with alcohols in the presence of hydrogen chloride gas, turning into an ester (more precisely, a hydrochloride salt of an ester):

H 2 N-CH(R)-COOH + R’OH H 2 N-CH(R)-COOR’ + H 2 O.

Amino acid esters do not have a bipolar structure and are volatile compounds.

The most important property of amino acids is their ability to condense to form peptides.

Qualitative reactions.

1) All amino acids are oxidized by ninhydrin

with the formation of products colored blue-violet. The imino acid proline gives a yellow color with ninhydrin. This reaction can be used to quantify amino acids by spectrophotometry.

2) When aromatic amino acids are heated with concentrated nitric acid, nitration of the benzene ring occurs and yellow-colored compounds are formed. This reaction is called xanthoprotein(from the Greek xanthos - yellow).

Amino acids exhibit properties of both acids and amines. So, they form salts (due to the acidic properties of the carboxyl group):

NH 2 CH 2 COOH + NaOH (NH 2 CH 2 COO)Na + H 2 O

glycine sodium glycinate

And esters(similar to other organic acids):

NH 2 CH 2 COOH + C 2 H 5 OHNH 2 CH 2 C(O)OC 2 H 5 + H 2 O

glycine ethylglycinate

With stronger acids, amino acids exhibit the properties of bases and form salts due to the basic properties of the amino group:

glycine wisteria chloride

The simplest protein is a polypeptide containing at least 70 amino acid residues in its structure and having a molecular weight of over 10,000 Da (dalton). Dalton - a unit of measurement for the mass of proteins, 1 dalton is equal to 1.66054·10 -27 kg (carbon mass unit). Similar compounds consisting of fewer amino acid residues are classified as peptides. Some hormones are peptides in nature - insulin, oxytocin, vasopressin. Some peptides are regulators of immunity. Some antibiotics (cyclosporin A, gramicidins A, B, C and S), alkaloids, toxins of bees and wasps, snakes, poisonous mushrooms (phalloidin and amanitin of the toadstool), cholera and botulinum toxins, etc. have a peptide nature.

Levels of structural organization of protein molecules.

The protein molecule has a complex structure. There are several levels of structural organization of a protein molecule - primary, secondary, tertiary and quaternary structures.

Primary structure is defined as a linear sequence of proteinogenic amino acid residues linked by peptide bonds (Fig. 5):

Fig.5. Primary structure of a protein molecule

The primary structure of a protein molecule is genetically determined for each specific protein in the nucleotide sequence of messenger RNA. The primary structure also determines higher levels of organization of protein molecules.

Secondary structure - conformation (i.e. location in space) of individual sections of the protein molecule. The secondary structure in proteins can be represented by an -helix, -structure (folded sheet structure) (Fig. 6).

Fig.6. Protein secondary structure

Protein secondary structure is maintained hydrogen bonds between peptide groups.

Tertiary structure - conformation of the entire protein molecule, i.e. spatial arrangement of the entire polypeptide chain, including the arrangement of side radicals. For a significant number of proteins, the coordinates of all protein atoms were obtained by X-ray diffraction analysis, with the exception of the coordinates of hydrogen atoms. All types of interactions take part in the formation and stabilization of the tertiary structure: hydrophobic, electrostatic (ionic), disulfide covalent bonds, hydrogen bonds. Radicals of amino acid residues participate in these interactions. Among the bonds holding the tertiary structure, it should be noted: a) disulfide bridge (- S - S -); b) ester bridge (between the carboxyl group and the hydroxyl group); c) salt bridge (between the carboxyl group and the amino group); d) hydrogen bonds.

In accordance with the shape of the protein molecule, determined by the tertiary structure, the following groups of proteins are distinguished:

1) Globular proteins , which have the shape of a globule (sphere). Such proteins include, for example, myoglobin, which has 5 α-helical segments and no β-folds, immunoglobulins, which do not have an α-helix; the main elements of the secondary structure are β-folds

2) Fibrillar proteins . These proteins have an elongated thread-like shape; they perform a structural function in the body. In the primary structure they have repeating sections and form a fairly uniform structure for the entire polypeptide chain secondary structure. Thus, protein α - keratin (the main protein component of nails, hair, skin) is built from extended α - helices. There are less common elements of secondary structure, for example, polypeptide chains of collagen, forming left-handed helices with parameters that differ sharply from the parameters of α-helices. In collagen fibers, three helical polypeptide chains are twisted into a single right-handed superhelix (Fig. 7):

Fig. 7 Tertiary structure of collagen

Quaternary structure of protein. The quaternary structure of proteins refers to the way in which individual polypeptide chains (identical or different) with a tertiary structure are arranged in space, leading to the formation of a structurally and functionally unified macromolecular formation (multimer). Not all proteins have a quaternary structure. An example of a protein with a quaternary structure is hemoglobin, which consists of 4 subunits. This protein is involved in the transport of gases in the body.

When breaking disulfide and weak types of bonds in molecules, all protein structures, except the primary one, are destroyed (completely or partially), and the protein loses its native properties (properties of a protein molecule inherent in it in its natural, natural (native) state). This process is called protein denaturation . Factors that cause protein denaturation include high temperatures, ultraviolet irradiation, concentrated acids and alkalis, salts of heavy metals and others.

Proteins are divided into simple (proteins), consisting only of amino acids, and complex (proteins), containing, in addition to amino acids, other non-protein substances, for example, carbohydrates, lipids, nucleic acids. The non-protein part of a complex protein is called a prosthetic group.

Simple proteins, consisting only of amino acid residues, are widespread in the animal and plant world. Currently, there is no clear classification of these compounds.

Histones

They have a relatively low molecular weight (12-13 thousand), with a predominance of alkaline properties. Localized mainly in cell nuclei, soluble in weak acids, precipitated by ammonia and alcohol. They have only tertiary structure. Under natural conditions, they are tightly bound to DNA and are part of nucleoproteins. The main function is the regulation of the transfer of genetic information from DNA and RNA (transmission can be blocked).

Protamines

These proteins have the lowest molecular weight (up to 12 thousand). Exhibits pronounced basic properties. Well soluble in water and weak acids. Contained in germ cells and make up the bulk of chromatin protein. Like histones, they form a complex with DNA and impart chemical stability to DNA, but unlike histones, they do not perform a regulatory function.

Glutelins

Plant proteins contained in gluten from the seeds of cereals and some other crops, in the green parts of plants. Insoluble in water, salt solutions and ethanol, but highly soluble in weak alkali solutions. They contain all essential amino acids and are complete food products.

Prolamins

Plant proteins. Contained in gluten of cereal plants. They are soluble only in 70% alcohol (this is explained by the high content of proline and non-polar amino acids in these proteins).

Proteinoids.

Proteinoids include proteins of supporting tissues (bone, cartilage, ligaments, tendons, nails, hair); they are characterized by a high sulfur content. These proteins are insoluble or poorly soluble in water, salt and water-alcohol mixtures. Proteinoids include keratin, collagen, fibroin.

Albumin

These are low acidic proteins molecular weight(15-17 thousand), soluble in water and weak saline solutions. Precipitated by neutral salts at 100% saturation. They participate in maintaining the osmotic pressure of the blood and transport various substances with the blood. Contained in blood serum, milk, egg white.

Globulins

Molecular weight up to 100 thousand. Insoluble in water, but soluble in weak salt solutions and precipitate in less concentrated solutions (already at 50% saturation). Contained in plant seeds, especially legumes and oilseeds; in blood plasma and some other biological fluids. They perform the function of immune defense and ensure the body's resistance to viral infectious diseases.

1.Amino acids exhibit amphoteric properties and acids and amines, as well as specific properties, due to the joint presence of these groups. In aqueous solutions, AMK exist in the form of internal salts (bipolar ions). Aqueous solutions of monoaminomonocarboxylic acids are neutral to litmus, because their molecules contain equal number-NH 2 - and -COOH groups. These groups interact with each other to form internal salts:

Such a molecule has opposite charges in two places: positive NH 3 + and negative on the carboxyl –COO -. In this regard, the internal salt of AMK is called a bipolar ion or Zwitter ion (Zwitter - hybrid).

A bipolar ion in an acidic environment behaves like a cation, since the dissociation of the carboxyl group is suppressed; in an alkaline environment - as an anion. There are pH values ​​specific for each amino acid, in which the number of anionic forms in solution is equal to the number of cationic forms. The pH value at which the total charge of the AMK molecule is 0 is called the isoelectric point of AMK (pI AA).

Aqueous solutions of monoaminodicarboxylic acids have an acidic reaction:

HOOC-CH 2 -CH-СOOH « - OOC-CH 2 -CH–COO - + H +

The isoelectric point of monoaminodicarboxylic acids is in an acidic environment and such AMAs are called acidic.

Diaminomonocarboxylic acids have basic properties in aqueous solutions (the participation of water in the dissociation process must be shown):

NH 2 -(CH 2) 4 -CH-COOH + H 2 O « NH 3 + -(CH 2) 4 -CH–COO - + OH -

The isoelectric point of diaminomonocarboxylic acids is at pH>7 and such AMAs are called basic.

Being bipolar ions, amino acids exhibit amphoteric properties: they are able to form salts with both acids and bases:

Interaction with hydrochloric acid HCl produces a salt:

R-CH-COOH + HCl ® R-CH-COOH

NH 2 NH 3 + Cl -

Interaction with a base leads to the formation of a salt:

R-CH(NH 2)-COOH + NaOH ® R-CH(NH 2)-COONa + H 2 O

2. Formation of complexes with metals– chelate complex. The structure of the copper salt of glycol (glycine) can be represented by the following formula:

Almost all the copper available in the human body (100 mg) is bound to proteins (amino acids) in the form of these stable claw-shaped compounds.

3. Similar to other acids amino acids form esters, halogen anhydrides, amides.

4. Decarboxylation reactions occur in the body with the participation of special decarboxylase enzymes: the resulting amines (tryptamine, histamine, serotinine) are called biogenic amines and are regulators of a number of physiological functions of the human body.

5. Interaction with formaldehyde(aldehydes)

R-CH-COOH + H 2 C=O ® R-CH-COOH

Formaldehyde binds the NH 2 group, the -COOH group remains free and can be titrated with alkali. Therefore, this reaction is used for the quantitative determination of amino acids (Sørensen method).

6. Interaction with nitrous acid leads to the formation of hydroxy acids and the release of nitrogen. Based on the volume of released nitrogen N2, its quantitative content in the object under study is determined. This reaction is used for the quantitative determination of amino acids (Van-Slyke method):

R-CH-COOH + HNO 2 ® R-CH-COOH + N 2 + H 2 O

This is one of the ways to deaminate AMK outside the body

7. Acylation of amino acids. The amino group of AMK can be acylated with acid chlorides and anhydrides already at room temperature.

The product of the recorded reaction is acetyl-α-aminopropionic acid.

Acyl derivatives of AMK are widely used in studying their sequence in proteins and in the synthesis of peptides (protection of the amino group).

8.Specific properties reactions associated with the presence and mutual influence of amino and carboxyl groups - the formation of peptides. Common property a-AMK is polycondensation process, leading to the formation of peptides. As a result of this reaction, amide bonds are formed at the site of interaction between the carboxyl group of one AMK and the amino group of another AMK. In other words, peptides are amides formed as a result of the interaction of amino groups and carboxyls of amino acids. The amide bond in such compounds is called a peptide bond (explain the structure of the peptide group and peptide bond: three-center p, p-conjugated system)

Depending on the number of amino acid residues in the molecule, di-, tri-, tetrapeptides, etc. are distinguished. up to polypeptides (up to 100 AMK residues). Oligopeptides contain from 2 to 10 AMK residues, proteins contain more than 100 AMK residues.B general view The polypeptide chain can be represented by the diagram:

H 2 N-CH-CO-NH-CH-CO-NH-CH-CO-... -NH-CH-COOH

Where R 1, R 2, ... R n are amino acid radicals.

Concept of proteins.

The most important biopolymers of amino acids are proteins - proteins. There are about 5 million in the human body. various proteins that make up the skin, muscles, blood and other tissues. Proteins (proteins) get their name from Greek word“protos” - first, most important. Proteins perform a number of important functions in the body: 1. Construction function; 2. Transport function; 3. Protective function; 4. Catalytic function; 5. Hormonal function; 6. Nutritional function.

All natural proteins are formed from amino acid monomers. When proteins are hydrolyzed, a mixture of AMK is formed. There are 20 of these AMKs.

4. Illustrative material: presentation

5. Literature:

Basic literature:

1. Bioorganic chemistry: textbook. Tyukavkina N.A., Baukov Yu.I. 2014

1. Seitembetov T.S. Chemistry: textbook - Almaty: EVERO LLP, 2010. - 284 p.
2. Bolysbekova S. M. Chemistry of biogenic elements: training manual- Semey, 2012. - 219 p. : silt
3. Verentsova L.G. Inorganic, physical and colloid chemistry: textbook - Almaty: Evero, 2009. - 214 p. : ill.
4. Physical and colloidal chemistry / Edited by A.P. Belyaev. - M.: GEOTAR MEDIA, 2008
5. Verentseva L.G. Inorganic, physical and colloidal chemistry, (verification tests) 2009

Further reading:

1. Ravich-Scherbo M.I., Novikov V.V. Physical and colloidal chemistry. M. 2003.

2. Slesarev V.I. Chemistry. Fundamentals of living chemistry. St. Petersburg: Khimizdat, 2001

3. Ershov Yu.A. General chemistry. Biophysical chemistry. Chemistry of biogenic elements. M.: VSh, 2003.

4. Asanbaeva R.D., Ilyasova M.I. Theoretical foundations buildings and reactivity biologically important organic compounds. Almaty, 2003.

1. Guide to laboratory exercises in bioorganic chemistry edited by N.A. Tyukavkina. M., Bustard, 2003.
2. Glinka N.L. General chemistry. M., 2003.
3. Ponomarev V.D. Analytical Chemistry Part 1.2 2003

6. Security questions(feedback):

1. What determines the structure of the polypeptide chain as a whole?

2. What does protein denaturation lead to?

3. What is the isoelectric point called?

4. What amino acids are called essential?

5. How are proteins formed in our body?

Related information.