The classification of amines is varied and is determined by which structural feature is taken as a basis.
Depending on the number of organic groups associated with the nitrogen atom, there are:
primary amines one organic group on nitrogen RNH 2
secondary amines two organic groups on nitrogen R 2 NH, organic groups can be different R "R" NH
tertiary amines three organic groups on nitrogen R 3 N or R"R"R""N
Based on the type of organic group associated with nitrogen, aliphatic CH 3 N6H 5 N are distinguished
Based on the number of amino groups in the molecule, amines are divided into monoamines CH 3 NH 2, diamines H 2 N(CH 2) 2 NH 2, triamines, etc.
Nomenclature of amines.
the word “amine” is added to the name of organic groups associated with nitrogen, and the groups are mentioned in alphabetical order, for example, CH 3 NHC 3 H 7 methylpropylamine, CH 3 N (C 6 H 5) 2 methyldiphenylamine. The rules also allow the name to be composed based on a hydrocarbon in which the amino group is considered as a substituent. In this case, its position is indicated using a numerical index: C 5 H 3 C 4 H 2 C 3 H(NH 2) C 2 H 2 C 1 H 3 3-aminopentane (the upper blue numerical indices indicate the numbering order of the C atoms) . For some amines, trivial (simplified) names have been preserved: C 6 H 5 NH 2 aniline (the name according to the rules of nomenclature is phenylamine).
In some cases, established names are used, which are distorted correct names: H 2 NCH 2 CH 2 OH monoethanolamine (correctly 2-aminoethanol); (OHCH 2 CH 2) 2 NH diethanolamine, the correct name is bis(2-hydroxyethyl)amine. Trivial, distorted and systematic (compiled according to the rules of nomenclature) names quite often coexist in chemistry.
Physical properties of amines.
The first representatives of a series of amines methylamine CH 3 NH 2, dimethylamine (CH 3) 2 NH, trimethylamine (CH 3) 3 N and ethylamine C 2 H 5 NH 2 are gaseous at room temperature, then with an increase in the number of atoms in R, amines become liquids , and with an increase in chain length R to 10 C atoms crystalline substances. The solubility of amines in water decreases as the chain length R increases and the number of organic groups associated with nitrogen increases (transition to secondary and tertiary amines). The smell of amines resembles the smell of ammonia; higher (with large R) amines are practically odorless.
Chemical properties of amines.
The distinctive ability of amines to attach neutral molecules (for example, hydrogen halides HHal, with the formation of organoammonium salts, similar to ammonium salts in inorganic chemistry. To form a new bond, nitrogen provides a lone electron pair, acting as a donor. The H + proton involved in the formation of the bond (from the hydrogen halide) plays the role of an acceptor (receiver), such a bond is called donor-acceptor (Fig. 1).The resulting covalent NH bond is completely equivalent to the NH bonds present in the amine.
Tertiary amines also add HCl, but when the resulting salt is heated in an acid solution, it decomposes, and R is cleaved from the N atom:
(C 2 H 5) 3 N+ HCl ® [(C 2 H 5) 3 N H]Cl
[(C 2 H 5) 3 N H]Cl ® (C 2 H 5) 2 N H + C 2 H 5 Cl
When comparing these two reactions, it is clear that the C 2 H 5 group and H seem to change places, as a result, a secondary amine is formed from a tertiary amine.
Dissolving in water, amines capture a proton in the same way, as a result OH ions appear in the solution, which corresponds to the formation of an alkaline environment, which can be detected using conventional indicators.
C2H5 N H 2 + H 2 O ® + + OH
With the formation of a donor-acceptor bond, amines can add not only HCl, but also haloalkyl RCl, thereby forming a new NR bond, which is also equivalent to the existing ones. If we take a tertiary amine as the starting material, we obtain a tetraalkylammonium salt (four R groups on one N atom):
(C 2 H 5) 3 N+ C 2 H 5 I ® [(C 2 H 5) 4 N]I
These salts, dissolving in water and some organic solvents, dissociate (disintegrate), forming ions:
[(C 2 H 5) 4 N]I ® [(C 2 H 5) 4 N] + + I
Such solutions, like all solutions containing ions, conduct electric current. In tetraalkylammonium salts, the halogen can be replaced with an HO group:
[(CH 3) 4 N]Cl + AgOH ® [(CH 3) 4 N]OH + AgCl
The resulting tetramethylammonium hydroxide is a strong base with properties similar to alkalis.
Primary and secondary amines react with nitrous acid HON=O, but they react in different ways. Primary alcohols are formed from primary amines:
C2H5 N H2+H N O 2 ® C 2 H 5 OH + N 2 +H 2 O
Unlike primary amines, secondary amines form yellow, poorly soluble nitrosamines with nitrous acid - compounds containing the fragment >NN = O:
(C 2 H 5) 2 N H+H N O 2 ® (C 2 H 5) 2 N N=O + H2O
Tertiary amines do not react with nitrous acid at ordinary temperatures, so nitrous acid is a reagent that allows one to distinguish between primary, secondary and tertiary amines.
When amines condense with carboxylic acids, acid amides are formed - compounds with the C(O)N fragment
The condensation of amines with aldehydes and ketones leads to the formation of so-called Schiff bases - compounds containing the N=C2 fragment.
When primary amines interact with phosgene Cl 2 C=O, compounds with the N=C=O group are formed, called isocyanates (Fig. 2D, preparation of a compound with two isocyanate groups).
Among the aromatic amines, the most famous is aniline (phenylamine) C 6 H 5 NH 2. Its properties are similar to aliphatic amines, but its basicity is less pronounced; in aqueous solutions it does not form an alkaline environment. Like aliphatic amines, it can form ammonium salts [C 6 H 5 NH 3 ] + Cl with strong mineral acids. When aniline reacts with nitrous acid (in the presence of HCl), a diazo compound containing the RN=N fragment is formed; it is obtained in the form of an ionic salt called the diazonium salt (Fig. 3A). Thus, the interaction with nitrous acid does not proceed in the same way as in the case of aliphatic amines. The benzene ring in aniline has a reactivity characteristic of aromatic compounds ( cm. AROMATICITY), during halogenation, hydrogen atoms in ortho- And pair-positions to the amino group are replaced, resulting in chloroanilines with varying degrees of substitution (Fig. 3B). The action of sulfuric acid leads to sulfonation in pair-position to the amino group, the so-called sulfanilic acid is formed (Fig. 3B).
Preparation of amines.
When ammonia reacts with haloalkyls, such as RCl, a mixture of primary, secondary and tertiary amines is formed. The resulting HCl byproduct combines with amines to form an ammonium salt, but if there is an excess of ammonia, the salt decomposes, allowing the process to proceed to the formation of quaternary ammonium salts (Fig. 4A). Unlike aliphatic alkyl halides, aryl halides, for example, C 6 H 5 Cl, react with ammonia with great difficulty; synthesis is possible only with catalysts containing copper. In industry, aliphatic amines are obtained by the catalytic interaction of alcohols with NH 3 at 300-500 ° C and a pressure of 1-20 MPa, resulting in a mixture of primary, secondary and tertiary amines (Fig. 4B).
When aldehydes and ketones interact with the ammonium salt of formic acid HCOONH 4, primary amines are formed (Fig. 4C), and the reaction of aldehydes and ketones with primary amines (in the presence of formic acid HCOOH) leads to secondary amines (Fig. 4D).
Nitro compounds (containing the NO 2 group) upon reduction form primary amines. This method, proposed by N.N. Zinin, is little used for aliphatic compounds, but is important for the production of aromatic amines and formed the basis for the industrial production of aniline (Fig. 4D).
Amines are rarely used as individual compounds; for example, polyethylenepolyamine [-C 2 H 4 NH-] is used in everyday life. n(trade name PEPA) as a hardener for epoxy resins. The main use of amines is as intermediate products in the preparation of various organic substances. The leading role belongs to aniline, on the basis of which a wide range of aniline dyes is produced, and color “specialization” is established already at the stage of obtaining aniline itself. Ultra-pure aniline without homologues is called in the industry “aniline for blue” (meaning the color of the future dye). “Aniline for red” must contain, in addition to aniline, a mixture ortho- And pair-toluidine (CH 3 C 6 H 4 NH 2).
Aliphatic diamines are the starting compounds for the production of polyamides, for example, nylon (Fig. 2), which is widely used for the manufacture of fibers, polymer films, as well as components and parts in mechanical engineering (polyamide gears).
From aliphatic diisocyanates (Fig. 2) polyurethanes are obtained, which have a complex of technically important properties: high strength combined with elasticity and very high abrasion resistance (polyurethane shoe soles), as well as good adhesion to a wide range of materials (polyurethane adhesives). They are also widely used in foamed form (polyurethane foams).
Anti-inflammatory drugs sulfonamides are synthesized based on sulfanilic acid (Fig. 3).
Diazonium salts (Fig. 2) are used in photosensitive materials for photocopying, which makes it possible to obtain an image bypassing conventional silver halide photography ( cm. BLACK COPYING).
Mikhail Levitsky
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:
The main distinguishing feature of the electronic structure of amines is the presence of a lone electron pair at 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
The chemical properties of 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 produce drugs and 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).
Aromatic amines are derivatives of aromatic hydrocarbons in which one or more hydrogen atoms of the benzene ring are replaced by amino groups (N.H. 2 ).
Aromatic amines can also be considered as derivatives of ammonia, in the molecule of which one or more hydrogen atoms are replaced by aromatic radicals.
As in the aliphatic (fatty) series, aromatic amines can be primary, secondary and tertiary.
Depending on which radicals (only aromatic or aromatic and aliphatic) are associated with the nitrogen atom, a distinction is made between purely aromatic and fatty-aromatic.
The amino group can be directly connected to the core or located in the side chain.
Aniline is the founder of the class of aromatic amines, in which the amino group is directly bonded to the benzene ring:
aniline (phenylamine, aminobenzene)
Nomenclature of aromatic amines
Aromatic amines are usually named trivial nomenclature.
For example, aniline, toluidine.
According to systematic (substitute) nomenclature the names of amines are formed from the names of radicals with the addition of the ending -amine or consoles amino
Trivial: ortho-toluidine meta-toluidine para-toluidine
Substitute: ortho-tolylamine meta-tolylamine para-tolylamine
ortho-aminotoluene meta-aminotoluene para-aminotoluene
(2-aminotoluene) (3-aminotoluene) (4-aminotoluene)
An aromatic ring can have two or more amino groups.
The names of compounds with two amino groups (diamines) are formed from the name of the divalent carbon residue and the ending –diamine or consoles diamino- and the name of the corresponding hydrocarbon:
o-phenylenediamine m-phenylenediamine p-phenylenediamine
o-diaminobenzene m-diaminobenzode p-diaminobenzene
(1,2-diaminobenzene) (1,3-diaminobenzene) (1,4-diaminobenzene)
Depending on the number of radicals associated with the nitrogen atom, secondary and tertiary aromatic amines are also distinguished.
The names of secondary and tertiary amines are most often formed according to the principles rational nomenclature, listing the radicals present in the compound and adding the ending -amine:
diphenylamine (secondary amine)
triphenylamine (tertiary amine)
If in an amine molecule both aromatic and aliphatic radicals are simultaneously bound to a nitrogen atom, then such amines are called fatty-aromatic.
In the case of fatty aromatic amines, the name is based on the word "aniline" and, to show that the radical is located at the nitrogen atom and not in the benzene ring, the name of the radical is preceded by the letter N:
N-methylaniline N,N-dimethylaniline
Rational: methylphenylamine dimethylphenylamine
Substitute: N-methylaminobenzene N,N-dimethylaminobenzene
Amines with an amino group in the side chain:
benzylamine
α-aminotoluene
Aromatic amines with an amino group in the side chain have the properties of aliphatic amines.
AMINES- a class of compounds that are organic derivatives of ammonia in which one, two or three hydrogen atoms are replaced by organic groups. A distinctive feature is the presence of the R–N fragment<, где R – органическая группа.
The classification of amines is varied and is determined by which structural feature is taken as a basis.
Depending on the number of organic groups associated with the nitrogen atom, there are:
primary amines - one organic group at nitrogen RNH2
secondary amines - two organic groups on nitrogen R2NH, organic groups can be different R"R"NH
tertiary amines - three organic groups on nitrogen R3N or R"R"R""N
Based on the type of organic group associated with nitrogen, aliphatic СH3 – N are distinguished< и ароматические С 6 H5 – N< амины, возможны и смешанные варианты.
Based on the number of amino groups in the molecule, amines are divided into monoamines CH3 - NH2, diamines H2N(CH2) 2 NH2, triamines, etc.
Chemical properties of amines. The distinctive ability of amines is to attach neutral molecules (for example, hydrogen halides HHal, with the formation of organoammonium salts, similar to ammonium salts in inorganic chemistry. To form a new bond, nitrogen provides a lone electron pair, acting as a donor. The H + proton involved in the formation of the bond (from the hydrogen halide) plays the role of an acceptor (receiver), such a bond is called donor-acceptor (Fig. 1).The resulting covalent N–H bond is completely equivalent to the bonds present in the amine
Tertiary amines also add HCl, but when the resulting salt is heated in an acid solution, it decomposes, and R is cleaved from the N atom:
(C 2 H 5) 3 N+ HCl [(C 2 H 5) 3 N H]Cl
[(C 2 H 5) 3 N H]Cl (C 2 H 5) 2 N H + C 2 H 5 Cl
When comparing these two reactions, it is clear that the C2H5 group and H seem to change places, as a result, a secondary amine is formed from a tertiary amine.
Dissolving in water, amines capture a proton in the same way, as a result OH – ions appear in the solution, which corresponds to the formation of an alkaline environment, which can be detected using conventional indicators.
C2H5 N H2 + H2O + + OH–
With the formation of a donor-acceptor bond, amines can add not only HCl, but also haloalkyl RCl, thereby forming a new N–R bond, which is also equivalent to the existing ones. If we take a tertiary amine as the starting material, we obtain a tetraalkylammonium salt (four R groups on one N atom):
(C 2 H 5) 3 N+ C 2 H 5 I [(C 2 H 5) 4 N]I
These salts, dissolving in water and some organic solvents, dissociate (disintegrate), forming ions:
[(C2H5) 4 N]I [(C2H5) 4 N] + + I–
Such solutions, like all solutions containing ions, conduct electric current. In tetraalkylammonium salts, the halogen can be replaced with an HO group:
[(CH 3) 4 N]Cl + AgOH [(CH 3) 4 N]OH + AgCl
The resulting tetramethylammonium hydroxide is a strong base with properties similar to alkalis.
Primary and secondary amines react with nitrous acid HON=O, but they react in different ways. Primary alcohols are formed from primary amines:
C2H5 N H2+H N O2 C2H5OH + N 2 +H2O
Unlike primary amines, secondary amines form yellow, poorly soluble nitrosamines with nitrous acid - compounds containing the fragment >N–N = O:
(C 2 H 5) 2 N H+H N O 2 (C 2 H 5) 2 N–N=O + H2O
Tertiary amines do not react with nitrous acid at ordinary temperatures, so nitrous acid is a reagent that allows one to distinguish between primary, secondary and tertiary amines.
When amines condense with carboxylic acids, acid amides are formed - compounds with the –C(O)N fragment< (рис. 2А). Если в качестве исходных соединений взять диамин и дикарбоновую кислоту (соединения, содержащие соответственно две амино- и две карбоксильные группы, соответственно), то они взаимодействуют по такой же схеме, но поскольку каждое соединение содержит две реагирующие группы, то образуется полимерная цепь, содержащая амидные группы (рис. 2Б). Такие полимеры называют полиамидами.
The condensation of amines with aldehydes and ketones leads to the formation of so-called Schiff bases - compounds containing the –N=C fragment< (рис. 2В). На схеме В видно, что для образования двойной связи между N и С азот должен предоставить два атома Н (для образования конденсационной воды), следовательно, в такой реакции могут участвовать только первичные амины RNH2.
When primary amines interact with phosgene Cl2C=O, compounds with the –N=C=O group are formed, called isocyanates (Fig. 2D, preparation of a compound with two isocyanate groups).
Among the aromatic amines, the most famous is aniline (phenylamine) C 6 H 5 NH 2. Its properties are similar to aliphatic amines, but its basicity is less pronounced - it does not form an alkaline environment in aqueous solutions. Like aliphatic amines, with strong mineral acids it can form ammonium salts [C 6 H 5 NH 3 ] + Cl–. When aniline reacts with nitrous acid (in the presence of HCl), a diazo compound containing the R–N=N fragment is formed; it is obtained in the form of an ionic salt called the diazonium salt (Fig. 3A). Thus, the interaction with nitrous acid does not proceed in the same way as in the case of aliphatic amines. The benzene ring in aniline has a reactivity characteristic of aromatic compounds (see AROMATICITY); during halogenation, hydrogen atoms in the ortho and para positions to the amino group are replaced, resulting in chloroanilines with varying degrees of substitution (Fig. 3B). The action of sulfuric acid leads to sulfonation in the para position to the amino group, the so-called sulfanilic acid is formed (Fig. 3B).
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 an important role in the formation of skin tissue. 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) - the relative 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 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 structure. 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 can enter into 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.