Chemical properties of amines reactions. General formula of amines
According to the nature of the hydrocarbon substituents, amines are divided into
General structural features of amines
As in the ammonia molecule, in the molecule of any amine, the nitrogen atom has an unshared electron pair directed to one of the vertices of the distorted tetrahedron:
For this reason, amines, like ammonia, have significantly pronounced basic properties.
So, amines, like ammonia, reversibly react with water, forming weak bases:
The bond of the hydrogen cation with the nitrogen atom in the amine molecule is realized using the donor-acceptor mechanism due to the lone electron pair of the nitrogen atom. Limit 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 nucleus, 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 the basic properties, in particular the ability to interact with water. So, 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 of the environment, due to the dissociation of the resulting bases:
Saturated amines react with water better than ammonia due to their stronger basic properties.
The main properties of saturated amines increase in the series.
Secondary limiting amines are stronger bases than primary limiting amines, which in turn are stronger bases than ammonia. As for the basic properties of tertiary amines, when it comes to reactions in aqueous solutions, the basic properties of tertiary amines are 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 prevent its interaction with H + cations.
Interaction with acids
Both free saturated amines and their aqueous solutions interact 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:
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 how ammonia is displaced by the action of alkalis on ammonium salts:
2. Primary limiting amines react with nitrous acid to form the corresponding alcohols, nitrogen N 2 and water. For example:
A characteristic feature of this reaction is the formation of gaseous nitrogen, in connection with which it is of high quality for primary amines and is used to distinguish them from secondary and tertiary. 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 an amine:
Secondary amines give oily liquids under similar conditions, the so-called N-nitrosamines, but this reaction in real USE assignments does not occur 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, during the interaction of hydrogen chloride with dimethylamine:
Getting amines:
1) Alkylation of ammonia with haloalkanes:
In the case of a lack of ammonia, instead of an amine, its salt is obtained:
2) Reduction by metals (to hydrogen in the activity series) in an acidic medium:
followed by treatment of the solution with alkali to release the free amine:
3) The reaction of ammonia with alcohols by passing their mixture through heated aluminum oxide. Depending on the proportions of alcohol / amine, primary, secondary or tertiary amines are formed:
Chemical properties of aniline
Aniline - the trivial name of aminobenzene, which has 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. So, in particular, aniline practically does not react with water and weak acids such as carbonic.
The interaction of aniline with acids
Aniline reacts with strong and moderately strong inorganic acids. In this case, phenylammonium salts are formed:
Reaction of aniline with halogens
As already mentioned 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 nucleus. An increase in the electron density in the aromatic nucleus 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. So, aniline easily interacts with bromine water, forming a white precipitate of 2,4,6-tribromaniline:
This reaction is qualitative for aniline and often allows you to determine it among other organic compounds.
The interaction of aniline with nitrous acid
Aniline reacts with nitrous acid, but due to the specificity and complexity of this reaction, it does not occur in the real exam in chemistry.
Aniline alkylation reactions
With the help of sequential alkylation of aniline at the nitrogen atom with halogen derivatives of hydrocarbons, secondary and tertiary amines can be obtained:
Chemical properties of amino acids
Amino acids call compounds in the molecules of which there are 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, the general formula of 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 acids have 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 enter into an esterification reaction 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 upon interaction 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 a 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 glycylanine, a reaction leading to alanylglycine can occur:
In addition, a glycine molecule does not necessarily react with an alanine molecule. Peptization reactions also take place between glycine molecules:
And alanine:
In addition, since the molecules of the resulting peptides, like the original molecules of amino acids, 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. So, in particular, using the polycondensation of 6-aminohexanoic (ε-aminocaproic) acid, nylon is synthesized in industry:
The nylon resin obtained as a result of this reaction is used for the production of textile fibers and plastics.
Formation of internal salts of amino acids in aqueous solution
In aqueous solutions, amino acids exist mainly in the form of internal salts - bipolar ions (zwitterions).
Amines - these are derivatives of ammonia (NH 3), in the molecule of which one, two or three hydrogen atoms are replaced by hydrocarbon radicals.
According to the number of hydrocarbon radicals that replace hydrogen atoms in the NH 3 molecule, all amines can be divided into three types:
The group - NH 2 is called an amino group. There are also amines that contain two, three or more amino groups.
Nomenclature
The word "amine" is added to the name of organic residues associated with nitrogen, while the groups are mentioned in alphabetical order: CH3NC3H - methylpropylamine, CH3N(C6H5)2 - methyldiphenylamine. For higher amines, the name is compiled, taking the hydrocarbon as a basis, adding the prefix "amino", "diamino", "triamino", indicating the numerical index of the carbon atom. Trivial names are used for some amines: C6H5NH2 - aniline (systematic name - phenylamine).
For amines, chain isomerism, functional group position isomerism, isomerism between types of amines is possible
Physical Properties
Lower limiting primary amines - gaseous substances, have the smell of ammonia, dissolve well in water. Amines with a higher relative molecular weight are liquids or solids, their solubility in water decreases with increasing molecular weight.
Chemical properties
Amines are chemically similar to ammonia.
1. Interaction with water - the formation of substituted ammonium hydroxides. Ammonia solution in water has weak alkaline (basic) properties. The reason for the main properties of ammonia is the presence of a lone electron pair at the nitrogen atom, which is involved in the formation of a donor-acceptor bond with a hydrogen ion. For the same reason, amines are also weak bases. Amines are organic bases.
2. Interaction with acids - the formation of salts (neutralization reactions). As a base, ammonia forms ammonium salts with acids. Similarly, when amines react with acids, substituted ammonium salts are formed. Alkalis, as stronger bases, displace ammonia and amines from their salts.
3. Combustion of amines. Amines are combustible substances. The combustion products of amines, as well as other nitrogen-containing organic compounds, are carbon dioxide, water and free nitrogen.
Alkylation is the introduction of an alkyl substituent into the molecule of an organic compound. Typical alkylating agents are alkyl halides, alkenes, epoxy compounds, alcohols, less often aldehydes, ketones, ethers, sulfides, diazoalkanes. Alkylation catalysts are mineral acids, Lewis acids and zeolites.
Acylation. When heated with carboxylic acids, their anhydrides, acid chlorides or esters, primary and secondary amines are acylated to form N-substituted amides, compounds with a -C(O)N moiety<:
The reaction with anhydrides proceeds under mild conditions. Acid chlorides react even more easily, the reaction is carried out in the presence of a base to bind the HCl formed.
Primary and secondary amines interact with nitrous acid in various ways. With the help of nitrous acid, primary, secondary and tertiary amines are distinguished from each other. Primary alcohols are formed from primary amines:
C2H5NH2 + HNO2 → C2H5OH + N2 +H2O
This releases gas (nitrogen). This is a sign that there is primary amine in the flask.
Secondary amines form yellow, sparingly soluble nitrosamines with nitrous acid - compounds containing the >N-N=O fragment:
(C2H5)2NH + HNO2 → (C2H5)2N-N=O + H2O
Secondary amines are hard to miss, the characteristic smell of nitrosodimethylamine spreads throughout the laboratory.
Tertiary amines simply dissolve in nitrous acid at ordinary temperatures. When heated, a reaction with the elimination of alkyl radicals is possible.
How to get
1. Interaction of alcohols with ammonia during heating in the presence of Al 2 0 3 as a catalyst.
2. Interaction of alkyl halides (haloalkanes) with ammonia. The resulting primary amine can react with excess alkyl halide and ammonia to form a secondary amine. Tertiary amines can be prepared similarly
Amino acids. Classification, isomerism, nomenclature, obtaining. Physical and chemical properties. Amphoteric properties, bipolar structure, isoelectric point. Polypeptides. Individual representatives: glycine, alanine, cysteine, cystine, a-aminocaproic acid, lysine, glutamic acid.
Amino acids- these are derivatives of hydrocarbons containing amino groups (-NH 2) and carboxyl groups -COOH.
General formula: (NH 2) f R(COOH) n where m and n most often equal to 1 or 2. Thus, amino acids are compounds with mixed functions.
Classification
isomerism
The isomerism of amino acids, as well as hydroxy acids, depends on the isomerism of the carbon chain and on the position of the amino group in relation to the carboxyl (a-, β - and γ - amino acids, etc.). In addition, all natural amino acids, except aminoacetic, contain asymmetric carbon atoms, so they have optical isomers (antipodes). There are D- and L-series of amino acids. It should be noted that all amino acids that make up proteins belong to the L-series.
Nomenclature
Amino acids usually have trivial names (for example, aminoacetic acid is called differently glycocol or iicin, and aminopropionic acid alanine etc.). The name of an amino acid according to the systematic nomenclature consists of the name of the corresponding carboxylic acid, of which it is a derivative, with the addition of the word amino- as a prefix. The position of the amino group in the chain is indicated by numbers.
How to get
1. Interaction of α-halocarboxylic acids with an excess of ammonia. In the course of these reactions, the halogen atom in halocarboxylic acids (for their preparation, see § 10.4) is replaced by an amino group. The hydrogen chloride released at the same time is bound by an excess of ammonia into ammonium chloride.
2. Hydrolysis of proteins. During the hydrolysis of proteins, complex mixtures of amino acids are usually formed, however, with the help of special methods individual pure amino acids can be isolated from these mixtures.
Physical Properties
Amino acids are colorless crystalline substances, readily soluble in water, melting point 230-300°C. Many α-amino acids have a sweet taste.
Chemical properties
1. Interaction with bases and acids:
a) as an acid (carboxyl group is involved).
b) as a base (amino group is involved).
2. Interaction within the molecule - the formation of internal salts:
a) monoaminomonocarboxylic acids (neutral acids). Aqueous solutions of monoaminomonocarboxylic acids are neutral (pH = 7);
b) monoaminodicarboxylic acids (acidic amino acids). Aqueous solutions of monoaminodicarboxylic acids have pH< 7 (кислая среда), так как в результате образования внутренних солей этих кислот в растворе появляется избыток ионов водорода Н + ;
c) diaminomonocarboxylic acids (basic amino acids). Aqueous solutions of diaminomonocarboxylic acids have pH > 7 (alkaline), because as a result of the formation of internal salts of these acids, an excess of OH - hydroxide ions appears in the solution.
3. The interaction of amino acids with each other - the formation of peptides.
4. Interact with alcohols to form esters.
The isoelectric point of amino acids that do not contain additional NH2 or COOH groups is the arithmetic mean between the two pK values: 
respectively for alanine 
.
The isoelectric point of a number of other amino acids containing additional acidic or basic groups (aspartic and glutamic acids, lysine, arginine, tyrosine, etc.) also depends on the acidity or basicity of the radicals of these amino acids. For lysine, for example, pI should be calculated from half the sum of pK" values for α- and ε-NH2 groups. Thus, in the pH range from 4.0 to 9.0, almost all amino acids exist predominantly in the form of zwitterions with a protonated amino group and a dissociated carboxyl group.
Polypeptides contain more than ten amino acid residues.
Glycine (aminoacetic acid, aminoethanoic acid) is the simplest aliphatic amino acid, the only amino acid that does not have optical isomers. Empirical formula C2H5NO2
Alanine (aminopropanoic acid) is an aliphatic amino acid. α-alanine is part of many proteins, β-alanine is part of a number of biologically active compounds. Chemical formula NH2 -CH -CH3 -COOH. Alanine is easily converted into glucose in the liver and vice versa. This process is called the glucose-alanine cycle and is one of the main pathways of gluconeogenesis in the liver.
Cysteine (α-amino-β-thiopropionic acid; 2-amino-3-sulfanylpropanoic acid) is an aliphatic sulfur-containing amino acid. Optically active, exists in the form of L- and D-isomers. L-cysteine is a component of proteins and peptides and plays an important role in the formation of skin tissues. It is important for detoxification processes. The empirical formula is C3H7NO2S.
Cystine (chem.) (3,3 "-dithio-bis-2-aminopropionic acid, dicysteine) is an aliphatic sulfur-containing amino acid, colorless crystals, soluble in water.
Cystine is a non-encoded amino acid that is a product of the oxidative dimerization of cysteine, during which two cysteine thiol groups form a cystine disulfide bond. Cystine contains two amino groups and two carboxyl groups and is a dibasic diamino acid. Empirical formula C6H12N2O4S2
In the body, they are found mainly in the composition of proteins.
Aminocaproic acid (6-aminohexanoic acid or ε-aminocaproic acid) is a hemostatic drug that inhibits the conversion of profibrinolysin to fibrinolysin. Gross-
formula C6H13NO2.
Lysine (2,6-diaminohexanoic acid) is an aliphatic amino acid with pronounced base properties; essential amino acid. Chemical formula: C6H14N2O2
Lysine is part of proteins. Lysine is an essential amino acid that is part of almost any protein, it is necessary for growth, tissue repair, production of antibodies, hormones, enzymes, albumins.
Glutamic acid (2-aminopentanedioic acid) is an aliphatic amino acid. In living organisms, glutamic acid in the form of glutamate anion is present in proteins, a number of low molecular weight substances, and in free form. Glutamic acid plays an important role in nitrogen metabolism. Chemical formula C5H9N1O4
Glutamic acid is also a neurotransmitter amino acid, one of the important members of the excitatory amino acid class. The binding of glutamate to specific receptors of neurons leads to the excitation of the latter.
Simple and complex proteins. peptide bond. The concept of the primary, secondary, tertiary and quaternary structure of the protein molecule. Types of bonds that determine the spatial structure of the protein molecule (hydrogen, disulfide, ionic, hydrophobic interactions). Physical and chemical properties of proteins (precipitation, denaturation, color reactions). isoelectric point. The value of proteins.
Squirrels - these are natural high-molecular compounds (biopolymers), the structural basis of which is polypeptide chains built from α-amino acid residues.
Simple proteins (proteins) are high-molecular organic substances consisting of alpha-amino acids connected in a chain by a peptide bond.
Complex proteins (proteids) are two-component proteins that, in addition to peptide chains (a simple protein), contain a component of a non-amino acid nature - a prosthetic group.
Peptide bond - a type of amide bond that occurs during the formation of proteins and peptides as a result of the interaction of the α-amino group (-NH2) of one amino acid with the α-carboxyl group (-COOH) of another amino acid.
The primary structure is the sequence of amino acids in a polypeptide chain. Important features of the primary structure are conservative motifs - combinations of amino acids that play a key role in protein functions. Conservative motifs are preserved in the course of species evolution; they often make it possible to predict the function of an unknown protein.
Secondary structure - local ordering of a fragment of a polypeptide chain, stabilized by hydrogen bonds.
Tertiary structure - the spatial structure of the polypeptide chain (a set of spatial coordinates of the atoms that make up the protein). Structurally, it consists of secondary structure elements stabilized by various types of interactions, in which hydrophobic interactions play an important role. In the stabilization of the tertiary structure take part:
covalent bonds (between two cysteine residues - disulfide bridges);
ionic bonds between oppositely charged side groups of amino acid residues;
hydrogen bonds;
hydrophilic-hydrophobic interactions. When interacting with surrounding water molecules, the protein molecule "tends" to curl up so that the non-polar side groups of amino acids are isolated from the aqueous solution; polar hydrophilic side groups appear on the surface of the molecule.
Quaternary structure (or subunit, domain) - 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 the end of synthesis form a common supramolecular structure. A protein with a quaternary structure can contain both identical and different polypeptide chains. The same types of interactions take part in the stabilization of the quaternary structure as in the stabilization of the tertiary. Supramolecular protein complexes can consist of dozens of molecules.
Physical Properties
The properties of proteins are as diverse as the functions they perform. Some proteins dissolve in water, forming, as a rule, colloidal solutions (for example, egg white); others dissolve in dilute salt solutions; others are insoluble (for example, proteins of integumentary tissues).
Chemical properties
In the radicals of amino acid residues, proteins contain various functional groups that are capable of entering into many reactions. Proteins enter into oxidation-reduction reactions, esterification, alkylation, nitration, they can form salts with both acids and bases (proteins are amphoteric).
For example, albumin - egg white - at a temperature of 60-70 ° is precipitated from a solution (coagulates), losing the ability to dissolve in water.
Amines entered our lives quite unexpectedly. Until recently, these were poisonous substances, a collision with which could lead to death. And now, after a century and a half, we are actively using synthetic fibers, fabrics, building materials, dyes, which are based on amines. No, they did not become safer, people were simply able to "tame" them and subdue them, deriving certain benefits for themselves. About which one, and we'll talk further.
Definition
For the qualitative and quantitative determination of aniline in solutions or compounds, a reaction with is used at the end of which a white precipitate in the form of 2,4,6-tribromaniline falls on the bottom of the test tube.
Amines in nature
Amines are found in nature everywhere in the form of vitamins, hormones, metabolic intermediates, they are also found in animals and plants. In addition, when living organisms rot, medium amines are also obtained, which, in a liquid state, spread an unpleasant smell of herring brine. The "cadaveric poison" widely described in the literature appeared precisely due to the specific ambergris of amines.
For a long time, the substances we are considering were confused with ammonia due to a similar smell. But in the mid-nineteenth century, the French chemist Wurtz was able to synthesize methylamine and ethylamine and prove that they release hydrocarbons when burned. This was the fundamental difference between the mentioned compounds and ammonia.
Obtaining amines in industrial conditions
Since the nitrogen atom in amines is in the lowest oxidation state, the reduction of nitrogen-containing compounds is the simplest and accessible way receiving them. It is he who is widely used in industrial practice because of its cheapness.
The first method is the reduction of nitro compounds. The reaction during which aniline is formed is named by the scientist Zinin and was carried out for the first time in the middle of the nineteenth century. The second method is to reduce amides with lithium aluminum hydride. Primary amines can also be reduced from nitriles. The third option is alkylation reactions, that is, the introduction of alkyl groups into ammonia molecules.
Application of amines
By themselves, in the form of pure substances, amines are used little. One rare example is polyethylenepolyamine (PEPA), which makes epoxy resin easier to cure in the home. Basically a primary, tertiary or secondary amine is an intermediate in the production of various organics. The most popular is aniline. It is the basis of a large palette of aniline dyes. The color that will turn out at the end depends directly on the selected raw material. Pure aniline gives a blue color, while a mixture of aniline, ortho- and para-toluidine will be red.
Aliphatic amines are needed to obtain polyamides such as nylon and others. They are used in mechanical engineering, as well as in the production of ropes, fabrics and films. In addition, aliphatic diisocyanates are used in the manufacture of polyurethanes. Due to their exceptional properties (lightness, strength, elasticity and the ability to attach to any surface), they are in demand in construction (mounting foam, glue) and in the shoe industry (anti-slip soles).
Medicine is another area where amines are used. Chemistry helps to synthesize antibiotics of the sulfonamide group from them, which are successfully used as second-line drugs, that is, reserve ones. In case bacteria develop resistance to essential drugs.
Harmful effects on the human body
It is known that amines are very toxic substances. Any interaction with them can cause harm to health: inhalation of vapors, contact with open skin or ingestion of compounds into the body. Death occurs from a lack of oxygen, since amines (in particular, aniline) bind to blood hemoglobin and prevent it from capturing oxygen molecules. Alarming symptoms are shortness of breath, blue nasolabial triangle and fingertips, tachypnea (rapid breathing), tachycardia, loss of consciousness.
In case of contact with these substances on bare areas of the body, it is necessary to quickly remove them with cotton wool previously moistened with alcohol. This must be done as carefully as possible so as not to increase the area of \u200b\u200bcontamination. If symptoms of poisoning appear, you should definitely consult a doctor.
Aliphatic amines are a poison for the nervous and cardiovascular systems. They can cause depression of liver function, its degeneration and even oncological diseases of the bladder.
The classification of amines is diverse and is determined by what feature of the structure is taken as the basis.
Depending on the number of organic groups associated with the nitrogen atom, there are:
primary amines - one organic group at the nitrogen RNH 2
secondary amines - two organic groups at the nitrogen R 2 NH, organic groups can be different R "R" NH
tertiary amines - three organic groups at nitrogen R 3 N or R "R" R "" N
According to the type of organic group associated with nitrogen, aliphatic CH 3 - N6H 5 - N are distinguished
According to 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.
Amine nomenclature.
the word "amine" is added to the name of the organic groups associated with nitrogen, while 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 (upper numerical indices of blue color indicate the numbering order of 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); (OHSN 2 CH 2) 2 NH - diethanolamine, correct name– bis(2-hydroxyethyl)amine. Trivial, distorted and systematic (composed 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 - at room temperature gaseous, then with an increase in the number of atoms in R, amines become liquids, and with an increase in the chain length R to 10 C atoms, they become crystalline substances. The solubility of amines in water decreases as the chain length R increases and as 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 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 an unshared electron pair, acting as a donor. The proton H + participating in the formation of the bond (from hydrogen halide) plays the role of an acceptor (receiver), such a bond is called a donor-acceptor bond (Fig. 1).The resulting N–H covalent bond is completely equivalent to the N–H bonds present in the amine.
Tertiary amines also add HCl, but when the resulting salt is heated in an acid solution, it decomposes, while R is split off 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 can be seen that the C 2 H 5 group and H, as it were, change places, as a result, a secondary is formed from the 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.
C 2 H 5 N H 2 + H 2 O ® + + OH -
With the formation of a donor-acceptor bond, amines can add not only HCl, but also halogenated RCl, thus forming new connection N–R, which is also equivalent to those already available. If we take a tertiary amine as the initial one, then we get 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 (decompose), forming ions:
[(C 2 H 5) 4 N]I ® [(C 2 H 5) 4 N] + + I –
Such solutions, like all solutions containing ions, conduct electricity. In tetraalkylammonium salts, the halogen can be replaced by an HO group:
[(CH 3) 4 N]Cl + AgOH ® [(CH 3) 4 N]OH + AgCl
The resulting tetramethylammonium hydroxide is a strong base, similar in properties to alkalis.
Primary and secondary amines interact with nitrous acid HON=O, but they react differently. Primary alcohols are formed from primary amines:
C 2 H 5 N H 2 + H N O 2 ® C 2 H 5 OH + N 2+H2O
Unlike primary amines, secondary amines form yellow, sparingly soluble nitrosamines with nitrous acid, compounds containing the >N–N = O moiety:
(C 2 H 5) 2 N H+H N O 2 ® (C 2 H 5) 2 N N\u003d O + H 2 O
Tertiary amines do not react with nitrous acid at ordinary temperatures, so nitrous acid is a reagent that makes it possible to distinguish between primary, secondary and tertiary amines.
When amines are condensed 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 the so-called Schiff bases, compounds containing the -N=C2 moiety.
The interaction of primary amines with phosgene Cl 2 C=O gives compounds with the –N=C=O group, called isocyanates (Fig. 2D, preparation of a compound with two isocyanate groups).
Among aromatic amines, aniline (phenylamine) C 6 H 5 NH 2 is the most famous. It is similar in properties to aliphatic amines, but its basicity is less pronounced - it does not form an alkaline medium in aqueous solutions. Like aliphatic amines, it can form ammonium salts with strong mineral acids [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 moiety is formed; it is obtained in the form of an ionic salt called the diazonium salt (Fig. 3A). Thus, the interaction with nitrous acid is not the same as in the case of aliphatic amines. The benzene ring in aniline has a reactivity characteristic of aromatic compounds ( cm. AROMATICITY), upon halogenation, hydrogen atoms in ortho- and pair-positions to the amino group are substituted, resulting in chloranilines with various 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).
Getting amines.
When ammonia reacts with haloalkyls, such as RCl, a mixture of primary, secondary and tertiary amines is formed. The resulting by-product HCl adds to the amines to form an ammonium salt, but with an excess of ammonia, the salt decomposes, which allows the process to be carried out up to the formation of quaternary ammonium salts (Fig. 4A). Unlike aliphatic haloalkyls, 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 NH3 at 300–500°C and a pressure of 1–20 MPa, resulting in a mixture of primary, secondary, and tertiary amines (Fig. 4B).
The reaction of aldehydes and ketones with the ammonium salt of formic acid HCOONH4 gives rise to primary amines (Fig. 4C), while 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) form primary amines upon reduction. This method, proposed by N.N. Zinin, is little used for aliphatic compounds, but is important for obtaining aromatic amines and formed the basis industrial production aniline (Fig. 4e).
As separate compounds, amines are used little, 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 production of various organic substances. The leading role belongs to aniline, on the basis of which a wide range of aniline dyes is produced, and the color "specialization" is laid already at the stage of obtaining the aniline itself. Ultrapure 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 initial 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).
Polyurethanes are obtained from aliphatic diisocyanates (Fig. 2), which have a set 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 materials (polyurethane adhesives). They are widely used in foamed form (polyurethane foams).
Based on sulfanilic acid (Fig. 3), anti-inflammatory drugs sulfonamides are synthesized.
Diazonium salts (Fig. 2) are used in photosensitive materials for blueprinting, which makes it possible to obtain an image bypassing the usual silver halide photograph ( cm. LIGHT COPYING).
Mikhail Levitsky
Organic bases - this name is often used in chemistry for compounds that are derivatives of ammonia. Hydrogen atoms in its molecule are replaced by hydrocarbon radicals. It's about about amines - compounds that repeat the chemical properties of ammonia. In our article, we will get acquainted with the general formula of amines and their properties.
The structure of the molecule
Depending on how many hydrogen atoms are replaced by hydrocarbon radicals, primary, secondary and tertiary amines are distinguished. For example, methylamine is a primary amine in which the hydrogen moiety has been replaced with a -CH 3 group. The structural formula of amines is R-NH 2 and can be used to determine the composition of organic matter. An example of a secondary amine can be dimethylamine, having the following form: NH 2 -NH-NH 2 . In the molecules of tertiary compounds, all three hydrogen atoms of ammonia are replaced by hydrocarbon radicals, for example, trimethylamine has the formula (NH 2) 3 N. The structure of amines affects their physical and chemical properties.
Physical characteristic
The aggregate state of amines depends on the molar mass of the radicals. The smaller it is, the lower the specific gravity of the substance. The lower substances of the amine class are represented by gases (for example, methylamine). They have a pronounced smell of ammonia. Medium amines are weakly smelling liquids, and compounds with large mass hydrocarbon radical - odorless solids. The solubility of amines also depends on the mass of the radical: the larger it is, the worse the substance dissolves in water. Thus, the structure of amines determines their the physical state and characteristic.
Chemical properties
The characteristics of substances depend mainly on the transformations of the amino group, in which the leading role is assigned to its unshared electron pair. Since organic substances of the amine class are derivatives of ammonia, they are capable of reactions characteristic of NH 3. For example, compounds are soluble in water. The products of such a reaction will be substances that exhibit the properties of hydroxides. For example, methylamine, whose atomic composition obeys the general formula of saturated amines R-NH 2, forms a compound with water - methylammonium hydroxide:
CH 3 - NH 2 + H 2 O \u003d OH
Organic bases interact with inorganic acids, while salt is found in the products. So, methylamine with hydrochloric acid gives methylammonium chloride:
CH 3 -NH 2 + HCl -> Cl
The reactions of amines, the general formula of which is R-NH 2 , with organic acids proceed with the replacement of the hydrogen atom of the amino group by a complex anion of the acid residue. They are called alkylation reactions. As in the reaction with nitrite acid, acyl derivatives can only form primary and secondary amines. Trimethylamine and other tertiary amines are not capable of such interactions. We also add that alkylation in analytical chemistry is used to separate mixtures of amines; it also serves as a qualitative reaction for primary and secondary amines. Among cyclic amines, aniline occupies an important place. It is extracted from nitrobenzene by reduction of the latter with hydrogen in the presence of a catalyst. Aniline is a raw material for the production of plastics, dyes, explosives and medicines.
Features of tertiary amines
Tertiary derivatives of ammonia differ in their chemical properties from one- or two-substituted compounds. For example, they can interact with halogen derivatives of saturated hydrocarbons. As a result, tetraalkylammonium salts are formed. Silver oxide reacts with tertiary amines, while the amines are converted into tetraalkylammonium hydroxides, which are strong bases. Aprotic acids, such as boron trifluoride, are capable of forming complex compounds with trimethylamine.
Qualitative test for primary amines
Nitrous acid can serve as a reagent with which one or disubstituted amines can be detected. Since it does not exist in a free state, to obtain it in solution, a reaction is first carried out between dilute hydrochloric acid and sodium nitrite. The dissolved primary amine is then added. The composition of its molecule can be expressed using the general formula of amines: R-NH 2. This process is accompanied by the appearance of molecules of unsaturated hydrocarbons, which can be determined by reaction with bromine water or a solution of potassium permanganate. The isonitrile reaction can also be considered qualitative. In it, primary amines interact with chloroform in a medium with an excess concentration of hydroxo group anions. As a result, isonitriles are formed, which have an unpleasant specific odor.
Features of the reaction of secondary amines with nitrite acid
The technology for obtaining the HNO 2 reagent is described by us above. Then, an organic ammonia derivative containing two hydrocarbon radicals is added to the solution containing the reagent, for example, diethylamine, the molecule of which corresponds to the general formula of secondary amines NH 2 -R-NH 2 . In the reaction products we find a nitro compound: N-nitrosodiethylamine. If it is treated with hydrochloric acid, then the compound decomposes into the chloride salt of the starting amine and nitrosyl chloride. We also add that tertiary amines are not capable of reacting with nitrous acid. This is explained by the following fact: nitrite acid is a weak acid, and its salts, when interacting with amines containing three hydrocarbon radicals, are completely hydrolyzed in aqueous solutions.
How to get
Amines, whose general formula is R-NH 2 , can be obtained by reducing compounds containing nitrogen. For example, it can be the reduction of nitroalkanes in the presence of a catalyst - metallic nickel - when heated to +50 ⁰C and at a pressure of up to 100 atm. Nitroethane, nitropropane or nitromethane is converted into amines by this process. Substances of this class can also be obtained by hydrogen reduction of compounds of the nitrile group. This reaction takes place in organic solvents and requires the presence of a nickel catalyst. If metallic sodium is used as a reducing agent, in this case the process is carried out in an alcoholic solution. Let us give two more methods as examples: amination of haloalkanes and alcohols.
In the first case, a mixture of amines is formed. Amination of alcohols is carried out in the following way: a mixture of methanol or ethanol vapors with ammonia is passed over calcium oxide, which acts as a catalyst. The resulting primary, secondary and tertiary amines can usually be separated by distillation.
In our article, we studied the structure and properties of nitrogen-containing organic compounds - amines.
