Amine oxygen. Chemical properties of amines
I. According to the number of hydrocarbon radicals in the amine molecule:
Primary amines R-NH 2
(derivatives of hydrocarbons in which the hydrogen atom is replaced by an amino group -NH 2),
Secondary amines R-NH-R"
II. According to the structure of the hydrocarbon radical:
Aliphatic, for example: C 2 H 5 -NH 2 ethylamine
Limit primary amines
General formula C n H 2n+1 NH 2 (n ≥ 1); or C n H 2n+3 N (n ≥ 1)
Nomenclature
The names of amines (especially secondary and tertiary) are usually given according to the radical-functional nomenclature, listing the radicals in alphabetical order and adding the class name - amine. The names of primary amines according to the substitution nomenclature are made up of the name of the parent hydrocarbon and the suffix - amine.
CH 3 -NH 2 methanamine (methylamine)
CH 3 -CH 2 -NH 2 ethanamine (ethylamine)
Primary amines are often referred to as derivatives of hydrocarbons, in the molecules of which one or more hydrogen atoms are replaced by NH 2 amino groups. The amino group is considered as a substituent, and its location is indicated by a number at the beginning of the name. For example:
H 2 N-CH 2 -CH 2 -CH 2 -CH 2 -NH 2 1,4-diaminobutane.
Aniline (phenylamine) C 6 H 5 NH 2 in accordance with this method is called aminobenzene.
Homologous series of saturated amines
CH 3 NH 2 - methylamine (primary amine), (CH 3) 2 NH - dimethylamine (secondary amine), (CH 3) 3 N - trimethylamine (tertiary amine), etc.
isomerism
Structural isomerism
Carbon skeleton, starting with C 4 H 9 NH 2:
Positions of the amino group, starting with C 3 H 7 NH 2:
Isomerism of the amino group associated with a change in the degree of substitution of hydrogen atoms at nitrogen:
Spatial isomerism
Optical isomerism is possible, starting with C 4 H 9 NH 2:
Optical (mirror) isomers - spatial isomers, the molecules of which relate to each other as an object and an incompatible mirror image (like left and right hands).
Physical properties
Lower limit amines are gaseous substances; the middle members of the homologous series are liquids; higher amines are solids. Methylamine has an ammonia smell, other lower amines have a sharp unpleasant smell, reminiscent of the smell of herring brine.
Lower amines are highly soluble in water, with an increase in the hydrocarbon radical, the solubility of amines decreases. Amines are formed during the decay of organic residues containing proteins. A number of amines are formed in human and animal organisms from amino acids (biogenic amines).
Chemical properties
Amines, like ammonia, exhibit pronounced properties of bases, which is due to the presence of a nitrogen atom in the amine molecules, which has an unshared pair of electrons.
1. Interaction with water
Solutions of amines in water are alkaline.
2. Interaction with acids (formation of salts)
Amines are released from their salts under the action of alkalis:
Cl + NaOH → CH 3 CH 2 NH 2 + NaCl + H 2 O
3. Combustion of amines
4CH 3 NH 2 + 9O 2 → 4CO 2 + 10H 2 O + 2N 2
4. Reaction with nitrous acid (the difference between primary amines and secondary and tertiary ones)
Under the action of HNO 2, primary amines are converted into alcohols with the release of nitrogen:
C 2 H 5 NH 2 + HNO 2 → C 2 H 5 OH + N 2 + H 2 O
How to get
1. Reaction of haloalkanes with ammonia
CH 3 Br + 2NH 3 → CH 3 NH 2 + NH 4 Br
2. Interaction of alcohols with ammonia
(In practice, these reactions produce a mixture of primary, secondary, tertiary amines and a quaternary ammonium salt.)
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 nitrogen has one organic group RNH 2
secondary amines two organic groups at 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 (the blue upper numerical indices indicate the numbering order of C atoms) . For some amines, trivial (simplified) names have been preserved: C 6 H 5 NH 2 aniline (name according to the nomenclature rules phenylamine).
In some cases, established names are used, which are distorted correct names: H 2 NCH 2 CH 2 OH monoethanolamine (correct 2-aminoethanol); (OHCH 2 CH 2) 2 NH diethanolamine, the correct name is 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 the 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 the chain length R up to 10 C atoms 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 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 + involved 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 NH covalent 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, 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 haloalkyls RCl, and a new NR bond is formed, which is also equivalent to the existing ones. 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 fragment >NN = O:
(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 temperature, thus, 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 a fragment C (O) N
Condensation of amines with aldehydes and ketones leads to the formation of the so-called Schiff bases compounds containing the fragment N=C2.
When primary amines react with phosgene Cl 2 C=O, compounds with the N=C=O group are formed, which are called isocyanates (Fig. 2d, obtaining a compound with two isocyanate groups).
Among aromatic amines, aniline (phenylamine) C 6 H 5 NH 2 is the most famous. Its properties are close to those of aliphatic amines, but its basicity is less pronounced; in aqueous solutions, it does not form an alkaline medium. 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 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 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 catalytic interaction of alcohols with NH 3 at 300500 ° C and a pressure of 120 MPa, resulting in a mixture of primary, secondary and tertiary amines (Fig. 4B).
The interaction of aldehydes and ketones with the ammonium salt of formic acid HCOONH4 gives 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 for the industrial production of 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 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 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).
Polyurethanes are obtained from aliphatic diisocyanates (Fig. 2), 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 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
LECTURE TOPIC: amines and amino alcohols
Questions:
General characteristics: structure, classification, nomenclature.
Acquisition Methods
Physical properties
Chemical properties
individual representatives. Identification methods.
General characteristics: structure, classification, nomenclature
Amines are called derivatives of ammonia, the molecule of which hydrogen atoms are replaced by hydrocarbon radicals.
Classification
1– Depending on the number of substituted hydrogen atoms of ammonia, amines are distinguished:
– primary contain an amino group an amino group (–NH 2), general formula: R–NH 2,
– secondary contain an imino group (–NH),
general formula: R 1 -NH - R 2
– tertiary contain a nitrogen atom, the general formula: R 3 -N
There are also known compounds with a quaternary nitrogen atom: quaternary ammonium hydroxide and its salts.
2– Depending on the structure of the radical, amines are distinguished:
– aliphatic (limiting and unsaturated)
– alicyclic
- aromatic (containing an amino group or side chain in the core)
- heterocyclic.
Nomenclature, amine isomerism
1. The names of amines according to rational nomenclature are usually derived from the names of their constituent hydrocarbon radicals with the addition of the ending -amine : methylamine CH 3 -NH 2, dimethylamine CH 3 -NH-CH 3, trimethylamine (CH 3) 3 N, propylamine CH 3 CH 2 CH 2 -NH 2, phenylamine C 6 H 5 - NH 2, etc.
2. According to the IUPAC nomenclature, the amino group is considered as a functional group and its name amino put before the name of the main chain:
The isomerism of amines depends on the isomerism of radicals.
Methods for obtaining amines
Amines can be obtained in various ways.
A) Action on ammonia by haloalkyls
2NH 3 + CH 3 I -–® CH 3 - NH 2 + NH 4 I
B) Catalytic hydrogenation of nitrobenzene with molecular hydrogen:
C 6 H 5 NO 2 -–® C 6 H 5 NH 2 + H 2 O
nitrobenzene cat aniline
C) Obtaining lower amines (С 1 -С 4) by alkylation with alcohols:
350 0 C, Al 2 O 3
R–OH + NH 3 –––––––––––® R–NH 2 +H 2 O
350 0 C, Al 2 O 3
2R–OH + NH 3 –––––––––––® R 2 –NH +2H 2 O
350 0 C, Al 2 O 3
3R–OH + NH 3 –––––––––––® R 3 –N + 3H 2 O
Physical properties of amines
Methylamine, dimethylamine and trimethylamine are gases, the middle members of the amine series are liquids, the higher ones are solids. With an increase in the molecular weight of amines, their density increases, the boiling point rises, and the solubility in water decreases. Higher amines are insoluble in water. Lower amines have an unpleasant odor, somewhat reminiscent of the smell of spoiled fish. Higher amines are either odorless or have a very low odor. Aromatic amines are colorless liquids or solids with an unpleasant odor and are poisonous.
Chemical properties of amines
The chemical behavior of amines is determined by the presence of an amino group in the molecule. The outer shell of the nitrogen atom has 5 electrons. In the amine molecule, as well as in the ammonia molecule, the nitrogen atom spends three electrons on the formation of three covalent bonds, and two remain free.
The presence of a free electron pair at the nitrogen atom makes it possible for it to attach a proton, therefore amines are similar to ammonia, exhibit basic properties, form hydroxides, salts.
Salt formation. Amines with acids give salts, which, under the action of a strong base, again give free amines:
Amines give salts even with weak carbonic acid:
Like ammonia, amines have basic properties due to the binding of protons into a weakly dissociating substituted ammonium cation:
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When an amine is dissolved in water, part of the water protons is spent on the formation of a cation; thus, an excess of hydroxide ions appears in the solution, and it has alkaline properties sufficient to color solutions of litmus blue and phenolphthalein solutions crimson. The basicity of amines of the limiting series varies within very small limits and is close to the basicity of ammonia.
The effect of methyl groups slightly increases the basicity of methyl- and dimethylamine. In the case of trimethylamine, the methyl groups already impede the solvation of the resulting cation and reduce its stabilization and, consequently, its basicity.
Amine salts should be considered as complex compounds. The central atom in them is a nitrogen atom, the coordination number of which is four. Hydrogen atoms or alkyls are bonded to the nitrogen atom and are located in the inner sphere; the acid residue is located in the outer sphere.
Acylation of amines. Under the action of some derivatives of organic acids (acid halides, anhydrides, etc.) on primary and secondary amines, amides are formed:
Secondary amines with nitrous acid give nitrosamines- yellowish liquids, slightly soluble in water:
Tertiary amines are resistant to the action of dilute nitrous acid in the cold (they form salts of nitrous acid), under more severe conditions one of the radicals is cleaved off and nitrosoamine is formed.
Diamines
Diamines play an important role in biological processes. As a rule, they are easily soluble in water, have a characteristic odor, have a strongly alkaline reaction, and interact with CO 2 in the air. Diamines form stable salts with two equivalents of acid.
Ethylenediamine (1,2-ethanediamine) H 2 NCH 2 CH 2 NH 2 . It is the simplest diamine; can be obtained by the action of ammonia on ethylene bromide:
Tetramethylenediamine (1,4-butanediamine), or putrescine, NH 2 CH 2 CH 2 CH 2 CH 2 NH 2 and pentamethylenediamine (1,5-pentanediamine) NH 2 CH 2 CH 2 CH 2 CH 2 CH 2 NH 2, or cadaverine. They were discovered in the decomposition products of protein substances; are formed during the decarboxylation of diamino acids and are named ptomains(from Greek - corpse), they were previously considered "cadaveric poisons." It has now been found that the toxicity of rotting proteins is not caused by ptomaines, but by the presence of other substances.
Putrescine and cadaverine are formed as a result of the vital activity of many microorganisms (for example, causative agents of tetanus and cholera) and fungi; they are found in cheese, ergot, fly agaric, brewer's yeast.
Some diamines are used as raw materials for the production of polyamide fibers and plastics. So, from hexamethylenediamine NH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 NH 2, a very valuable synthetic fiber was obtained - nylon(US) or anid(Russia).
Amino alcohols
Amino alcohols- compounds with mixed functions, the molecule of which contains amino and hydroxy groups.
Aminoethanol(ethanolamine) HO-CH 2 CH 2 -NH 2, or colamine.
Ethanolamine is a thick oily liquid, miscible with water in all respects, and has strong alkaline properties. Along with monoethanolamine, diethanolamine and triethanolamine are also obtained:
Choline is part of lecithins- fat-like substances, very common in animal and plant organisms, and can be isolated from them. Choline is a crystalline, highly hygroscopic mass that easily deflates in air. It has strong alkaline properties and readily forms salts with acids.
When choline is acylated with acetic anhydride, choline acetate, also called acetylcholine:
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Acetylcholine plays an extremely important biochemical role, as it is a mediator (intermediary) that transmits excitation from nerve receptors to muscles.
Since amines, being derivatives of ammonia, have a structure similar to it (i.e., they have an unshared pair of electrons in the nitrogen atom), they exhibit properties similar to it. Those. amines, like ammonia, are bases, since the nitrogen atom can provide an electron pair to form a bond with electron-deficient particles according to the donor-acceptor mechanism (corresponding to the definition of Lewis basicity).
I. Properties of amines as bases (proton acceptors)
1. Aqueous solutions of aliphatic amines show an alkaline reaction, because when they interact with water, alkylammonium hydroxides are formed, similar to ammonium hydroxide:
CH 3 NH 2 + H 2 O CH 3 NH 3 + + OH -
Aniline practically does not react with water.
Aqueous solutions are alkaline in nature:
The bond of a proton with an amine, as with ammonia, is formed according to the donor-acceptor mechanism due to the lone electron pair of the nitrogen atom.
Aliphatic amines are stronger bases than ammonia, because alkyl radicals increase the electron density on the nitrogen atom due to + I-effect. For this reason, the electron pair of the nitrogen atom is held less firmly and interacts more easily with the proton.
2. Interacting with acids, amines form salts:
C 6 H 5 NH 2 + HCl → (C 6 H 5 NH 3) Cl
phenylammonium chloride
2CH 3 NH 2 + H 2 SO 4 → (CH 3 NH 3) 2 SO 4
methyl ammonium sulfate
Amine salts are solids that are highly soluble in water and poorly soluble in non-polar liquids. When reacting with alkalis, free amines are released:
Aromatic amines are weaker bases than ammonia, since the lone electron pair of the nitrogen atom shifts towards the benzene ring, conjugating with the π-electrons of the aromatic nucleus, which reduces the electron density on the nitrogen atom (-M effect). On the contrary, the alkyl group is a good electron density donor (+I-effect).
or 
A decrease in the electron density on the nitrogen atom leads to a decrease in the ability to split off protons from weak acids. Therefore, aniline interacts only with strong acids (HCl, H 2 SO 4), and its aqueous solution does not color litmus blue.
The nitrogen atom in amine molecules has an unshared pair of electrons, which can participate in the formation of a bond by the donor-acceptor mechanism.
aniline ammonia primary amine secondary amine tertiary amine
the electron density on the nitrogen atom increases.
Due to the presence of a lone pair of electrons in the molecules, amines, like ammonia, exhibit basic properties.
aniline ammonia primary amine secondary amine
the basic properties are enhanced, due to the influence of the type and number of radicals.
C6H5NH2< NH 3 < RNH 2 < R 2 NH < R 3 N (в газовой фазе)
II. Amine oxidation
Amines, especially aromatic ones, are easily oxidized in air. Unlike ammonia, they are capable of being ignited by an open flame. Aromatic amines spontaneously oxidize in air. Thus, aniline quickly turns brown in air due to oxidation.
4CH 3 NH 2 + 9O 2 → 4CO 2 + 10H 2 O + 2N 2
4C 6 H 5 NH 2 + 31O 2 → 24CO 2 + 14H 2 O + 2N 2
III. Interaction with nitrous acid
Nitrous acid HNO 2 is an unstable compound. Therefore, it is used only at the moment of selection. HNO 2 is formed, like all weak acids, by the action of a strong acid on its salt (nitrite):
KNO 2 + HCl → HNO 2 + KCl
or NO 2 - + H + → HNO 2
The structure of the reaction products with nitrous acid depends on the nature of the amine. Therefore, this reaction is used to distinguish between primary, secondary and tertiary amines.
Primary aliphatic amines with HNO 2 form alcohols:
R-NH 2 + HNO 2 → R-OH + N 2 + H 2 O
- Of great importance is the reaction of diazotization of primary aromatic amines under the action of nitrous acid obtained by the reaction of sodium nitrite with hydrochloric acid. And then phenol is formed:
Secondary amines (aliphatic and aromatic) under the action of HNO 2 are converted into N-nitroso derivatives (substances with a characteristic odor):
R 2 NH + H-O-N=O → R 2 N-N=O + H 2 O
alkylnitrosamine
· The reaction with tertiary amines leads to the formation of unstable salts and is of no practical importance.
IV. Special properties:
1. Formation of complex compounds with transition metals:
2. Addition of alkyl halides Amines add haloalkanes to form a salt:
By treating the resulting salt with alkali, you can get a free amine:
V. Aromatic electrophilic substitution in aromatic amines (reaction of aniline with bromine water or nitric acid):
In aromatic amines, the amino group facilitates substitution in the ortho and para positions of the benzene ring. Therefore, aniline halogenation occurs rapidly even in the absence of catalysts, and three hydrogen atoms of the benzene ring are replaced at once, and a white precipitate of 2,4,6-tribromaniline precipitates:
This reaction with bromine water is used as a qualitative reaction for aniline.
In these reactions (bromination and nitration) predominantly formed ortho- and pair-derivatives.
4. Methods for obtaining amines.
1. Hoffmann reaction. One of the first methods for obtaining primary amines is the alkylation of ammonia with alkyl halides:
This is not the best method, since the result is a mixture of amines of all degrees of substitution:
etc. Not only alkyl halides, but also alcohols can act as alkylating agents. To do this, a mixture of ammonia and alcohol is passed over aluminum oxide at high temperature.
2. Zinin's reaction- a convenient way to obtain aromatic amines in the reduction of aromatic nitro compounds. The following are used as reducing agents: H 2 (on a catalyst). Sometimes hydrogen is generated directly at the moment of the reaction, for which metals (zinc, iron) are treated with dilute acid.
2HCl + Fe (shavings) → FeCl 2 + 2H
C 6 H 5 NO 2 + 6 [H] C 6 H 5 NH 2 + 2H 2 O.
In industry, this reaction proceeds by heating nitrobenzene with water vapor in the presence of iron. In the laboratory, hydrogen "at the moment of isolation" is formed by the reaction of zinc with alkali or iron with hydrochloric acid. In the latter case, anilinium chloride is formed.
3. Recovery of nitriles. Use LiAlH 4:
4. Enzymatic decarboxylation of amino acids:
5. The use of amines.
Amines are used in the pharmaceutical industry and organic synthesis (CH 3 NH 2, (CH 3) 2 NH, (C 2 H 5) 2 NH, etc.); in the production of nylon (NH 2 - (CH 2) 6 -NH 2 - hexamethylenediamine); as a raw material for the production of dyes and plastics (aniline), as well as pesticides.
List of sources used:
- O.S. Gabrielyan and others. Chemistry. Grade 10. Profile level: textbook for educational institutions; Bustard, Moscow, 2005;
- "Tutor in Chemistry" edited by A. S. Egorov; "Phoenix", Rostov-on-Don, 2006;
- G. E. Rudzitis, F. G. Feldman. Chemistry 10 cells. M., Education, 2001;
- https://www.calc.ru/Aminy-Svoystva-Aminov.html
- http://www.yaklass.ru/materiali?mode=lsntheme&themeid=144
- http://www.chemel.ru/2008-05-24-19-21-00/2008-06-01-16-50-05/193-2008-06-30-20-47-29.html
- http://cnit.ssau.ru/organics/chem5/n232.htm
Amines are the only class of organic compounds with appreciable basicity. However, amines are weak bases. Now it will be useful to return to Table. 12-1 to recall the three definitions of acids and bases. According to the three definitions of basicity, three aspects of the chemical behavior of amines can be distinguished.
1. Amines react with acids, acting as proton acceptors:
Therefore, amines are Bronsted bases. 2. Amines are electron pair donors (Lewis bases):
3. Aqueous solutions of amines have, therefore, amines, when interacting with water, are able to generate hydroxide anions
Therefore, amines are Arrhenius bases. Although all amines are weak bases, their basicity depends on the nature and number of hydrocarbon radicals attached to the nitrogen atom. Alkylamines are much more basic than aromatic amines. Among the alkylamines, the secondary ones are the most basic, the primary ones are somewhat less basic, followed by the tertiary amines and ammonia. In general, the basicity decreases in the series:
A measure of the basicity of a substance is the basicity constant, which is the equilibrium constant for the interaction of an amine with water (see above for the definition of Arrhenius basicity). Since water is present in large excess, its concentration does not appear in the expression for the basicity constant:
The stronger the base, the more protons will be detached from the water molecules and the higher the concentration of hydroxide ions in the solution. Thus, stronger bases are characterized by
large K values Values for some amines are given below:
These values illustrate the relationship between the basicity of amines and their structure, which was discussed above. The strongest base is the secondary dimethylamine, and the weakest is the aromatic amine aniline.
Aromatic amines are very weak bases, since the lone electron pair of the nitrogen atom (which determines the basic properties of amines) interacts with the -electron cloud of the aromatic nucleus and, as a result, is less accessible to the proton (or other acid). The higher basicity of secondary amines compared to primary ones is explained by the fact that alkyl groups, due to their positive inductive effect, donate electrons via α-bonds to the nitrogen atom, which facilitates the socialization of the unshared electron pair. Two alkyl groups donate more electrons to the nitrogen atom than one, so secondary amines are stronger bases. Based on this, one would expect that tertiary amines are even stronger bases than secondary ones. However, this assumption is justified only for the gas phase, and the basicity of tertiary amines in an aqueous solution is not so high. This is probably due to solvation effects.
