Amines interact with General formula of amines. Properties and structure of amines. Basic properties of amino acids
AMINES- a class of compounds representing 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 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 RNH2
secondary amines - two organic groups at the nitrogen R2NH, organic groups can be different R "R" NH
tertiary amines - three organic groups at the nitrogen R3N or R "R" R "" N
According to the type of organic group associated with nitrogen, aliphatic CH3 - N are distinguished< и ароматические С 6 H5 – N< амины, возможны и смешанные варианты.
According to the number of amino groups in the molecule, amines are divided into monoamines CH3 - NH 2, diamines H2N (CH2) 2 NH 2, 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 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 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 C2H5 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.
C2H5 N H2 + H2O + + OH–
With the formation of a donor-acceptor bond, amines can add not only HCl, but also haloalkyls RCl, and a new N–R 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:
[(C2H5)4 N]I [(C2H5) 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:
C2H5 N H2+H N O2 C2H5OH + 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< (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 the 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.
The interaction of primary amines with phosgene Cl2C=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 [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 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 (see AROMATICITY); during halogenation, hydrogen atoms in the ortho and para positions to the amino group are replaced, chloroanilines with various degrees of substitution are obtained (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 are organic compounds that are considered as derivatives of ammonia, in which hydrogen atoms (one, two or three) are replaced by hydrocarbon radicals. Amines are divided into primary, secondary, tertiary, depending on how many hydrogen atoms are replaced by a radical: />
| primary | secondary | tertiary |
| amines | amines | amines |
There are also organic analogues of ammonium salts - these are quaternary salts type [ R 4 N] + Cl -.
Depending on the nature of the radicals, amines can be aliphatic(marginal and non-marginal), alicyclic, aromatic or mixed.
Limit aliphatic amines
The general formula of limiting aliphatic amines C n H 2 n +3 N .
Building. /> The nitrogen atom in amine molecules is in the statesp 3 -hybridization. Three of the four hybrid orbitals are involved in the formation of σ-bonds N-C and N-H , in the fourth orbital is a lone electron pair, which determines the basic properties of amines.The names of amines are usually produced by listing the hydrocarbon radicals (in alphabetical order) and adding the ending -amine, for example:
Electron donor substituents (saturated hydrocarbon radicals) increase the electron density on the nitrogen atom and enhance the basic properties of amines, therefore secondary amines are stronger bases than primary ones, since two radicals create a greater electron density on the nitrogen atom than one. In tertiary amines, the spatial factor plays an important role: three radicals block the electron pair of the nitrogen atom and make it difficult for it to interact with other molecules, so the basicity of tertiary amines is less than that of primary or secondary ones.
Basicity constants of ammonia and lower amines: X + H 2 O 
XH + + OH -
isomerism amines is associated with the structure of the carbon skeleton and the position of the amino group:
In addition, primary, secondary and tertiary amines containing the same number of carbon atoms are isomeric with each other, for example:
CH 3 -CH 2 -NH 2 CH 3 -NH-CH 3
ethylamine dimethylamine
Nomenclature.
C 2 H 5 - NH 2 CH 3 - NH - C 2 H 5 (CH 3) 3 N
ethylamine methylethylamine trimethylamine
According to another system, the names of primary amines are built based on the name of the parent hydrocarbon and adding the ending -amine indicating the number of the carbon atom associated with the amino group.
Physical Properties. />Methylamine, dimethylamine and trimethylamine are gases, the middle members of the aliphatic series are liquids, the higher ones are solids. Weak hydrogen bonds are formed between amine molecules in the liquid phase, so the boiling points of amines are higher than those of the corresponding hydrocarbons.
Amines also form weak hydrogen bonds with water, therefore lower amines are highly soluble in water, as the carbon skeleton grows, the solubility in water decreases. Lower amines have a characteristic "fishy" odor, higher amines are odorless.
Amines- organic derivatives of ammonia, in the molecule of which one, two or all three hydrogen atoms are replaced by a carbon residue.
Usually isolated three types of amines:
Amines in which the amino group is bonded directly to the 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 nitrogen atom, which is part of the functional group, lone electron pair. This leads to the fact that amines exhibit the properties of bases.
There are ions that are the product of formal substitution for a hydrocarbon radical of all hydrogen atoms in the ammonium ion:
These ions are part of salts similar to ammonium salts. They are called quaternary ammonium salts.
Isomerism and nomenclature
1. Amines are characterized structural isomerism:
a) isomerism of the carbon skeleton:
b) functional group position isomerism:
2. Primary, secondary and tertiary amines are isomeric to each other ( interclass isomerism):
As can be seen from the above examples, in order to name an amine, the substituents associated with the nitrogen atom are listed (in order of precedence), and the suffix is \u200b\u200badded -amine.
Physical properties of amines
The simplest amines(methylamine, dimethylamine, trimethylamine) - gaseous substances. Others lower amines liquids that are highly soluble in water. They have a characteristic smell reminiscent of the smell of ammonia.
Primary and secondary amines are capable of forming hydrogen bonds. This leads to a marked increase in their boiling points compared to compounds having the same molecular weight but not capable of forming hydrogen bonds.
Aniline is an oily liquid, sparingly soluble in water, boiling at 184°C.
Aniline
The chemical properties of amines are determined in mainly by the presence of a lone electron pair at the nitrogen atom.
Amines as bases. The nitrogen atom of the amino group, like the nitrogen atom in the ammonia molecule, due to lone pair of electrons can form covalent bond by the donor-acceptor mechanism, acting as a donor. In this regard, amines, like ammonia, are able to attach a hydrogen cation, i.e., act as a base:
1. Reaction of amions with water leads to the formation of hydroxide ions:
A solution of amine in water is alkaline.
2. Reaction with acids. Ammonia reacts with acids to form ammonium salts. Amines are also able to react with acids:
Basic properties of aliphatic amines more pronounced than in 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. Increasing the electron density turns nitrogen into a stronger electron pair donor, which increases its basic properties:
combustion of amines. Amines burn in air to form carbon dioxide, water and nitrogen:
Chemical properties of amines - compendium
Application of amines
Amines are widely used to obtain medicines, polymer materials. Aniline is the most important compound of this class, which is used for the production of aniline dyes, drugs (sulfanilamide preparations), polymeric materials (aniline-formaldehyde resins).
Reference material for passing the test:
periodic table
Solubility table
Amines ammonia derivatives are called, in which one, two or three hydrogen atoms are replaced by hydrocarbon radicals.
Depending on the number of hydrocarbon radicals, there are primary , secondary and tertiary amines. There are also quaternary ammonium salts and grounds , which are derivatives of the ammonium ion, in which all four hydrogen atoms are replaced by organic radicals. According to the nature of the radical, amines are divided into aliphatic and aromatic.
For amines, names based on radical functional , and not according to the replacement nomenclature.
generic name amines refers to compounds RNH 2 , RR"NH and RR"R"N, which are primary, secondary and tertiary amines, respectively. In a broader sense, amines also include compounds containing an -NH- group in the cycle.
Titles primary amines formed by adding the suffix -amine to the name of the radical R (method a) or to the name of the parent structure (method b). So, the compound CH 3 CH 2 CH 2 NH 2 will be called propylamine (a) or propanamine-1 (b). Way a usually used for derivatives of simple compounds, and the method b - for complex cyclic compounds. In the way a the principle of substitution of the hydrogen atom in the ammonia molecule, which is formally the parent structure, is applied. In essence, it is similar to the principle of radical-functional nomenclature, but in the IUPAC rules it refers to a substitute.
In cases where the -NH 2 group is not the eldest, it is indicated by the prefix amino -:
Some amines retain trivial titles:
Primary diamines and polyamines, in which all amino groups are attached to an aliphatic chain or cyclic nucleus, are called by adding suffixes - diamine , -triamine etc. to the name of the parent structure or polyvalent radical. The trivial name "benzidine" is retained.
symmetrical secondary and tertiary amines called by adding multiplying prefixes di- or three- to the names of alkyl radicals with the suffix -amine. Unsymmetrical compounds are named as L-substituted derivatives of primary amines, and a compound with a more complex radical is taken as the initial primary amine:
Amine radicals RNH-, R 2 N-, RR "N- are called as substituted amino groups or a letter is added to the trivial names of amines about:
Lower aliphatic amines are gases or liquids with an ammonia-like odor. The higher homologues of aliphatic amines and aromatic amines are either liquids or solids. Amines form weak hydrogen bonds and unstable associates, therefore their boiling points are lower than those of alcohols and carboxylic acids with the same number of carbon atoms, but higher than those of aldehydes or ethers. Lower aliphatic amines are highly soluble in water; with an increase in the number of hydrocarbon radicals and their length, the solubility decreases. Aromatic amines are poorly soluble in water.
Representatives.
Aniline - C 6 H 5 NH 2 - a colorless liquid with a slight odor similar to the smell of benzene, when standing in air, it quickly oxidizes and acquires a yellow-brown color and an unpleasant odor. Toxic.
More than half of the aniline produced is spent on the production of stabilizers and rubber vulcanization accelerators. Its second most important area of application is the production of isocyanates used to produce polyurethanes. They are also used in the production of dyes of various classes, medicines, photographic materials and plant protection products. In our country, aniline is used to produce caprolactam.
N-methylaniline(monomethylaniline) - C 6 H 5 NHCH 3 - is a yellow oily liquid with a density of 0.98 g / cm 3, soluble in gasolines, alcohols and ethers. The main task of monomethylaniline is to obtain the necessary detonation properties of gasoline during its production. In addition, when it is added to the fuel, the octane number of the product and its environmental friendliness are regulated.
Dimethylaniline - C 6 H 5 N (CH 3) 2 - tertiary fatty aromatic amine, colorless liquid. It is used in the production of polyester resins and in organic synthesis. Dimethylaniline is used in the synthesis of dyes (malachite green, methylene blue, etc.), explosives, etc.
Toluidines - CH 3 C 6 H 4 NH 2 - colorless crystalline compounds with peculiar odors, quickly oxidize and darken in air. Obtained by the reduction of nitrotoluenes. It is used in the production of dyes of different classes (triphenylmethane, azo dyes, thiazine, sulfur), as well as for the production of cresols. Toluidines, like some other aromatic amines, are poisonous and carcinogenic.
Fenetidines (ethoxyanilines, aminophenetols) - NH 2 -C 6 H 4 -OC 2 H 3 (ortho-, para- and meta-) - are liquids. Used in the production of azotols; n-fenetidine is also used in the synthesis of drugs (phenacetin, rivanol). Fenethidines cause poisoning by contact with the skin and inhalation of vapors, affect the liver and kidneys.
Diphenylamine ((N-phenyl)-aniline) - (C 6 H 5) 2 NH - colorless crystals, darkening in the light. Diphenylamine is an initial product in the production of antioxidants for polymers; stabilizer and phlegmatizer for thermal and weather resistance of cellulose nitrates, including pyroxylin powders; an intermediate product in the synthesis of triarylmethane and azo dyes, insecticides; mild steel corrosion inhibitor. Used in analytical chemistry to detect ions, as a redox indicator.
Spectral characteristics.
IR spectroscopy . The position of the absorption bands of amino groups in the spectrum is determined by the conditions for recording the spectra (in solid form, liquid state, in solutions or gas phase) and depends on whether the amino group is free (non-associated) or whether it participates in the formation of inter- and intramolecular hydrogen bonds.
Absorption bands due to stretching vibrations of N-H bonds appear in the IR spectra in the region of 3500-3200 cm -1 . Primary amines have two absorption bands. A higher frequency is due to asymmetric N-H stretching vibrations, a lower frequency is due to symmetrical ones. In the spectra of amines in dilute solutions in inert solvents, these two narrow bands are observed at 3500 and 3400 cm -1 . Secondary amines have one absorption band corresponding to N-H stretching vibrations. For aliphatic amines in inert solvents, it is observed in the region of 3350-3310 cm -1 , in the spectra of mixed amines Ar-NH-Alk, the N-H absorption band is located at higher frequencies of 3450 cm -1 .
If the amino group participates in an inter- or intramolecular hydrogen bond (in a solid or liquid state, in concentrated solutions), then the absorption bands of N-H stretching vibrations are shifted to the low-frequency side. However, this shift is not so significant. Associated primary amines give absorption bands in the regions of 3420-3330 cm -1 (v asNH 2) and 3330-3250 cm -1 (v sNH 2), secondary - in the region of 3300-3150 cm -1 . With incomplete association, one can simultaneously observe bands of the free and associated amino groups, therefore, in the region of 3500-3200 cm -1 there may be more than two bands characteristic of primary amines, and more than one band characteristic of secondary ones.
Deformation vibrations of the amino group are observed in the region of 1650-1500 and 950-650 cm -1 . Primary amines have absorption bands of planar deformation vibrations of average intensity 1650-1580 cm -1 , secondary - weak intensity in the range of 1600-1500 cm -1 . When hydrogen bonds are formed, the frequencies of deformation vibrations increase.
Amines also have C-N stretching absorption bands. In aliphatic amines, these vibrations correspond to absorption in the region of 1250-1020 cm -1 of medium intensity, in aromatic amines - intense absorption in the frequency range of 1340-1260 cm -1 .
The interaction of amines with acids causes strong changes in the spectra. In salts of primary amines, N-H vibrations correspond to a wide strong band in the region of 3100-2600 cm -1 . Salts of secondary and tertiary amines have intense absorption in the region of 2700-2250 cm -1 . Amine salts can be further identified by bending vibrations. Salts of primary amines absorb in the range of 1600-1575 and 1550-1500 cm -1 , salts of secondary amines - in the range of 1620-1560 cm -1 .
PMR spectroscopy . Signals of protons of the NH group of aliphatic and cyclic amines are observed in the range of 0.5-3.0 ppm, aromatic amines - at 3.0-5.0 ppm. Since amines can form hydrogen bonds, the position of the signals depends on the concentration amine, nature of solvent and temperature. The protons of the NH group can be exchanged for deuterium, and when D 2 O is added to the sample of heavy water, these signals disappear.
The amino group, which is in conjugation with the benzene ring, increases the electron density in ortho- and pair -positions of the ring, which leads to screening of the corresponding protons and mixing of their signals in a stronger field compared to benzene. In the PMR spectra of amines, the signals of aromatic protons are complex multiplets.
Electronic spectroscopy . Aliphatic amines in the UV and visible region do not absorb . The conjugation of amino groups with the benzene ring leads to a significant bathochromic shift of the absorption bands of benzene with an increase in their intensity. It is believed that, along with the local π → π * transition of the benzene ring, this absorption is contributed by the transition with charge transfer from the donor group to the ring (aniline. Aniline in the near UV region has two absorption bands - 230 nm and 280 nm.
Amines: acid-base properties; nucleophilic properties - amine and ammonia alkylation reactions, quaternary ammonium salts, opening -oxide cycle by amines with the formation of amino alcohols.
Chemical properties.
In the molecules of aliphatic amines, the nitrogen atom is in the state sp 3 -hybridization, so they, like ammonia, have a pyramidal configuration. For example, the C-N-C bond angles in trimethylamine are 108° and are very close to the H-N-H angles in the ammonia molecule.
Theoretically, secondary and tertiary amines with different hydrocarbon radicals can exist as enantiomers, but conventional aliphatic and aromatic amines have not yet been isolated as individual enantiomers. This is due to the fact that the ammonia and amine molecules constantly undergo a pyramidal inversion, which should be considered as a rapid configuration reversal. The inversion is done through a trigonal transition state (in the center of the diagram):
In aromatic amine molecules, the lone pair of electrons of the nitrogen atom is conjugated with π -electrons of the aromatic ring, as a result of which the amplitude with which the pyramidal inversion occurs is significantly reduced.
Quaternary ammonium salts having four different radicals can be separated into individual enantiomeric forms, i.e. these forms are configurationally stable. So, allylbenzylmethylphenylammonium iodide is isolated as individual enantiomers, each of which has optical activity:
Basic properties.
Amines, like ammonia, exhibit basic properties, which is due to the presence in their molecules of a nitrogen atom with an unshared pair of electrons. When reacting with acids, amines are converted into ammonium salts :
Amine salts, unlike other onium salts, are hydrolytically stable, highly soluble in water, easily crystallize from aqueous solutions, and, as a rule, are more stable than free bases. Many medicinal substances belonging to the class of amines are used in the form of salts with mineral and less often organic acids.
Aliphatic amines - strong bases . Aqueous solutions of amines have an alkaline environment according to litmus:
It can be assumed that tertiary amines with three alkyl substituents with +I-effect will be stronger bases than secondary and primary amines. However, steric factors that determine the accessibility of the main center for proton attack have the opposite effect. The more radicals the nitrogen atom has and the more branched they are, the stronger the lone pair of electrons of the nitrogen atom is shielded and its interaction with the proton is more difficult. Therefore, the strongest bases should be primary and secondary amines with relatively short and unbranched radicals. Solvation (the interaction of a solute molecule with solvent molecules) has an effect on basicity similar to the effect of steric factors, since with an increase in the number and branching of hydrocarbon radicals, the ability of the substituted ammonium cation (conjugate acid) to bind solvent molecules decreases.
Many experimental data do not fit into the relatively simple schemes outlined above. Thus, purely speculative reasoning cannot serve as a reliable basis for predicting the relative basicity of aliphatic amines. In practice, one can be guided by the fact that the pK values of BH+ of most aliphatic amines fit into a relatively narrow range: from 10.6 to 11.2. Such a small difference in basicity does not provide a significant advantage to any of the amines in the competitive protonation reaction.
The basicity of aromatic amines is significantly lower than that of aliphatic amines. This is explained by the fact that the lone pair of electrons of the nitrogen atom enters p, π-conjugation with the electrons of the benzene ring:
Substituents in the ring have a significant effect on basicity: electron-supporting substituents increase it, while electron-withdrawing substituents decrease it.
If, due to steric hindrance, the lone pair of electrons is removed from conjugation, then the basicity of the amine increases significantly. So, the bulky alkyl radicals of N,N-diisopropylaniline cannot be located in the same plane with the benzene ring due to mutual repulsion with hydrogen atoms in the ortho positions, therefore its basicity (pK BH + 7.4) is much higher than that of aniline. A similar kind of steric hindrance occurs in N,N-dialkylanilines, which simultaneously have substituents in positions 2 and 6. In the 1,8-bis(dimethylamino)naphthalene molecule, both dimethylamino groups also cannot be located in the same plane with the aromatic system, and this compound has a surprisingly high basicity (pKin + 12.4), its protonated form is stable due to the fact that the proton is firmly held by lone pairs of electrons of two nitrogen atoms.
acid properties.
NH-Acidic properties of amines are expressed to a much lesser extent than the basic ones. For aliphatic and aromatic primary and secondary amines pK A have values of 30-35. Thus, only alkanes are weaker acids than amines. Amines are acidic only in the presence of very strong bases , such as, for example, organometallic compounds, and are converted into metal amides (not to be confused with amides of carboxylic and sulfonic acids!):
Alkali metal amides are very strong bases and are used in organic synthesis.
nucleophilic properties.
The nucleophilic properties of amines, like the basic ones, are due to the presence of a lone pair of electrons on the nitrogen atom. Some reactions in which amines participate as nucleophilic reagents will continue and have been in the past. These are alkylation of amines [(1)], interaction with carbonyl compounds [(2)], and acylation with carboxylic acid derivatives [(3)]:
Alkylation. Amines, like ammonia, undergo alkylation with haloalkanes. Alkylation of ammonia leads to the formation of a primary amine, secondary amines are formed from primary amines, tertiary ones from secondary ones, and quaternary ammonium salts from tertiary ones. The substituted ammonium salt formed during the reaction exchanges a proton with ammonia or an amine, therefore, in the alkylation reaction, a mixture of amines with a different number of alkyl radicals is obtained:
The alkylation reaction can rarely be stopped at any particular stage due to the fact that the differences in nucleophilicity and basicity of primary, secondary and tertiary amines are not so significant as to affect the difference in the rates of alkylation reactions of amines of different degrees of substitution.
In industry, ammonia and lower amines are alkylated with lower alcohols in the gas phase at a temperature of 300-500 ° C over oxides of aluminum, silicon, thorium, chromium, etc. In this case, mixtures of primary, secondary and tertiary amines are formed. In this way, mainly methyl and ethylamines are obtained:
Reactions of amines with epoxides. When primary and secondary amines interact with epoxides (oxiranes), the nucleophilic opening of the strained three-membered α-oxide cycle occurs and β-aminoalcohols are formed. In substituted epoxides, the nucleophilic attack occurs, as a rule, at the least substituted carbon atom of the oxide cycle ( Krasuski's rule ):
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.
