Nitro compounds chemical properties. Structure of the nitro group
Nitro compounds
Nitro compounds are organic compounds containing one or more nitro groups -NO2. Nitro compounds usually mean C-nitro compounds in which the nitro group is bonded to a carbon atom (nitroalkanes, nitroalkenes, nitro arenes). O-nitro compounds and N-nitro compounds are divided into separate classes - nitroesters (organic nitrates) and nitramines.
Depending on the radical R, aliphatic (saturated and unsaturated), acyclic, aromatic and heterocyclic nitro compounds are distinguished. Based on the nature of the carbon atom to which the nitro group is bonded, nitro compounds are divided into primary, secondary and tertiary.
Nitro compounds are isomeric to nitrous acid esters HNO2 (R-ONO)
In the presence of α-hydrogen atoms (in the case of primary and secondary aliphatic nitro compounds), tautomerism is possible between nitro compounds and nitronic acids (aci forms of nitro compounds):
From halogen derivatives:
Nitration
Nitration is the reaction of introducing the nitro group -NO2 into the molecules of organic compounds.
The nitration reaction can proceed by an electrophilic, nucleophilic or radical mechanism, with the active species in these reactions being, respectively, the nitronium cation NO2+, the nitrite ion NO2- or the NO2 radical. The process consists of replacing the hydrogen atom at the C, N, O atoms or adding a nitro group to a multiple bond.
Electrophilic nitration[edit | edit source text]
In electrophilic nitration, the main nitrating agent is nitric acid. Anhydrous nitric acid undergoes autoprotolysis according to the reaction:
Water shifts the equilibrium to the left, so in 93-95% nitric acid the nitronium cation is no longer detected. In this regard, nitric acid is used in a mixture with water-binding concentrated sulfuric acid or oleum: in a 10% solution of nitric acid in anhydrous sulfuric acid, the equilibrium is almost completely shifted to the right.
In addition to a mixture of sulfuric and nitric acids, various combinations of nitrogen oxides and organic nitrates with Lewis acids (AlCl3, ZnCl2, BF3) are used. A mixture of nitric acid with acetic anhydride, in which a mixture of acetyl nitrate and nitrogen oxide (V) is formed, as well as a mixture of nitric acid with sulfur oxide (VI) or nitrogen oxide (V) has strong nitrating properties.
The process is carried out either by direct interaction of the nitrating mixture with a pure substance, or in a solution of the latter in a polar solvent (nitromethane, sulfolane, acetic acid). A polar solvent, in addition to dissolving reactants, solvates the + ion and promotes its dissociation.
In laboratory conditions, nitronium nitrates and salts are most often used, the nitrating activity of which increases in the following series:
Mechanism of benzene nitration:
In addition to replacing the hydrogen atom with a nitro group, substitutive nitration is also used, when a nitro group is introduced instead of sulfo-, diazo- and other groups.
The nitration of alkenes under the action of aprotic nitrating agents occurs in several directions, which depends on the reaction conditions and the structure of the starting reagents. In particular, reactions of proton abstraction and addition of functional groups of solvent molecules and counterions can occur:
Nitration of amines leads to N-nitroamines. This process is reversible:
Nitration of amines is carried out with concentrated nitric acid, as well as its mixtures with sulfuric acid, acetic acid or acetic anhydride. The product yield increases when moving from strongly basic to weakly basic amines. Nitration of tertiary amines occurs with the cleavage of the C-N bond (nitrolysis reaction); this reaction is used to produce explosives - hexogen and octogen - from methenamine.
Substitutive nitration of acetamides, sulfonamides, urethanes, imides and their salts proceeds according to the following scheme:
The reaction is carried out in aprotic solvents using aprotic nitrating agents.
Alcohols are nitrated by any nitrating agents; the reaction is reversible:
Nucleophilic nitration[edit | edit source text]
This reaction is used to synthesize alkyl nitrites. The nitrating agents in this type of reaction are alkali metal nitrite salts in aprotic dipolar solvents (sometimes in the presence of crown ethers). The substrates are alkyl chlorides and alkyl iodides, α-halocarboxylic acids and their salts, alkyl sulfates. By-products of the reaction are organic nitrites.
Radical nitration[edit | edit source text]
Radical nitration is used to obtain nitroalkanes and nitroalkenes. Nitrating agents are nitric acid or nitrogen oxides:
In parallel, the oxidation reaction of alkanes occurs due to the interaction of the NO2 radical with the alkyl radical at the oxygen atom rather than nitrogen. The reactivity of alkanes increases when moving from primary to tertiary. The reaction is carried out both in the liquid phase (nitric acid at normal pressure or nitrogen oxides, at 2-4.5 MPa and 150-220°C) and in the gas phase (nitric acid vapor, 0.7-1.0 MPa, 400 -500°C)
Nitration of alkenes by a radical mechanism is carried out with 70-80% nitric acid, sometimes with dilute nitric acid in the presence of nitrogen oxides. Cycloalkenes, dialkyl- and diarylacetylenes are nitrated with N2O4 oxide, resulting in the formation of cis- and trans-nitro compounds, by-products are formed due to the oxidation and destruction of the original substrates.
The anion-radical nitration mechanism is observed in the interaction of tetranitromethane salts of mono-nitro compounds.
Konovalov reaction (for aliphatic hydrocarbons)
Konovalov's reaction is the nitration of aliphatic, alicyclic and fatty-aromatic compounds with dilute HNO3 at elevated or normal pressure (free radical mechanism). The reaction with alkanes was first carried out by M.I. Konovalov in 1888 (according to other sources, in 1899) with 10-25% acid in sealed ampoules at a temperature of 140-150°C.
Typically a mixture of primary, secondary and tertiary nitro compounds is formed. Fatty aromatic compounds are easily nitrated at the α-position of the side chain. Side reactions include the formation of nitrates, nitrites, nitroso and polynitro compounds.
In industry, the reaction is carried out in the vapor phase. This process was developed by H. Hess (1930). The alkane and nitric acid vapors are heated to 420-480°C for 0.2-2 seconds, followed by rapid cooling. Methane gives nitromethane, and its homologues also undergo cleavage of C--C bonds, so that a mixture of nitroalkanes is obtained. It is separated by distillation.
The active radical in this reaction is O2NO·, a product of the thermal decomposition of nitric acid. The reaction mechanism is given below.
2HNO3 -t°→ O2NO· + ·NO2 + H2O
R-H + ONO2 → R + HONO2
R· + ·NO2 → R-NO2
Nitration of aromatic hydrocarbons.
Chemical properties[edit | edit source text]
In terms of their chemical behavior, nitro compounds show a certain similarity to nitric acid. This similarity is manifested in redox reactions.
Reduction of nitro compounds (Zinin reaction):
Condensation reactions
Tautomerism of nitro compounds.
Tautomerism (from the Greek ταύτίς - the same and μέρος - measure) is the phenomenon of reversible isomerism, in which two or more isomers easily transform into each other. In this case, tautomeric equilibrium is established, and the substance simultaneously contains molecules of all isomers (tautomers) in a certain ratio.
Most often, tautomerization involves the movement of hydrogen atoms from one atom in a molecule to another and back again in the same compound. A classic example is acetoacetic ester, which is an equilibrium mixture of ethyl ester of acetoacetic (I) and hydroxycrotonic acids (II).
Tautomerism is strongly manifested for a whole range of substances derivatives of hydrogen cyanide. So hydrocyanic acid itself exists in two tautomeric forms:
At room temperature, the equilibrium of the conversion of hydrogen cyanide to hydrogen isocyanide is shifted to the left. The less stable hydrogen isocyanide has been shown to be more toxic.
Tautomeric forms of phosphorous acid
A similar transformation is known for cyanic acid, which is known in three isomeric forms, but tautomeric equilibrium binds only two of them: cyanic and isocyanic acids:
For both tautomeric forms, esters are known, that is, products of the substitution of hydrocarbon radicals for hydrogen in cyanic acid. Unlike these tautomers, the third isomer, fulminate (fulmic) acid, is not capable of spontaneous transformation into other forms.
Many chemical and technological processes are associated with the phenomenon of tautomerism, especially in the field of synthesis of medicinal substances and dyes (production of vitamin C - ascorbic acid, etc.). The role of tautomerism in processes occurring in living organisms is very important.
The amide-iminol tautomerism of lactams is called lactam-lactim tautomerism. It plays an important role in the chemistry of heterocyclic compounds. The equilibrium in most cases is shifted towards the lactam form.
The list of organic pollutants is especially large. Their diversity and large numbers make it almost impossible to control the content of each of them. Therefore, they highlight priority pollutants(about 180 compounds, grouped into 13 groups): aromatic hydrocarbons, polynuclear aromatic hydrocarbons (PAHs), pesticides (4 groups), volatile and low-volatile organochlorine compounds, chlorophenols, chloroanilines and chloronitroaromatic compounds, polychlorinated and polybrominated biphenyls, organometallic compounds and others. The sources of these substances are atmospheric precipitation, surface runoff, and industrial and municipal wastewater.
Related information.
The nitro group has a structure intermediate between two limiting resonance structures:
The group is planar; the N and O atoms have sp 2 hybridization, the N-O bonds are equivalent and almost one-and-a-half; bond lengths, e.g. for CH 3 NO 2, 0.122 nm (N-O), 0.147 nm (C-N), ONO angle 127°. The C-NO 2 system is planar with a low barrier to rotation around the C-N bond.
N itro compounds having at least one a-H atom can exist in two tautomeric forms with a common mesomeric anion.
O-form called aci-nitro compound or nitronic compound:
Various known derivatives of nitronic compounds: salts of the form RR"C=N(O)O - M + (salts of nitro compounds), ethers (nitronic ethers), etc. Esters of nitronic compounds exist in the form of is- and trans- isomers. There are cyclic esters, for example N-oxides of isoxazolines.
Name nitro compounds are produced by adding the prefix “nitro” to the name. base connections, adding a digital indicator if necessary, e.g. 2-nitropropane. Name salts of nitro compounds are produced from the name. either the C-form, or the aci-form, or the nitronic acid.
Physical properties.
The simplest nitroalkanes are colorless. liquids Phys. The properties of certain aliphatic nitro compounds are given in the table. Aromatic nitro compounds are colorless. or light yellow high-boiling liquids or low-melting solids with a characteristic odor, poorly soluble. in water, as a rule, they are distilled with steam.
In the UV spectra of aliphatic nitro compounds, l max 200-210 nm (intense band) and 270-280 nm (weak band);
for salts and ethers of nitronic acid, resp. 220-230 and 310-320 nm; for heme-dinitro-containing
320-380 nm; for aromatic nitro compounds 250-300 nm (the intensity of the band decreases sharply when coplanarity is violated).
In the PMR spectrum of chem. shifts of the a-H atom, depending on the structure, 4-6 ppm. In the NMR spectrum 14 N and 15 N chemical. shift 5 from - 50 to + 20 ppm The nitro group is one of the most strong electron-withdrawing groups and is able to effectively delocalize negative. charge. In aromatic conn. as a result of inductive and especially mesomeric effects, it affects the distribution of electron density: the nucleus becomes partially positive. charge, which is localized Ch. arr. in ortho and para positions; Hammett constants for the NO 2 group s m 0.71, s n 0.778, s + n 0.740, s - n 1.25. Thus, the introduction of the NO 2 group sharply increases the reaction. ability to org. conn. in relation to the nucleophile. reagents and makes it difficult to deal with electroph.
reagents This determines the widespread use of nitro compounds in org. synthesis: the NO 2 group is introduced into the desired position of the org molecule. connection, carry out decomposition. ptions associated, as a rule, with a change in the carbon skeleton, and then transformed into another function or removed. In aromatic In some cases, a shorter scheme is often used: nitration-transformation of the NO 2 group.
Mn. transformations of aliphatic nitro compounds take place with pre-treatment. isomerization into nitronic compounds or the formation of the corresponding anion. In solutions, the equilibrium is usually almost completely shifted towards the C-form;
at 20 °C the proportion of the aci form for nitromethane is 1 10 -7, for nitropropane 3. 10 -3. Nitron compounds are free. the form is usually unstable;< 3 или нитроновые к-ты, напр.:
Acyclic alkyl esters of nitronic acids are thermally unstable and disintegrate intramol. mechanism:
;
this
The solution can be used to obtain carbonyl compounds. Silyl ethers are more stable. For the formation of C-alkylation products, see below.
Nitro compounds are characterized by reactions with the rupture of the C-N bond, along the bonds N=O, O=N O, C=N -> O, and solutions with preservation of the NO 2 group.
R-ts and s r a r s in about m with connections and S-N. Primary and secondary nitro compounds when heated. with mineral K-tami is present.
alcohol or aqueous solution of alkali form carbonyl compounds. (see Nave reaction). R-tion passes through the gaps. formation of nitron compounds:
As initial conn.
Silyl nitrone ethers can be used. The effect of strong compounds on aliphatic nitro compounds can lead to hydroxamic compounds, for example:
The method is used in industry for the synthesis of CH 3 COOH and hydroxylamine from nitroethane. Aromatic nitro compounds are inert to the action of strong compounds.When reducing agents (for example, TiCl 3 -H 2 O, VCl 2 -H 2 O-DMF) act on nitro compounds or oxidizing agents (KMnO 4 -MgSO 4, O 3) on the salts of nitro compounds, ketones and aldehydes are formed.
In aromatic conn. nucleoph.
the substitution of the NO 2 group depends on its position in relation to other substituents: the NO 2 group, located in the meta position with respect to the electron-withdrawing substituents and in the ortho- and para-positions with respect to the electron-donating ones, has a low reactivity. ability; reaction the ability of the NO 2 group located in the ortho- and para-positions to accept electron-withdrawing substituents increases markedly. In some cases, the substituent enters the ortho position to the NO 2 leaving group (for example, when heating aromatic nitro compounds with an alcohol solution KCN, Richter solution):
R-ts and i about connections and N = O. One of the most important r-tions is restoration, which generally leads to a set of products:
Azoxy-(II), azo-(III) and hydrazo-containing. (IV) are formed in an alkaline environment as a result of condensation of intermediate nitroso compounds. with amines and hydroxylamines. Carrying out the process in an acidic environment eliminates the formation of these substances. Nitroso-containing are reduced faster than the corresponding nitro compounds, and isolate them from the reaction. the mixture usually fails. Aliphatic nitro compounds are reduced to azoxy or azo compounds under the action of Na alcoholates, aromatic compounds under the action of NaBH 4, treatment of the latter with LiAlH 4 leads to azo compounds. Electrochem. the reduction of aromatic nitro compounds under certain conditions makes it possible to obtain any of the presented derivatives (with the exception of nitroso compounds); Using the same method, it is convenient to obtain hydroxylamines from mononitroalkanes and amidoximes from salts of gem-dinitroalkanes:
There are many known methods for the reduction of nitro compounds to amines. Iron filings, Sn and Zn are widely used.
Under the same conditions, silyl ethers of nitronic compounds are transformed into silyl derivatives of oximes. Treatment of primary nitroalkanes PCl 3 in pyridine or NaBH 2 S leads to nitriles. Aromatic nitro compounds containing a double bond substituent or a cyclopropyl substituent in the ortho position are rearranged in an acidic environment to form o-nitrosoketones, for example:
N itro compounds and nitrone esters react with excess Grignard reagent to give hydroxylamine derivatives:
Rations for the O = N O and C = N O bonds. Nitro compounds enter into 1,3-dipolar cycloaddition relationships, for example:
Naib. This process easily occurs between nitron esters and olefins or acetylenes. In cycloaddition products (mono- and bicyclic dialkoxyamines) under the influence of nucleophiles. and electroph. N - O bond reagents are easily broken down, which leads to decomposition. aliphatic and hetero-cyclic.
conn.:
For preparative purposes, stable silyl nitrone esters are used in the region.
R-ts and preservation of the NO 2 group. Aliphatic nitro compounds containing an a-H atom are easily alkylated and acylated, usually forming O-derivatives. However, mutual mod. dilithium salts of primary nitro compounds with alkyl halides, anhydrides or carboxylic acid halides leads to C-alkylation or C-acylation products, for example:
There are known examples of intramol.
C-alkylation, e.g.:
Primary and secondary nitro compounds react with aliphatic compounds. amines and CH 2 O with the formation of p-amino derivatives (Mannich solution); in the solution you can use previously prepared methylol derivatives of nitro compounds or amino compounds:
The nitro group facilitates aromatic rearrangements. conn. according to the intramol mechanism. nucleoph. substitution or through the stage of formation of carbanions (see Smiles rearrangement).
The introduction of a second NO 2 group accelerates the nucleoph. substitution N itro compounds present. bases are added to aldehydes and ketones, giving nitro alcohols (see Henri reactions), primary and secondary nitro compounds - to compounds containing activator.
double bond (Michael's r-tion), for example:Primary nitro compounds can enter into a Michael reaction with a second molecule of an unsaturated compound; this district with the last one.
trance
formation of the NO 2 group is used for the synthesis of poly-functional. aliphatic connections.
The combination of Henri and Michael solutions leads to 1,3-dinitro compounds, for example:
K inactive Only Hg derivatives of gem-di- or trinitro compounds, as well as IC(NO 2) 3 and C(NO 2) 4, are added to the double bond, resulting in the formation of C- or O-alkylation products; the latter can enter into a cyclo-addition reaction with a second olefin molecule: Nitroolefins easily enter into addition solutions: with water in a slightly acidic or slightly alkaline environment with the last. by Henri's retroreaction they form carbonyl compounds. and nitroalkanes; with nitro compounds containing a-H atom, poly-nitro compounds; add other CH acids, such as acetylacetone, acetoacetic and malonic esters, Grignard reagents, as well as nucleophiles such as OR - , NR - 2, etc., for example:
Nitroolefins can act as dienophiles or dipolarophiles in the processes of diene synthesis and cycloaddition, and 1,4-dinitrodienes as diene components, for example:
Receipt.
Saturated open-chain (non-cyclic) nitro compounds have the general formula C n H 2n+1 NO 2 . They are isomers of alkyl nitrites (esters of nitrous acid) with the general formula R-ONO. The differences are as follows:
Alkyl nitrites have lower boiling points
Nitro compounds are highly polar and have a large dipole moment
Alkyl nitrites are easily saponified by alkalis and mineral acids to form the corresponding alcohols and nitrous acid or its salt.
Reduction of nitro compounds leads to amines, alkyl nitrites - to alcohols and hydroxylamine.
Receipt
According to the Konovalov reaction - nitration of paraffins with dilute nitric acid when heated. All hydrocarbons enter into the liquid-phase nitration reaction, but the reaction rate is low and the yields are low. The reaction is accompanied by oxidation and the formation of polyniro compounds. The best results are obtained with hydrocarbons containing a tertiary carbon atom. Vapor-phase nitration occurs at 250-500 o C with nitric acid vapor. The reaction is accompanied by cracking of hydrocarbons, resulting in all kinds of nitro derivatives, and oxidation, which results in the formation of alcohols, aldehydes, ketones, and acids. Unsaturated hydrocarbons are also formed. Nitric acid can be replaced by nitrogen oxides. Nitration occurs via the S R mechanism.
Interaction of halogen derivatives of saturated hydrocarbons with silver nitrite when heated. The attacking particle is the NO 2 - ion, which exhibits dual reactivity (ambidence), i.e. add a radical to nitrogen (S N 2) to form a nitro compound R-NO 2 or oxygen to form a nitrous acid ester R-O-N=O. (S N 1). The reaction mechanism and its direction strongly depend on the nature of the solvent. Solvating solvents (water, alcohols) favor the formation of ether.
Chemical properties
When nitro compounds are reduced, primary amines are formed:
Primary and secondary nitro compounds are soluble in alkalis to form salts. The hydrogen atoms at the carbon bonded to the nitro group are activated, as a result, in an alkaline environment, the nitro compounds are rearranged into the acini-nitro form:
When an alkaline solution of a nitro compound is treated with a mineral acid, a strongly acidic aci form is formed, which quickly isomerizes into the usual neutral form:
Nitro compounds are classified as pseudoacids. Pseudoacids are neutral and non-conductive, but nevertheless form neutral alkali metal salts. Neutralization of nitro compounds with alkalis occurs slowly, and of true acids - instantly.
Primary and secondary nitro compounds react with nitrous acid, tertiary ones do not react:
Alkaline salts of nitrolic acids in solution are red, pseudonitroles are blue or greenish-blue.
Primary and secondary nitro compounds condense in the presence of alkalis with aldehydes, forming nitro alcohols (nucleophilic addition):
Aci forms of primary and secondary nitro compounds in aqueous solutions under the action of mineral acids form aldehydes or ketones:
Primary nitro compounds, when heated with 85% sulfuric acid, transform into carboxylic acids with the elimination of hydroxylamine. This occurs as a result of hydrolysis of the resulting aci form.
Nitro compounds.Nitro compounds- these are substances in which an alkyl or aromatic radical is bonded to a nitro group - NO 2 .
The nitrogen in the nitro group is bonded to two oxygen atoms, and one of the bonds is formed by a donor-acceptor mechanism. The nitro group has a strong electron-withdrawing effect - it attracts electron density from neighboring atoms: CH 3 δ+ -CH 2 - NO 2 δ-
Nitro compounds are divided into aliphatic (fatty) and aromatic. The simplest representative of aliphatic nitro compounds is nitromethane CH 3 -NO 2:
The simplest aromatic nitro compound is nitrobenzene C 6 H 5 -NO 2:
Preparation of nitro compounds:
a) CH 3 – CH 2 – CH – CH 3 + HNO 3 (p-p) -(t,p) H 2 O + CH 3 – CH 2 – C – CH 3 (Konovalov’s reaction proceeds selectively: tertiary atom C > secondary > primary
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b) |
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When toluene is nitrated, a trisubstituted molecule can be obtained:
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2. Replacement of halogen with a nitro group: interaction of AgNO 2 with alkyl halides. R-Br + AgNO 2 AgBr + R - NO 2 |
Properties of nitro compounds.
In reduction reactions, nitro compounds are converted to amines.
1. Hydrogenation with hydrogen: R – NO 2 + H 2 -t R- NH 2 + H 2 O
2. Reduction in solution:
a) in an alkaline and neutral environment, amines are obtained:
R-NO 2 + 3(NH 4) 2 S RNH 2 + 3S + 6NH 3 +2H 2 O (Zinin reaction)
R-NO 2 + 2Al + 2KOH + 4H 2 O RNH 2 + 2K
b) in an acidic environment (iron, tin or zinc in hydrochloric acid) are obtained amine salts: R-NO 2 + 3Fe + 7HCl Cl - + 2H 2 O + 3FeCl 2
AMINES
Amines– organic derivatives of ammonia NH 3, in the molecule of which one, two or three hydrogen atoms are replaced by hydrocarbon radicals:
R-NH 2 , R 2 NH,R 3 N
The simplest representative
Structure
The nitrogen atom is in a state of sp 3 hybridization, so the molecule has the shape of a tetrahedron.
Also, the nitrogen atom has two unpaired electrons, which determines the properties of amines as organic bases.
CLASSIFICATION OF AMINES.
According to the number and type of radicals, associated with a nitrogen atom:
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AMINES |
Primary amines |
Secondary |
Tertiary amines |
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Aliphatic |
CH 3 - N.H. 2 Methylamine |
(CH 3 ) 2 N.H. |
(CH 3 ) 3 N Trimethylamine |
|
Aromatic |
 |
(C 6 H 5 ) 2 N.H. Diphenylamine |
 |
NOMENCLATURE OF AMINES.
1. In most cases, the names of amines are formed from the names of hydrocarbon radicals and the suffix amine . The various radicals are listed in alphabetical order. If there are identical radicals, prefixes are used di And three .
CH 3 -NH 2 Methylamine CH 3 CH 2 -NH 2 Ethylamine
CH 3 -CH 2 -NH-CH 3 Methylethylamine (CH 3 ) 2 N.H.
2. Primary amines are often referred to as derivatives of hydrocarbons, in the molecules of which one or more hydrogen atoms are replaced by amino groups -NH 2 .
In this case, the amino group is indicated in the name with the prefix amino :
CH 3
-CH 2
-CH 2
-NH 2
1-aminopropane H 2
N-CH 2
-CH 2
-CH(NH 2
)-CH 3
1,3-diaminobutane
For mixed amines containing alkyl and aromatic radicals, the name is usually based on the name of the first representative of aromatic amines. 
SymbolN-
is placed before the name of the alkyl radical to indicate that this radical is associated with a nitrogen atom and is not a substituent on the benzene ring.
ISOMERISM OF AMINES
1) carbon skeleton, starting with C 4 H 9 NH 2:
CH 3 -CH 2 - CH 2 -CH 2 –NH 2 n-butylamine (1-aminobutane)
CH 3 -CH- CH 2 -NH 2 iso-butylamine (1-amine-2-methylpropane)
2) positions of the amino group, starting with C 3 H 7 NH 2:
CH 3 -CH 2 - CH 2 -CH 2 –NH 2 1-aminobutane (n-butylamine)
CH 3 -CH- CH 2 -CH 3 2-aminobutane (sec-butylamine)
3) isomerism between types of amines – primary, secondary, tertiary:
PHYSICAL PROPERTIES OF AMINES.
Primary and secondary amines form weak intermolecular hydrogen bonds:
This explains the relatively higher boiling point of amines compared to alkanes with similar molecular weights. For example:
Tertiary amines do not form associating hydrogen bonds (there is no N–H group). Therefore, their boiling points are lower than those of isomeric primary and secondary amines:
Compared to alcohols, aliphatic amines have lower boiling points because in alcohols the hydrogen bond is stronger:
At ordinary temperature only lower aliphatic amines CH 3 NH 2 , (CH 3 ) 2 NH and (CH 3 ) 3 N – gases (with the smell of ammonia), medium homologs –liquids (with a strong fishy smell), Higher ones are odorless solids.
Aromatic amines– colorless, high-boiling liquids or solids.
Amines are capable of forminghydrogen bonds with water :
Therefore, lower amines are highly soluble in water.
With an increase in the number and size of hydrocarbon radicals, the solubility of amines in water decreases, because spatial obstacles to the formation of hydrogen bonds increase. Aromatic amines are practically insoluble in water.
Aniline: WITH 6
H 5
-NH 2
– the most important of the aromatic amines:
It is widely used as an intermediate in the production of dyes, explosives and medicines (sulfonamide drugs).
Aniline is a colorless oily liquid with a characteristic odor. In air it oxidizes and acquires a red-brown color. Poisonous.
OBTAINING AMINES.
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1. Primary amines can be obtained reduction of nitro compounds. a) Hydrogenation with hydrogen: R-NO 2 + H 2 -t R- N.H. 2 +H2O b) Reduction: in an alkaline and neutral environment, amines are obtained: R-NO 2 + 3(NH 4) 2 S R-NH 2 + 3S + 6NH 3 +2H 2 O (Zinin reaction) R-NO 2 + 2Al + 2KOH + 4H 2 O R-NH 2 +2K Aniline is obtained by reduction of nitrobenzene. c) in an acidic environment (iron, tin or zinc in hydrochloric acid) amine salts are obtained: R-NO 2 + 3Fe + 7HCl Cl - + 2H 2 O + 3FeCl 2 Amines are isolated from solution using alkali: Cl - +KOH = H 2 O + KCl + R- N.H. 2 |
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2. Alkylation of ammonia and amines. When ammonia reacts with alkyl halides, a primary amine salt is formed, from which the primary amine itself can be isolated by the action of an alkali. This amine is able to react with a new portion of a haloalkane to form a secondary amine: CH 3 Br + NH 3 Br -(+KOH) CH 3 - N.H. 2 + KBr + H 2 O primary amine CH 3 -NH 2 + C 2 H 5 Br Br - - (+KOH) CH 3 - N.H.+ KBr + H 2 O secondary amine C2H5 C 2 H 5 Further alkylation to a tertiary amine is possible. |
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3. Reduction of nitriles with the formation of primary amines: R–CN + 4[H] R–CH 2 NH 2 This method is used in industry to obtain , which is used in the production of polyamide fiber nylon . |
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4. Reaction of ammonia with alcohols: R-OH + NH 3 -(t,p) R –NH 2 + H 2 O |
Chemical properties of amines.
Amines have a structure similar to ammonia and exhibit similar properties.
In both ammonia and amines, the nitrogen atom has a lone pair of electrons:
Therefore, amines and ammonia have properties reasons.
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1. Basic properties. Being derivatives of ammonia, all amines have basic properties. Aliphatic amines are stronger bases than ammonia, while aromatic amines are weaker bases. This is explained by CH radicals 3 -, WITH 2 N 5 - and others exhibitpositive inductive (+I) effect and increase electron density on the nitrogen atom: CH 3 → N.H. 2 This leads to an increase in basic properties. Phenyl radical C 6 H 5 - shows negative mesomeric (-M) effect and reduces the electron density on the nitrogen atom:
In aqueous solution amines react reversibly with water, and the medium becomes slightly alkaline: R-NH 2 +H 2 O ⇄ + + OH - |
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2. Amines react with acids to form salts: CH 3 -NH 2 + H 2 SO 4 HSO 4 C 6 H 5 NH 2 + HCl Cl C
amines
- odorless solids, highly soluble in water, but insoluble in organic solvents (unlike amines). Cl + NaOH -t CH 3 NH 2 + NaCl + H 2 O Amine salts enter into exchange reactions in solution: Cl + AgNO 3 -t NO 3 + AgCl ↓ |
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3. Amines are capable of precipitatingheavy metal hydroxides from aqueous solutions: 2R-NH 2 + FeCl 2 + 2H 2 O Fe(OH) 2 ↓+ 2Cl |
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4. Combustion. Amines burn in oxygen, forming nitrogen, carbon dioxide and water: 4 C 2 H 5 NH 2 + 15O 2 8CO 2 + 2N 2 + 14 H 2 O |
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5. Reactions with nitrous acid. A) Primary aliphatic amines under the action of nitrous acid converted to alcohols: R-NH 2 + NaNO 2 + HCl R-OH + N 2 + NaCl + H2O qualitative reaction, accompanied by the release of nitrogen gas! b) Secondary amines(aliphatic and aromatic) give nitroso compounds - substances with a characteristic odor: R 2 NH + NaNO 2 + HCl R 2 N-N=O + NaCl + H 2 O |
Features of the properties of aniline.
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Aniline is characterized by reactions both on the amino group and on the benzene ring. The features of these reactions are due to mutual influence atoms. - the benzene ring weakens the basic properties of the amino group compared to aliphatic amines and even ammonia. - the benzene ring becomes more active in substitution reactions than benzene. Amino group - substituent of the 1st kind (activating ortho-para-orienting agent in electrophilic substitution reactions in the aromatic ring).
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AMINO ACIDS
Amino acids- organic bifunctional compounds containing carboxyl groups –COUN and amino groups -NH 2
.
The simplest representative is aminoacetic acid H 2 N-CH 2 -COOH ( glycine)
All natural amino acids can be divided into the following main groups:
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1) aliphatic saturated amino acids (glycine, alanine) |
NH 2 -CH(CH 3)-COOH alanine |
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2) sulfur-containing amino acids (cysteine) |
NH 2 -CH(CH 2 SH)-COOH cysteine |
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3) amino acids with an aliphatic hydroxyl group (serine) |
NH 2 -CH(CH 2 OH)-COOH |
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4) aromatic amino acids (phenylalanine, tyrosine) |
NH 2 -CH(CH 2 C 6 H 5)-COOH phenylalanine |
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5) amino acids with two carboxyl groups (glutamic acid, aspartic acid) |
NH 2 -CH(CH 2 CH 2 COOH)-COOH glutamic acid |
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6) amino acids with two amino groups (lysine) |
NH 2 (CH 2) 4 -CH(NH 2)-COOH |
Some essential α-amino acids
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Name |
-R |
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Glycine |
-N |
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Alanin |
-CH 3 |
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Cysteine |
-CH 2 -SH |
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Serin |
-CH 2 -OH |
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Phenylalanine |
-CH 2 -C 6 H 5 |
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Tyrosine |
 |
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Glutamic acid |
-CH 2 -CH 2 -COOH |
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Lysine |
-(CH 2) 4 -NH 2 |
Nomenclature of amino acids
According to systematic nomenclature, the names of amino acids are formed from the names of the corresponding acids by adding the prefix amino and indicating the location of the amino group in relation to the carboxyl group:
Another method of constructing the names of amino acids is also often used, according to which the prefix is added to the trivial name of the carboxylic acid amino indicating the position of the amino group by a letter of the Greek alphabet. Example:
For α-amino acids R-CH(NH 2)COOH, which play an extremely important role in the life processes of animals and plants, trivial names are used.
If an amino acid molecule contains two amino groups, then the prefix is used in its name diamino-, three NH 2 groups – triamino- etc.
The presence of two or three carboxyl groups is reflected in the name by the suffix -diovy or -triic acid:
OBTAINING AMINO ACIDS.
1. Replacement of a halogen with an amino group in the corresponding halogenated acids:
2. Addition of ammonia to α,β-unsaturated acids to form β-amino acids ( against Markovnikov's rule):
CH 2 =CH–COOH + NH 3 H 2 N–CH 2 –CH 2 –COOH
3. Reduction of nitro-substituted carboxylic acids (usually used to obtain aromatic amino acids): O 2 N–C 6 H 4 –COOH + 3H 2 H 2 N–C 6 H 4 –COOH + 2H 2 O
PROPERTIES OF AMINO ACIDS .
Physical properties
Amino acids are solid crystalline substances with a high melting point. Highly soluble in water, aqueous solutions are electrically conductive. When amino acids are dissolved in water, the carboxyl group removes a hydrogen ion, which can attach to the amino group. This creates internal salt, the molecule of which is bipolar ion:
H 2
N-CH 2
-COOH⇄
+
H 3
N-CH 2
-COO -
CHEMICAL PROPERTIES OF AMINO ACIDS.
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1. Acid-base properties: Amino acids areamphoteric connections. They contain two functional groups of opposite nature in the molecule: an amino group with basic properties and a carboxyl group with acidic properties. Amino acids react with both acids and bases: H 2 N-CH 2 -COOH + HCl Cl H 2 N-CH 2 -COOH + NaOH H 2 N-CH 2 -COONa + H 2 O Acid-base transformations of amino acids in various environments can be represented by the following diagram:
Aqueous solutions of amino acids have a neutral, alkaline or acidic environment depending on the number of functional groups. So, glutamic acid forms an acidic solution (two -COOH groups, one -NH 2), lysine- alkaline (one group -COOH, two -NH 2). |
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2. Like acids, amino acids can react with metals, metal oxides, salts of volatile acids: 2H 2 N-CH 2 -COOH +2 Na 2H 2 N-CH 2 -COONa + H 2 2H 2 N-CH 2 -COOH + Na 2 O 2H 2 N-CH 2 -COONa + H 2 O H 2 N-CH 2 -COOH + NaHCO 3 H 2 N-CH 2 -COONa + CO 2 + H 2 O |
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3. Amino acids can react with alcohols in the presence of hydrogen chloride gas, becoming an ester: H 2 N-CH 2 -COOH + C 2 H 5 OH –(HCl) H 2 N-CH 2 -COOC 2 H 5 + H 2 O |
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4. Intermolecular interaction of α-amino acids leads to the formation peptides. When two α-amino acids interact, it is formed.
Fragments of amino acid molecules that form a peptide chain are called amino acid residues, and the CO–NH bond is peptide bond. From three molecules of α-amino acids (glycine + alanine + glycine) you can get tripeptide: H 2 N-CH 2 CO-NH-CH(CH 3)-CO-NH-CH 2 COOH glycylalanylglycine |
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6. When heated decompose (decarboxylation): NH 2 -CH 2 - COO H –(t) NH 2 -CH 3 + CO 2 |
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7. Decarboxylation with alkali: NH 2 -CH 2 -COOH +Ba(OH) 2 –(t) NH 2 -CH 3 + BaCO 3 + H 2 O |
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8. C nitrous acid: NH 2 -CH 2 -COOH + HNO 2 HO-CH 2 -COOH + N 2 + H 2 O |
PROTEINS
Proteins (polypeptides) – biopolymers built from α-amino acid residues connectedpeptide(amide) bonds. Formally, the formation of a protein macromolecule can be represented as a polycondensation reaction of α-amino acids:
The molecular weights of various proteins (polypeptides) range from 10,000 to several million. Protein macromolecules have a stereoregular structure, which is extremely important for their manifestation of certain biological properties.
Despite the large number of proteins, they contain residues of no more than 22 α-amino acids.
PROTEIN STRUCTURE.
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Primary structure- a specific sequence of α-amino acid residues in a polypeptide chain. |
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Secondary structure- conformation of the polypeptide chain, secured by many hydrogen bonds between N-H and C=O groups. One model of secondary structure is the α-helix. |
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Tertiary structure- the shape of a twisted helix in space, formed mainly due to disulfide bridges -S-S-, hydrogen bonds, hydrophobic and ionic interactions. |
 |
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Quaternary structure- aggregates of several protein macromolecules (protein complexes), formed through the interaction of different polypeptide chains |
Physical properties proteins are very diverse and are determined by their structure. Based on their physical properties, proteins are divided into two classes:
- globular proteins dissolve in water or form colloidal solutions,
- fibrillar proteins
insoluble in water.
In the PMR spectrum of chem. shifts of the a-H atom, depending on the structure, 4-6 ppm. In the NMR spectrum 14 N and 15 N chemical. shift 5 from - 50 to + 20 ppm
1 . Protein denaturation. This is the destruction of its secondary and tertiary protein structure while maintaining the primary structure. It occurs when heated, changes in the acidity of the environment, or exposure to radiation. An example of denaturation is the coagulation of egg whites when eggs are boiled.
Denaturation can be reversible or irreversible. Irreversible denaturation can be caused by the formation of insoluble substances when proteins are exposed to salts of heavy metals - lead or mercury.
2. Protein hydrolysis is the irreversible destruction of the primary structure in an acidic or alkaline solution with the formation of amino acids . By analyzing hydrolysis products, it is possible to determine the quantitative composition of proteins.
3. Qualitative reactions to proteins:
1)Biuret reaction – purple coloring upon action on proteins of freshly precipitated copper hydroxide ( II ) .
2) Xanthoprotein
reaction - yellow coloring
when acting on proteins concentrated nitric acid
.
Biological significance of proteins:
1. Proteins are very powerful and selective catalysts. They speed up reactions millions of times, and each reaction has its own single enzyme.
2. Proteins perform transport functions and transport molecules or ions to sites of synthesis or accumulation. For example, the protein contained in the blood hemoglobin carries oxygen to tissues, and protein myoglobin stores oxygen in muscles.
3. Proteins are cell building material . Supporting, muscle, and integumentary tissues are built from them.
4. Proteins play an important role in the body's immune system. There are specific proteins (antibodies), who are capable recognize and associate foreign objects - viruses, bacteria, foreign cells.
5. Receptor proteins perceive and transmit signals coming from neighboring cells or from the environment. For example, receptors activated by low molecular weight substances such as acetylcholine transmit nerve impulses at the junctions of nerve cells.
6. Proteins are vital for any organism and are the most important component of food. During the digestion process, proteins are hydrolyzed to amino acids, which serve as the starting material for the synthesis of proteins necessary for a given organism. There are amino acids that the body is not able to synthesize itself and acquires them only with food. These amino acids are called irreplaceable.
NITRO COMPOUNDS, contain one or more in a molecule. nitro groups directly bonded to the carbon atom. N- and O-nitro compounds are also known. The nitro group has a structure intermediate between two limiting resonance structures:
The group is planar; the N and O atoms have sp 2 hybridization, the N-O bonds are equivalent and almost one-and-a-half; bond lengths, e.g. for CH 3 NO 2, 0.122 nm (N-O), 0.147 nm (C-N), ONO angle 127°. The C-NO 2 system is planar with a low barrier to rotation around the C-N bond.
Nitro compounds having at least one a-H atom can exist in two tautomeric forms with a common mesomeric anion. O-form called aci-nitro compound or nitronic compound:
Esters of nitronic compounds exist in the form of cis- and trans-isomers. There are cyclical ethers, e.g. Isoxazoline N-oxides.
Name nitro compounds are produced by adding the prefix “nitro” to the name. base connections, adding a digital indicator if necessary, e.g. 2-nitropropane. Name salts of nitro compounds are produced from the name. either the C-form, or the aci-form, or the nitronic acid.
NITRO COMPOUNDS OF ALIPHATIC SERIES
Nitroalkanes have the general formula C n H 2n+1 NO 2 or R-NO 2 . They are isomeric with alkyl nitrites (esters of nitric acid) with the general formula R-ONO. The isomerism of nitroalkanes is associated with the isomerism of the carbon skeleton. Distinguish primary RCH 2 NO 2 secondary R 2 CHNO 2 and tertiary R 3 CNO 2 nitroalkanes, for example:
Nomenclature
The names of nitroalkanes are based on the name of the hydrocarbon with the prefix nitro(nitromethane, nitroethane, etc.). According to systematic nomenclature, the position of the nitro group is indicated by a number:
^ Methods for obtaining nitroalkanes
1. Nitration of alkanes with nitric acid (Konovalov, Hess)
Concentrated nitric acid or a mixture of nitric and sulfuric acids oxidizes alkanes. Nitration occurs only under the influence of dilute nitric acid (specific weight 1.036) in the liquid phase at a temperature of 120-130°C in sealed tubes (M.I. Konovalov, 1893):
^ R-H + HO-NO 2 → R-NO 2 + H 2 O
For nitration Konovalov M.I. First time using nonaphthene
It was found that the ease of replacing a hydrogen atom with a nitro group increases in the series:
The main factors influencing the rate of the nitration reaction and the yield of nitro compounds are the acid concentration, temperature and process duration. For example, nitration of hexane is carried out with nitric acid (d 1.075) at a temperature of 140°C:
The reaction is accompanied by the formation of polynitro compounds and oxidation products.
The method of vapor-phase nitration of alkanes has gained practical importance (Hess, 1936). Nitration is carried out at a temperature of 420°C and a short stay of the hydrocarbon in the reaction zone (0.22-2.9 sec). Nitration of alkanes according to Hess leads to the formation of a mixture of nitroparaffins:
The formation of nitromethane and ethane occurs as a result of cracking of the hydrocarbon chain.
The nitration reaction of alkanes proceeds by a free radical mechanism, and nitric acid is not a nitrating agent, but serves as a source of nitrogen oxides NO2:
2. Meyer's reaction (1872)
The interaction of alkyl halides with silver nitrite leads to the production of nitroalkanes:
A method for producing nitroalkanes from alkyl halides and sodium nitrite in DMF (dimethylformamide) was proposed by Kornblum. The reaction proceeds according to the mechanism S N 2.
Along with nitro compounds, nitrites are formed in the reaction, this is due to the ambidentity of the nitrite anion:
^ Structure of nitroalkanes
Nitroalkanes can be represented by Lewis octet formula or resonance structures:
One of the bonds of a nitrogen atom with oxygen is called donor-acceptor or semipolar.
^
Chemical properties
Chemical transformations of nitroalkanes are associated with reactions at the a-hydrogen carbon atom and the nitro group.
Reactions involving the a-hydrogen atom include reactions with alkalis, nitrous acid, aldehydes and ketones.
1. Formation of salts
Nitro compounds belong to pseudoacids - they are neutral and do not conduct electric current, but they interact with aqueous solutions of alkalis to form salts, upon acidification of which the aci form of the nitro compound is formed, which then spontaneously isomerizes into a true nitro compound:
The ability of a compound to exist in two forms is called tautomerism. Nitroalkane anions are ambident anions with dual reactivity. Their structure can be represented in the following forms:
2. Reactions with nitrous acid
Primary nitro compounds react with nitrous acid (HONO) to form nitrolic acids:
Nitrolic acids, when treated with alkalis, form a blood-red salt:
Secondary nitroalkanes form pseudonitroles (heme-nitronitroso-alkanes) of blue or greenish color:
Tertiary nitro compounds do not react with nitrous acid. These reactions are used for the qualitative determination of primary, secondary and tertiary nitro compounds.
3. Synthesis of nitro alcohols
Primary and secondary nitro compounds react with aldehydes and ketones in the presence of alkalis to form nitro alcohols:
Nitromethane with formaldehyde gives trioxymethylnitromethane NO 2 C (CH 2 OH) 3. When the latter is reduced, amino alcohol NH 2 C (CH 2 OH) 3 is formed - the starting material for the production of detergents and emulsifiers. Tri(hydroxymethyl)nitromethane trinitrate, NO 2 C(CH 2 ONO 2) 3, is a valuable explosive.
Nitroform (trinitromethane) reacts with formaldehyde to form trinitroethyl alcohol:
4. Reduction of nitro compounds
Complete reduction of nitro compounds into the corresponding amines can be achieved by many methods, for example, the action of hydrogen sulfide, iron in hydrochloric acid, zinc and alkali, lithium aluminum hydride:
Methods of incomplete reduction are also known, as a result of which oximes of the corresponding aldehydes or ketones are formed:
5. Interaction of nitro compounds with acids
The reactions of nitro compounds with acids are of practical value. Primary nitro compounds, when heated with 85% sulfuric acid, are converted into carboxylic acids. It is assumed that stage 1 of the process is the interaction of nitro compounds with mineral acids to form the aci form:
Aci salts of primary and secondary nitro compounds form aldehydes or ketones in the cold in aqueous solutions of mineral acids (Nef reaction):
. Aromatic nitro compounds. Chemical properties
Chemical properties. Reduction of nitro compounds in acidic, neutral and alkaline media. The practical significance of these reactions. The activating effect of the nitro group on nucleophilic substitution reactions. Polynitro compounds of the aromatic series.
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