1. Nitro compounds

1.2. Reactions of nitro compounds

1. NITRO COMPOUNDS

Nitrocompounds are derivatives of hydrocarbons in which one or more hydrogen atoms are replaced by a nitro group -NO 2 . Depending on the hydrocarbon radical to which the nitro group is attached, nitro compounds are divided into aromatic and aliphatic. Aliphatic compounds are distinguished as primary 1o, secondary 2o and tertiary 3o, depending on whether a nitro group is attached to the 1o, 2o or 3o carbon atom.

The nitro group -NO2 should not be confused with the nitrite group -ONO. The nitro group has the following structure:

The presence of a total positive charge on the nitrogen atom determines the presence of a strong -I-effect. Along with a strong -I-effect, the nitro group has a strong -M-effect.

Ex. 1. Consider the structure of the nitro group and its influence on the direction and rate of the electrophilic substitution reaction in the aromatic nucleus.

1.1. Methods for obtaining nitro compounds

Almost all methods for obtaining nitro compounds have already been considered in previous chapters. Aromatic nitro compounds are obtained, as a rule, by direct nitration of arenes and aromatic heterocyclic compounds. Nitrocyclohexane under industrial conditions is obtained by nitration of cyclohexane:

(1)

Nitromethane is also obtained in the same way, however, under laboratory conditions, it is obtained from chloroacetic acid as a result of reactions (2-5). The key step among them is reaction (3) proceeding via the SN2 mechanism.

(2)

Chloroacetic acid Sodium chloroacetate

(3) (4)

Nitroacetic acid

(5)

Nitromethane

1.2. Reactions of nitro compounds

1.2.1. Tautomerism of aliphatic nitro compounds

Due to the strong electron-withdrawing properties of the nitro group, a-hydrogen atoms have increased mobility and therefore primary and secondary nitro compounds are CH-acids. So, nitromethane is a rather strong acid (pKa 10.2) and in an alkaline medium it easily turns into a resonance-stabilized anion:

(6)

Nitromethane pKa 10.2 Resonance stabilized anion

Exercise 2. Write the reactions of (a) nitromethane and (b) nitrocyclohexane with an aqueous solution of NaOH.

1.2.2. Condensation of aliphatic nitro compounds with aldehydes and ketones

The nitro group can be introduced into aliphatic compounds by an aldol reaction between the nitroalkane anion and an aldehyde or ketone. In nitroalkanes, a-hydrogen atoms are even more mobile than in aldehydes and ketones, and therefore they can enter into addition and condensation reactions with aldehydes and ketones, providing their a-hydrogen atoms. With aliphatic aldehydes, addition reactions usually take place, and with aromatic ones, only condensations.

So, nitromethane is added to cyclohexanone,

(7)

1-nitromethylcyclohexanol

but condenses with benzaldehyde,

(8)

All three hydrogen atoms of nitromethane participate in the addition reaction with formaldehyde and 2-hydroxymethyl-2-nitro-1,3-dinitropropane or trimethylolnitromethane is formed.

(9)

By condensation of nitromethane with hexamethylenetetramine, we obtained 7-nitro-1,3,5-triazaadamantane:

(10)

Ex. 3. Write the reactions of formaldehyde (a) with nitromethane and (b) with nitrocyclohexane in an alkaline medium.

1.2.3. Recovery of nitro compounds

The nitro group is reduced to the amino group by various reducing agents (11.3.3). Aniline is obtained by hydrogenation of nitrobenzene under pressure in the presence of Raney nickel under industrial conditions.

(11) (11 32)

In laboratory conditions, instead of hydrogen, hydrazine can be used, which decomposes in the presence of Raney nickel with the release of hydrogen.

(12)

7-nitro-1,3,5-triazaadamantane 7-amino-1,3,5-triazaadamantane

Nitro compounds are reduced with metals in an acid medium, followed by alkalization

(13) (11 33)

Depending on the pH of the medium and the reducing agent used, various products can be obtained. In a neutral and alkaline environment, the activity of conventional reducing agents with respect to nitro compounds is less than in an acidic environment. A typical example is the reduction of nitrobenzene with zinc. In an excess of hydrochloric acid, zinc reduces nitrobenzene to aniline, while in a buffer solution of ammonium chloride it reduces to phenylhydroxylamine:

(14)

In an acidic environment, arylhydroxylamines undergo a rearrangement:

(15)

p-Aminophenol is used as a developer in photography. Phenylhydroxylamine can be further oxidized to nitrosobenzene:

(16)

Nitrosobenzene

Reduction of nitrobenzene with tin(II) chloride produces azobenzene, and zinc in an alkaline medium produces hydrazobenzene.

(17)
(18)

Treatment of nitrobenzene with a solution of alkali in methanol gives azoxybenzene, while the methanol is oxidized to formic acid.

(19)

Known methods of incomplete recovery and nitroalkanes. One of the industrial methods for producing capron is based on this. By nitration of cyclohexane, nitrocyclohexane is obtained, which is converted by reduction into cyclohexanone oxime and then, using the Beckmann rearrangement, into caprolactam and polyamide - the starting material for the preparation of fiber - capron:

Reduction of the nitro group of aldol addition products (7) is a convenient way to obtain b-amino alcohols.

(20)

1-Nitromethylcyclohexanol 1-Aminomethylcyclohexanol

The use of hydrogen sulfide as a reducing agent makes it possible to reduce one of the nitro groups in dinitroarenes:

(11 34)

m-Dinitrobenzene m-Nitroaniline

(21)

2,4-Dinitroaniline 4-Nitro-1,2-diaminobenzene

Exercise 4. Write the reduction reactions of (a) m-dinitrobenzene with tin in hydrochloric acid, (b) m-dinitrobenzene with hydrogen sulfide, (c) p-nitrotoluene with zinc in ammonium chloride buffer solution.

Exercise 5. Complete reactions:

(b)
Nitro compounds.
Nitro compounds 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 the donor-acceptor mechanism. The nitro group has a strong electron-withdrawing effect - it draws the 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:

Obtaining nitro compounds:

Nitration of alkanes and aromatic hydrocarbons: NO 2 a) CH 3 - CH 2 - CH - CH 3 + HNO 3 (p-p) - (t,p)  H 2 O + CH 3 - CH 2 - C - CH 3 (reaction Konovalov- proceeds selectively: tertiary C atom > secondary > primary

b)

When toluene is nitrated, a three-substituted molecule can be obtained:

2. Substitution of a halogen for 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. Recovery in solution:

a) in an alkaline and neutral medium, 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.

By the number and type of radicals, associated with the nitrogen atom:

AMINES	Primary amines	Secondary	Tertiary amines
Aliphatic	CH 3 -NH 2 methylamine	(CH 3 ) 2 NH	(CH 3 ) 3 N Trimethylamine
aromatic		(C 6 H 5 ) 2 NH 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. In the presence of 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 NH

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 by 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 an alkyl radical to indicate that this radical is bonded to the nitrogen atom and not a substituent on the benzene ring.
Isomerism of amines

1) carbon skeleton, starting from 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 from 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 amine types – 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 Hydrogen bonds are stronger in alcohols:

At ordinary temperature, only the lower aliphatic amines CH 3 NH 2 , (CH 3 ) 2 NH and (CH 3 ) 3 N - gases (with the smell of ammonia), average homologues -liquids (with a sharp fishy smell), higher - 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 (sulfanilamide preparations).

Aniline is a colorless oily liquid with a characteristic odor. It oxidizes in air and acquires a red-brown color. Poisonous.
OBTAINING AMINES.

1. Primary amines can be obtained reduction of nitro compounds. a) Hydrogenation with hydrogen: R-NO 2 + H 2 -t R- NH 2 + H2O b) Recovery: 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 the solution using alkali: Cl - + KOH \u003d H 2 O + KCl + R- NH 2

2. Alkylation of ammonia and amines. When ammonia interacts with alkyl halides, the formation of a salt of the primary amine occurs, from which the primary amine itself can be isolated by the action of alkali. This amine is able to interact with a new portion of the haloalkane to form a secondary amine: СH 3 Br + NH 3  Br -(+KOH) CH 3 - NH 2 + KBr + H 2 O primary amine CH 3 -NH 2 + C 2 H 5 Br  Br - - (+KOH) CH 3 - NH+ KBr + H 2 O secondary amine C 2 H 5 C 2 H 5 Further alkylation to a tertiary amine is possible.

3. Reduction of nitriles with the formation of primary amines: R–CN + 4[H] R–CH 2 NH 2 In this way, in industry, , which is used in the production of polyamide fiber nylon .

4. Interaction 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 the properties grounds.

1. Basic properties. Being derivatives of ammonia, all amines have basic properties. Aliphatic amines are stronger bases than ammonia, while aromatic ones are weaker. This is explained by CH radicals 3 -, WITH 2 H 5 - and others showpositive inductive (+I) effect and increase the electron density on the nitrogen atom: CH 3 → NH 2 This leads to an increase in the 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, while the medium becomes weakly alkaline: R-NH 2 + H 2 O ⇄ + + OH -

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 oli amines - odorless solids, highly soluble in water, but insoluble in organic solvents (unlike amines). Under the action of alkalis on amine salts, free amines are released: 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 ↓

3. Amines can precipitateheavy metal hydroxides from aqueous solutions: 2R-NH 2 + FeCl 2 + 2H 2 O  Fe(OH) 2 ↓+ 2Cl

4. Combustion. Amines burn in oxygen to form nitrogen, carbon dioxide and water: 4 C 2 H 5 NH 2 + 15O 2  8CO 2 + 2N 2 + 14 H 2 O

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 + H 2 O qualitative reaction, accompanied by the release of gas-nitrogen! b) Secondary amines(aliphatic and aromatic) give nitroso compounds - substances with a characteristic odor: R 2 NH + NaNO 2 + HCl  R 2 N-N \u003d O + NaCl + H 2 O

Features of the properties of aniline.

Aniline is characterized by reactions both on the amino group and on the benzene ring. The features of these reactions are due 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 pair-orientant in the reactions of electrophilic substitution in the aromatic nucleus). Qualitative reaction to aniline: reacts with bromine water to form2,4,6-tribromoaniline (white precipitate ↓ ).

AMINO ACIDS

Amino acids- organic bifunctional compounds, which include carboxyl groups –COOH 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:

1) aliphatic limiting amino acids (glycine, alanine)	NH 2 -CH (CH 3) -COOH alanine
2) sulfur-containing amino acids (cysteine)	NH 2 -CH (CH 2 SH) -COOH cysteine
3) amino acids with an aliphatic hydroxyl group (serine)	NH 2 -CH (CH 2 OH) -COOH
4) aromatic amino acids (phenylalanine, tyrosine)	NH 2 -CH (CH 2 C 6 H 5) -COOH phenylalanine
5) amino acids with two carboxyl groups (glutamic acid, aspartic acid)	NH 2 -CH (CH 2 CH 2 COOH) -COOH glutamic acid
6) amino acids with two amino groups (lysine)	NH 2 (CH 2) 4 -CH (NH 2) -COOH

Some essential α-amino acids

Name	-R
Glycine	-N
Alanine	-CH 3
Cysteine	-CH 2 -SH
Serene	-CH 2 -OH
Phenylalanine	-CH 2 -C 6 H 5
Tyrosine
Glutamic acid	-CH 2 -CH 2 -COOH
Lysine	-(CH 2) 4 -NH 2

Amino acid nomenclature

According to the 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 amino acid names 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 the 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 its name uses the prefix diamino, three groups of NH 2 - triamino- etc.

The presence of two or three carboxyl groups is reflected in the name by the suffix - diovaya or -triic acid:

OBTAINING AMINO ACIDS.

1. Substitution of a halogen for an amino group in the corresponding halogenated acids:

2. Attachment of ammonia to α,β-unsaturated acids with the formation of β-amino acids ( against Markovnikov's rule):

CH 2 \u003d CH–COOH + NH 3  H 2 N–CH 2 –CH 2 –COOH

3. Recovery 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 crystalline solids with a high melting point. Highly soluble in water, aqueous solutions are electrically conductive. When amino acids are dissolved in water, the carboxyl group splits off a hydrogen ion, which can join the amino group. This creates internal salt, whose molecule is bipolar ion:

H 2 N-CH 2 -COOH⇄ + H 3 N-CH 2 -COO -
CHEMICAL PROPERTIES OF AMINO ACIDS.

1. Acid-base properties: Amino acids areamphoteric connections. They contain two functional groups of the 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 scheme: 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 groups -COOH, one -NH 2), lysine- alkaline (one group -COOH, two -NH 2).

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

3. Amino acids can react with alcohols in the presence of gaseous hydrogen chloride, turning into 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

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 - 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

6. When heated decompose (decarboxylation): NH 2 -CH 2 - COO H - (t) NH 2 -CH 3 + CO 2

7. Decarboxylation with alkali: NH 2 -CH 2 -COOH + Ba (OH) 2 - (t) NH 2 -CH 3 + BaCO 3 + H 2 O

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 no more than 22 α-amino acid residues.

PROTEIN STRUCTURE.

Primary Structure- a specific sequence of α-amino acid residues in the polypeptide chain.
	secondary structure- the conformation of the polypeptide chain, fixed by many hydrogen bonds between the N-H and C=O groups. One of the secondary structure models is the α-helix.
Tertiary structure- the form of a twisted spiral in space, formed mainly due to disulfide bridges -S-S-, hydrogen bonds, hydrophobic and ionic interactions.
	Quaternary structure- aggregates of several protein macromolecules (protein complexes) formed due to the interaction of different polypeptide chains

Physical properties proteins are very diverse and are determined by their structure. According to their physical properties, proteins are divided into two classes:

- globular proteins dissolve in water or form colloidal solutions,

- fibrillar proteins insoluble in water.
Chemical properties.

1 . protein denaturation. This is the destruction of its secondary and tertiary protein structure while maintaining the primary structure. It occurs when heated, changing the acidity of the medium, the action of radiation. An example of denaturation is the curdling of egg whites when eggs are boiled.

Denaturation is either reversible or irreversible. Irreversible denaturation can be caused by the formation of insoluble substances when heavy metal salts - lead or mercury - act on proteins.

2. Hydrolysis of proteins is the irreversible destruction of the primary structure in an acidic or alkaline solution with the formation of amino acids . Analyzing the products of hydrolysis, it is possible to establish the quantitative composition of proteins.

3. Qualitative reactions to proteins:

1)Biuret reaction - purple staining under the action of freshly precipitated copper hydroxide ( II ) .

2) xantoprotein reaction - yellow staining when acting on proteins concentrated nitric acid .
The 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, protein in the blood hemoglobin transports oxygen to tissues, and protein myoglobin stores oxygen in the muscles.

3. Proteins are cell building material . Of these, supporting, muscle, integumentary tissues are built.

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 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. In the process of digestion, proteins are hydrolyzed to amino acids, which serve as the raw material for the synthesis of proteins necessary for this 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 in the molecule one or several. nitro groups directly attached to the carbon atom. N- and O-nitro compounds are also known. The nitro group has a structure intermediate between the two limiting resonance structures:

The group is planar; the N and O atoms have sp 2 hybridization, the N-O bonds are equivalent and practically one and a half; bond lengths, eg. 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-shape aci-nitro compound or nitrone to-that:

Ethers of nitrone to-t exist in the form of cis- and trans-isomers. There are cyclic ethers, for example. N-oxides of isoxazolines.

Name nitro compounds are produced by adding the prefix "nitro" to the name. base connections, if necessary adding a digital indicator, e.g. 2-nitropropane. Name salts of nitro compounds are produced from the names. either C-form, or aci-form, or nitrone to-you.

NITRO COMPOUNDS OF THE ALIPHATIC SERIES

Nitroalkanes have the general formula C n H 2n+1 NO 2 or R-NO 2 . They are isomeric alkyl nitrites (esters of nitric acid) with the general formula R-ONO. The isomerism of nitroalkanes is related to 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 name of the nitroalkanes is based on the name of the hydrocarbon with the prefix nitro(nitromethane, nitroethane, etc.). According to the 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 oxidize alkanes. Nitration proceeds only under the action of dilute nitric acid (sp. 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 used nonaphthene

It was found that the ease of replacing a hydrogen atom with a nitro group increases in the series:

The main factors affecting the rate of the nitration reaction and the yield of nitro compounds are the concentration of the acid, the temperature, and the duration of the process. So, for example, the 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 Hass leads to the formation of a mixture of nitroparaffins:

The formation of nitromethane and ethane occurs as a result of the cracking of the hydrocarbon chain.

The nitration reaction of alkanes proceeds according to the free radical mechanism, and nitric acid is not a nitrating agent, but serves as a source of nitrogen oxides NO 2:

2. Meyer reaction (1872)

The interaction of halide alkyls 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 ambivalence of the nitrite anion:

^ Structure of nitroalkanes

Nitroalkanes can be represented by the Lewis octet formula or by resonance structures:

One of the bonds of the 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 at the a-hydrogen atom include reactions with alkalis, with nitrous acid, aldehydes and ketones.

1. Formation of salts

Nitro compounds are pseudoacids - they are neutral and do not conduct electric current, however, 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 by 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 pseudonitrols (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 nitroalcohols

Primary and secondary nitro compounds interact 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, an amino alcohol NH 2 C (CH 2 OH) 3 is formed - the starting material for the production of detergents and emulsifiers. Tri(oxymethyl)nitromethane trinitrate, NO 2 C(CH 2 ONO 2) 3 , is a valuable explosive.

Nitroform (trinitromethane) when interacting with formaldehyde forms trinitroethyl alcohol:

4. Recovery of nitro compounds

The complete reduction of nitro compounds to the corresponding amines can be carried out by many methods, for example, by 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

Of practical value are the reactions of nitro compounds with acids. Primary nitro compounds, when heated with 85% sulfuric acid, are converted into carboxylic acids. It is assumed that the 1st stage of the process is the interaction of nitro compounds with mineral acids with the formation of the aci-form:

Salts of aci-forms of primary and secondary nitro compounds in the cold in aqueous solutions of mineral acids form aldehydes or ketones (Nef reaction):

. Aromatic nitro compounds. Chemical properties

Chemical properties. Recovery of nitro compounds in acidic, neutral and alkaline media. The practical significance of these reactions. Activating effect of the nitro group on nucleophilic substitution reactions. Aromatic polynitro compounds.

Nitro compounds

Nitro compounds are organic compounds containing one or more nitro groups -NO2. Nitro compounds are usually understood as C-nitro compounds in which the nitro group is bonded to the carbon atom (nitroalkanes, nitroalkenes, nitro arenes). O-nitro compounds and N-nitro compounds are separated into separate classes - nitro esters (organic nitrates) and nitramines.

Depending on the radical R, aliphatic (limiting and unsaturated), acyclic, aromatic and heterocyclic nitro compounds are distinguished. According to the nature of the carbon atom to which the nitro group is attached, nitro compounds are divided into primary, secondary and tertiary.

Nitro compounds are isomeric to esters of nitrous acid HNO2 (R-ONO)

In the presence of α-hydrogen atoms (in the case of primary and secondary aliphatic nitro compounds), tautomerism between nitro compounds and nitronic acids (aci-forms of nitro compounds) is possible:

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 according to the electrophilic, nucleophilic, or radical mechanism, while the active species in these reactions are the nitronium cation NO2+, the nitrite ion NO2-, or the radical NO2, respectively. The process consists in replacing a hydrogen atom at C, N, O atoms or adding a nitro group to a multiple bond.

Electrophilic nitration[edit | edit source]

In electrophilic nitration, nitric acid is the main nitrating agent. Anhydrous nitric acid undergoes autoprotolysis according to the reaction:

Water shifts the equilibrium to the left, so the nitronium cation is no longer found in 93-95% nitric acid. 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 has strong nitrating properties, in which a mixture of acetyl nitrate and nitric oxide (V) is formed, as well as a mixture of nitric acid with sulfur oxide (VI) or nitric oxide (V).

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 the reactants, solvates the + ion and promotes its dissociation.

In laboratory conditions, nitrates and nitronium salts are most often used, the nitrating activity of which increases in the following series:

Benzene nitration mechanism:

In addition to replacing a hydrogen atom with a nitro group, substitutional 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 proceeds in several directions, which depends on the reaction conditions and the structure of the initial 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 yield of the product increases with the transition from strongly basic to weakly basic amines. Nitration of tertiary amines occurs with the breaking of the C-N bond (nitrolysis reaction); this reaction is used to produce explosives - hexogen and octogen - from urotropine.

Substitutive nitration of acetamides, sulfamides, urethanes, imides and their salts proceeds according to the scheme

The reaction is carried out in aprotic solvents using aprotic nitrating agents.

Alcohols are nitrated by any nitrating agent; the reaction is reversible:

Nucleophilic nitration[edit | edit source]

This reaction is used to synthesize alkyl nitrites. Nitrating agents in this type of reactions 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]

Radical nitration is used to obtain nitroalkanes and nitroalkenes. Nitrating agents are nitric acid or nitrogen oxides:

In parallel, the oxidation reaction of alkanes proceeds due to the interaction of the NO2 radical with the alkyl radical at the oxygen atom, not nitrogen. The reactivity of alkanes increases with the transition 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, and cis- and trans-nitro compounds are formed, side products are formed due to the oxidation and destruction of the initial substrates.

An anion-radical nitration mechanism is observed in the interaction of tetranitromethane salts of mono-nitro compounds.

Konovalov's reaction (for aliphatic hydrocarbons)

The Konovalov 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.

Usually a mixture of primary, secondary and tertiary nitro compounds is formed. Fatty aromatic compounds are easily nitrated in the α-position of the side chain. Side reactions are 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). Vapors of alkane and nitric acid are heated to 420-480°C for 0.2-2 seconds, followed by rapid cooling. Methane gives nitromethane, and its homologues also undergo C--C bond cleavage, 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]

According to the chemical behavior of nitro compounds, they show a certain similarity with nitric acid. This similarity is manifested in redox reactions.

Recovery of nitro compounds (Zinin reaction):

Condensation reactions

Tautomerism of nitro compounds.

Tautomerism (from the Greek ταύτίς - the same and μέρος - measure) is a phenomenon of reversible isomerism, in which two or more isomers easily pass 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, during tautomerization, hydrogen atoms move from one atom in a molecule to another and back 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 derived from hydrogen cyanide. So hydrocyanic acid itself already exists in two tautomeric forms:

At room temperature, the equilibrium for the conversion of hydrogen cyanide to 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 the tautomeric equilibrium binds only two of them: cyanic and isocyanic acids:

For both tautomeric forms, esters are known, that is, the products of substitution of hydrogen in cyanic acid for hydrocarbon radicals. Unlike these tautomers, the third isomer, explosive (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 (the production of vitamin C - ascorbic acid, etc.). The role of tautomerism in the processes occurring in living organisms is very important.

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, allocate priority pollutants(about 180 compounds combined into 13 groups): aromatic hydrocarbons, polynuclear aromatic hydrocarbons (PAH), pesticides (4 groups), volatile and low-volatile organochlorine compounds, chlorophenols, chloranilines and chloronitroaromatic compounds, polychlorinated and polybrominated biphenyls, organometallic compounds and others. The sources of these substances are atmospheric precipitation, surface runoff, and industrial and domestic wastewater.

Similar information.

The nitro group has a structure intermediate between the two limiting resonance structures:

The group is planar; the N and O atoms have sp 2 hybridization, the N-O bonds are equivalent and practically one and a half; bond lengths, eg. 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.

H Itro compounds having at least one a-H-atom can exist in two tautomeric forms with a common mesomeric anion. O-shape aci-nitro compound or nitrone to-that:

Known diff. derivatives of nitronic acids: salts of the f-ly RR "C \u003d N (O) O - M + (salts of nitro compounds), ethers (nitronic esters), etc. Ethers of nitronic acids exist in the form of iis- and trans- isomers There are cyclic ethers, for example N-oxides of isoxazolines.

Name nitro compounds are produced by adding the prefix "nitro" to the name. base connections, if necessary adding a digital indicator, e.g. 2-nitropropane. Name salts of nitro compounds are produced from the names. either C-form, or aci-form, or nitrone to-you.

physical properties. The simplest nitroalkanes are colorless. liquids. Phys. Holy Islands of certain aliphatic nitro compounds are given in the table. Aromatic nitro compounds-bestsv. or light yellow, high-boiling liquids or low-melting solids, with a characteristic odor, poorly sol. in water tends to be distilled with steam.

PHYSICAL PROPERTIES OF SOME ALIPHATIC NITRO COMPOUNDS

* At 25°C. ** At 24°C. *** At 14°C.

In the IR spectra of nitro compounds, there are two characteristic. bands corresponding to antisymmetric and symmetric stretching vibrations of the N-O bond: for primary nitro compounds, respectively. 1560-1548 and 1388-1376 cm -1 , for secondary 1553-1547 and 1364-1356 cm -1 , for tertiary 1544-1534 and 1354-1344 cm -1 ; for nitroolefins RCH=CHNO 2 1529-1511 and 1351-1337 cm -1 ; for dinitroalkanes RCH(NO 2) 2 1585-1575 and 1400-1300 cm -1 ; for trinitroalkanes RC(NO 2) 3 1610-1590 and 1305-1295 cm -1; for aromatic nitro compounds 1550-1520 and 1350-1330 cm -1 (electron-withdrawing substituents shift the high-frequency band to the region 1570 -1540, and electron-donor - to the region 1510-1490 cm -1); for salts of nitro compounds 1610-1440 and 1285-1135 cm -1 ; nitrone ethers have an intense band at 1630-1570 cm, the C-N bond has a weak band at 1100-800 cm -1 .

In the UV spectra of aliphatic nitro compounds l max 200-210 nm (intense band) and 270-280 nm (weak band); for salts and esters of nitrone to-t resp. 220-230 and 310-320 nm; for gem-dinitrocomponent. 320-380 nm; for aromatic nitro compounds, 250–300 nm (the intensity of the band sharply decreases when the coplanarity is violated).

In the PMR spectrum, chem. shifts of a-H-atom depending on the structure 4-6 ppm In the NMR spectrum 14 N and 15 N chem. shift 5 from - 50 to + 20 ppm

In the mass spectra of aliphatic nitro compounds (with the exception of CH 3 NO 2), the peak mol. ion is absent or very small; main fragmentation process - elimination of NO 2 or two oxygen atoms to form a fragment equivalent to nitrile. Aromatic nitro compounds are characterized by the presence of a peak mol. and she ; main the peak in the spectrum corresponds to the ion produced by elimination of NO 2 .

Chemical properties. The nitro group is one of the most strong electron-withdrawing groups and is able to effectively delocalize negative. charge. In the aromatic conn. as a result of induction and especially mesomeric effects, it affects the electron density distribution: the nucleus acquires a partial positive. charge, to-ry 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. So arr., the introduction of the NO 2 group dramatically increases the reaction. ability org. conn. in relation to the nucleoph. reagents and makes it difficult to R-tion with elektrof. 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. Comm., carry out decomp. p-tion associated, as a rule, with a change in the carbon skeleton, and then transformed into another function or removed. In the aromatic In a row, a shorter scheme is often used: nitration-transformation of the NO 2 group.

Mn. transformations of aliphatic nitro compounds take place with a preliminary. isomerization to nitrone to-you or the formation of the corresponding anion. In solutions, the balance is usually almost completely shifted towards the C-form; at 20 °С, the proportion of the aci-form for nitromethane is 1 10 -7, for nitropropane 3. 10 -3 . Nitronovye to-you in svob. the form is usually unstable; they are obtained by careful acidification of salts of nitro compounds. Unlike nitro compounds, they conduct current in solutions and give a red color with FeCl 3 . Aci-nitro compounds are stronger CH-acids (pK a ~ 3-5) than the corresponding nitro compounds (pK a ~ 8-10); the acidity of nitro compounds increases with the introduction of electron-withdrawing substituents in the a-position to the NO 2 group.

The formation of nitrone to-t in a series of aromatic nitro compounds is associated with the isomerization of the benzene ring into the quinoid form; for example, nitrobenzene forms with conc. H 2 SO 4 colored salt product f-ly I, o-nitrotoluene exhibits photochromism as a result vnutrimol. proton transfer to form a bright blue O-derivative:

Under the action of bases on primary and secondary nitro compounds, salts of nitro compounds are formed; ambident anions of salts in p-tions with electrophiles are able to give both O- and C-derivatives. So, during the alkylation of salts of nitro compounds with alkyl halides, trialkylchlorosilanes or R 3 O + BF - 4, O-alkylation products are formed. Recent m.b. also obtained by the action of diazomethane or N,O-bis-(trimethylsilyl)acetamide on nitroalkanes with pK a< 3 или нитроновые к-ты, напр.:

Acyclic alkyl esters of nitrone to-t are thermally unstable and decompose according to intramol. mechanism:

; this

p-tion can be used to obtain carbonyl compounds. Silyl ethers are more stable. See below for the formation of C-alkylation products.

For nitro compounds, p-tions with a break in the C-N bond, along the bonds N \u003d O, O \u003d N O, C \u003d N -\u003e O and p-tions with the preservation of the NO 2 group are characteristic.

R-ts and and with r and ry v o m s vyaz z and C-N. Primary and secondary nitro compounds at loading. with a miner. to-tami in the presence. alcohol or aqueous solution of alkali form carbonyl Comm. (see Neph reaction). R-tion passes through the interval. the formation of nitrone to-t:

As a source Comm. silyl nitrone ethers can be used. The action of strong to-t on aliphatic nitro compounds can lead to hydroxamic to-there, for example:

The method is used in the industry for the synthesis of CH 3 COOH and hydroxylamine from nitroethane. Aromatic nitro compounds are inert to the action of strong to-t.

Under the action of reducing agents (eg, TiCl 3 -H 2 O, VCl 2 -H 2 O-DMF) on nitro compounds or oxidizing agents (KMnO 4 -MgSO 4, O 3) on salts of nitro compounds, ketones and aldehydes are formed.

Aliphatic nitro compounds containing a mobile H atom in the b-position to the NO 2 group, under the action of bases, easily eliminate it in the form of HNO 2 with the formation of olefins. Thermal flows in the same way. decomposition of nitroalkanes at temperatures above 450 °. Vicinal dinitrocomponents. when treated with Ca amalgam in hexamstanol, both NO 2 groups are cleaved off, Ag-salts of unsaturated nitro compounds can dimerize upon loss of NO 2 groups:

Nucleof. substitution of the NO 2 group is not typical for nitroalkanes, however, when thiolate ions act on tertiary nitroalkanes in aprotic p-solvents, the NO 2 group is replaced by a hydrogen atom. P-tion proceeds by an anion-radical mechanism. In the aliphatic and heterocyclic. conn.the NO 2 group with a multiple bond is relatively easily replaced by a nucleophile, for example:

In the aromatic conn. nucleoph. the substitution of the NO 2 group depends on its position with respect to other substituents: the NO 2 group, which is in the meta position with respect to the electron-withdrawing substituents and in the ortho and para positions to the electron donor, has a low reaction. ability; reaction the ability of the NO 2 group, located in the ortho- and para-positions to electron-withdrawing substituents, increases markedly. In some cases, the substituent enters the ortho position to the leaving NO 2 group (for example, when aromatic nitro compounds are loaded with an alcohol solution of KCN, Richter's solution):

R-ts and and about with I z and N \u003d O. One of the most important p-tsy-restoration, leading in the general case to a set of products:

Azoxy-(II), azo-(III) and hydrazo compounds. (IV) are formed in an alkaline environment as a result of the condensation of intermediate nitroso compounds. with amines and hydroxylamines. Carrying out the process in an acidic environment excludes the formation of these substances. Nitroso-compound. recover faster than the corresponding nitro compounds, and select them from the reaction. mixtures usually fail. Aliphatic nitro compounds are reduced to azoxy or azo compounds by the action of Na alcoholates, aromatic ones by the action of NaBH 4, the treatment of the latter with LiAlH 4 leads to azo compounds. Electrochem. the reduction of aromatic nitro compounds under certain conditions allows you to get any of the presented derivatives (with the exception of nitroso compounds); it is convenient to obtain hydroxylamines from mononitroalkanes and amidoximes from salts of gem-dinitroalkanes by the same method:

Many methods are known for the reduction of nitro compounds to amines. Widely used iron filings, Sn and Zn in the presence. to-t; with catalytic hydrogenation as catalysts use Ni-Raney, Pd / C or Pd / PbCO 3, etc. Aliphatic nitro compounds are easily reduced to amines LiAlH 4 and NaBH 4 in the presence. Pd, Na and Al amalgams, when heated. with hydrazine over Pd/C; for aromatic nitro compounds, TlCl 3, CrCl 2 and SnCl 2 are sometimes used, aromatic. polynitro compounds are selectively reduced to nitramines with Na hydrosulfide in CH 3 OH. There are ways to choose. recovery of the NO 2 group in polyfunctional nitro compounds without affecting other f-tions.

Under the action of P(III) on aromatic nitro compounds, a succession occurs. deoxygenation of the NO 2 group with the formation of highly reactive nitrenes. R-tion is used for the synthesis of condenser. heterocycles, for example:

Under the same conditions, silyl esters of nitrone acids are transformed into silyl derivatives of oximes. Treatment of primary nitroalkanes with 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 rearrange in an acidic medium into o-nitrosoketones, for example:

H itro compounds and nitrone ethers react with an excess of Grignard's reagent to give hydroxylamine derivatives:

R-tions for bonds O \u003d N O and C \u003d N O. Nitro compounds enter into p-tions of 1,3-dipolar cycloaddition, for example:

Naib. this p-tion easily flows between nitrone esters and olefins or acetylenes. In cycloaddition products (mono- and bicyclic dialkoxyamines) under the action of nucleoph. and elektrof. N - O bond reagents are easily cleaved, which leads to decomp. aliphatic and hetero-cyclic. conn.:

For preparative purposes, stable silyl nitrone esters are used in the district.

R-ts and with the preservation of the NO 2 group. Aliphatic nitro compounds containing an a-H-atom are easily alkylated and acylated to form, as a rule, O-derivatives. However, mutually mod. dilithium salts of primary nitro compounds with alkyl halides, anhydrides or carboxylic acid halides leads to products of C-alkylation or C-acylation, for example:

Known examples vnutrimol. C-alkylations, e.g.:

Primary and secondary nitro compounds react with aliphatic. amines and CH 2 O with the formation of p-amino derivatives (p-tion Mannich); in the district, you can use pre-obtained methylol derivatives of nitro compounds or amino compounds:

The activating effect of the NO 2 group on the nucleoph. substitution (especially in the ortho position) is widely used in org. synthesis and industry. P-tion proceeds according to the scheme of accession-cleavage from the intermediate. the formation of an s-complex (Meisenheimer complex). According to this scheme, halogen atoms are easily replaced by nucleophiles:

Known examples of substitution by the anion-radical mechanism with electron capture aromatic. connection and emission of a halide ion or other groups, for example. alkoxy, amino, sulfate, NO - 2. In the latter case, the district passes the easier, the greater the deviation of the NO 2 group from coplanarity, for example: in 2,3-dinitrotoluene it is replaced in the main. the NO 2 group in position 2. The H atom in aromatic nitro compounds is also capable of nucleophage. substitution-nitrobenzene at heating. with NaOH forms o-nitrophenol.

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 the second NO 2 group accelerates the nucleophane. substitution. H introconnections in the presence. bases are added to aldehydes and ketones, giving nitroalcohols (see Henri reactions), primary and secondary nitro compounds, to Comm., containing activir. double bond (Michael region), for example:

Primary nitro compounds can enter into the Michael p-tion with the second molecule of the unsaturated compound; this p-tion with the last. trancethe formation of the NO 2 group is used for the synthesis of poly-function. aliphatic connections. The combination of Henri and Michael p-tions leads to 1,3-dinitro compounds, for example:

To inactivated 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, while products of C- or O-alkylation are formed; the latter can enter into a cyclo-addition p-tion with the second olefin molecule:

Easily enter into p-tion accession nitroolefins: with water in a slightly acidic or slightly alkaline medium with the latter. Henri retroreaction they form carbonyl Comm. 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 districts of diene synthesis and cycloaddition, and 1,4-dinitrodienes can act as diene components, for example:

Receipt. In the industry, lower nitroalkanes are obtained by liquid-phase (Konovalov's district) or vapor-phase (Hess method) nitration of a mixture of ethane, propane and butane, isolated from natural gas or obtained by oil refining (see Nitration). Higher nitro compounds are also obtained in this way, for example. nitrocyclohexane is an intermediate in the production of caprolactam.

In the laboratory, nitration of nitric acid is used to obtain nitroalkanes. with activated a methylene group; a convenient method for the synthesis of primary nitroalkanes is the nitration of 1,3-indanedione with the last. alkaline hydrolysis of a-nitroketone:

Aliphatic nitro compounds also receive interaction. AgNO 2 with alkyl halides or NaNO 2 with esters of a-halocarboxylic-new to-t (see Meyer reaction). Aliphatic nitro compounds are formed from the oxidation of amines and oximes; oxidation of oximes - a method for obtaining gem-di- and gem-trinitro compounds, for example: