Nitro chemistry. Preparation of nitro compounds by nitration

The electronic structure of the nitro group is characterized by the presence of seven polar (semipolar) bonds:

Fatty nitro compounds are liquids that are insoluble in water, but readily soluble in alcohol and ether. Aromatic nitro compounds are liquids or solids with a specific odor. A very important property of nitro compounds is that when reduced, they transform into primary amines.

C 6 H 5 - NO 2 + 6 [H] C 6 H 5 - NH 2 + 2 H 2 O

All nitro compounds are poisonous. Many aromatic nitro compounds have explosive properties.

Chemical properties. The chemical behavior of nitro compounds is determined by the presence of a nitro group in the molecule and its features, as well as the structure of the hydrocarbon radical and their mutual influence.

1. Recovery of nitro compounds . During the reduction of nitro compounds, primary amines are formed. Of particular great industrial importance is the reduction of aromatic nitro compounds:

Depending on the reduction conditions (in acidic, alkaline, or neutral media) and the nature of the reducing agent, various intermediate products are formed during the reaction, many of which are widely used in technology.

2. The action of alkalis on nitro compounds . When a nitro group is introduced into a hydrocarbon molecule, due to its electron-withdrawing properties, it sharply increases the mobility of hydrogen atoms in the α-position. Primary and secondary nitro compounds acquire the ability to dissolve in alkalis with the formation of salts. When an acid reacts with a salt, a nitro compound is formed in the acinitro form:

which then goes into the nitro form:

The mutual transformation of two forms of nitro compounds is a typical example of dynamic isomerism (tautomerism).

3. Reactions of the benzene ring of aromatic nitro compounds , The nitro group orients the entry of the second substituent in the case of electrophilic substitution preferably in the g-position, in the case of nucleophilic substitution, in the o- and n-positions. An example of derivatives of nitro compounds of aromatic hydrocarbons is 2, 4, 6-trinitrophenol (picric acid):

Picric acid and its salts are used as explosives and in analytical chemistry.

Application. Nitroparaffins are used in industry as solvents, additives to diesel fuels that reduce their ignition temperature, in the production of explosives, plastics, in jet technology; as intermediates in the synthesis of amines, aldehydes and ketones, fatty acids. Aromatic nitro compounds are widely used to obtain dyes, plastics, fragrant and explosives.

individual representatives.

Nitromethane C H 3 -NO 2. Liquid, t kip -101.2 °C. It is used as a solvent, as rocket fuel. By chlorination of nitromethane, trichloronitromethane (chloropicrin) CCl 3 NO 2 is obtained, which is used to control rodents in grain stores and warehouses, as well as in various syntheses.

Nitroethane CH 3 CH 2 -NO 2. Liquid, t bale = 113 °С *Boil=PZ°С. It is used to obtain hydroxylamine:

Nitrocyclohexane C 6 CH 2 NO 2. Liquid, t kip =205 °C. Obtained by nitration of cyclohexane. It is used as an intermediate in the synthesis of caprolactam.

Nitrobenzene C 6 H 6 NO 2 . Yellowish liquid, with the smell of bitter almonds, bp = 211 °C. We will poorly dissolve in water and we will well dissolve in many organic solvents. The initial product in the production of aniline is widely used in the aniline-colorful, perfumery, and pharmaceutical industries.

Trinitrotoluene ( tol, trotyl)

Solid substance, t pl = 80°C. Widely used as an explosive.

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.

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:

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.

Chloroacetic acid Sodium chloroacetate

Nitroacetic acid

Nitromethane

Reactions of nitro compounds

Tautomerism of aliphatic nitro compounds

Due to the strong electron-withdrawing properties of the nitro group, -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:

Nitromethane pKa 10.2 Resonance stabilized anion

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

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, -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 -hydrogen atoms. With aliphatic aldehydes, addition reactions usually take place, and with aromatic ones, only condensations.

So, nitromethane is added to cyclohexanone,

1-nitromethylcyclohexanol

but condenses with benzaldehyde,

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.

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

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

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.

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

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

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:

In an acidic environment, arylhydroxylamines undergo a rearrangement:

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

Nitrosobenzene

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

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

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 α-amino alcohols.

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:

m-Dinitrobenzene m-Nitroaniline

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 a buffered ammonium chloride solution.

Exercise 5. Complete reactions:

1. Nitro compounds

1.2. Reactions of nitro compounds

1. NITRO COMPOUNDS

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

(1)

Chloroacetic acid Sodium chloroacetate

Nitroacetic acid

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:

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,

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.

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

(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)

(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

The reduction of nitrobenzene with tin (II) chloride produces azobenzene, and with zinc in an alkaline medium, hydrazobenzene is obtained.

(17)

(18)

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

(19)

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 5. Complete reactions:

(A) (b)

According to the systematic nomenclature, amines are named by adding the prefix amine to the name of the hydrocarbon. According to the rational nomenclature, they are considered as alkyl or arylamines.

Methanamine Ethanamine N-Methylethanamine N-Ethylethaneamine

(methylamine) (ethylamine) (methylethylamine) (diethylamine)

N,N-Diethylethanamine 2-Aminoethanol 3-Aminopropane

triethylamine) (ethanolamine) acid

Cyclohexanamine Benzolamine N-Methylbenzenamine 2-Methylbenzenamine

(cyclohexylamine) (aniline) (N-methylaniline) (o-toluidine)

Heterocyclic amines are named after the corresponding hydrocarbon, inserting the prefix aza-, diaza- or triaza- to indicate the number of nitrogen atoms.

1-Azacyclopeta- 1,2-Diazacyclopeta- 1,3-Diazacyclopeta-

2,4 diene 2,4 diene 2,4 diene

Nitration of aromatic compounds is the main way to obtain nitro compounds. The process of nitration as a special case of electrophilic substitution in the aromatic series has already been considered earlier. Therefore, it seems appropriate to focus on the synthetic possibilities of this reaction.

Benzene itself is nitrated quite easily and with good results.

Under more severe conditions, nitrobenzene is also able to nitrate with the formation m- dinitrobenzene

Due to the deactivating effect of two nitro groups, introduce a third nitro group into m-dinitrobenzene is possible only with great difficulty. 1,3,5-Trinitrobenzene was obtained in 45% yield by nitration m-dinitrobenzene at 100-110 about C and the duration of the reaction is 5 days.

The difficulties in obtaining trinitrobenzene by direct nitration of benzene led to the development of indirect methods. According to one of them, trinitrotoluene, which is more accessible than trinitrobenzene, is oxidized to 2,4,6-trinitrobenzoic acid, which is easily decarboxylated when heated in water.

Similarly, indirect methods have to be resorted to if it is necessary to obtain 1,2-dinitrobenzene. In this case, the ability of the amino group to be oxidized to the nitro group in O-nitroaniline

Even in those cases where the preparation of nitro compounds by nitration should not have encountered any special difficulties, one has to turn to indirect methods. So, it is not possible to obtain picric acid by nitration of phenol, because Phenol is not nitrated with nitric acid, but oxidized. Therefore, the following scheme is usually used

The subtleties of this scheme are that, due to the deactivation of the ring by chlorine and two already existing nitro groups, it is not possible to introduce a third nitro group into it. Therefore, chlorine in dinitrochlorobenzene is preliminarily replaced by hydroxyl, which the nitro groups just contribute to (bimolecular substitution). The resulting dinitrophenol easily accepts another nitro group without being oxidized to a noticeable degree. The existing nitro groups protect the benzene ring from oxidation.

Another non-obvious way to obtain picric acid is the sulfonation of phenol to 2,4-phenol disulfonic acid, followed by nitration of the resulting compound. In this case, simultaneously with nitration, the replacement of sulfo groups by nitro groups occurs

One of the most important aromatic nitro derivatives, trinitrotoluene, is obtained in technology by the nitration of toluene, which proceeds according to the following scheme

Chemical properties

Aromatic nitro compounds are capable of reacting both with the participation of the benzene ring and the nitro group. These structural elements affect each other's reactivity. So, under the influence of the nitro group, nitrobenzene is reluctant to enter into the electrophilic substitution reaction and the new substituent accepts m-position. The nitro group affects not only the reactivity of the benzene ring, but also the behavior of neighboring functional groups in chemical reactions.

Consider the reactions of aromatic nitro compounds at the expense of the nitro group.

16.2.1. Recovery. One of the most important reactions of nitro compounds is their reduction to aromatic amines, which are widely used in the production of dyes, drugs, and photochemicals.

The possibility of converting a nitro group into an amino group by the reduction of nitro compounds was first shown by Zinin in 1842 using the example of the reaction of nitrobenzene with ammonium sulfide

Subsequently, the reduction of aromatic nitro compounds was the subject of deep study. It was found that, in the general case, the reduction is complex, proceeding through a number of stages with the formation of intermediate products. Amines are only the end product of the reaction. The result of the reduction is determined by the strength of the reducing agent and the pH of the medium. In electrochemical reduction, the composition of the products depends on the magnitude of the potential at the electrodes. By varying these factors, it is possible to delay the recovery process at intermediate stages. In neutral and acidic media, the reduction of nitrobenzene proceeds sequentially through the formation of nitrosobenzene and phenylhydroxylamine

When the reduction is carried out in an alkaline medium, the resulting nitrosobenzene and phenylhydroxylamine are able to condense with each other to form azoxybenzene, in which nitrogen and oxygen atoms are linked by a semipolar bond

The proposed mechanism of condensation resembles the mechanism of aldol condensation

The reduction of azoxybenzene to aniline goes through azo- and hydrazobenzenes

All of the intermediates mentioned above for the reduction of nitrobenzene to aniline can be obtained either directly from nitrobenzene or starting from each other. Here are some examples

16.2.2. Influence of the nitro group on the reactivity of other functional groups. In the study of aromatic halogen derivatives, we have already encountered the case where a suitably located nitro group(s) significantly influenced the nucleophilic substitution of the halogen (bimolecular substitution of the aromatic halogen). For example O- And P-dinitrobenzenes, it was found that the nitro group can contribute to the nucleophilic substitution of not only the halogen, but even another nitro group

The mechanism of bimolecular substitution of a nitro group by a hydroxyl group can be represented as the following two-stage process

The carbanion formed at the first stage of the reaction under consideration is resonantly stabilized due to the contribution of the limiting structure 1, in which the nitro group withdraws electrons from precisely that carbon of the benzene ring, which has an excess of them.

A feature of the nucleophilic substitution of one nitro group under the influence of another nitro group is that the reaction is very sensitive to the location of the nitro groups relative to each other. It is known that m-dinitrobenzene does not react with an alcohol solution of ammonia even at 250 o C.

Other examples of promoting nitro group substitution, in this case hydroxyl, are the transformations of picric acid

16.2.3. Complex formation with aromatic hydrocarbons. A characteristic property of aromatic nitro compounds is their tendency to form complexes with aromatic hydrocarbons. Bonds in such complexes are electrostatic in nature and arise between electron-donor and electron-acceptor particles. The complexes under consideration are called π -complexes or complexes with charge transfer.

π –Complexes in most cases are crystalline substances with characteristic melting points. If necessary π -complex can be destroyed with the release of hydrocarbons. Due to the combination of these properties π -complexes are used for isolation, purification and identification of aromatic hydrocarbons. Especially often picric acid is used for complexation, the complexes of which are incorrectly called picrates.

Chapter 17

Amines

According to the degree of substitution of hydrogen atoms in ammonia for alkyl and aryl substituents, primary, secondary and tertiary amines are distinguished. Depending on the nature of the substituents, amines can be fatty-aromatic or purely aromatic.

Aromatic amines are named by adding the ending "amine" to the names of the groups associated with nitrogen. In complex cases, the amino group with a smaller substituent is designated by the prefix "amino" (N-methylamino-, N,N-dimethylamino), which is added to the name of the more complex substituent. Below are the most common amines and their names

Acquisition Methods

We have already encountered many of the methods for preparing amines in the study of aliphatic amines. When applying these methods to the synthesis of aromatic amines, some features are encountered, therefore, without fear of repetition, we will consider them.

17.1.1. Recovery of nitro compounds. The reduction of nitro compounds is the main method for both laboratory and industrial production of amines, which can be carried out in several ways. These include catalytic hydrogenation, atomic hydrogen reduction, and chemical reduction.

Catalytic reduction is carried out with molecular hydrogen in the presence of finely ground nickel or platinum, copper complex compounds on carriers. When choosing a catalyst and reduction conditions, it must be borne in mind that other functional groups can be reduced in this case. In addition, the catalytic reduction of nitro compounds must be carried out with some care due to the extreme exothermicity of the reaction.

When using ammonium sulfide as a chemical reducing agent, it becomes possible to reduce only one of several nitro groups

17.1.2. Amination of halogen derivatives. Difficulties that arise during the amination of aromatic halogen derivatives by the "elimination - addition" mechanism are known. However, as has already been mentioned more than once, electron-withdrawing substituents in the benzene ring, properly located, greatly facilitate the substitution of the halogen in aryl halides, directing the process along a bimolecular mechanism. For comparison, below are the conditions for the amination of chlorobenzene and dinitrochlorobenzene

17.1.3. Splitting according to Hoffmann. Cleavage of acid amides according to Hoffmann makes it possible to obtain primary amines, which contain one carbon less than the original amides.

The reaction proceeds with the migration of phenyl from the carbonyl carbon to the nitrogen atom (1,2-phenyl shift) according to the following proposed mechanism

17.1.4. Alkylation and arylation of amines. Alkylation of primary and secondary aromatic amines with halogenated alkyls or alcohols makes it possible to obtain secondary and tertiary fatty aromatic amines.

Unfortunately, with the participation of primary amines in the reaction, a mixture is obtained. This can be avoided if the starting amine is first acylated and then alkylated

This method of protecting the amino group makes it possible to obtain pure secondary aromatic amines, as well as tertiary amines with different substituent radicals.

Arylation of amines makes it possible to obtain pure secondary and tertiary aromatic amines

Chemical properties

Aromatic amines react both with the participation of the amino group and the benzene ring. In this case, each functional group is influenced by another group.

Reactions on the amino group

Due to the presence of an amino group, aromatic amines enter into numerous reactions. Some of them have already been considered: alkylation, acylation, reaction with aldehydes to form azomethines. Other reactions to which attention will be paid are easily predictable, but they have certain peculiarities.

Basicity

The presence of a lone pair of electrons at the nitrogen atom, which can be presented to form a bond with a proton, provides aromatic amines with the main properties

Of interest is the comparison of the basicity of aliphatic and aromatic amines. As has already been shown in the study of aliphatic amines, it is convenient to judge the basicity of amines by the basicity constant K in

Let's compare the basicity of aniline, methylamine and ammonia

Ammonia 1.7. 10-5

Methylamine 4.4. 10-4

Aniline 7.1. 10 -10

It can be seen from these data that the appearance of an electron-donating methyl group increases the electron density at the nitrogen atom and leads to an increase in the basicity of methylamine compared to ammonia. At the same time, the phenyl group weakens the basicity of aniline by more than 105 times compared to ammonia.

The decrease in the basicity of aniline compared to aliphatic amines and ammonia can be explained by the conjugation of the lone pair of nitrogen electrons with the electron sextet of the benzene ring

This reduces the ability of the lone pair of electrons to accept a proton. This trend is even more pronounced for aromatic amines, which contain electron-withdrawing substituents in the benzene ring.

So, m-nitroaniline as a base is 90 times weaker than aniline.

As might be expected, electron-donating substituents on the benzene ring enhance the basicity of aromatic amines.

Fatty-aromatic amines under the influence of an alkyl group exhibit greater basicity than aniline and amines with electron-withdrawing groups in the ring.

Limit open-chain nitro compounds (non-cyclic) have the general formula C n H 2n+1 NO 2 . They are isomeric to alkyl nitrites (esters of nitrous acid) with the general formula R-ONO. The differences are:

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 - by 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 polynyrocompounds. The best results are obtained with hydrocarbons containing a tertiary carbon atom. Vapor-phase nitration proceeds 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, acids. Unsaturated hydrocarbons are also formed. Nitric acid can be replaced by nitrogen oxides. Nitration proceeds by 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 (ambivalence), i.e. add a radical on 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 mechanism of the reaction and its direction strongly depend on the nature of the solvent. Solvating solvents (water, alcohols) favor the formation of ether.

Chemical properties

When reducing nitro compounds, primary amines are formed:

Primary and secondary nitro compounds are soluble in alkalis with the formation of salts. Hydrogen atoms at the carbon bound to the nitro group are activated, as a result, in an alkaline environment, the niro compounds are rearranged into the aci-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 referred to as pseudoacids. Pseudoacids are neutral and non-conductive, but nevertheless form neutral alkali metal salts. Neutralization of nitro compounds with alkalis occurs slowly, and 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, pseudonitrols are blue or greenish-blue.

Primary and secondary niro 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.