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Nitro compounds(-NO2) play an essential role in many organic compounds in chemistry. In organic compounds, nitrogen is an important constituent. Any organic compound which contains nitro as a functional group is known as nitro compound. Nitro compounds(-NO2) are either colorless or pale yellow. Most of the nitro compounds(-NO2) are produced for commercial use such as explosives, solvents and chemical intermediates which are further used as raw material in many chemical processes.
Apart from this, nitro compounds(-NO2) are widely used in many fields such as pharmaceutical industries, agriculture(to control pests in soil), chemical industries, etc. Also, it is necessary for all the living beings in the cells to form proteins, DNA, RNA as well as amino acids.
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Key Terms: Nitro Compounds, Amino Acids, Nitration, Organic Compounds, Substitution Reaction.
What are Nitro Compounds?
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Nitro compounds(-NO2) are those organic compounds which contain at least one or more nitro groups as a functional group. Nitro compounds(-NO2) are polar in nature. There is a covalent bond present between the carbon atom and nitrogen atom in organic substances. Moreover, the nitro group is strongly electron withdrawing in organic compounds.
Covalent Bond in Nitro Compounds
Apart from this, nitro groups are rarely found in nature. In fact, nitro compounds are ordinarily produced by the nitration reaction. Nitration complexes is made up of two main processes:
- Nitrification
- De-nitrification
Electronic Structure Diagram of Nitro Compounds
In the above diagram, the functional group(-NO2) is contained in nitro compounds. The central nitrogen atom connected to oxygen in the (-NO2) group is stabilized by resonance.
Read More:
| Class 12 Chemistry Related Concepts | ||
|---|---|---|
| Etard reaction | Williamson Ether Synthesis | Electrophilic Aromatic Substitution |
| Ester Hydrolysis | Reimer Tiemann Reaction | Esterification |
Classification of Nitro Compounds
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There are lots of compounds which are made up of nitrogen because nitrogen is an important constituent of many organic compounds. There are three classifications of nitro compounds that are mentioned below:
- Primary Nitroalkanes: In primary alkanes, the nitrogen group is attached to a primary carbon atom. For example: RCH2NO2
- Secondary Nitroalkanes: In secondary alkanes, the nitrogen group is attached to a secondary carbon atom. For example: R2CHNO2
- Tertiary Nitroalkanes: In tertiary alkanes, the nitrogen group is attached to a tertiary carbon atom. For example: R3CNO2
Classification of Nitro Compounds
Preparation of Nitro Compounds
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Nitration is the reaction which is used to prepare the nitro compounds. In nitration reaction, nitric reacts with the organic compound. There are main three ways to prepare the nitro compounds such as:
- Form Alkyl halides
- From Tertiary alkyl amines
- From Hydrocarbons
Preparation of Nitro Compounds from Alkyl Halides
In this reaction, by heating alkyl halides at a temperature of 695-795K with aqueous ethanolic solution of silver nitrate then nitroalkanes are obtained. Also, a little amount of isomeric alkyl nitrites is obtained. When bromoethane reacts with silver nitrite, it gives nitroethene. The chemical reaction takes place as follows.
R-X + AgNO2 → R-NO2 + AgX
CH3CH2Br + AgNO2 → CH3CH2NO2 + AgBr
Preparation of Nitro Compounds from Tertiary Alkyl Amines
When methylpropanamine reacts with potassium permanganate then methyl nitropropane is obtained. It is represented by the chemical equation,
(CH3)3CNH2 → (CH3)3CNO2
Preparation of Nitro Compounds from Aromatic Hydrocarbons
When aromatic hydrocarbons react with concentrated nitric acid either directly or in the presence of strong catalysts such as sulphuric acid then nitro derivatives are obtained. It is represented by the chemical equation,
C6H6 + (conc.HNO3 + conc.H2SO4) → (333K) C6H5NO2 + H2O
Properties of Nitro Compounds
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Nitro compounds have various properties. Some of the properties of nitro compounds are discussed below:
- Nitroalkanes have no color i.e. colorless and pleasant smelling liquids.
- In Aromatic nitro compounds, they can be either pale yellow liquids or solids as well as having a distinct smells such as Nitrobenzene (pale yellow liquid and having a smell of bitter almonds)
- Nitroalkanes are less soluble in water i.e. sparingly soluble.
- Nitroarenes are insoluble in water.
- Most of the aromatic compounds are steam volatile in nature. As a result, they can be easily purified by steam distillation.
- Many nitroalkanes are quite stable as well as easily distilled without any requirement of decomposition under atmospheric pressure.
- Many nitroarenes are not distilled easily under atmospheric pressure. They require a strong heating to explode or decompose.
- Nitroalkanes and nitroarenes both are highly polar compounds which have strong dipole dipole interactions. Such as:
| Nitro Compounds | Boiling point of Nitro Compounds(K) |
|---|---|
| Nitromethane | 374 |
| Butane | 138 |
| Nitroethene | 388 |
| Pentane | 143.3 |
| Nitrobenzene | 484 |
| Benzene | 353.1 |
Uses of Nitro Compounds
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Nitro compounds are used for many purposes. Some of the main applications or uses are given below:
- In the soil, chloropicrin is used to control pests. Also, it is the constituent of tear gas.
- Nitroarenes are used as an intermediate in manufacturing detergents, dyes, pharmaceuticals as well as explosives. For example, 2,4,6- Trinitrotoluene(TNT).
- In industries, nitromethane, nitroethene which are lower nitroalkanes are widely used as solvents.
- As propellants, nitroalkanes are used.
- Pyrazines which is a cyclic compound used as flavor enhancer in many baked and natural foods.
- Nitrous oxide(N2O) i.e. laughing gas has clinical properties. Due to this, it is used for anaesthesia in hospitals as well as in dental clinics.
- Urea is the most used nitro compound in the production of fertilizers. Also, it is used as a raw material in many industries.
Things to Remember
- Any molecular formula which contains one or more nitro as a functional group is known as nitro compound.
- Nitro compounds either have no color or pale yellow.
- Nitro compounds have strong dipole-dipole interactions. Also, the covalent bond is present between the nitrogen atom and oxygen.
- Nitroalkanes are less soluble in water whereas nitroarenes are insoluble.
- Nitro compounds are usually formed by nitration.
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Sample Questions
Ques. What do you mean by nitration? [2 marks]
Ans. Nitration is defined as the process in which a nitric group is added to the organic compound. Most of the electrophilic aromatic substitution(EAS) reactions come under the category of nitration. Chemically, it can be represented by,
Ques. Can tertiary amines undergo acetylation reactions? Explain? [2 marks]
Ans. No, tertiary amines cannot undergo acetylation reactions because they do not have replaceable hydrogen atoms. As a result, they do not react with the acid chloride and reaction with acetylation does not occur.
Ques. Sulphuric acid is soluble in oil. NaOH but not in dilute(dil.) HCL.Why? [3 marks]
Ans. Sulphuric acid exists as a zwitterion such as
The weakly acidic NH3+ group transfers its H+ to OH- to form a soluble p-NH2C6H4SO3-Na+ in the presence of dil.HCl. The SO3- group is a very weak base and as a result, does not accept protons from the dil.HCl to form p-NH3+C6H4SO3H. Therefore, it does not dissolve in dil.HCl.
Ques. Arrange the following on the basis of basicity in decreasing order:
Ethylamine,2-aminoethanol, 3-amino-1-propanol. [2 marks]
Ans. The correct order of decreasing basicity follows as:
CH3CH2NH2 > HO(CH2)3 NH3 > HO(CH2)2 NH2
This is happening because the effect of basicity decreases when the distance from the amino group increases. The electron withdrawing group OH- decreases the electron density on nitrogen N which is responsible for lowering the basicity.
Ques. How do you convert the following terms:
(i) Benzene into aniline?
(ii) benzene into N,N-dimethylaniline
(iii) Cl-(CH2)4-Cl into hexan-1,6-diamine? [5 marks]
Ans. The conversion of the following terms are:
(i) Conversion of Benzene into aniline: When benzene is treated with concentrated HNO3 or concentrated H2SO4 then nitrobenzene is obtained. Aniline is formed when nitrobenzene is reduced with Sn/HCl.Chemically, it can be represented by,
(ii) Conversion of benzene into N, N-dimethylaniline: When benzene is treated with concentrated HNO3 or concentrated H2SO4 then nitrobenzene is obtained. Aniline is formed when nitrobenzene is reduced with Sn/HCl. After That, Aniline is further treated with methyl chloride to obtain N, N-dimethylaniline. It is represented by the chemical reaction,
(iii) Conversion of Cl-(CH2)4-Cl into hexan-1,6-diamine: When 1,4-Dichlorohexane is treated with ethanolic sodium cyanide then didinitrate is obtained. After that, it is further reduced to obtain Hexan-1,6-diamine. It is represented by the chemical reaction,
Ques. Why is the presence of base required in the ammonolysis of alkyl halides? [2 marks]
Ans. The presence of base is required because ammonolysis of alkyl halides provides quaternary ammonia salt. By using a strong base, the free amine can be obtained from ammonium salt. That’s why the presence of a base is needed.
For Example:
RNH3+X- + NaOH → RNH2 + H2O + Na+X-
Ques. Write down the name of a chemical test that distinguish between aniline and N-methylaniline. [2 marks]
Ans. The chemical test which is used to distinguish between aniline and N- methylaniline is Hinsberg’s reagent. In aniline, aniline reacts with hinsberg’s reagent to form N-phenyl benzene sulphonamide that is soluble in KOH. While, when N-methylaniline reacts with hinsberg’s reagent to form N-phenyl,-N-methyl benzene sulphonamide that is insoluble in KOH.
Ques. Write down the IUPAC name of the following: [2 marks]
(i) C6H5CH2NH2
(ii) C2H5 —-N—-C2H5
Ans. (i) IUPAC name of C6H5CH2NH2 is Phenylmethanamine.
(ii)IUPAC name of C2H5 —-N—-C2H5 is 2-(N,N-diethyl)ethanamine.
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C2H5
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