Education Journalist | Study Abroad Lead
Nitration is one of the most commonly used chemical processes. Nitration includes the addition of a nitro group into an organic compound using several nitrating agents. The nitrating agents donate the nitro group, -NO2 group to the compound. Nitration is a type of substitution reaction. It is a highly exothermic reaction and requires a few things to be carried out successfully.
Key Terms: Nitration, Nitrating agents, Aromatic groups, Substitutions, Nitrates, Nitric acid, Nitro groups.
Substitution Reactions
[Click Here for Sample Questions]
Substitution reactions include the replacement, that is the substitution of one of the groups on an organic compound with another group. For example, in Chloroethane, the chlorine group has substituted one hydrogen atom in ethane to produce chloroethane.
Substitution Reaction
Similarly, nitration is a type of substitution reaction, which substitutes one of the groups with a nitro group, that is the -NO2 group. For example, in nitrobenzene, the nitro group has substituted one hydrogen atom in benzene to produce nitrobenzene.
Nitrobenzene Reaction
Read More:
Nitration
[Click Here for Sample Questions]
Nitration is one of the most commonly used chemical processes. Nitration includes the addition of a nitro group into an organic compound using several nitrating agents. The nitrating agents donate the nitro group, -NO2 group to the compound. Nitration is a type of substitution reaction.
Nitration Reaction
The nitro group can be attached to different atoms to form a nitrate compound, it can be attached to oxygen, in nitrate esters, to carbon atoms, in nitrobenzene, other nitrogen atoms, etc. There are several environmental problems associated with nitration such as high temperatures, explosive nature of products and by-products, production of acidic vapors, etc.
It is a highly exothermic reaction, thus the temperature of the reaction should be frequently cooled down.
Also Read:
Nitrating Agents
[Click Here for Sample Questions]
Nitrating agents are the compounds that donate the nitro group in the process of nitration to the organic compounds. The several nitrating agents are:
| Nitrating agent | Characteristics |
|---|---|
| Nitric acid (HNO3) | It can be concentrated, and fuming, or diluted and aqueous. |
| The mixture of nitric acid (HNO3) |
|
| Dinitrogen Pentoxide | Mildly explosive, unstable |
| Dinitrogen tetroxide | Mildly explosive, unstable, unpleasant odor |
Read More:
Process of Nitration
[Click Here for Sample Questions]
The nitration cannot be carried out on lower alkane compounds. However, they are carried out easily on the aromatic compound. The process of nitration is a type of electrophilic substitution reaction. An electrophile is any compound that has the affinity to attract electrons towards itself.
The process of nitration is explained using the example of benzene.
Step 1: Formation of the electrophile NO2+ ion:
Here the nitrating agent used is a mixture of sulphuric acid and nitric acid. Sulphuric acid performs two major functions, it removes the water produced as a by-product during nitration and it is a stronger acid than nitric acid, it protonates the nitric acid to form a nitryl ion. This ion is a strong nitrating agent.
HNO3 + 2H2SO4 → NO2+ + H3O+ + 2HSO4¯
Here, NO2+ is the electrophile that proceeds the nitration.
Step 2: Loss of proton, H+ ion
This electrophile replaces the H atom as - H+ ion, on the benzene ring, and attaches itself to the ring, to form the substituted compound. This forms the carbocation.
Step 3: Attack of the electrophile on the carbocation: The electrophile produced in step one, finally attaches itself to the carbocation and forms the complex.
The same procedure is performed for both aliphatic and aromatic compounds. Nitration is one of the most commonly used reactions in the chemical industry.
Read More: Hoffmann Bromamide Degradation Reaction
Factors essential to carry out aromatic nitration:
- Proper orientation of the compounds: Nitration is an electrophilic substitution reaction, thus the substituents on the benzene ring may promote or reduce the substitution of the group.
- Kinetics of the reaction: Compounds such as nitrobenzene or ethyl-benzoate have strongly deactivated groups that are nitrated at a rate that is proportional to the concentration of the substrate i.e. the reaction is a first-order reaction. Compounds that are more reactive than benzene such as toluene, xylene, etc react at a rate that is independent of the concentration of the substrate i.e. the reaction is zero order.
Also Read:
Things to Remember
- Nitration includes the addition of a nitro group into an organic compound using several nitrating agents.
- The nitro group can be attached to different atoms to form a nitrate compound, it can be attached to oxygen, in nitrate esters, to carbon atoms, in nitrobenzene, other nitrogen atoms, etc.
- It is a highly exothermic reaction; thus, the temperature of the reaction should be frequently cooled down.
- Different nitrating agents used are nitric acid, mixed acids, dinitrogen pentoxide, dinitrogen tetroxide, etc.
- Nitration requires proper orientation of the compounds and proper rate kinetics.
Read More:
Sample Questions
Ques: What is nitration? (2 marks)
Ans: Nitration is one of the most commonly used chemical processes used in chemistry. Nitration includes the addition of a nitro group into an organic compound using several nitrating agents. The nitrating agents donate the nitro group, -NO2 group to the compound. Nitration is a type of substitution reaction. It is a highly exothermic reaction.
Ques: What are the factors essential to carry out nitration? (3 marks)
Ans: There are two factors essential to carry out nitration:
Proper orientation of the compounds: Nitration is an electrophilic substitution reaction, thus the substituents on the benzene ring may promote or reduce the substitution of the group.
Kinetics of the reaction: Kinetics Rate =K(HNO3) (ArH) Overall rate = 2.
Ques: What are the different nitrating agents used? (3 marks)
Ans: There are several nitrating agents commonly used, they are:
- Nitric acid (HNO3)
- The mixture of nitric acid (HNO3) with acetic acid (CH3COOH), Sulphuric acid (H2SO4), Acetic anhydride (CH3COCH3), Phosphoric acid (H3PO4), or trichloromethane (CHCl3).
- Dinitrogen Pentoxide
- Dinitrogen tetroxide
Ques: What are substitution reactions, and their types? (2 marks)
Ans: Substitution reactions include the replacement, that is the substitution of one of the groups on an organic compound with another group. For example, in Chloroethane, the chlorine group has substituted one hydrogen atom in ethane to produce chloroethane. It is carried out on both aliphatic and aromatic compounds. Substitution reaction is of two types:
- Electrophilic substitution reaction
- Nucleophilic substitution reaction
Ques: What are the applications of nitration? (2 marks)
Ans: There are several applications:
- Production of explosives like trinitrotoluene, nitroguanidine, etc.
- Production of chemical intermediates, and precursors, like isatin, pyridine, etc.
- Nitration also deactivates the aromatic ring and stops the process.
Ques: What is halogenation? (2 marks)
Ans: Halogenation is the process of adding any halogen to an organic compound. It is also a type of substitution reaction. Different halogens that undergo halogenation are, Chlorine, Bromine, Iodine, Fluorine, etc. They are carried out for both aromatic and aliphatic compounds.
Ques: Briefly explain the mechanism of nitration (3 marks)
Ans: The process of nitration can be explained in three steps:
- Generation of electrophile, here NO2+
- Formation of the carbocation
- Removal of proton
Ques: How does the solvent affect the nitration process? (2 marks)
Ans: The solvent also affects the nitration process, a strong acid, or a highly polar solvent fastens the rate of reaction by facilitating the formation of NO2 + ion, thus enhancing the reaction process. In a less acidic, and less polar medium, this process is slower.
Ques. Why is alkylamine more basic than ammonia? (Delhi 2009) (2 marks)
Ans. Due to the electron releasing inductive effect (+1) of the alkyl group, the electron density on the nitrogen atom increases and thus, it can donate the lone pair of electrons more easily than ammonia.
Ques. Describe the following giving the relevant chemical equation in each case :
(i) Carbylamine reaction
(ii) Hofmann’s bromamide reaction (CBSE 2012) (3 marks)
Ans.
Carbylamine reaction: Aliphatic and aromatic primary amines on heating with chloroform and ethanolic KOH form isocyanides or carbylamines which are foul smelling substances. This reaction is known as carbylamine reaction.
Hofmann’s bromamide reaction: Primary amines can be prepared by treating an amide with Br2 in an aqueous or alcoholic soln of NaOH.
Read More:
Comments