JEE Chapter - Organic Compounds Containing Nitrogen

In the atmosphere, a wide range of nitrogenous compounds has been found. Some of the organic compounds of nitrogen are Amines, amides, alkyl nitrates, nitrosamines, nitroarenes, and peroxyacyl nitrates. Amphetamines, amides, and nitro compounds are among the most crucial topics that must be covered in order to pass entrance exams.

In this article, we'll go over all of the main aspects of amine, amide, and nitro compounds.

JEE Main Chemistry Chapter-wise Solutions 2022-23 

Important Topics of Organic Compound of Nitrogen

• Aliphatic amine

• Carbylamine reaction

• Coupling reaction

• Amide

• Hoffman bromamide reaction

• Aromatic amine

• Nitro camide compounds

• Nitration

• Diazonium salt

Important Concepts of Organic Compounds Containing Nitrogen

What are Amines?

Amines are ammonia derivatives that are made by replacing one, two, or all three hydrogen atoms with alkyl and/or aryl groups.

Structure of Amine

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Classification of Nitrogenous Compounds (Amine)

Number of hydrogen atoms in ammonia molecules that are replaced by alkyl or aryl groups decide the class of amines. RNH2 or ArNH2, a primary amine, is formed when one hydrogen atom of ammonia is replaced by R or Ar (1o).

If two hydrogen atoms of ammonia or one hydrogen atom of primary amine (R-NH2) are substituted by another alkyl/aryl(R') group, secondary (2o) amines are formed.

Tertiary amines (R3N) are formed when another hydrogen atom is replaced by an alkyl/aryl group.

Nomenclature of Amines

An aliphatic amine is named in the common system by prefixing the alkyl group to amine, resulting in alkylamine as a single word (e.g., methylamine). When two or more groups in a secondary or tertiary amine are the same, the prefix di or tri is added before the name of the alkyl group. Alkanamines are the names given to amines in the IUPAC system.

If more than one amino group is present at different places in the parent chain, their positions are indicated by assigning numbers to the carbon atoms bearing –NH2 groups and attaching a suitable prefix to the amine such as di, tri, etc. The letter 'e' from the hydrocarbon part's suffix is kept.

Properties of Organic Compounds Containing Nitrogen (Amines)

• Lower (amines with less carbon) aliphatic amines exist in gaseous state with a fishy odour.

• Aniline and other arylamines are generally colourless, but due to air oxidation, they become coloured with storage.

• Because they can establish hydrogen bonds with water molecules, lower aliphatic amines are soluble in water. However, when the molecular mass of amines (R-NH2) increases, solubility declines due to the increased size of the hydrophobic alkyl component.

• Because of hydrogen bonding between the nitrogen of one molecule and the hydrogen of another, primary and secondary amines form intermolecular associations. Because primary amines have two hydrogen atoms available for hydrogen bond formation, they have higher intermolecular interaction than secondary amines. Because there is no hydrogen atom available for hydrogen bond formation, tertiary amines do not exhibit intermolecular interaction. As a result, the boiling temperatures of isomeric amines are in the following order:

Primary > Secondary > Tertiary.

• Benzenediazonium chloride is a crystalline substance that is colourless. It is generally water (H2O) soluble and generally stable at room temperature, but when warmed, it reacts with water. In the dry state, it decomposes quickly. Water insoluble, benzenediazonium fluoroborate is stable at ambient temperature.

• Amines are reactive because of the difference in electronegativity between nitrogen and hydrogen atoms, as well as the presence of an unshared pair of electrons above the nitrogen atom.

Preparation Reaction for Amines

1. Reduction of Nitro Compounds

By passing hydrogen gas through finely divided nickel, palladium, or platinum, nitro compounds are reduced to amines, as well as by reduction with metals in an acidic media.

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2. Ammonolysis of Alkyl Halide

A nucleophile can easily cleave carbon-halogen bonds in alkyl or benzyl halides. As a result, when an alkyl or benzyl halide reacts with an ethanolic solution of ammonia, the halogen atom is replaced by an amino (–NH2) group in a nucleophilic substitution reaction.

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Treatment with a strong base yields the free amine from the ammonium salt:

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3. Reduction of Nitriles

Primary amines are formed when nitriles are reduced with lithium aluminium hydride (LiAlH4) or hydrogenated catalytically.

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4. Reduction of Amides

When amides are reduced with lithium aluminium hydride, amines are formed.

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5. Gabriel Phthalimide Reaction

Primary amines are made via the Gabriel synthesis method. When phthalimide is treated with ethanolic potassium hydroxide, it generates a potassium salt, which when heated with an alkyl halide and then alkaline hydrolyzed yields the primary amine.

Because aryl halides do not undergo nucleophilic substitution with the anion generated by phthalimide, this approach cannot be used to make aromatic primary amines.

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6. Hoffmann Bromamide Degradation Reaction

By treating an amide with bromine in an aqueous or ethanolic solution of sodium hydroxide, Hoffmann created a method for preparing primary amines.

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Chemical Reactions of Amine

1. Carbylamine Reaction

When primary amines are heated with chloroform and ethanolic potassium hydroxide, they generate isocyanides or carbylamines, which have a horrible odour. This reaction does not occur in secondary or tertiary amines.

R-NH2 + CHCl3 + 3KOH → R-NC + 3KCl + 3H2O     (on heating)

2. Reaction with Nitrous Acid

When primary aliphatic amines react with nitrous acid, they produce aliphatic diazonium salts, which are unstable and release nitrogen gas and alcohols in large quantities.

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At low temperatures (273-278 K), aromatic amines react with nitrous acid to create diazonium ions.

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3. Reaction with Arylsulphonyl Chloride

Hinsberg's reagent, benzenesulphonyl chloride (C6H5SO2Cl), interacts with primary and secondary amines to produce sulphonamides.

(a) N-ethylbenzenesulphonyl amide is formed by reacting benzenesulphonyl chloride with primary amine.

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Due to the presence of a strong electron withdrawing sulfonyl group, the hydrogen linked to nitrogen in sulphonamide is extremely acidic. As a result, it is alkali soluble.

(b) N,N-diethylbenzenesulphonamide is produced in the reaction with secondary amine.

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Tertiary amines do not react with benzenesulfonyl chloride.

4. Electrophilic Substitution Reaction

An ortho-para directing group is the Amine group. It is subjected to a number of electrophilic substitution processes.

a. Bromination:

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At room temperature, aniline reacts with bromine water to form a white precipitate of 2,4,6-tribromoaniline. In the presence of an acetyl group, controlled bromination can occur. It shields the amine group and keeps uncontrolled halogenation under control (bromination).

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(b) Nitration

Aniline is protonated to create the meta directing anilinium ion in a very acidic solution. As a result, in addition to ortho and para derivatives, a considerable number of meta derivatives are generated.

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The nitration reaction can be regulated and the p-nitro derivative obtained as the primary product by protecting the –NH2 group via an acetylation reaction with acetic anhydride.

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(C) Sulphonation

Aniline combines with concentrated sulphuric acid to make anilinium hydrogensulphate, which produces p-aminobenzene sulphonic acid when heated with sulphuric acid at 453-473K.

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Why Aniline do not Undergo Friedel Crafts Reaction

Because the Lewis acid, aluminium chloride, is utilised as a catalyst, aniline does not undergo Friedel-Crafts reaction (alkylation and acetylation). As a result, the nitrogen in aniline gains a positive charge, acting as a powerful deactivate group for subsequent reactions.

Resonance in Diazonium Salt

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Preparation Method of Diazonium Salt

The reaction of aniline with nitrous acid at 273-278K produces benzenediazonium chloride. The reaction of sodium nitrite with hydrochloric acid produces nitrous acid in the reaction mixture. Diazotization is the process of converting primary aromatic amines into diazonium ions.

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Reactions of Diazonium Salt

1. Sandmayer’s Reaction

Replacement by halide or cyanide ion: In the presence of Cu(I) ions, the nucleophiles Cl–, Br–, and CN– can easily be introduced into the benzene ring. The Sandmeyer reaction is the name for this reaction.

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2. Gatterman Reaction 

By treating the diazonium salt solution with the appropriate halogen acid in the presence of copper powder, chlorine or bromine can be introduced into the benzene ring. The Gatterman reaction is the name for this.

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3. Replacement by Iodide Ion

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4. Replacement by Fluoride Ion

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5. Replacement by H

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6. Replacement by Hydroxyl Group

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7. Replacement by –NO2 Group

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8. Coupling Reaction

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Solved Examples/Problems from the Chapter: Organic Compounds Containing Nitrogen

1. Complete the given reactions following the acid-base combination and name the products:

1. CH3CH2CH2NH2 + HCl →

2. C2H5)3N + HCl →

Ans: 

(i)

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(ii)

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Key point: It is a general acid base reaction in which an amine group of primary amine and secondary amine accepts a proton by forming salt and behaves like a base.

2.Write down the chemical reaction between aniline and benzoyl chloride, as well as the name of the resulting product.

Ans: 

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Key Point: This reaction is an acetylation reaction, which is used to protect the amine group from uncontrolled substitution of the electrophile in the electrophilic substitution reaction.

Solved Problems of Previous Year Question from the Chapter: Organic Compounds Containing Nitrogen

1. The major product formed in the following reaction is:

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a)

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b)

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c)

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d)

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Ans: The correct answer is option 3. Only primary amines react with hinsberg reagents and forms precipitate that dissolves in addition to alkali.

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Trick: Acylation takes place in the presence of SOCl2. Acyl group in the presence of alcohol produces esters. 

2. The major product of the following reaction is:

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Ans:  The correct answer is option c. 

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Trick: This reaction will follow hoffmann’s bromamide degradation reaction. The aliphatic diazonium salt is not stable, it gets converted into an alcohol.

3. In the following sequence of the reaction, the final product D is:

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Ans: The correct answer is option c.

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Trick: Chromyl chloride is an oxidising agent and hydrogen in the presence of palladium is a reducing agent. Secondary alcohol is oxidised to form ketone.

Practice Questions

1. To discriminate between the following pairs of substances, perform one chemical test.

(i) Methylamine and dimethylamine (ii) Secondary and tertiary amines 

Ans: (i) Carbylamine test. (ii) Libermann nitrosoamine test. 

2. Describe a method for determining which amines are primary, secondary, and tertiary. Also, write down the chemical equations for the reactions.

Ans: Hinsberg's test

Conclusion

In this article, we have provided important information regarding the chapter compounds of nitrogen such as important definitions, reactions, and concepts. Students should work on more solved examples and organic compounds of nitrogen examples for securing good grades in the JEE exams.

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