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The Hoffmann Bromamide degradation reaction was given by August Wilhelm Von Hoffmann. In this reaction, amide is transformed into primary amine by reacting with bromine and sodium hydroxide. Sodium hydroxide is mixed with water and turned into an aqueous solution for this reaction. Hoffmann Bromamide Degradation Reaction is used to form primary amines.
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Key Terms: Hoffmann Bromamide degradation, Amides, Bromine, Carbamic acid, Nitrogen, Carbon, Amines, Aqueous solution, Sodium hydroxide
Hoffmann Bromamide Degradation Reaction
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The Hoffmann Bromamide degradation reaction was identified by August Wilhelm Von Hoffmann, a German chemist. The main purpose of the Hoffmann Bromamide degradation reaction is the formation of primary amines.
- Only primary amides show Hoffmann Bromamide degradation reaction.
- Secondary and tertiary amides do not display this reaction.
- The Hoffmann Bromamide degradation reaction is often used for the preparation of methylamine and the preparation of Aniline.
- Here are some examples of Hoffmann Bromamide degradation reaction:
R-CO-NH2 + Br2 + 4NaOH R-NH2 + Na2CO3 + 2NaBr + 2H2O
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Mechanism of Hoffmann Bromamide Degradation Reaction
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The Hoffmann Bromamide degradation reaction follows the following steps:-
Step 1: The primary amide reacts with sodium hydroxide. The primary amide is attacked by the hydroxide ion of sodium hydroxide. This leads to the formation of water and a negative charge in the primary amide ion. This happens due to the dehydrogenation of primary amide.
Step 2: The bromine molecules react with primary amide ions. The bond of bromine-bromine breaks. One atom of bromine develops a partially negative charge while the other atom develops a partially positive charge. The negative charge on bromine occurs due to the negative charge in the primary amide ion. This leads to the generation of bromamide.
Step 3: The water molecule is removed and one molecule of sodium hydroxide reacts with R-CO-NHBr. Due to the elimination of water molecules, only R-CO-NBr is left.
Step 4: The R separates from the bromamide ion and only OC-NBr is left behind at the end of this step. The detached R (alkyl or aryl group) turns into R-.
Step 5: In this step, the formation of isocyanate takes place. The detached R- attacks the O=C=NBr, specifically the nitrogen atom. Carbamic acid is formed.
Step 6: This is the last step in the Hoffmann Bromamide degradation mechanism. The carbon atom attaches itself with oxygen and nitrogen (highly electronegative elements) and builds up a positive charge (partially). Isocyanate reacts with water. The elimination of carbon takes place in this step. This leads to the formation of primary amine.
Hoffmann Bromamide Degradation Reaction Mechanism
Uses of Hoffmann Bromamide Degradation Reaction:
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- It is used in the production of aliphatic amines.
- It is utilized in the preparation of anthranilic acid.
- It is employed in the production of primary aromatic compounds.
- When using nicotinic acid, the Hoffmann Bromamide degradation reaction can be used for the production of 3-Aminopyridine.
- It is used in the preparation of phthalimide and aniline.
Things to Remember
- The Hoffmann Bromamide degradation reaction was identified by August Wilhelm Von Hoffmann.
- In the Hoffmann Bromamide degradation reaction, amide is transformed into primary amine by reacting with bromine and sodium hydroxide. Sodium hydroxide is mixed with water and turned into an aqueous solution for this reaction.
- The primary amine has one carbon atom less than the primary amide.
- When bromine-bromine bonds break, one atom of bromine develops a partially negative charge while the other atom develops a partially positive charge.
- After the formation of Isocyanate, it reacts with water and the elimination of carbon atoms takes place.
- Hoffmann Bromamide degradation reaction is used to produce aliphatic amines, aniline, phthalimide, anthranilic acid, primary aromatic, and 3-Aminopyridine.
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| Sulphonation | Diazotisation | Group 15 Elements |
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| Gabriel Phthalimide Synthesis | Hell-Volhard-Zelinsky Reaction | Uses of Amines |
Important Questions
Ques: State one limitation of Hoffmann Bromamide Degradation Reaction. (1 Mark)
Ans: Hoffmann Bromamide Degradation Reaction cannot be used to produce primary amines by employing secondary and tertiary amides.
Ques: What forms the basis of the classification of amines into primary, secondary, or tertiary? (1 Mark)
Ans: The number of hydrogen atoms that have been replaced by aryl or alkyl groups determine the classification of amines into primary, secondary, or tertiary amines.
Ques: 3-Aminopyridine can be produced through Hoffmann Bromamide degradation reaction by using: (1 Mark)
a) Nicotinic acid
b) Sodium hydroxide
c) Anthranilic acid
d) Carbamic acid
Ans: a) Nicotinic acid
Ques: Specify the IUPAC names for the following compounds and mention their amines (primary, secondary or tertiary): (1 Mark)
1) (CH3)3 CNH2
2) CH3(CH2)2NH2
3) C6H5NHCH3
Ans:
- 2-Methylpropan-2-amine (Primary amine)
- Propan-1-amine (Primary amine)
- N-MethylbenzenamineorN-methylaniline (Secondary amine)
Ques: Mention the pkb values of the following amines in Aqueous Phase: (2 Marks)
a) Ethanamine
b) N,N-Diethylethanamine
c) Phenylmethanamine
d) Methanamine
e) N-Methylmethanamine
Ans: Following are the pkb values of the above-mentioned amines:
- Ethanamine - 3.29
- N,N-Diethylethanamine- 3.25
- Phenylmethanamine - 4.70
- Methanamine- 3.38
- N-Methylmethanamine- 3.27
Ques: Mention some of the methods for the preparation of amines. (3 Marks)
Ans: Some of the methods for the preparation of amines are the following:
- Reduction of nitro compounds
- Reduction of amides
- Ammonolysis of alkyl halides
- Reduction of nitriles
- Hoffmann bromamide degradation reaction
- Gabriel phthalimide synthesis
Ques: What are some of the uses of Hoffmann Bromamide Degradation Reaction? (3 Marks)
Ans: Hoffmann Bromamide degradation reaction can be used to turn acetamide into methanamine. It can turn propanamide to ethanamine.
Hoffmann Bromamide degradation reaction can also be used to produce aliphatic amines, aniline, phthalimide, anthranilic acid, primary aromatic, and 3-Aminopyridine.
Ques: How does the Hoffmann Bromamide degradation reaction derive its name? (3 Marks)
Ans: The Hoffmann Bromamide degradation reaction was named after August Wilhelm Von Hoffmann. There is a use of amide and bromine molecules in the reaction which constitutes the ‘bromamide’ in the name. The ‘degradation’ in the name is due to the degradation of one carbon atom in the final product compared to the reactant. The primary amine has one carbon atom less than the primary amide.
Ques: Explain the Hoffmann Bromamide Degradation Reaction Mechanism. (3 Marks)
Ans: First, the primary amide reacts with sodium hydroxide. The primary amide is attacked by the hydroxide ion of sodium hydroxide. This leads to the formation of water and negative charge in the primary amide ion. This happens due to dehydrogenation of primary amide. Then, the bromine molecules react with the primary amide ion. The bond of bromine-bromine breaks. One atom of bromine develops a partially negative charge while the other atom develops a partially positive charge. This leads to the generation of bromamide.
The water molecule is removed and one molecule of sodium hydroxide reacts with R-CO-NHBr. Due to the elimination of water molecules, only R-CO-NBr is left. The R separates from the bromamide ion and only OC-NBr is left behind at the end of this step. The detached R (alkyl or aryl group) turns into R-.
The detached R- attacks the O=C=NBr, specifically the nitrogen atom. Finally, the carbon atom attaches itself with oxygen and nitrogen (highly electronegative elements) and builds up a positive charge (partially). Isocyanate reacts with water. The carbon atom is eliminated and the primary amine is formed.
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