Problem 109 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following reaction is given by a primary amine? (1) Carbyl amine reaction (2) Mustard oil reaction (3) Reaction with ceric ammonium nitrate (4) Diazotization (a) 3 and 4 (b) 1,2 and 3 (c) 1,2 and 4 (d) 2 and 3

Step-by-Step Solution

Answer

Option (c) 1, 2, and 4.

Step 1: Understanding Primary Amine Reactions

Primary amines can undergo several reactions, but not all reactions are exclusive to or primarily involve primary amines. We need to identify the reactions given specifically by a primary amine.

Step 2: Carbyl Amine Reaction

A carbyl amine reaction is a chemical reaction that involves a primary amine, chloroform, and an alcoholic base such as KOH, leading to the formation of isocyanides or carbylamines. This reaction is specific to primary amines.

Step 3: Mustard Oil Reaction

Mustard oil reaction, also known as Hofmann's mustard oil reaction, occurs when primary amines react with carbon disulfide (CS2) and further treatment. This reaction is specific to primary amines and involves the formation of isothiocyanates.

Step 4: Reaction with Ceric Ammonium Nitrate

A reaction with ceric ammonium nitrate is generally used to test for alcohols, not primary amines. Hence, this reaction is not particularly relevant for identifying primary amines.

Step 5: Diazotization

Diazotization involves the reaction of primary amines with nitrous acid (HNO2), resulting in diazonium salts. This reaction is a characteristic of primary aromatic amines, such as aniline.

Step 6: Final Selection of Reactions

From the analysis above, the reactions that occur specifically with primary amines are the carbylamine reaction (1), mustard oil reaction (2), and diazotization (4). Therefore, the correct options are 1, 2, and 4.

Key Concepts

Carbyl Amine Reaction

The Carbyl Amine Reaction is an important reaction involving primary amines. In this particular reaction, a primary amine, typically an aliphatic or aromatic amine, is treated with chloroform and an alcoholic base, such as potassium hydroxide (KOH). This leads to the formation of an isocyanide, also known as a carbylamine. This reaction is notable because it is a straightforward diagnostic test to identify primary amines. If you perform this reaction and obtain a foul-smelling isocyanide, you can confidently determine the presence of a primary amine in your sample.

• The reactants needed are a primary amine, chloroform, and an alcoholic base.
• It is a unique reaction to primary amines, meaning that secondary or tertiary amines will not yield the same result.
• It results in the notorious offensive odor of the isocyanide formed.

This reaction is simple, specific, and does not require complex apparatus, making it a favorite among chemists to test for primary amines.

Mustard Oil Reaction

The Mustard Oil Reaction, also known as Hofmann's Mustard Oil Reaction, is another specific test for primary amines where they react with carbon disulfide (CS₂) under basic conditions. The initial reaction forms a dithiocarbamate salt with the primary amine, which upon heating forms an isothiocyanate, similar to mustard oil in smell. This distinct process is highly specific to primary amines and is frequently used within laboratory settings to determine their presence.

• The primary amine reacts with carbon disulfide to form a dithiocarbamate intermediate.
• Further treatment or heating converts this intermediate to an isothiocyanate.
• As the reaction proceeds, the unmistakable smell akin to mustard oil is produced, serving as the identification mark for primary amines.

This resembles the sensory method of determining primary amines due to the noticeable production of a characteristic smell.

Diazotization

Diazotization is a chemical reaction that is characteristically undergone by primary aromatic amines, such as aniline. When treated with nitrous acid (often generated in situ from sodium nitrite and a mineral acid such as hydrochloric acid), primary aromatic amines are converted into diazonium salts. These diazonium salts are significant intermediates in organic synthesis and can undergo further transformations to form a wide variety of other compounds.

• Primary aromatic amines react with nitrous acid to form diazonium salts.
• Diazotization is a crucial step for synthesizing azo dyes, medicinal compounds, and aromatic substitution reactions.
• This process makes primary aromatic amines versatile tools in synthetic chemistry tasks.

Notably, this reaction does not typically occur with aliphatic amines. The diazo group formed in diazonium salts is a cornerstone for further chemical innovations due to its high reactivity.