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

(c) 1, 2, and 4, but 2 is questionable; (1) and (4) are primary amine reactions.

Step 1: Identify character reactions of primary amines

Primary amines are known for specific reactions such as the carbylamine reaction and diazotization. The carbylamine reaction is distinctive for primary amines, leading to the formation of isocyanides. Diazotization involves forming diazonium salts and is usually performed with primary aromatic amines.

Step 2: Analysis of given options with primary amines

1. The carbylamine reaction is specific to primary amines, producing an isocyanide from chloroform and base. 2. The mustard oil reaction (also known as Hinsberg’s test) involves primary amines forming sulfonamides, however, it's not as directly linked to primary amines as the carbylamine reaction. 3. Reaction with ceric ammonium nitrate is a test for alcohols and phenols, but not characteristic for identifying primary amines. 4. Diazotization is applicable to primary aromatic amines to form diazonium salts.

Step 3: Selecting the correct options

From Step 1 and Step 2 analysis, reactions 1 (carbylamine reaction) and 4 (diazotization) are specifically known to involve primary amines. Mustard oil reaction and reaction with ceric ammonium nitrate either do not apply or are not specific to primary amines.

Key Concepts

Carbylamine Reaction

The Carbylamine reaction is a unique and identifying reaction for primary amines, which include both aliphatic and aromatic types. When a primary amine is heated with chloroform and an alcoholic solution of potassium hydroxide (KOH), it undergoes the Carbylamine reaction. This reaction results in the formation of isocyanides or carbylamines. The process can be represented simply as follows:

• The primary amine is first converted into an isocyanide when treated with chloroform (CHCl₃) in the presence of KOH.
• This reaction is specifically useful because it only occurs with primary amines, thereby serving as a qualitative test to detect their presence.
• The newly formed isocyanides are known for their distinctly unpleasant odors, which also helps in confirming the reaction visually and by smell.

The Carbylamine reaction is especially interesting because it highlights the distinguishing characteristics of primary amines, differentiating them from secondary and tertiary amines. This selective reactivity is a hallmark of primary amines and showcases their chemical uniqueness.

Diazotization

Diazotization is another key reaction exclusive to primary aromatic amines. In this process, the amine group (2-oh) in a primary aromatic amine is transformed into a diazonium salt via a reaction with nitrous acid (HNO₂). This reaction is typically carried out in a cold, acidic aqueous medium. Here's how diazotization generally proceeds:

• When a primary aromatic amine, such as aniline, is treated with nitrous acid, diazonium salts are formed. Nitrous acid is typically generated in situ, at the moment of reaction, by mixing sodium nitrite (NaNO₂) with a strong acid like hydrochloric acid (HCl).
• The resulting diazonium salt is a versatile intermediate, paving the way for numerous subsequent reactions such as azo coupling and Sandmeyer reactions.
• This reaction is an important step in synthesizing aromatic compounds, facilitating substitutions that otherwise might not be feasible.

Diazotization demonstrates the significant role of primary aromatic amines in synthetic chemistry, providing a pathway to various complex organic molecules by exploiting the unique characteristics of the diazonium intermediate.

Amines Characteristic Reactions

Amines, broadly categorized into primary, secondary, and tertiary, display varied reactivity due to their differing structures. The unique reactions of primary amines make them a subject of interest when differentiating them from their derivatives. Here are some important characteristics to note:

• Primary amines: These are reactive in Carbylamine and diazotization reactions, helping distinguish them from other amine types.
• Secondary and tertiary amines: These do not participate in Carbylamine reactions or diazotization, making primary amines stand out in these contexts.
• Importance of selectivity: These characteristic reactions of primary amines are often used for qualitative analysis to confirm the presence and identity of primary amines in a sample.
• Applications: From forming pharmaceuticals to being precursors in dyes, the reactivity of primary amines is crucial in various chemical syntheses.

Amines' characteristic reactions are essential in both analytical and synthetic chemistry, showcasing how primary amines can be uniquely identified and utilized for their reactive properties.