Problem 10 - A Complete Resource Book in Chemistry for JEE Main

Question

Hinsberg reagent is (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2} \mathrm{Cl}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl}\) (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{3} \mathrm{H}\)

Step-by-Step Solution

Answer

The Hinsberg reagent is \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl}\) (option c).

Step 1: Identify the Functional Group in Hinsberg Reagent

The Hinsberg reagent is known for its role in distinguishing between primary, secondary, and tertiary amines. It reacts specifically with the amine group (-NH2).

Step 2: Analyze the Given Options

Look at the molecular formulas provided: 1. (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NO}\) is phenyl nitrosyl, which is not used as Hinsberg's reagent.2. (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{~N}_{2} \mathrm{Cl}\) is benzene diazonium chloride, typically not used as Hinsberg's reagent.3. (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl}\) is benzenesulfonyl chloride, which can make sulfonamide derivatives used for distinguishing amines.4. (d) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{3} \mathrm{H}\) is benzenesulfonic acid, not used as Hinsberg's reagent.

Step 3: Choose the Correct Option

From the analysis, option (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl}\) is the correct Hinsberg reagent as it reacts with amines to form sulfonamide derivatives, allowing for the differentiation of primary, secondary, and tertiary amines.

Key Concepts

Functional Groups

Functional groups are specific groups of atoms within molecules that have distinct chemical properties no matter what they're attached to. They are the "building blocks" of organic chemistry that determine the characteristics and chemical reactions of molecules.
Understanding functional groups is crucial in identifying how different organic molecules, like amines, interact with reagents.
For example, all alcohols (-OH group) will behave similarly in chemical reactions due to their shared functional group.

Consider amines, which contain the functional group -NH2. This group has unique reactivity and is central to many organic chemistry reactions. Each functional group will have certain predictable properties, which helps chemists design reactions to obtain desired outcomes.

• Amines: Contain the -NH2 group.
• Alcohols: Characterized by the -OH group.
• Carboxylic Acids: Have a -COOH group.

Recognizing and understanding these groups help in predicting the behavior of compounds during reactions, such as when using Hinsberg's reagent to distinguish amines.

Amines

Amines are organic compounds and functional groups that contain a nitrogen atom with a lone pair. They come in three varieties: primary, secondary, and tertiary. The difference lies in how many hydrogen atoms in ammonia (NH3) are replaced by organic groups (R-groups).

Amines have the general structure:

• Primary Amines (R-NH2): Only one hydrogen atom replaced.
• Secondary Amines (R2-NH): Two hydrogen atoms replaced.
• Tertiary Amines (R3-N): All three hydrogen atoms replaced.

These distinctions are important because each type of amine reacts differently. Hinsberg reagent, for instance, is a powerful tool in distinguishing these three. It reacts with primary and secondary amines but not with tertiary amines, allowing chemists to identify the type of amine they are working with. This property makes amines very useful and versatile in various chemical reactions.

Their diverse reactivity is used in drugs, agriculture, and dye manufacture, making them a vital part of organic chemistry.

Sulfonamide Derivatives

Sulfonamide derivatives are compounds that result from the reaction of an amine (particularly primary amines) with a sulfonyl chloride, such as Hinsberg's reagent (benzenesulfonyl chloride). This reaction produces a sulfonamide linkage - that's characterized by a sulfur atom double bonded to two oxygen atoms and single-bonded to a nitrogen atom from the amine.

Sulfonamide derivatives are critical because they help in distinguishing between primary, secondary, and tertiary amines. Here's why:

• Primary amines form sulfonamide derivatives making them easily isolable. They are soluble in alkaline solutions, like NaOH.
• Secondary amines also yield sulfonamide derivatives but are insoluble in NaOH.
• Tertiary amines do not react with Hinsberg’s reagent at all, therefore do not form any sulfonamide derivative.

Beyond their role in identifying amines, sulfonamide derivatives are also significant in pharmaceuticals. They form the basis of sulfa drugs, which are used to fight bacterial infections. Understanding their formation and properties can lead to insights into designing new and effective drugs.