Problem 12 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Hinsberg's reagent is:(a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COCl}\) (b) \(\mathrm{SOCl}_{2}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl}\) (d) \((\mathrm{COCl})_{2}\)

Step-by-Step Solution

Answer

(c) \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{SO}_{2}\mathrm{Cl}\)

Step 1: Understanding Hinsberg's Reagent

Hinsberg's reagent is used to distinguish between primary, secondary, and tertiary amines. The reagent is an aromatic sulfonyl chloride, which reacts with amines to form sulfonamides.

Step 2: Identify the Chemical Structure Required

Hinsberg's reagent is specifically benzene sulfonyl chloride, which can be represented as \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{SO}_{2}\mathrm{Cl}\). This compound has a benzene ring attached to a sulfonyl group \((-SO_2-)\) and a chloride \((-Cl)\).

Step 3: Match the Compound with the Given Options

Look at the given options to find the one that matches the structure of an aromatic sulfonyl chloride, specifically \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{SO}_{2}\mathrm{Cl}\). Only option (c) matches this structure.

Key Concepts

Amines

Amines are organic compounds derived from ammonia \((\mathrm{NH}_{3})\). They play a significant role in both chemistry and biology. Amines are categorized based on the number of carbon-containing groups attached to the nitrogen atom. Here's a simple breakdown:

• Primary amines: These have one carbon group attached to the nitrogen. An example is methylamine \((\mathrm{CH}_{3}\mathrm{NH}_{2})\).
• Secondary amines: These have two carbon groups attached to the nitrogen, such as dimethylamine \((\mathrm{(CH}_{3})_{2}\mathrm{NH})\).
• Tertiary amines: These have three carbon groups connected to the nitrogen. An example is trimethylamine \((\mathrm{(CH}_{3})_{3}\mathrm{N})\).

Amines react differently with Hinsberg's reagent based on their structure. Primary amines form sulfonamides that are soluble in alkaline solutions. Secondary amines give insoluble sulfonamides. Tertiary amines, however, do not react with Hinsberg's reagent. This difference makes Hinsberg's reagent a useful tool for identifying the type of amine in a sample. Their importance in both industrial and laboratory settings cannot be overstated.

Sulfonamides

Sulfonamides are compounds formed when sulfonyl chlorides react with amines. This reaction is a key step in Hinsberg's test, which involves the use of Hinsberg's reagent. When an amine reacts with benzene sulfonyl chloride \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{SO}_{2}\mathrm{Cl}\), it results in the formation of a sulfonamide.
This reaction helps in distinguishing between different types of amines because:

• Primary amines react to form sulfonamides that are soluble in alkaline solutions. This solubility is due to the presence of a replaceable hydrogen atom in primary amines that reacts to form a water-soluble product.
• Secondary amines also react to form sulfonamides, but these are insoluble in alkaline solutions.
• Tertiary amines, generally, do not form sulfonamides because they lack a hydrogen atom on the nitrogen for reaction.

Sulfonamides also hold importance beyond organic reactions. They are the foundation of many antibiotics known as sulfa drugs, showcasing their role in both chemistry and medicine.

Benzene Sulfonyl Chloride

Benzene sulfonyl chloride, represented by the chemical formula \(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{SO}_{2}\mathrm{Cl}\), serves as the critical component of Hinsberg's reagent. This aromatic compound consists of a benzene ring attached to a sulfonyl chloride group.
This combination gives benzene sulfonyl chloride its unique properties:

• The benzene ring contributes to the stability and structure of the compound.
• The sulfonyl chloride group is highly reactive, making it effective in forming sulfonamides with amines.

Benzene sulfonyl chloride acts selectively with primary and secondary amines, while tertiary amines remain unreactive. Its role is pivotal in both synthetic and analytical chemistry, particularly because it aids in easily distinguishing between types of amines. Benzene sulfonyl chloride, due to its reactivity and specificity, remains a staple reagent within organic laboratories.