Question

Benzamide and aniline can be distinguished by (A) Hinsberg test (B) Carbyl amine test (C) Dye azo test (D) Ethyl oxalate test

Short answer

The correct test to distinguish between benzamide and aniline is the (B) Carbyl amine test, as it reacts positively with aniline (amine) and not with benzamide (amide). Alternatively, the Dye azo test and Ethyl oxalate test can also be used, as one reacts with aniline and the other with benzamide, respectively.

Step-by-step solution

Analyze the Reaction Mechanism for Hinsberg Test

In the Hinsberg test, the amine reacts with benzene sulfonyl chloride (C₆H₅SO₂Cl) in the presence of a base like NaOH. A primary amine forms an N-alkylbenzenesulfonamide, which is soluble in alkali. A secondary amine forms an N,N-dialkylbenzenesulfonamide that is insoluble in alkali, while a tertiary amine does not react. However, both benzamide (amide) and aniline (amine) do not react differently in the Hinsberg test.

Analyze the Reaction Mechanism for Carbyl Amine Test

In the Carbyl amine test, the amine (such as aniline) reacts with chloroform (CHCl₃) and an alkali (KOH) to form an isocyanide or carbylamine compound (very foul-smelling). Since aniline is a primary amine, it will give a positive Carbyl amine test, whereas benzamide (amide) will not react in this test.

Analyze Dye Azo Test and Ethyl Oxalate Test

The Dye azo test will react with aniline (aromatic amine) but not with benzamide (amide). In contrast, Ethyl oxalate test reacts with benzamide (amide) but not with aniline (amine).

Determine the Correct Test to Distinguish Benzamide and Aniline

We found that the Carbyl amine test is suitable for distinguishing between benzamide and aniline, as it reacts with aniline (amine) only and not with benzamide (amide). Alternatively, the Dye azo test or Ethyl oxalate test could also be used, one detecting aniline while the other detecting benzamide, respectively. Therefore, the correct answer is: (B) Carbyl amine test

Key concepts

Amine Reaction Mechanisms

Understanding how amines react is crucial for their identification in organic chemistry. Amine reaction mechanisms primarily involve the functional group –NH₂ in primary amines, –NHR in secondary amines, and –NR₂ in tertiary amines. These groups influence how amines interact with different reagents, enabling us to identify them through specific tests.

One common reaction involves the Hinsberg test, which utilizes benzene sulfonyl chloride. Here, amines behave distinctly depending on their class. Primary amines form products soluble in alkali. Secondary amines yield insoluble products, and tertiary amines do not react at all. This allows us to distinguish the type of amine involved.

The carbyl amine test is another essential mechanism mainly used for testing the presence of primary amines, specifically aniline. This test involves reacting the amine with chloroform and a strong base like KOH, resulting in the formation of a characteristic foul-smelling isocyanide. Such unique reactions of amines are central to distinguishing them from other compounds such as amides.

Functional Group Identification

Identifying functional groups is a cornerstone of organic chemistry, enabling chemists to understand how molecules will behave in reactions. A functional group is a specific group of atoms within a molecule that is responsible for a particular set of chemical reactions.

For amines, the presence of nitrogen groups such as –NH₂ is significant. These nitrogen groups contribute to the molecule's basicity and reactivity. By conducting various tests such as the Hinsberg and carbyl amine tests, chemists can ascertain the type and classification of the amine present based on its reaction outcomes.

In contrast, amides, like benzamide, feature a carbonyl group bonded to a nitrogen atom, giving them distinct properties from amines. Understanding these functional groups' reactivity is essential for choosing the correct tests to differentiate compounds like benzamide from aniline.

Organic Compound Distinction

In organic chemistry, distinguishing between compounds like benzamide and aniline is crucial due to their differing properties and functionalities. Reactions that target specific functional groups are used to achieve this distinction.

The carbyl amine test, for example, selectively identifies aniline by producing a strong-smelling isocyanide when a primary amine is present. Amides like benzamide do not react in this test due to the absence of the primary amine functional group. As a result, this test provides a clear method to distinguish between these compounds.

Similarly, the dye azo test reacts with aniline, highlighting its aromatic amine group, while benzamide remains untouched. On the flip side, the ethyl oxalate test targets the amide functionality in benzamide, distinguishing it from the non-reactive aniline. Understanding and utilizing such tests allow for accurate differentiation of organic compounds in practical settings.