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Question: A positive carbylamine test is given by: A.\(N,N - Dimethylaniline\) B.\(2,4 - Dimethylaniline\)...

A positive carbylamine test is given by:
A.N,N−DimethylanilineN,N - Dimethylaniline
B.2,4−Dimethylaniline2,4 - Dimethylaniline
C.N−methyl−o−methylanilineN - methyl - o - methylaniline
D.p−methylbenzylaminep - methylbenzylamine

Explanation

Solution

We need to know that the carbylamine reaction is called Hoffman isocyanide synthesis. It is the method of synthesis of an isocyanide by the reaction of a primary amine, chloroform and a base. Its mechanism involves the addition of amine to dichlorocarbene, after two base-catalyzed dehydrochlorination, it results in the formation of isocyanide.

Complete step by step answer:
We know that carbylamine reaction is processed using primary amines. Hence, it is clear that the test for carbylamine will be done to check whether the compound contains primary amines or not.
This test is also called Saytzeff's isocyanide test. In this reaction, the analyte is heated with alcoholic potassium hydroxide and chloroform. If a primary amine is present, the isocyanide (carbylamine) is formed. It is indicated by a foul odor. The carbylamine test does not give positive results with secondary and tertiary amines.
Let us look at the chemical composition of each compound given above.
We can draw the structure ofN,N−DimethylanilineN,N - Dimethylaniline-

It contains tertiary amines. Hence, this is not the correct answer.
We can draw the structure of 2,4−Dimethylaniline2,4 - Dimethylaniline-

It contains primary. Hence, this product will give positive results for carbylamine test.
We can draw the structure of N−methyl−o−methylanilineN - methyl - o - methylaniline-

It contains a secondary amine. Hence, it is not the correct answer.
We can draw the structure of p−methylbenzylaminep - methylbenzylamine

It contains primary amine. Hence, it will pass the positive carbylamine test.
Therefore, the correct answer to the question is option B and option D.

Note:
We must remember that the carbylamine test is only given by primary amines. This test is used to detect whether primary amines are present in a compound or not. When secondary amines and tertiary amines are present then the reaction does not proceed. The presence of primary amine is indicated by a foul odor released after the completion of reaction. Saytzeff’s isocyanide test is generally used for carbylamine tests. While the carbylamine reaction is known as Hoffman isocyanide synthesis.