Give one chemical test to distinguish between aniline and benzylamine.

To differentiate between aniline and benzylamine, one effective chemical test involves the use of nitrous acid (HNO2). This test capitalizes on the distinct reactivity of the two amines with nitrous acid, leading to observable differences in their behavior.

Understanding the Reaction

Aniline (C6H5NH2) is a primary aromatic amine, while benzylamine (C6H5CH2NH2) is a primary aliphatic amine. When each of these amines is treated with nitrous acid, they react differently due to the structural variations in their molecular frameworks.

The Test Procedure

• Prepare a solution of nitrous acid by mixing sodium nitrite (NaNO2) with hydrochloric acid (HCl).
• In a separate container, dissolve a small amount of the amine (either aniline or benzylamine) in water.
• Slowly add the nitrous acid solution to the amine solution while keeping the mixture cool.

Observations

After adding nitrous acid:

• Aniline: The reaction will produce a diazonium salt, which is typically stable at low temperatures. If the solution is warmed, the diazonium salt can decompose, leading to the formation of a colored azo compound, which can be identified by its characteristic color.
• Benzylamine: In contrast, benzylamine will react with nitrous acid to form benzyl alcohol and nitrogen gas. This reaction does not produce a stable diazonium salt, and you may observe the evolution of gas bubbles, indicating the release of nitrogen.

Summary of Results

By observing the outcomes of the reaction with nitrous acid, you can effectively distinguish between aniline and benzylamine:

• If you see the formation of a stable diazonium salt or a colored azo compound, you are dealing with aniline.
• If gas bubbles are produced without the formation of a stable compound, then the amine is benzylamine.

This test is a straightforward and reliable method for differentiating these two amines based on their unique chemical properties. Understanding these reactions not only aids in identification but also provides insight into the behavior of different functional groups in organic chemistry.