The presence of primary amine can be confirmed by its
reaction with :

Options

A. `HNO_2`
B. `CHCI_3 + NaOH`
C. `CS_2 and HgCI_2`
D. `H_(2) SO_(4)`

Answer

To confirm the presence of a primary amine, we can utilize various chemical reactions. Let's analyze the options provided in the question step by step.

### Step 1: Reaction with Nitrous Acid (HNO2)
- **Reaction**: When a primary amine (RNH2) reacts with nitrous acid (HONO) at low temperatures (273-278 K), nitrogen gas (N2) is evolved.
- **Observation**: The evolution of nitrogen gas is a clear indication of the presence of a primary amine.
- **Conclusion**: This reaction is known as the nitrous acid test and confirms the presence of a primary amine.

### Step 2: Reaction with Chloroform and KOH
- **Reaction**: When a primary amine (RNH2) reacts with chloroform (CHCl3) in the presence of alcoholic KOH and is heated, it produces an isocyanide (R-NC) along with KCl and water.
- **Observation**: The formation of isocyanide indicates the presence of a primary amine. This is known as the carbylamine reaction or isocyanide test.
- **Conclusion**: This reaction is also used to distinguish primary amines from secondary and tertiary amines.

### Step 3: Reaction with Carbon Disulfide (CS2) and Mercury(II) Chloride (HgCl2)
- **Reaction**: When a primary amine reacts with carbon disulfide (CS2) and then with mercury(II) chloride (HgCl2), it results in the formation of alkyl isothiocyanates.
- **Observation**: The formation of isothiocyanates is characterized by a mustard oil smell and confirms the presence of a primary amine. This is known as the Hofmann mustard oil reaction.
- **Conclusion**: This reaction is also a valid test for the presence of primary amines.

### Step 4: Reaction with Sulfuric Acid (H2SO4)
- **Reaction**: The reaction of amines with sulfuric acid typically pertains to sulfonation, which is relevant for aromatic amines under drastic conditions (high temperatures).
- **Observation**: This reaction does not specifically confirm the presence of primary amines and is more applicable to aromatic amines.
- **Conclusion**: Therefore, this option is not a valid test for primary amines.

### Final Conclusion
From the analysis above, the presence of primary amines can be confirmed by their reactions with:
1. Nitrous acid (HNO2) - evolution of N2 gas.
2. Chloroform (CHCl3) and KOH - formation of isocyanide.
3. Carbon disulfide (CS2) and HgCl2 - formation of isothiocyanates.

The only incorrect option for confirming primary amines is sulfuric acid (H2SO4).