Question

Which of the following nitrogen containing compound does not give Lassaigne’s test ?

• A. Phenyl hydrazine
• B. Glycene
• C. Urea
• D. Hydrazine

Answer 1

The Correct Option is D

Understanding Lassaigne’s Test:

Lassaigne’s test is used to detect the presence of nitrogen, sulfur, and halogens in organic compounds. In this test, the compound is fused with sodium to convert these elements into ionic forms (e.g., NaCN for nitrogen).

Requirement for Lassaigne’s Test:

To give a positive result for nitrogen in Lassaigne’s test, the compound must contain a carbon-nitrogen bond. During fusion with sodium, nitrogen forms cyanide ions (\( \text{CN}^- \)), which can be detected in subsequent steps.

Analyzing Each Compound:

Phenyl hydrazine (\( \text{C}_6\text{H}_5\text{NHNH}_2 \)): Contains a carbon-nitrogen bond and will give a positive result for Lassaigne’s test.

Glycine (\( \text{NH}_2\text{CH}_2\text{COOH} \)): Contains a carbon-nitrogen bond in the amino acid structure and will give a positive result for Lassaigne’s test.

Urea (\( \text{NH}_2\text{CONH}_2 \)): Contains a carbon-nitrogen bond in the amide linkage and will give a positive result for Lassaigne’s test.

Hydrazine (\( \text{NH}_2\text{NH}_2 \)): Does not contain any carbon atoms; therefore, it cannot form \( \text{NaCN} \) and does not give a positive Lassaigne’s test for nitrogen.

Conclusion:

Hydrazine does not contain a carbon-nitrogen bond and hence does not give Lassaigne’s test.
The correct answer is Option (4).