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

Lassaigne’s Test Explained:

Lassaigne’s test is employed to identify nitrogen, sulfur, and halogens within organic compounds. This method involves fusing the compound with sodium, transforming these elements into their ionic counterparts (e.g., sodium cyanide, \( \text{NaCN} \), for nitrogen).

Lassaigne’s Test Requirement:

A positive Lassaigne’s test for nitrogen is contingent on the presence of a carbon-nitrogen bond in the compound. During sodium fusion, nitrogen is converted to cyanide ions (\( \text{CN}^- \)), which are subsequently detectable.

Compound Analysis:

Phenylhydrazine (\( \text{C}_6\text{H}_5\text{NHNH}_2 \)): Possesses a carbon-nitrogen bond, yielding a positive Lassaigne’s test result.

Glycine (\( \text{NH}_2\text{CH}_2\text{COOH} \)): Features a carbon-nitrogen bond within its amino acid structure, resulting in a positive Lassaigne’s test.

Urea (\( \text{NH}_2\text{CONH}_2 \)): Contains a carbon-nitrogen bond in its amide linkage, leading to a positive Lassaigne’s test.

Hydrazine (\( \text{NH}_2\text{NH}_2 \)): Lacks carbon atoms. Consequently, it cannot form \( \text{NaCN} \) and therefore produces a negative Lassaigne’s test for nitrogen.

Conclusion:

Hydrazine does not contain a carbon-nitrogen bond and consequently fails to yield a positive Lassaigne’s test.
The correct answer is Option (4).