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  4. Which of the following compounds will give red colour on Lassaigne test?

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Q. Which of the following compounds will give red colour on Lassaigne test?

UPSEEUPSEE 2011Organic Chemistry – Some Basic Principles and Techniques

Solution:

When nitrogen and sulphur both are present in the organic compound, they combine during fusion to form sodium thiocyanate (sulphocyanide). This when heated with $FeSO _{4}$ or $FeCl _{3}$, produces a red blood colouration due to ferric thiocyanate (or sulphocyanide). Thus, thiourea and $p$ -aminobenzene sulphonic acid give red colour on Lassaigne test.

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