Question

Give reaction for test of sulphur with sodium nitroprusside in organic compound.

Answer 1

To detect elements like nitrogen, sulphur, and halogens in organic compounds, we use Lassaigne's Test. This test was invented by the French Chemist named J.L. Lassaigne.  

In this test, the organic compound that is under study is being fused with metallic sodium for converting the elements into sodium salts. These sodium salts would be soluble in water.

Now this extract would then undergo qualitative tests to detect the required element .

Now here, the test is for detecting sulphur in an organic compound. The preparation of Lassaigne's extract involves the fusion process of metallic sodium and the sulphur from organic compound. This reaction forms sodium sulphide.

$2Na\quad +\quad \underset { (from\quad organic\quad compound) }{ S } \longrightarrow { Na }_{ 2 }S$

This sodium sulphide gives deep violet colour when it reacts with sodium nitroprusside because the product formed due to the reaction is sodium thionitroprusside. This indicates the presence of sulphur.

$\underset { (from\quad sodium\quad extract) }{ { Na }_{ 2 }S } \quad +\quad \underset { (sodium\quad nitroprusside) }{ { Na }_{ 2 }[Fe{ (CN) }_{ 5 }NO] } \longrightarrow \underset { Deep\quad violet\quad colouration }{ { Na }_{ 4 }[Fe{ (CN) }_{ 5 }NOS] }$