Test for Sulphur in Organic Compounds

Sulphur present in an organic compound is detected by Lassaigne’s test. The element present in the compound is converted from covalent form into the ionic form by fusing the compound with sodium metal.

Sulphide of sodium so formed on sodium fusion is extracted from the fused mass by boiling it with distilled water. This extract is known as sodium fusion extract.

The sodium fusion extract is acidified with acetic acid and lead acetate is added to it. A black precipitate of lead sulphide indicates the presence of sulphur. On treating sodium fusion extract with sodium nitroprusside, appearance of a violet colour further indicates the presence of sulphur.