Detection of Nitrogen, Halogens and Sulphur by Lassaigne's Test
Lassaigne's test is the most reliable test for the detection of nitrogen, halogens and sulphur in an organic compound.
The compound is heated with sodium metal to convert the elements present in the organic compound into the water-soluble salts of sodium. Sodium is fused with the organic compound and then the fused mass is extracted with water. The extract is filtered and the filtrate is called sodium extract or Lassaigne's filtrate. Nitrogen, if present in the compound, is converted into NaCN in Lassaigne's filtrate. Halogens form a salt of sodium, such as NaCl, NaBr or NaI, while sulphur forms sodium sulphide (Na2S) on fusion of the organic compound with sodium
Na + C + N NaCN
Na + Cl NaCl
Na + Br NaBr
Na + I NaI
2Na + S Na2S