Lassaigne's Test - QS Study
QS Study

Lassaigne’s Test: Nitrogen, Sulphur and halogens are detected in any organic compound by Lassaigne’s test. It is a general test for the detection of halogens, nitrogen and sulphur in an organic compound. These elements are covalently bonded to the organic compounds. In order to detect them, these have to be converted into their ionic forms. This is done by fusing the organic compound with sodium metal.

Principle: In Lassaigne’s test, the organic compound is fused with sodium to form ionic compounds & an aqueous solution is made. The aqueous solution obtained by extracting the fused mass in H2O— is called solution extract or Lassaigne’s extract/Stock solution. An organic compound containing C. H, N, S, X when fused with Na metal gives the following reactions:

Why Sodium (Na) is used in Lassaigne’s test?

  1. It is highly reactive
  2. It is cheap
  3. The salts of Na are highly water soluble

Estimation of S & P can be done together by callus method.

Estimation of Sulphur:

  • It is estimated by modified Caries method.
  • Estimation of Halogen: The amount of halogen person in an organic compound is estimated by Carius method.