Detection of Nitrogen,Sulphur and Halogens in Organic Compounds

Revison points


Detection of Elements (N,S, halogens)

Lassaigne test is used for this.

First sodium extract of the given organic compound is prepared.
A pea sized dry piece of sodium metal (freshly cut) is taken in an ignition tube and the tube is heated to melt the sodium metal piece to shining globule. Then a pinch of the organic compound is introduced in the tube. Then the tube is further heated first gently and strongly till the lower end of the tube becomes red hot. The tube is then plunged and broken in about 20 ml. of distilled water taken in porcelain dish. The solution is boiled for about 5 minutes and filtered. The filtrate obtained is known as sodium extract.



Test for Nitrogen

To 2ml of sodium extract, a little ferrous sulphate is added. The solution is boiled and a little dilute sulphuric acid is added. Appearance of prussian blue or green colouration indicates the presence of nitrogen in the compound.

Test for sulphur

if sodium extract is acidified, H2S is formed.

Halogens are identified by treating the acqeous solution of sodium extract by silver ion reagent. It will precipitate halogens.

Down a note on this topic

http://www.bibliobase.com/Chemistry/Hall/pdf_doc/37.pdf