Detection of Halogens in an Organic Compound There are many organic compounds containing
halogens such as: fluorine, chlorine, bromine and iodine. They are called organohalogen
compounds. Some commonly known examples are carbon tetrachloride, chlorofluoro carbons,
DDT, iodomethane and bromobenzene. Upon fusion with sodium metal, the halogens in the organic
compound are converted to ionic sodium halides. Ionic sodium halides can be extracted by boiling
the fused mass with distilled water and are used for the detection of halides. Our aim here is to detect the presence of
halogens in an organic compound. There are two tests to detect the presence
of halogens. They are: Silver nitrate test
Carbon disulphide test Silver Nitrate Test Materials Required: Lassaigne’s extract, concentrated nitric acid,
silver nitrate solution, ammonium hydroxide solution, test tube, droppers, test tube holder
and Bunsen burner Procedure: Take a small portion of Lassaigne’s extract
in a test tube. To this, add a small amount of concentrated
nitric acid using a dropper. Boil the contents of the test tube over a
Bunsen burner and cool. Using another dropper, add silver nitrate
solution to the test tube. If the organic compound contains chlorine,
the sodium chloride formed during fusion reacts with silver nitrate to form a white precipitate
of silver chloride. If the organic compound contains bromine,
the sodium bromide formed during fusion reacts with silver nitrate to form a pale yellow
precipitate of silver bromide. If the organic compound contains iodine, the
sodium iodide formed during fusion reacts with silver nitrate to form a yellow precipitate
of silver iodide. Now, using another dropper, add the excess
of ammonium hydroxide to the precipitates. Silver chloride is soluble in ammonium hydroxide. Silver bromide is sparingly soluble in ammonium
hydroxide. Silver iodide is insoluble in ammonium hydroxide. Carbon Disulphide Test Materials required: Lassaigne’s extract, dilute hydrochloric acid,
carbon disulphide, chlorine water, test tube and droppers. Procedure: Take a small portion of Lassaigne’s extract
in a test tube. Using a dropper, add a small amount of dilute
hydrochloric acid to acidify the Lassaigne’s extract.
Using another dropper, add a small amount of carbon disulphide to the test tube. Carbon
disulphide forms a separate layer above the Lassaigne’s extract.
Now add freshly prepared chlorine water using another dropper and shake the test tube vigorously.
If the organic compound contains bromine, the sodium bromide formed during fusion is
oxidized to bromine, which is dissolved in carbon disulphide and imparts orange colour
to the carbon disulphide layer. If the organic compound contains iodine, the
sodium iodide formed during fusion is oxidized to iodine, which is dissolved in carbon disulphide
and imparts violet colour to the carbon disulphide layer. Precautions: Handle the apparatus and chemicals carefully.
Use droppers to take reagents from the bottles.