Question

What are different distinguish test in organic chemistry in 12

Answer 1

Identification of functional groups:
Experiment
Observation
Inference
1. Action of sodium hydroxide solution
i) A little of the substance is boiled with dil.NaOH .

ii)Substance is boiled strongly with 20%NaOH solution. Then cooled & acidified with dil.HCl.
a. Ammonia is evolved.
b. Substance dissolved.
White crystalline ppt.
Presence of amides.
Presence of acidic substances.
Presence of aromatic amides.
2. Action of NaHCO3
To a few ml of the saturated NaHCO3solution taken in a test tube, a little of the substance is added.

Brisk effervescence with the liberation of CO2.

Presence of acids.

3. Action of FeCl3 solution.
To a little of the substance in water or alcohol a few drops of neutral FeCl3solution is added.

Violet colour.

Presence of phenols.

4. Action of Schiff’s reagent
A little of the substance is added to 1ml of the Schiff’s reagent.

Violet colour developed within 2 minutes.

Presence of aldehydes.
5. Action of Borsche’s reagent.
A little of the substance in methanol is heated with few drops of Borsches reagent in a water bath.

A yellowish orange ppt.


Presence of aldehydes or ketones.
6. Diazotisation
Dissolve a little of the sample in 2ml con HCl diluted with water& cool in ice. Dissolve sodium nitrite in water & add the solution dropwise to the cold solution nitrite in water & add the solution drop wise to the cold solution.

Rapid foaming.


Presence of primary aliphatic amines.



Tests for aldehydes:


1. Action of Tollen’s reagent:
A little of the substance is boiled with few drops of Tollen’s reagent.

Black ppt.

Presence of aldehydes

Tests for ketones:

1. Nitroprusside test:
Add a few drops of sodium nitroprusside solution to few drops of ketone. Then add NaOH solution in excess.

Wine red colour.

Presence of methyl ketones.

Test for acids:



Presence of dicarboxylic acid.
2. Anhydride formation:
A little of the acid is heated in a dry china dish covered with an inverted funnel whose stem is closed. It is then cooled.
White shiny needles are deposited on the sides of the funnel.
Presence of dicarboxylic acid

Tests for amides:

1. Biuret reaction:
A little of the substance is heated first gently in a dry test tube followed by strong heating. The solid residue is warmed with1 ml 10% NaOH then cooled and one drop of dil.CuSO4 added.

On heating smell of ammonia is evolved & violet colour on adding CuSO4.

Presence of diamide.



Test for aromatic amines (primary):

1. Confirmatory Tests for Functional Groups:

1. Add 2ml of cold diazonium solution to a solution of 0.1g 2 -naphthol in 2ml 10% NaOH. & 5 ml water.

Test for aliphatic amines (primary):

1.a. To 0.3 mL or 300 mg of unknown substance in a test tube add 5 mL of 10% NaOH solution and 0.4 mL of benzenesulfonyl chloride. Close the test tube with a cork and shake the mixture vigorously. Test the solution to make sure that it is still alkaline using litmus paper.
b. Cool the solution & add 10% HCl solution dropwise.


Soluble in base.

A precipitate is formed.


Presence of aliphatic primary amines.


Tests for aromatic alcohol (Phenol):

1. Azo-dye formation:
Dissolve two drops of aniline in 1 ml dil.HCl well cooled in ice. Few drops of saturated sodium nitrite solution are added. Then it is added to a well cooled solution of the phenolic compound in aqueous sodium hydroxide.

A red coloured substance is formed.

Presence of phenols.