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Organic Chemistry

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Detection Of Functional Group

a) Test for Hydroxyl group (alcoholic and phenolic): Alcohol is treated as a neutral compound, and they are soluble in water or dioxane.

  • Sodium test:

  • Ceric ammonium nitrate test: For alcohol less than ten carbon, this test is useful.

The following tests are for a phenolic compound.

  • Neutral FeCl3 test: phenols on reaction with neutral ferric chloride solution, they form coloured complexes of violet, red, blue or green colour. This is due to the enolic group (=C-OH).
  • Bromine water test:

  • Ceric ammonium nitrate test:  

  • Liebermann’s test: Small amount of compound is fused with NaNO2 in a test tube, then cool the test tube and add H2SO4. A deep green colour is found, and when poured more than water, green colour changes to red. Finally, a little NaOH solution is added in aq. The answer, the deep blue coloured, is seen in the solution.

b) Test for carbonyl (aldehyde and ketone):

1)Aldehyde:

  • Fehling’s test:

  • Tollen’s test:

  • Schiff's Analysis:

2) Ketone: Unlike aldehydes, they do not restore the pink colour of the Schiff’s reagent, nor they reduce Fehling’s reagent or ammoniacal silver nitrate solution. A red or yellow crystalline ppt with 2,4-dinitrophenylhydrazine and also with sodium bisulphite reagent.

Ketones add on sodium hydrogen sulphite to form crystalline bisulphite compounds.

c)Tests for carboxylic acid:

  • Sodium bicarbonate test: On addition to a small amount of organic compound to sodium bicarbonate solution taken in a test tube. Compound dissolves with brisk effervescences.

d)Test for an amino group:

  • The carbylamine test: Only primary amine reacts with chloroform and alc. A solution of NaOH or KOH to give evil smell compound isocyanide compound, i.e. carbylamine compound.

20 and 30 amines do not give this test.

  • The nitrous acid test: amine reacts with to give different products, as follows:

 

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