Important Distinguish between organic pairs

Class XII Chemistry Distinguish between organic pairs

Lucas test

• Used to distinguish primary, secondary and tertiary alcohols.

• Lucas reagent – equimolar mixture of conc. HCl and anhydrous ZnCl2

• Alcohol is treated with Lucas reagent, turbidity due to the formation of insoluble alkyl chloride is observed.

• If the turbidity appears immediately, the alcohol is tertiary.

• If the turbidity appears in about five minutes, the alcohol is secondary.

• A primary alcohol does not react with Lucas reagent at room temperature and hence no turbidity is formed.

Iodoform test

• Iodoform test is a test for the CH3-CO group and is characteristic for alcohols and methyl ketones

• Reagents- compounds containing CH3-CO or CH3-CH(OH) group, sodium hydroxide and iodine 

• Product formed- iodoform,(CHI3) which is a pale yellow in colour

Tollens’ test

• Given by aldehydes and formic acid.

• Tollen’s reagent- ammoniacal silver nitrate solution 

• The aldehydes are oxidised to corresponding carboxylate anion.The reaction occurs in alkaline medium.

• A bright silver mirror is produced due to the formation of silver metal.

• Also known as Silver mirror test.

Fehling’s test

• Fehling reagent comprises of two solutions,

• Fehling solution A and Fehling solution B

• Fehling solution A is aqueous copper sulphate 

• Fehling solution B is alkaline sodium potassium tartarate (Rochelle salt).

• On heating an aldehyde with Fehling’s reagent, a reddish brown precipitate is obtained

this test is not given by benzaldehyde

Azo dye test

• It involves the reaction of any aromatic primary amine with nitrous acid followed by treatment with an alkaline solution of 2-naphthol, when a brilliant yellow , orange or red coloured dye is obtained.

• Used to distinguish between aliphatic primary amine and aromatic primary amine.

Hinsberg’s test

• Used for distinguishing primary, secondary and tertiary amines.

• Hinsberg’s reagent- benzenesulphonyl chloride (C6H5SO2Cl)

• In this test amine is shaken with Hinsberg’s reagent in presence of excess of aqueous KOH solution.

• A primary amine gives a clear solution which on acidification gives an insoluble N-alkylbenzenesulphonamide.10

• A secondary amine gives an insoluble N,N-dialkylbenzenesulphonamide which remains unaffected on addition of acid.

• A tertiary amine does not react at all. Therefore, it remains insoluble in the alkaline solution but dissolves on acidification to give a clear solution.

Carbylamine test-

only Primary aliphatic and aromatic amines are treated with chloroform and KOH . they produce isocynide (RNC) compound having foul smells.

Sodium bicarbonate test-

Carboxylic acids react with NaHCO3 with Brisk effeverscene and librates CO2 gas passed lime water becomes milky due to formation of calcium carbonates.futher more passed through it. its milkiness disappears due to formation of calcium bicarbonate 

while phenol being acidic it does not give this test because phenol is weak acid than carboxylic acids(carboxylic acids having most stable resonating structures)

Ferric chloride tests FeCl3.- phenol reacts with FeCl3 ,forms purple/violet coloured complex 

The given organic samples are teated with ferric chlorides If the sample turns to red, green, purple, or blue colouration then it indicates the presence of phenols and its derivatives.

Ferric chloride will not react with any aliphatic alcohol

Differentiate 

1. Phenol and benzoic acid

2. Butan-1-ol and 2-methylpropan-2ol

3. CH3CH2NH2 and(CH3)2NH

4. Ethyl amine and diethyl amine

5. Propan-1-ol and propan-2-ol

6. Methyl ethanoate and ethyl ethanoate

7. Aniline and N-ethyl aniline

8.  N methyl propane-2 amine and N -ethyl-N methyl ethanmine

9. Aniline and benzylamine

10. Ethylamine and Aniline