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Aim:
Systematically identify the functional groups in the given organic compound and perform the confirmatory tests after identifying the functional groups.
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Reactions of amides:
Amides are decomposed by NaOH to evolve ammonia. The gas can be tested by a moist red litmus paper which is then turned blue.
![](http://vlab.amrita.edu/userfiles/1/1456300104_eq 1.png)
- Alkaline hydrolysis of aromatic amides to aromatic acid:
The soluble sodium salt of aromatic acid formed from aromatic amides upon hydrolysis is regenerated as white precipitate in acidic medium.
![](http://vlab.amrita.edu/userfiles/1/1456300661_eq 2.png)
- Biuret Reaction for aliphatic diamide:
When aliphatic diamide is heated at a temperature above its melting point, ammonia is evolved and crystalline biuret is formed. This biuret in alkaline medium gives a violet colour with a drop of copper sulphate solution.
![](http://vlab.amrita.edu/userfiles/1/1456303935_eq3.png)
Biuret reaction
- Hydroxamic acid test for aromatic primary amides:
Hydrogen peroxide reacts with aromatic primary amides to form the hydroxamic acid, which then reacts with ferric chloride to form ferric hydroxamate complex having a violet colour.
![](http://vlab.amrita.edu/userfiles/1/1456305445_eq4.png)
![](http://vlab.amrita.edu/userfiles/1/1456305935_Eq5.png)
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Reactions of carboxylic acids:
Carboxylic acids being acidic dissolves in NaOH to form sodium salt.
![](http://vlab.amrita.edu/userfiles/1/1456307802_eq6.png)
Forms salt with sodium bicarbonate solution with the evolution of carbon dioxide.
![](http://vlab.amrita.edu/userfiles/1/1456308166_eq7.png)
The anhydrides of aromatic 1,2-dicarboxylic acids on heating with resorcinol gives a dye fluorescein. This dye in NaOH solution gives a yellowish red solution with green fluorescence.
![](/userfiles/1/image/noname01(1).png)
Aromatic 1,2-dicarboxylic acids decomposes to give its anhydride when heated at its melting point.
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Reactions of phenols:
- Reaction of neutral ferric chloride solution:
Phenol form characteristic coloured iron complexes when treated with neutral ferric chloride solution. E.g. phenol & resorcinol - violet colour, catechol-green etc.
![](http://vlab.amrita.edu/userfiles/1/1456309100_eq8.png)
Aryldiazonium salts react with aromatic rings of phenols to form highly coloured azo compounds. These reactions are called coupling reactions.
![](/userfiles/1/image/hij.JPG)
Phenols react with benzoyl chloride in presence of NaOH, to form esters.
![](http://vlab.amrita.edu/userfiles/1/1456310213_eq9.png)
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Reactions of primary amines:
At low temperature (0-5oC) aromatic primary amines dissolved in strong acids (HCl & H2SO4) reacts with nitrous acid (NaNO2 +HCl) to form water soluble diazonium salts.
Aliphatic primary amines do not form stable diazonium salts under similar condition. They react with nitrous acid to yield alcohols and nitrogen (causes rapid foaming).
![](http://vlab.amrita.edu/userfiles/1/1456310840_eq11.png)
- Azo dye formation for aromatic primary amines:
Aryldiazonium salts react with aromatic rings of phenols to form highly coloured azo compounds. These reactions are called coupling reactions.
![](/userfiles/1/image/klm.JPG)
Primary aromatic amines react with benzoyl chloride in presence of NaOH, replacing the H atom attached to the N atom with the benzoyl group to give anilides.
![](http://vlab.amrita.edu/userfiles/1/1456311172_eq12.png)
Hinsberg reagent is called benzenesulfonyl chloride. Primary aliphatic amines on reaction with benzenesulfonyl chloride & NaOH gives N-alkylsulphonamide which contains an acidic hydrogen and hence dissolve in NaOH solution to form the soluble sodium salt. The solution thus obtained on acidification gives a precipitate of free sulfonamide which is insoluble in HCl.
![](/userfiles/1/image/abc%281%29.jpg)
5. Reactions of aldehydes:
Action of Schiff’s reagent:
Schiff’s reagent is a red solution of rosaniline hydrochloride dissolved in water which is decolourised by passing sulphur dioxide.
Dilute solutions of aldehydes when added to Schiff’s reagent restores its red colour slowly.
![](/userfiles/1/image/hij%281%29.jpg)
Action of Borsche’s Reagent:
Aldehydes reacts with 2,4-dinitrophenyl hydrazine solution to give a orange/red precipitate of aldehyde 2,4-dintrophenylhydrazone derivative.
Action of Tollen’s Reagent:
Aldehydes are oxidized to carboxylic acids accompanied by the reduction of silver ions to metallic silver which appears as a mirror under proper conditions.
![](http://vlab.amrita.edu/userfiles/1/1456553196_eq14.png)
Action of sodium bisulphite solution:
Saturated solution of sodium bisulphite in water, when mixed with aldehydes gives a white crystalline bisulphite addition compounds.
![](/userfiles/1/image/acr.JPG)
6. Reactions of ketones:
Action of Borsche’s Reagent:
Ketones reacts with 2, 4 dinitrophenyl hydrazine solution to give an orange/red precipitate of ketone 2,4 dintrophenylhydrazone derivative.
![](/userfiles/1/image/jisha/fun.JPG)
Action of sodium nitroprusside solution:
The nitroprusside ion, which may be regarded as a special carrier of the nitrosonium ion, forms a coloured complex with methyl ketones. In presence of alkali eg acetone is converted to CH3COCH2- ion which reacts with nitroprusside ion [Fe(CN)5NO]2- to give highly coloured ion [Fe(CN)5NOCH2COCH3]2-.
![](http://vlab.amrita.edu/userfiles/1/1456552992_eq13.png)
Identification of functional groups:
Experiment
No |
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.
c. 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 NaHCO3 solution 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 FeCl3 solution 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:
Action of Tollen’s reagent:
A little of the substance is boiled with few drops of Tollen’s reagent.
|
Black ppt.
|
Presence of aldehydes
|
Action of sodium bisulphite solution:
Two drops of the aldehyde is shaken with saturated solution of NaHSO3
|
White crystalline ppt.
|
Presence of aldehydes.
|
Tests for ketones:
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:
Fluorescein Reaction:
A little of the substance is heated with Conc.H2SO4 & Resorcinol in a dry test tube. It is cooled & then poured into a beaker containing excess of NaOH.
|
A red solution with intense green fluorescence.
|
Presence of dicarboxylic acid.
|
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:
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.
|
Hydroxamic acid test:
Place a little of the substance in 5mL water. Add few drops 3% hydrogen peroxide and 2 drops of 5% ferric chloride. Heat the solution.
|
Magenta colour.
|
Presence of aromatic primary amide.
|
Test for aromatic amines (primary):
- Confirmatory Tests for Functional Groups:
Add 2mL of cold diazonium solution to a solution of 0.1g 2 -naphthol in 2ml 10% NaOH. & 5 mL water.
|
Orange –red dye.
|
Presence of aromatic amines.
|
Benzoylation:
Dissolved a little of the substance in 10mL 10% NaOH solution contained in a boiling tube. About 1mL of benzoyl chloride is added. The boiling tube is corked and shaken vigorously for about 15 minutes.
|
A white ppt is formed.
|
Presence of aromatic amines.
|
Test for aliphatic amines (primary):
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.
|
Soluble in base.
|
Presence of aliphatic primary amines.
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Cool the solution & add 10% HCl solution dropwise.
|
A precipitate is formed.
|
Presence of aliphatic primary amines.
|
Tests for aromatic alcohol (Phenol):
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.
|
Benzoylation:
Dissolved a little of the substance in 5mL 20% NaOH solution contained in a boiling tube. About 1mL of benzoyl chloride is added. The boiling tube is corked and shaken vigorously for about 15 minutes.
|
A precipitate is formed.
|
Presence of phenols.
|