Picric acid from Phenol Synthesis: Pharmaceutical Chemistry Practical D Pharm
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Aim:
To synthesize Picric acid from phenol and to find out its percentage yield and melting point.
Apparatus:
Glassware:
Flat bottom flask (500ml), Condenser, Beaker (250ml) Beaker (500ml), Buchner’s flask and funnel; Vacuum pump, 25 ml measuring cylinder, 10 ml graduate pipette, Thiel’s tube, Capillary.
Chemicals:
Phenol, Con. Sulphuric acid, Con. Nitric acid, Alcohol: Water mixture (2:1), Ice.
Theory:
Nitration
Nitration is the process in which hydrogen atom is replaced by nitro group.(NO₂).Phenol being an activated nucleus towards Electrophilic aromatic substitution the nitration, sulphonation or halogenation reaction occurs very easily. It under goes nitration with dilute nitric acid even at room temperature.
Phenols when treated with concentrated nitric acid in presence of concentrated sulphuric acid, undergoes nitration at both ortho and para position to give picric acid.It is better if phenol is first converted to phenol sulphonic acid by treatment with sulphuric acid and then nitrated with concentrated nitric acid, when the- S0 H (sulphonicacid) groups are replace by-N02(nitro)groups.
Procedure:
1. Weigh 4 g of phenol (or take 5.0 ml of liquefied phenol) and place in 500 ml bottom flask.
2. Add 5.0 ml Con. sulphuric acid and mix thoroughly. As there action is exothermic, mixture becomes warm.
3. Heat the flask on water bath for 30 minutes to complete the formation of phenol sulphonic acid. Cool the flask thoroughly in ice-water mixture.
4. Place the flask on wooden surface infume cupboard and add immediately 15ml of con nitric acid and mix toughly by shaking for few seconds.
5. A vigorous reaction take place and harmless red nitrous fumes comes out from the flask.
6. After the reaction subsides, heat the flask on boiling water bath for 1-2 hours with constant shaking. Initially a heavy oily layer is formed, which gets converted to crystalline mass.
7. Add about 50 ml cold water and chill the mixture in ice-cold water.
8. Collect the product on Buchners funnel by vacuum filtration, wash thoroughly with cold water till free from acidity and drain completely.
9. Recrystallize the product from alcohol water mixture (2:1) (about 50 ml solvent is required).
10. Filter off the crystalline material at pump and dry by pressing between filter paper.
Precautions:
1. Sulphuric Acid & nitric acid are very strong acids and corrosive; therefore, handle them carefully to avoid acid burns.
2. Perform the reaction fume cupboard.
3.Do not dry the product in the oven.
Observations:
1. Amount of phenol taken for synthesis = 4g
2. Practical yield of the recrystallized product =
3. Melting point of the product=
Calculations :
1. Theoretical Yield of the product. From the reaction, 94g of phenol gives 229g of picric acid 4g of phenol will give 9.74g of picric acid
2. Percentage Practical Yield
%Yield= Practical Yield/ Theoretical Yield × 100
= __________________________%
Results:
1. Percentage yield of Picric acid __________________%
2. Melting point of Picric acid is________________
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