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 a hydrogen atom is replaced by a nitro group. (NO₂). Phenol being an activated nucleus towards Electrophilic aromatic substitution the nitration, sulphonation, or halogenation reaction occurs very easily. It undergoes nitration with dilute nitric acid even at room temperature.
Phenols when treated with concentrated nitric acid in the presence of concentrated sulphuric acid, undergo 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 (sulphonic acid) groups are replaced by N02 (nitro) groups.
Procedure:
1. Weigh 4 g of phenol (or take 5.0 ml of liquefied phenol) and place in a 500 ml bottom flask.
2. Add 5.0 ml Con. sulphuric acid and mix thoroughly. As their action is exothermic, the mixture becomes warm.
3. Heat the flask in a water bath for 30 minutes to complete the formation of phenol sulphonic acid. Cool the flask thoroughly in an ice-water mixture.
4. Place the flask on a wooden surface in a fume cupboard and add immediately 15ml of con nitric acid and mix toughly by shaking for a few seconds.
5. A vigorous reaction takes place and harmless red nitrous fumes come out from the flask.
6. After the reaction subsides, heat the flask in a boiling water bath for 1-2 hours with constant shaking. Initially, a heavy oily layer is formed, which gets converted to a crystalline mass.
7. Add about 50 ml of 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 the alcohol-water mixture (2:1) (about 50 ml solvent is required).
10. Filter off the crystalline material at the 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________________
Frequently Asked Questions (FAQs)
Picric acid is a well-known aromatic compound with various applications in chemistry, industry, and explosives. Here are some frequently asked questions about the structure of picric acid:
Picric acid, also known as 2,4,6-trinitrophenol (TNP), is a powerful and highly explosive yellow crystalline compound. It is primarily used as a yellow dye, a reagent in analytical chemistry, and in the manufacture of explosives.
The chemical formula of picric acid is C6H3N3O7.
The molecular weight of picric acid is approximately 229.11 g/mol.
The structure of picric acid consists of a phenol ring (a benzene ring with a hydroxyl group) that is substituted with three nitro (NO2) groups. The nitro groups are located at positions 2, 4, and 6 on the phenol ring.
Yes, picric acid is an aromatic compound due to the presence of a benzene ring in its structure.
Picric acid is known for its brilliant yellow color, high melting point, and explosive nature under certain conditions. It is sparingly soluble in water but more soluble in organic solvents.
Picric acid can be synthesized through the nitration of phenol with a mixture of concentrated nitric acid and sulfuric acid. The process involves substituting hydrogen atoms on the phenol ring with nitro groups.
Picric acid has various uses, including:
A yellow dye for textiles and wood.
An explosive component in military and industrial applications.
A reagent for the determination of metals in analytical chemistry (forming highly colored complexes).
An antiseptic agent (historically used).
Picric acid is explosive due to its highly reactive nitro groups. It can form sensitive explosive salts under certain conditions, making it hazardous and requiring careful handling.
Picric acid is highly sensitive to shock, friction, and heat. It should be handled with extreme caution, stored away from other chemicals, and stored in a cool and dry place.
Yes, picric acid can form explosive salts, such as picrate salts, which are highly sensitive and hazardous.
Picric acid should be disposed of through established hazardous waste disposal procedures, as it is considered a hazardous substance. Consult local regulations and guidelines for proper disposal methods.
Yes, there are alternatives to picric acid for various applications. For example, safer dyes are available for coloring purposes, and less sensitive explosives are used in military and industrial applications.
Picric acid and its derivatives can pose environmental risks due to their explosive nature and potential for soil and water contamination. Proper handling, storage, and disposal are essential to mitigate these risks.
Understanding the structure of picric acid is important for both its practical applications and for ensuring safe handling and storage due to its explosive properties. Always follow proper safety protocols when working with picric acid or any other hazardous chemicals.
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