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Questions and Answers
Phenol reduce ______ solution and undergo oxidation to quinones.
pot.Permanganate
The manganese is reduced from +7, which gives a ______ solution, to +4, which is brown.
purple
Add 0.1 g or 0.2 ml (3-4 drops) of the compound to 2 ml of ______ or ethanol.
water
The disappearance of the ______ colour and the formation of brown suspension, which is manganese (II) oxide, at the bottom of the test tube is a positive result for the presence of phenols.
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On adding an excess, a ______ or yellowish – white precipitate of a poly bromo-derivative is produced with all except hydroquinone and α and β naphthol.
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Study Notes
Phenol Structure and Properties
- Phenols are organic compounds with a hydroxyl group attached directly to a benzene ring or substituted benzene, with the general formula Ar-OH.
- Phenol is a white crystalline solid that is volatile and mildly acidic.
- Phenols are generally colorless solids or liquids, but may appear light-colored due to oxidation by air in the presence of light.
- Phenols are soluble in water due to the formation of hydrogen bonds with water.
Physical and Chemical Properties
- Phenols have relatively high boiling points due to intermolecular hydrogen bonding.
- They are highly toxic in nature and possess antiseptic properties.
- Phenols burn with a yellow smoky flame due to the presence of an aromatic ring.
- Phenols are weak acidic compounds, soluble in strong alkaline solutions only (e.g., sodium hydroxide).
Reactions of Phenols
Reaction at the Phenolic Hydroxyl Group (-OH)
- Phenol reacts with sodium hydroxide to form sodium phenoxide.
- Phenol reacts with ethyl iodide to form ethyl phenyl ether.
Substitution at the Aromatic Ring
- Phenol reacts with bromine water to form a polybromo-derivative.
- Phenol reacts with diluted nitric acid to form a nitrophenol.
Identification Tests for Phenols
Ferric Chloride Test
- Phenol reacts with ferric chloride to give colored compounds due to the presence of the enol group.
- Procedure: Add 1 drop of ferric chloride solution to a very diluted solution of phenol or a few crystals of solid phenol dissolved in water.
Bromine Water Test
- Phenol reacts with bromine water to form a white or yellowish-white precipitate of a polybromo-derivative.
- Procedure: Add bromine water gradually to a concentrated aqueous solution of the phenol or to the phenol itself.
Potassium Permanganate Test
- Phenol reduces potassium permanganate solution, causing the manganese to be reduced from +7 to +4, resulting in a brown suspension.
- Procedure: Add the compound to 2 ml of water or ethanol, then add 2% aqueous potassium permanganate solution drop by drop with shaking until the purple colour of the permanganate persists.
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Description
Learn about phenols, a type of organic compound with a hydroxyl group attached to a benzene ring. Understand their general formula, physical and chemical properties, and examples of phenolic compounds. This quiz is perfect for students of Practical Organic Chemistry II.
