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Preparation of phenols

  1. Dow’s process
     
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  2. By nucleophilic substitution of aryl halides
     
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  3. By fusing sodium arylsulphonates with NaOH
     
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  4. By steam distillation of diazonium salts
     
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  5. From Grignard reagents
     
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  6. From cumene hydroperoxide
     
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Chemical properties

  1. Acylation
     
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  2. Fries rearrangement
     
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  3. Reaction with benzoyl chloride
     
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  4. Bromination: Phenol on treatment with chlorine or bromine water gives an immediate precipitate of 2,4,6-trihalogen derivative.
     
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    If the halogenation is carried out in non-aqueous medium such as CS2 or CCl4, only monosubstitution takes place.
     
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  5. Nitration:
     
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  6. Friedel–Crafts reaction
     
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  7. Kolbe’s reaction: Sodium phenoxide is heated with carbon dioxide at 120–140°C under pressure to yield sodium salicylate, which upon acidification produces salicylic acid.
     
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    A small amount of p-derivative is also formed. If the temperature rises above 140°C, the p-isomer is the main product.
     
    Mechanism
     
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    Salicylic acid is used for the preparation of Aspirin, oil of winter green (methyl salicylate), and salol (phenyl salicylate).
  8. ReimerTiemann reaction: An alkaline solution of phenol is refluxed with chloroform at 60°C, distilling off the excess of chloroform and acidifying the residual liquid with sulphuric acid. As a result, o-hydroxybenzaldehyde and p-hydroxybenzaldehyde are formed, which are separated by steam distillation.
     
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    Mechanism
     
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  9. Gattermann’s reaction:
     
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  10. Liebermann test: When phenol is dissolved in concentrated sulphuric acid and a few drops of aqueous sodium nitrite is added, a red color is obtained on dilution and turns blue when aqueous sodium hydroxide is added.




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