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Chapter 2 Phenols

Chapter 2 Phenols. 1-Nomenclature of Phenols. Phenols are compounds that have hydroxyl group bonded directly to benzene ring. Named on basis of phenol as parent, substituents listed in alphabetical order. 2-Physical Properties.

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Chapter 2 Phenols

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  1. Chapter 2Phenols

  2. 1-Nomenclature of Phenols • Phenols are compounds that have hydroxyl group bonded directly to benzene ring. Named on basis of phenol as parent, substituents listed in alphabetical order.

  3. 2-Physical Properties 1-The OH group of phenols allows hydrogen bonding to other phenol molecules and to water. 2-Compared to compounds of similar size and molecular weight, hydrogen bonding in phenol raises its melting point, boiling point, and solubility in water.

  4. O O H Hydrogen Bonding of Phenols

  5. Hydrogen Bonding with Water

  6. 3- Acidity of Phenols • Most characteristic property of phenols is their acidity. • Phenols(pKa = 10) are more acidic than alcohols(pKa = 16-20) but less acidic than Carboxylic acids (pKa = 5).

  7. To explain why, let’s compare the ionization of Ethanol and Phenols

  8. Substituent Effects on the Acidity of Phenols. 1-Electron-releasing groups ( CH3, OCH3) have little or no effect. 2-Electron-withdrawing groups ( NO2, Cl, OH) increase acidity. 3- Multiple substituent of electron- withdrawing group greatly increase acidity of phenols.

  9. Electron-releasing groups have little or no effect. Electron-withdrawing groups increase acidity.

  10. Effect of electron-withdrawing groups is mostpronounced at ortho and para positions. Effect of strong electron-withdrawing groups is cumulative.

  11. 4-Sources of Phenols • Phenols was first isolated from coal tar. • Phenol is an important industrial chemical. • Major use is in phenolic resins for adhesives and plastics.

  12. Industrial preparation of Phenols

  13. Laboratory Synthesis of Phenols

  14. 5- Reactions of Phenols A hydroxyl group is very powerful activating substituent, and electrophilic aromatic substitution in phenol occurs far faster, and under milder condition, than in benzene. a- Halogenation

  15. b- Sulfonation

  16. c- Nitration d- Nitrosation

  17. d-Friedal Crafts Alkylation e-Friedal Crafts Acylation

  18. In the absence of ALCL3, However O-acylation occurs instead.

  19. f- Reaction with arenediazonium salts.

  20. 6- Aspirin and the Klobe – Schmitt Reaction.

  21. Preparation of Salicylic Acid This reaction is called the Kolbe- Schmitt reaction. Acidification coverts the sodium salt shown above to salicylic acid.

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