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24.6 Sources of Phenols

24.6 Sources of Phenols. Phenol is an important industrial chemical. Major use is in phenolic resins for adhesives and plastics. Annual U.S. production is about 4 billion pounds per year. CH(CH 3 ) 2. Cl. SO 3 H. 1. NaOH heat. 2. H +. 1. O 2. 1. NaOH heat.

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24.6 Sources of Phenols

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  1. 24.6Sources of Phenols • Phenol is an important industrial chemical. • Major use is in phenolic resins for adhesives and plastics. • Annual U.S. production is about 4 billion pounds per year.

  2. CH(CH3)2 Cl SO3H 1. NaOH heat 2. H+ 1. O2 1. NaOH heat 2. H2O H2SO4 OH 2. H+ IndustrialPreparationsof Phenol

  3. 1. NaNO2, H2SO4, H2O O2N O2N NH2 OH 2. H2O, heat Laboratory Synthesis of Phenols • from arylamines via diazonium ions (81-86%)

  4. 24.7Naturally Occurring Phenols • Many phenols occur naturally

  5. Example: Thymol OH CH3 CH(CH3)2 Thymol(major constituent of oil of thyme)

  6. Example: 2,5-Dichlorophenol OH Cl Cl 2,5-Dichlorophenol(from defensive secretion ofa species of grasshopper)

  7. 24.8Reactions of Phenols:Electrophilic Aromatic Substitution Hydroxyl group strongly activates the ringtoward electrophilic aromatic substitution

  8. Electrophilic Aromatic Substitution in Phenols • Halogenation • Nitration • Nitrosation • Sulfonation • Friedel-Crafts Alkylation • Friedel-Crafts Acylation

  9. OH OH ClCH2CH2Cl 0°C Br Halogenation • monohalogenation in nonpolar solvent(1,2-dichloroethane) + Br2 (93%)

  10. OH OH Br Br F F Br Halogenation • multiple halogenation in polar solvent(water) H2O + 3Br2 25°C (95%)

  11. Electrophilic Aromatic Substitution in Phenols • Halogenation • Nitration • Nitrosation • Sulfonation • Friedel-Crafts Alkylation • Friedel-Crafts Acylation

  12. OH OH NO2 HNO3 acetic acid5°C CH3 CH3 Nitration • OH group controls regiochemistry (73-77%)

  13. Electrophilic Aromatic Substitution in Phenols • Halogenation • Nitration • Nitrosation • Sulfonation • Friedel-Crafts Alkylation • Friedel-Crafts Acylation

  14. OH NaNO2 H2SO4, H2O0°C Nitrosation NO • only strongly activated rings undergo nitrosation when treated with nitrous acid OH (99%)

  15. Electrophilic Aromatic Substitution in Phenols • Halogenation • Nitration • Nitrosation • Sulfonation • Friedel-Crafts Alkylation • Friedel-Crafts Acylation

  16. OH OH H3C CH3 H3C CH3 Sulfonation • OH group controls regiochemistry H2SO4 100°C SO3H (69%)

  17. Electrophilic Aromatic Substitution in Phenols • Halogenation • Nitration • Nitrosation • Sulfonation • Friedel-Crafts Alkylation • Friedel-Crafts Acylation

  18. OH OH CH3 CH3 (CH3)3COH H3PO460°C CH3 C H3C CH3 Friedel-Crafts Alkylation • (CH3)3COH reacts with H3PO4 to give (CH3)3C+ (63%)

  19. Electrophilic Aromatic Substitution in Phenols • Halogenation • Nitration • Nitrosation • Sulfonation • Friedel-Crafts Alkylation • Friedel-Crafts Acylation

  20. 24.9Acylation of Phenols Acylation can take place either on the ringby electrophilic aromatic substitution or onoxygen by nucleophilic acyl substitution

  21. OH OH O CH3CCl C CH3 O Friedel-Crafts Acylation • under Friedel-Crafts conditions, acylation of the ring occurs(C-acylation) + ortho isomer AlCl3 (74%) (16%)

  22. O OH OC(CH2)6CH3 O + CH3(CH2)6CCl O-Acylation • in the absence of AlCl3, acylation of the hydroxyl group occurs (O-acylation) (95%)

  23. O OH OC(CH2)6CH3 C CH3 O O- versus C-Acylation • O-Acylation is kinetically controlled process; C-acylation is thermodynamically controlled • AlCl3 catalyzes the conversion of the aryl ester to the aryl alkyl ketones; this is called the Fries rearrangement AlCl3 formed faster more stable

  24. O OCCH3 COH O 24.10Carboxylation of Phenols • Aspirin and the Kolbe-Schmitt Reaction

  25. O O O OH OCCH3 CH3COCCH3 COH COH O O Aspirin is prepared from salicylic acid • how is salicylic acid prepared? H2SO4

  26. OH ONa CONa O Preparation of Salicylic Acid CO2 • called the Kolbe-Schmitt reaction • acidification converts the sodium salt shownabove to salicylic acid 125°C, 100 atm

  27. •• •• – O H O •• •• •• •• – C O •• •• O •• •• What Drives the Reaction? • acid-base considerations provide an explanation:stronger base on left; weaker base on right + CO2 stronger base: pKa of conjugate acid = 10 weaker base: pKa of conjugate acid = 3

  28. OH ONa CONa O Preparation of Salicylic Acid CO2 • how does carbon-carbon bond form? • recall electron delocalization in phenoxide ion • negative charge shared by oxygen and by the ring carbons that are ortho and para to oxygen 125°C, 100 atm

  29. – •• •• O O •• •• •• H H – H H •• H H H H H H •• •• O O •• •• H H – H H •• •• H H – H H H H

  30. •• O •• – •• O •• •• C O H •• •• •• O H •• •• – C O •• •• O •• •• Mechanism of ortho Carboxylation •• O •• – •• C O •• •• O •• •• H

  31. – •• O •• •• •• •• O H O H •• •• •• – – •• C O C O •• •• •• •• O •• •• O •• •• stronger base: pKa of conjugate acid = 4.5 weaker base: pKa of conjugate acid = 3 Why ortho?Why not para?

  32. O H – O C O Intramolecular Hydrogen Bondingin Salicylate Ion Hydrogen bonding between carboxylate and hydroxylgroup stabilizes salicylate ion. Salicylate is less basic than para isomer and predominates under conditionsof thermodynamic control.

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