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24.11 Preparation of Aryl Ethers

24.11 Preparation of Aryl Ethers. O Na. O R. Typical Preparation is by Williamson Synthesis. S N 2. +. +. Na X. R X. O Na. O R. +. X. R O Na. Typical Preparation is by Williamson Synthesis. S N 2. +. +. Na X. R X. but the other combination.

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24.11 Preparation of Aryl Ethers

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  1. 24.11Preparation of Aryl Ethers

  2. ONa OR Typical Preparation is by Williamson Synthesis SN2 + + NaX RX

  3. ONa OR + X RONa Typical Preparation is by Williamson Synthesis SN2 + + NaX RX but the other combination fails because aryl halides are normally unreactivetoward nucleophilic substitution

  4. OCH3 ONa Example acetone + CH3I heat (95%)

  5. H2C CHCH2Br OH OCH2CH CH2 Example + K2CO3 acetone, heat (86%)

  6. F OCH3 NO2 NO2 Aryl Ethers from Aryl Halides • nucleophilic aromatic substitution is effective with nitro-substituted (ortho and/or para) aryl halides CH3OH + + KOCH3 KF 25°C (93%)

  7. 24.12Cleavage of Aryl Ethersby Hydrogen Halides

  8. Ar – •• •• •• •• + Br O H Br H •• •• •• •• •• •• R Cleavage of AlkylAryl Ethers Ar + O + R

  9. Ar – •• •• •• •• + Br O H Br H •• •• •• •• •• •• R Ar •• •• Br R O H •• •• •• Cleavage of AlkylAryl Ethers Ar • An alkyl halide is formed; never an aryl halide! + O + R +

  10. OCH3 OH OH OH Example HBr + CH3Br heat (85-87%) (57-72%)

  11. 24.13Claisen Rearrangementof Allyl Aryl Ethers

  12. OCH2CH CH2 200°C OH CH2CH CH2 Allyl Aryl Ethers Rearrange on Heating • allyl group migrates to ortho position (73%)

  13. OCH2CH CH2 O O H Mechanism rewrite as keto-to-enolisomerization OH

  14. O O H Sigmatropic Rearrangement Claisen rearrangement is an example of a sigmatropic rearrangement. A s bond migratesfrom one end of a conjugated p electron systemto the other. this s bond breaks “conjugated p electron system” is the allyl group this s bond forms

  15. 24.14Oxidation of Phenols:Quinones

  16. OH O Na2Cr2O7, H2SO4 H2O OH O Quinones • The most common examples of phenol oxidationsare the oxidations of 1,2- and 1,4-benzenediolsto give quinones. (76-81%)

  17. OH OH CH3 CH3 Quinones • The most common examples of phenol oxidationsare the oxidations of 1,2- and 1,4-benzenediolsto give quinones. O O Ag2O diethyl ether (68%)

  18. O OH OH O Some quinones are dyes Alizarin(red pigment)

  19. O CH3 CH3O CH3O n O Some quinones are important biomolecules Ubiquinone (Coenzyme Q) n = 6-10 involved in biological electron transport

  20. O CH3 CH3 CH3 CH3 CH3 CH3 O Some quinones are important biomolecules Vitamin K (blood-clotting factor)

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