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Oxidation of Alcohols

Oxidation of Alcohols. A Peer-Assisted Learning Demonstration. Discussion.

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Oxidation of Alcohols

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  1. Oxidation of Alcohols A Peer-Assisted Learning Demonstration

  2. Discussion • The most important reaction of alcohols is their oxidation to carbonyl compounds. Primary alcohols yield either aldehydes or carboxylic acids, depending on the conditions used. Secondary alcohols yield ketones - and tertiary alcohols do not react under the usual oxidizing conditions. • 1-propanol is oxidized rapidly, 2-propanol more slowly. Under the given reaction conditions tert-butanol does not react. • Primary and secondary alcohol reduce yellow Cr2O72- ions (Cr6+) to blue Cr3+ ions.

  3. Mechanism for Oxidation of Alcohols

  4. 1o Alcohol Oxidations • Primary alcohols  aldehydes • PCC/CH2Cl2 (pyridinium chlorochromate, C5H5NH+ClCrO3-)\ • Primary alcohols  carboxylic acids • CrVI in one form or another (H2CrO4 or K2Cr2O7) • MnVII (KMnO4/NaOH/H2O/heat) • Color of reagents can be useful. • CrVI is yellow; CrIII is blue

  5. 2o Alcohol Oxidations • Secondary alcohols  ketones • CrVI in one form or another • CrO3/aqueous acetone = “Jones Reagent” – good oxidizer, doesn’t affect alkenes where KMnO4 would.

  6. 3o Alcohol Oxidations • Tertiary alcohols cannot be oxidized under normal conditions. • Heat them too much in the presence of strong oxidizers; start cleaving C-C bonds.

  7. Why? • When an alcohol is oxidized, a hydrogen is removed from the carbon. If that hydrogen is not present, no oxidation can occur.

  8. Examples

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