Return to Contents  Chapter 17: Aldehydes and Ketones. Nucleophilic Addition to C=O  Ch 17 contents

Oxidation of Primary and Secondary Alcohols
(review of Chapter 15)

general scheme for the oxidation of alcohols
Reaction type: Oxidation-Reduction

Summary

reagents for the oxidation of alcohols
Study Tip:
If you see Cr reagents, you are probably looking at an oxidation reaction of a alcohol or an aldehyde.
oxidation of RCH2OH
1o alcohol                      aldehyde
oxidation of R2CHOH
2o alcohol                       ketone
oxidation of R3COH
3o alcohol

 

Cr OXIDATION OF ALCOHOLS
The mechanism is not trivial, so attention here is focussed on the actual oxidation step. Prior to this, the alcohol reacts to form a chromate ester (shown). A base (here a water molecule) abstracts a proton from the chromate ester, the C=O forms and a Cr species leaves. 
This demonstrates the importance of the carbinol H to this mechanism.
oxidation of alcohols

 

QUESTIONS

 
  • What type of reaction could the oxidation step be decribed as ?
  • ANSWER
     
  • What is the oxidation state of Cr in chromic acid ?
  • ANSWER
     
  • What is the oxidation state of the Cr in the chromate ester intermediate ? 
  • ANSWER
     
  • What is the oxidation state of the Cr in the "leaving group", HCrO3- ?
  • ANSWER

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    © Dr. Ian Hunt, Department of Chemistry, University of Calgary