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

Ozonolysis of Alkenes
(review of Chapter 6)

ozonolysis of alkenes
Reaction type: Electrophilic Addition

Summary

  • Overall transformation :  C=C to 2 x C=O
  • Reagents : ozone, O3,  followed by a reducing work-up,usually Zn in acetic acid. 
  • It is convenient to view the process as cleaving the alkene into two carbonyls:
  • The substituents on the C=O depend on the substituents on the C=C.
how to visualise ozonolysis

QUESTIONS  What would be the products of the ozonolysis reactions of:

 
  • (a) ethene ?
  • ANSWER   (c) 2-butene ? ANSWER
     
  • (b) 1-butene ?
  • ANSWER   (d) 2-methylpropene ?  ANSWER

     

    MECHANISM FOR REACTION OF ALKYNES WITH O3
    Step 1:
    The π electrons act as the nucleophile,attacking the ozone at the electrophilic terminal O. A second C-O is formedby the nucleophilic O attacking the other end of the C=C
    ozonolysis of C=C to C=O
    Step 2:
    The cyclic species called the ozonide rearranges to the malozonide. 
    Step 3:
    On work-up (usually Zn / acetic acid) the malozonide decomposes togive two carbonyl groups.
     
     


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