Return to Contents Chapter 16: Ethers, Epoxides and Sulfides Ch 16 contents

Using Halohydrins to Synthesise Epoxides
(review of Chapter 6 and 8)

preparation of a 1,2-halohydrin
intramolecular S<sub>N</sub>2 to give an epoxide
Reaction type: Electrophilic Addition then Nucleophilic Substitution

Summary

QUESTIONS

 
  • What named reaction is the ring closure step most like ?
  • ANSWER
     
  • If the ring closure is an SN2 reaction then what arrangement of the -O-C-C-X system is required in the reactive conformation ?
  • ANSWER
     
  • What is the stereochemistry of the halohydrin formation ?
  • ANSWER

    Related reactions

    MECHANISM OF HALOHYDRIN TO EPOXIDE
    Step 1:
    An acid/base reaction.  The base deprotonates the alcohol forming an alkoxide intermediate that has enhanced nucleophilicity.
    Friedel-Crafts alkylation of benzene
    Step 2:
    An intramolecular SN2 reaction where the alkoxide nucleophile attacks the electrophilic C displacing the leaving group, the halide ion. The nucleophile has to attack anti to the C-X bond.

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