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Preparation of Alkynes via Elimination Reaction

Article ID: 133
Last updated: 04 Sep, 2012
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Reaction Type: Elimination (E2)

Summary

  • The two p bonds of an alkyne can be formed using two consecutive elimination reactions.
  • The leaving groups are usually halides (esp. Br or Cl)
  • Reagent : usually NaNH2 (a strong base, pKa = 35)
  • Either geminal (e.g. 1,1-) or vicinal (e.g. 1,2-) dihalides can be used.
  • Since 1,2-dihalides can be prepared by addition of X2 to an alkene, an alkene can be converted into an alkyne in two steps.
  • These reactions are typically E2 reactions and occur via an alkenyl halide.
  • The strong base is needed in order to cause elimination of the alkenyl halide.

 Vicinal (1,2-)

Geminal (1,1-)

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Alkynes     Allylic and Conjugated Systems

Department of Chemistry & Chemical Biology