Dihaloalkane Elimination : Preparation of Alkynes

This is a general picture of the reaction taking place without any of the mechanisms shown.

or

* With a terminal haloalkane the equation above is modified in that 3 equivalents of base will be used instead of 2.

Lets look at the mechanism of a reaction between 2,3-Dibromopentane with sodium amide in liquid ammonia.

• Liquid ammonia is not part of the reaction, but is used as a solvent
• Notice the intermediate of the alkyne synthesis. It is stereospecifically in its anti form. Because the second proton and halogen are pulled off the molecule this is unimportant to the synthesis of alkynes. For more information on this see the page on preparation of alkenes from haloalkanes.