Deprotonation of alkynes with base to give acetylide ions

by James

Description: Treatment of an acetylene with a strong base such as NaNH2 results in acetylide ions
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Notes: Alkynes are quite acidic for hydrocarbons (pKa of 25) so a strong base such as NaNH2 can remove the proton. However a base like NaOH is not nearly strong enough.

Examples:

Notes: Note that NH3 is the byproduct here.

Mechanism: This is a straightforward acid-base reaction. The strong base NaNH2 deprotonates the acetylide C–H (Step 1, arrows A and B) leaving behind the conjugate base of the acetylene (i.e. the acetylide)

Notes: Again, note that bases weaker than (-)NH2 will not be very effective. The acetylide ions are extremely useful nucleophiles for forming C–C bonds.

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