Deprotonation of alkynes with base to give acetylide ions
Description: Treatment of an acetylene with a strong base such as NaNH2 results in acetylide ions
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.
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.