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Which of the following reactions proceeds in the forward direction as written?

1. CH3-C≡CH + NaNH2 -> CH3-C≡C-Na + NH3
2. Phenol + NaHCO3 -> Sodium phenoxide + H2CO3
3. Toluene + NaHCO3 -> Sodium salt of toluene + H2CO3
4. None of the above

Correct answer: CH3-C≡CH + NaNH2 -> CH3-C≡C-Na + NH3

Solution

NaNH2 is the sodium salt of NH3 (pKa ~38). Propyne (pKa ~25) is a stronger acid than NH3, so NH2⁻ deprotonates propyne, driving the equilibrium forward to give propyne sodium salt and NH3. Phenol (pKa ~10) cannot displace H2CO3 (pKa1 ~6.4) from NaHCO3, and toluene is far too weak an acid to react.

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