Acetylene (pKa 25) is to be converted completely into its sodium salt. Which reagent in an inert solvent is NOT suitable? (pKa of conjugate acids: $NH X_{3}$ 38, $H X_{2}$ about 35, $H X_{2} O$ 15.7, $CH X_{4}$ about 48)

A $NaOH$
B $NaNH X_{2}$
C $NaH$
D $CH X_{3} Li$

Answer: A

A base deprotonates an acid essentially completely only if its conjugate acid is much weaker than the acid. Amide (38), hydride (35) and methyl anion (48) all exceed 25 by far, but hydroxide (conjugate acid 15.7) is a weaker base than acetylide, so the equilibrium lies on the side of acetylene and hydroxide.

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Acetylene (pKa 25) is to be converted completely into its sodium salt. Which reagent in an inert solvent is NOT suitable? (pKa of conjugate acids: NHX3​ 38, HX2​ about 35, HX2​O 15.7, CHX4​ about 48)

Answer: A

More questions on Basic strength of amines and heterocycles

Acetylene (pKa 25) is to be converted completely into its sodium salt. Which reagent in an inert solvent is NOT suitable? (pKa of conjugate acids: $NH X_{3}$ 38, $H X_{2}$ about 35, $H X_{2} O$ 15.7, $CH X_{4}$ about 48)