Question

Question 7 You are ready to carry out a reaction between propyne and sodium amide (NaNH2), and you reaction. In which of the following solvents this reaction can only proceed? ethanol: pk. - 16 NH3: pK,-38 terminal proton of propyne: pk, -25 water: pK. 15.7 acetone: pKa-19 methanol: pK, 15.5 H3C-CECNa CH3OH acetone Liquid NH3 H2O CH CH2OH

Answer 1

Alkyne is losing hydrogen ion therefore acting as an acid .

NaNH2 on the other hand is a base.

So we need to use a solvent in which the acidic properties of alkyne is not affected. As alkyne is not a strong acid so if we would use any solvent whose pka value is less than 25 (pka of alkyne) then that solvent will be acting as acid by donating hydrogen ion.

So a solvent of choice should be the one having more pka value that that of alkyne . In all the solvents listed above , only ammonia is the one having pka= 38 more than acetic acid .

So it should be the better choice of solvent therefore option C ie liquid ammonia is the ans.