Question

How many of the reagents listed below would give effervercence, when treated with propyne?
(I) $NaOH$ (II) $C{H}_{3}C{H}_{2}ONa$
(III) $NaH$ (IV) $NaN{H}_2$
(V) $NaHC{O}_3$ (VI) $\left\{\right(C{H}_3{)}_{2}CH{\}}_{2}NLi$
(VII) $C{H}_{3}C{H}_{2}Li$

Answer 1

Effervescence is the formation of gas bubbles in a liquid. It is the escape of gas from an aqueous solution by the chemical reaction.
(I) $NaOH$ does not react with propyne since the alkynes are weak acids.
(II) Sodium methoxide $\left(NaOC{H}_3\right)$ is not a strong enough base to deprotonate the terminal alkyne.
(III) $NaH$ reacts with propyne liberating $H_2$.
Hence, it gives effervescence.
$NaH+C{H}_3-C\equiv CH\to C{H}_3-C\equiv CNa+H_2$
(IV) Propyne reacts with $NaN{H}_2$ evolving ammonia.
(V) Acids only give brisk effervescence with $NaHC{O}_3$ by evolving $C{O}_2$ from the carboxylic acids.
(VI) & (VII) Lithium diethylamide is a weaker base than ethyl lithium. Both react with propyne giving no effervescence.
Hence, only $NaH,NaN{H}_2$ are the correct choices here.