Question

Which of the following reactions is not feasible?
A) $PhS{O_3}H + NaHC{O_3} \to$
B) $Ph - OH + NaN{H_2} \to$
C) $C{H_3} - N{H_2} + NaOH \to$
D) $Ph - C = CH + NaH \to$

Answer 1

The given above reactions are a type of acid-base reaction only. The feasibility of such reactions depends on the strength of the acids. If strong acids are present, it favours the reaction in forward direction, whereas weak acids do not favour the reaction. The reactions in which weak acids are present on the reactant sides are mostly not feasible.

Complete answer:
In an acid base organic reaction remember this principle: $Strong{\text{ }}Acid + Strong{\text{ }}Base \to Weak{\text{ }}Acid + Weak{\text{ }}Base$
Consider this reaction is Option C) : $NaOH + C{H_3}N{H_2} \to {H_2}O + C{H_3}N{H^ - }$
In this reaction NaOH on the reactant side is a strong base, so $C{H_3}N{H_2}$ has to act like an acid. On the product side water acts like an acid so $C{H_3}N{H^ - }$ will act as base only. But we know that $C{H_3}N{H^ - }$ is a stronger base than NaOH on the reactant side, and water is a stronger acid than $C{H_3}N{H_2}$ . The principle is not followed; therefore the reaction is not feasible. Hence the correct option is Option C).
The products of all the remaining reactions are given one by one:
A) $PhS{O_3}H + NaHC{O_3} \to PhSO_3^ - N{a^ + }$ . Water and carbon dioxide are also formed as byproducts. Strong acid (benzene sulphonic acid) gives a weak acid as a product.
B) $Ph - OH + NaN{H_2} \to Ph - {O^ - }N{a^ + }$ : Sodium Azide is a strong base, it gives a weak base sodium phenoxide.
All the given reactions, give $Strong{\text{ }}Acid + Strong{\text{ }}Base \to Weak{\text{ }}Acid + Weak{\text{ }}Base$ or vice versa.

Note:
The feasibility of an acid-base reaction can also be found out by comparing the strength of the acids given. The strength of the acid depends upon the value of $p{K_a}$ . Higher the value of $p{K_a}$ more stronger will be the acid.