Question

The most reactive amine towards dilute hydrochloric acid is _________.

• A.
• B.
• C. $C{H}_3-N{H}_2$
• D.

Answer 1

The correct option is B

Comparing basicity of amines

The reaction of amine towards dilute hydrochloric acid is basically an acid base reaction.
As the electron density on $N-$atom in amine increases the availability of electron pairs to share with proton of an acid, increases. Thus, basic strength increases.
The basic strength of amine is also affected by solvation with water molecules (dilute $HCl$). The ammonium ion formed on protonation is stabilised by solvation. The greater the size of the ion, lesser will be the solvation and the less stabilised is the ion.

A)
B)
C) Where, $I$ is inductive effect and $M$ is mesomeric effect. Compound in option $\left(B\right)$ will be more basic than $\left(A\right)$ because of more number of electron releasing groups (alkyl) and also more basic as compared to $\left(C\right)$ because of less steric hinderance so greater solvation.

D)
Aniline, option $\left(D\right)$ will be least basic because unshared electron pair on nitrogen atom is in conjugation with the benzene ring and thus making it less available for protonation.
Hence, the correct answer is option $\left(B\right)$.