Question 15 Marks
$i.$ Give reasons$:$
$a.$ Although $- NH _2$ group is o$/$p directing in electrophilic substitution reactions, yet aniline, on nitration gives good yield of m$-$nitroaniline.
$b. \left( CH _3\right)_2 NH$ is more basic than $\left( CH _3\right)_3 N$ in an aqueous solution.
$c.$ Ammonolysis of alkyl halides is not a good method to prepare pure primary amines.
$ii.$ Distinguish between the following$:$
$a. CH _3 CH _2 NH _2$ and $\left( CH _3 CH _2\right)_2 NH$
$b.$ Aniline and $CH _3 NH _2$
$a.$ Although $- NH _2$ group is o$/$p directing in electrophilic substitution reactions, yet aniline, on nitration gives good yield of m$-$nitroaniline.
$b. \left( CH _3\right)_2 NH$ is more basic than $\left( CH _3\right)_3 N$ in an aqueous solution.
$c.$ Ammonolysis of alkyl halides is not a good method to prepare pure primary amines.
$ii.$ Distinguish between the following$:$
$a. CH _3 CH _2 NH _2$ and $\left( CH _3 CH _2\right)_2 NH$
$b.$ Aniline and $CH _3 NH _2$
Answer
View full question & answer→$i. a.$ Nitration is carried out in acidic medium. In an acidic medium, aniline is protonated to form the anilinium ion which is meta directing. That is why besides the ortho and para derivatives, a substantial amount of meta derivative (m$-$nitroaniline) is also formed.
$b. (CH_3)_2NH$ is a secondary amine and $(CH_3)_3N$ is a tertiary amine. Tertiary amine due to the presence of three alkyl groups is more hindered than secondary amine which has only two alkyl groups attached to it. Therefore formation of ammonium ion is easier in secondary amine than the tertiary amine. Therefore, it makes secondary amine less basic than the tertiary amine.
$c.$ The ammonolysis of alkyl halide leads to the formation of the mixture of primary, secondary and tertiary amine along with the formation of quaternary salt. It is very difficult to separate pure primary amine from this mixture.
$(a)$
$(b)$
$b. (CH_3)_2NH$ is a secondary amine and $(CH_3)_3N$ is a tertiary amine. Tertiary amine due to the presence of three alkyl groups is more hindered than secondary amine which has only two alkyl groups attached to it. Therefore formation of ammonium ion is easier in secondary amine than the tertiary amine. Therefore, it makes secondary amine less basic than the tertiary amine.
$c.$ The ammonolysis of alkyl halide leads to the formation of the mixture of primary, secondary and tertiary amine along with the formation of quaternary salt. It is very difficult to separate pure primary amine from this mixture.
$(a)$
| Test | $CH_3CH_2NH_2$ | $(CH_3CH_2)_2NΗ$ |
| Carbylamine test (add chloroform and alcoholic $ \text{KOH}$ to both the compounds separately in a test tube) | Forms a foul$-$smelling compound (gives positive test) | No reaction take place (gives negative test) |
| Azo dye Test | Aniline | Methyl Amine $(CH_3NH_2)$ |
| Add a small amount of nitrous acid with aq. $ \text{HCI}$ | Forms a yellow coloured dye (gives positive test) | No dye is formed(gives negative test) |
