CBSE Class 12 Chemistry 2018 Solved Paper

Question : 26 of 26

Marks: +1, -0

(a) Write the reactions involved in the following:
(i) Hoffmann bromamide degradation reaction
(ii) Diazotisation
(iii) Gabriel phthalimide synthesis
(b) Give reasons:
(i)

( {\CH}_3) _2 {\NH}

is more basic than

( {\CH}_3) _3 {\N}

in an aqueous solution.
(ii) Aromatic diazonium salts are more stable than aliphatic diazonium salts.
OR
(a) Write the structures of the main products of the following reactions:

(b) Give a simple chemical test to distinguish between aniline and N,N-dimethylaniline.
(c) Arrange the following in the increasing order of their

{\pK}_{ {\b}}

values:

{\C}_6 {\H}_5 {\NH}_2, {\C}_2 {\H}_5 {\NH}_2, {\C}_6 {\H}_5 {\NHCH}_3

Solution:

(a) (i)

{\Ar} \/ {\R}- {\CONH}_2+ {\Br}_2+4 {\NaOH} →

{\Ar} \/ {\R}- {\NH}_2+2 {\NaBr}+ {\Na}_2 {\CO}_3+2 {\H}_2 {\O}

(ii)

{\C}_6 {\H}_5 {\NH}_2+ {\NaNO}_2+2 {\HCI} {{ ────▸ }}↖{273-278 {\K}}

{\C}_6 {\H}_5 {\N}_2^{+} {\Cl}^{-}+ {\NaCl}+2 {\H}_2 {\O}

(iii) Gabriel Pthalimide reaction:

(b) (i)

2^{∘}

amine salt form are more stable than

3^{∘}

amine due to inductive effect and higher degree of hydration. Therefore, higher the stability of salt, greater will be the reactivity of corresponding compound.
(ii) Aromatic diazonium salts are more stable than aliphatic diazonium salts due to dispersion of positive charge over the benzene ring caused by resonance. This is not found in aliphatic diazonium salts.

OR
(a)

(b) Add chloroform in the presence of

{\KOH}

and heat, Aniline gives a offensive smell while

{\N}, {\N}

dimethylaniline does not. (or any other correct test)
(c)

{\C}_2 {\H}_5 {\NH}_2 < {\C}_6 {\H}_5 {\NHCH}_3 < {\C}_6 {\H}_5 {\NH}_2

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