CBSE 2022 · Region 2 · Set 3 · Q12 · 5 marks
Read the following passage and answer the questions that follow : Amines constitute an important class of organic compounds derived by replacing one or more hydrogen atoms of ammonia molecule by alkyl/aryl groups. Amines are usually formed from nitro compounds, halides, amides, etc. They exhibit hydrogen bonding which influences their physical properties. Alkyl amines are found to be stronger bases than ammonia. In aromatic amines, electron releasing and withdrawing groups, respectively increase and decrease their basic character. Reactions of amines are governed by availability of the unshared pair of electrons on nitrogen. Influence of the number of hydrogen atoms at nitrogen atom on the type of reactions and nature of products is responsible for identification and distinction between primary, secondary and tertiary amines. Reactivity of aromatic amines can be controlled by acylation process.(i)Why does aniline not give Friedel-Crafts reaction ? $\displaystyle 1$(ii)Arrange the following in the increasing order of their $\displaystyle \mathrm{pK}_{\mathrm{b}}$ values : $\displaystyle 1$ \[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}, \mathrm{NH}_{3}, \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2},\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N} \](iii)How can you distinguish between $\displaystyle \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}$ and $\displaystyle \left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}$ by Hinsberg test ? $\displaystyle 1$(iv)Write the structures of A and B in the following reactions :(I) $\displaystyle \xrightarrow{\mathrm{Sn+HCl}}$ A $\displaystyle \xrightarrow{\mathrm{Br}_2 \text{ water}}$ B(II)$\displaystyle \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CONH}_{2} \xrightarrow{\mathrm{Br}_{2} / \text { alc. } \mathrm{KOH}} \mathrm{A} \xrightarrow[\text { Pyridine }]{\mathrm{CH}_{3} \mathrm{COCl}} \mathrm{B}$How will you convert the following :(I)Benzoic acid to aniline(II)Aniline to p-bromoaniline
Read the following passage and answer the questions that follow : Amines constitute an important class of organic compounds derived by replacing one or more hydrogen atoms of ammonia molecule by alkyl/aryl groups. Amines are usually formed from nitro compounds, halides, amides, etc. They exhibit hydrogen bonding which influences their physical properties. Alkyl amines are found to be stronger bases than ammonia. In aromatic amines, electron releasing and withdrawing groups, respectively increase and decrease their basic character. Reactions of amines are governed by availability of the unshared pair of electrons on nitrogen. Influence of the number of hydrogen atoms at nitrogen atom on the type of reactions and nature of products is responsible for identification and distinction between primary, secondary and tertiary amines. Reactivity of aromatic amines can be controlled by acylation process.
(i)
Why does aniline not give Friedel-Crafts reaction ? $\displaystyle 1$
(ii)
Arrange the following in the increasing order of their $\displaystyle \mathrm{pK}_{\mathrm{b}}$ values : $\displaystyle 1$ \[\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}, \mathrm{NH}_{3}, \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2},\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N} \]
(iii)
How can you distinguish between $\displaystyle \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}$ and $\displaystyle \left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}$ by Hinsberg test ? $\displaystyle 1$
(iv)
Write the structures of A and B in the following reactions :
(I)
$\displaystyle \xrightarrow{\mathrm{Sn+HCl}}$ A $\displaystyle \xrightarrow{\mathrm{Br}_2 \text{ water}}$ B
(II)
$\displaystyle \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CONH}_{2} \xrightarrow{\mathrm{Br}_{2} / \text { alc. } \mathrm{KOH}} \mathrm{A} \xrightarrow[\text { Pyridine }]{\mathrm{CH}_{3} \mathrm{COCl}} \mathrm{B}$
How will you convert the following :
(I)
Benzoic acid to aniline
(II)
Aniline to p-bromoaniline
Marking-scheme solution
(i) Aniline is a Lewis base and it reacts with \(\displaystyle \mathrm{AlCl}_{3}\) to form a salt / N of aniline acquires positive charge with \(\displaystyle \mathrm{AlCl}_{3}\) and hence is a deactivating group.
(ii) \[\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}<\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2}<\mathrm{NH}_{3}<\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}
\] \(\displaystyle \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2}<\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}<\mathrm{NH}_{3}<\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}\) (As no medium (aqueous /gaseous) or phase is given both answers to be considered).
(iii)
Add Hinsberg reagent (benzene sulphonyl chloride) to both the compounds. \(\displaystyle \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}\) gives ppt. that is soluble in alkali while the ppt. formed by \(\displaystyle \left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2} \mathrm{NH}\) is insoluble in alkali.
(a)
(I)(A)
(B)
(II)(A)
$\displaystyle \mathrm{CH_3CH_2NH_2}$
(B)
$\displaystyle \mathrm{CH_3CH_2NHCOCH_3}$
(I)
$\displaystyle \xrightarrow[\Delta]{\mathrm{NH_3}}$ $\displaystyle \xrightarrow{\mathrm{NaOBr}}$
(II)
$\displaystyle \xrightarrow{\mathrm{CH_3COCl/Py}}$ $\displaystyle \xrightarrow[\mathrm{FeBr_3}]{\mathrm{Br_2}}$ $\displaystyle \xrightarrow{\mathrm{H_2O}}$
AminesChemical Reactions of AminesUnderstandlong_answermedium
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CBSE Class 12 Chemistry past-paper question from the 2022board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.