CBSE Class 12 Chemistry 2018 Solved Paper

Question : 9 of 26

Marks: +1, -0

How do you convert the following ?
(a) Ethanal to Propanone
(b) Toluene to Benzoic acid
OR
Account for the following:
(a) Aromatic carboxylic acids do not undergo Friedel-Crafts reaction.
(b)

{\pK}_{ {\a}}

value of 4-nitrobenzoic acid is lower than that of benzoic acid.

Solution:

(a)

{\CH}_3 {\CHO} { ──────────▸ }↖↖{\;\text " (i) "\; {\CH}_3 {\MgBr} \;\text ", Dryether "\;} ↙{{\;\text " (ii) "\; {\H}_2\O\/\H^{+}}}

{\CH}_3 {\CH}( {\OH}) {\CH}_3 {{ ────▸ }}↖{ {\CrO}_3}

{\CH}_3 {\COCH}_3

OR
(a) because the carboxyl group is deactivating and the catalyst aluminium chloride (Lewis acid) gets bonded to the carboxyl group
(b) Nitro group is an electron withdrawing group (-I effect) so it stabilises the carboxylate anion and strengthens the acid/ due to the presence of an electron withdrawing nitro group (-I effect).

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