Show how each of the following compounds can be converted to benzoic acid. (i) Ethylbenzene (ii) Acetophenone (iii) Bromobenzene (iv) Phenylethene (Styrene)
Ethylbenzene can be converted to benzoic acid by oxidation with KMnO4/KOH followed by acidification. The ethyl side chain is completely oxidised to a carboxyl group: C6H5CH2CH3 → C6H5COOH.
Acetophenone can be converted to benzoic acid by oxidation with KMnO4/KOH. The methyl ketone is oxidised to a carboxyl group, yielding benzoic acid after acid treatment: C6H5COCH3 → C6H5COOH.
Bromobenzene is first converted to a Grignard reagent (phenylmagnesium bromide) by reaction with Mg in ether. This is then treated with CO2 (dry ice) and hydrolysed with H3O+ to give benzoic acid: C6H5Br → C6H5MgBr → C6H5COOH.
Phenylethene (Styrene) undergoes oxidative cleavage with KMnO4-H2SO4 to give benzoic acid as one of the products: C6H5CH=CH2 → C6H5COOH.
Explanation
The conversions are based on reactions shown in the context: oxidation of alkyl/aryl ketones with KMnO4/KOH (as for 4-Methylacetophenone), Grignard reaction with CO2 (as for 3-Nitrobromobenzene), and oxidative cleavage of alkenes with KMnO4-H2SO4 (as for Cyclohexene). Ethylbenzene oxidation follows the same principle as oxidation of a methyl group attached to an aromatic ring.