JEE Main · 2021 · 27 Aug 2021 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

Carbonation of a Grignard reagent adds one carbon: $1$-bromopropane gives propylmagnesium bromide, which with $\mathrm{C}{\mathrm{O}}_2$ and acid yields butanoic acid, a four-carbon acid, not propionic acid. Oxidation of propane, hydrolysis of $1,1,1$-trichloropropane and the haloform reaction of butan-$2$-one each keep the three-carbon $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2\mathrm{COOH}$ framework and do give propionic acid. The route that fails to give propionic acid is the Grignard carbonation of $1$-bromopropane.