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47.[4] The following reaction sequence is shown: benzene + HNO3 / H2SO4 → nitrobenzene; nitrobenzene + Br2 / AlBr3 → m-bromonitrobenzene; m-bromonitrobenzene + Mg (Ether) → corresponding Grignard reagent; then CO2 / H+ → 3-nitrobenzoic acid. Which of the following is the correct intermediate/product sequence?

1. Benzene → nitrobenzene → m-bromonitrobenzene → m-nitrophenylmagnesium bromide → 3-nitrobenzoic acid
2. Benzene → aniline → p-bromonitrobenzene → p-nitrophenylmagnesium bromide → 4-nitrobenzoic acid
3. Benzene → nitrobenzene → o-bromonitrobenzene → o-nitrophenylmagnesium bromide → 2-nitrobenzoic acid
4. Benzene → nitrobenzene → p-bromonitrobenzene → p-nitrophenylmagnesium bromide → 4-nitrobenzoic acid

Correct answer: Benzene → nitrobenzene → m-bromonitrobenzene → m-nitrophenylmagnesium bromide → 3-nitrobenzoic acid

Solution

The correct option accurately follows the sequence of reactions starting from benzene, where nitration produces nitrobenzene, followed by bromination that selectively yields m-bromonitrobenzene due to the meta-directing effect of the nitro group. The subsequent formation of the Grignard reagent and its reaction with carbon dioxide leads to the formation of 3-nitrobenzoic acid, aligning perfectly with the described reaction pathway.

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