Aromatic Reactions: Grignard Reaction to form Benzoic Acid

Bromobenzene molecules react with magnesium to form a Grignard reagent intermediary. Once formed, the benzene Grignard-reactant reacts with carbon dioxide (CO2) to form benzoic acid:

Mechanism

The reaction mechanism is depicted below:

In the first step, the magnesium (Mg) inserts itself inbetween the benzene molecule and the bromine atom (not explicitly shown). Once the Grignard reagent is formed, the electrons from the newly formed benzene-Mg bond attack the CO2 molecule, breaking one of the C=O double bonds, sending the pi electrons to the O atom.

In the second step, the negatively charged O atom reacts with an acid (H3O+) to become protonated, thereby completing the reaction and forming the benzoic acid product.

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