The preparation of 2,4-dinitrobenzoic acid from benzoic acid and nitric acid involves an electrophilic aromatic substitution reaction. The mechanism proceeds as follows:1. Nitration of benzoic acid: Nitric acid HNO3 reacts with a strong acid, usually sulfuric acid H2SO4 , to form the nitronium ion NO2+ , which is a strong electrophile.HNO3 + H2SO4 -> NO2+ + HSO4- + H2O2. Electrophilic attack: The nitronium ion NO2+ attacks the benzene ring of benzoic acid, forming a resonance-stabilized carbocation intermediate. The ortho and para positions are more reactive due to the electron-donating effect of the carboxyl group -COOH in benzoic acid.3. Deprotonation: A hydrogen ion H+ is removed from the carbocation intermediate by the bisulfate ion HSO4- or water H2O , restoring the aromaticity of the benzene ring. This results in the formation of 3-nitrobenzoic acid.4. Second nitration: The 3-nitrobenzoic acid undergoes another nitration reaction with nitric acid and sulfuric acid, forming the nitronium ion NO2+ again.5. Electrophilic attack: The nitronium ion NO2+ attacks the benzene ring of 3-nitrobenzoic acid at the para position relative to the nitro group due to steric hindrance at the ortho position, forming a resonance-stabilized carbocation intermediate.6. Deprotonation: A hydrogen ion H+ is removed from the carbocation intermediate by the bisulfate ion HSO4- or water H2O , restoring the aromaticity of the benzene ring. This results in the formation of 2,4-dinitrobenzoic acid.The overall reaction can be summarized as:C6H5COOH benzoic acid + 2 HNO3 nitric acid -> C6H3 NO2 2COOH 2,4-dinitrobenzoic acid + 2 H2O water