[CH3:1][C:2]1[CH:3]=[C:4]([CH:8]=[CH:9][C:10]=1N)[C:5]([OH:7])=[O:6].S(=O)(=O)(O)O.N([O-])=O.[Na+].[I-:21].[K+]>O.C(OCC)(=O)C.[Cu](I)I>[CH3:1][C:2]1[CH:3]=[C:4]([CH:8]=[CH:9][C:10]=1[I:21])[C:5]([OH:7])=[O:6]20 g (0.132 mol) of 3-methyl-4-aminobenzoic acid and 175 ml of sulfuric acid (20%) were introduced into a three-necked flask. A solution of 11.9 g (0.172 mol) of sodium nitrite in 50 ml of water was added dropwise at -10° C. and stirring was carried out for two hours. This solution was introduced dropwise via a refrigerated dropping funnel at -50° C. into a solution of 35 g (0.211 mol) of potassium iodide, 35.2 g (0.185 mol) of copper iodide and 175 ml of sulfuric acid (20%). Stirring was carried out for eight hours, the reaction mixture was filtered and the solid obtained was dissolved in ethyl acetate. Washing was carried out with water and then with a sodium sulfite solution, drying was carried out over magnesium sulfate and evaporation was carried out. 24.4 g (70%) of 3-methyl-4-iodobenzoic acid, with a melting point of 205°-210° C., were recovered.
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