[CH3:1][C:2]1[CH:10]=[C:9]([CH3:11])[CH:8]=[CH:7][C:3]=1[C:4]([OH:6])=[O:5].[I:12]([O-])(=O)(=O)=O.[Na+].II.S(=O)(=O)(O)O.[O-]S([O-])(=S)=O.[Na+].[Na+]>C(O)(=O)C.O>[I:12][C:8]1[C:9]([CH3:11])=[CH:10][C:2]([CH3:1])=[C:3]([CH:7]=1)[C:4]([OH:6])=[O:5]A solution of 2,4-dimethylbenzoic acid (20 g, 133.18 mmol, 1.00 equiv), sodium periodate (14.27 g, 66.72 mmol, 0.50 equiv), iodine (37.25 g, 146.76 mmol, 1.10 equiv), and sulfuric acid (1.96 g, 19.98 mmol, 0.15 equiv) in acetic acid (150 mL) was stirred at 110° C. in an oil bath. After 6 h, the reaction mixture was allowed to reach ambient temperature and was then diluted with 1.2 L of water. To this was carefully added 800 mL of aq Na2S2O3 (aq., sat.). The resulting solids were collected by filtration, dissolved in 1.2 L of ethyl acetate, and washed with 1×300 mL of Na2S2O3 (aq., sat.) followed by 1×400 mL of brine. The organic layer was dried (Na2SO4) and concentrated under reduced pressure. The crude residue was re-crystallized from ethanol:H2O (2:1) to yield 30 g (82%) of the title compound as a white solid.
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