[CH3:1][O:2][C:3]1[CH:4]=[C:5]([CH3:13])[CH:6]=[C:7]([O:11]C)[C:8]=1[O:9][CH3:10].OO.[N+]([O-])(O)=[O:17].O>CC(O)=O.O.C1(C)C=CC(S(O)(=O)=O)=CC=1>[CH3:10][O:9][C:8]1[C:7](=[O:11])[CH:6]=[C:5]([CH3:13])[C:4](=[O:17])[C:3]=1[O:2][CH3:1]
To a round-bottom flask (20 mL) equipped with a reflux condenser was added a solution of commercial 3,4,5-trimethoxy-toluene (0.547 g, 3 mmol) in AcOH (3 mL), followed by para-toluenesulfonic acid monohydrate (57 mg, 0.3 mmol) as catalyst. The oxidant H2O2 (30%, 0.65 mL, 6 mmol) was then added. The reaction mixture was stirred and heated at 75° C. for 30 min. The resulting dark-red solution was cooled to 0-5° C., and concentrated HNO3 (90%, 1.5 mmol) was then slowly added. The cold solution was poured into H2O (50 mL) and extracted with CH2Cl2 (3×50 mL). The combined organic layers were washed with H2O (80 mL) in order to remove traces of AcOH, dried (Na2SO4) and filtered. When the solvent was evaporated under vacuum, the final crude (0.528 g, dark-red oil) was dissolved in boiling hexane (70 mL), filtered, and the solvent was removed to give the pure 2,3-Dimethoxy-5- methyl-[1,4]benzoquinone (0.480 g, 88% yield) as red needles. 1H NMR (400 MHz, CDCl3, ppm): δ2.04 [d, 3H, J=1.6 Hz, CH3], 4.00 [s, 3H, OCH3], 4.02 [s, 3H, OCH3], 6.43-6.44 [q, 1H, Jm=1.6 Hz]. 13C NMR (400 MHz, CDCl3, ppm): δ15.4, 31.1, 61.2, 131.3, 144.0, 144.9, 145.1, 184.1, 184.4. MS m/z (%): 182 (85), 167 (32), 153 (13), 137 (100), 121 (6), 111(23), 96 (12), 83 (67), 69 (31), 53 (15).
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