A solution of 5-hydroxy-2-methylbenzoic acid( 5.00 g, 32.9 mmol, 1.0 eq) in H2SO4 (50 mL, 98% purity) was cooled to 0 °C and to this mixture was added KNO3 (3.49 g, 34.5 mmol, 1.1 eq) at 0 °C. The mixture was stirred at 20 °C for 1 h. TLC indicated that the starting material was completely consumed, and a main spot was detected. The mixture was treated with ice water (40 mL) slowly and extracted with DCM(20 mL x 5). The combined organic layers were dried over NazSC，filtered, and concentrated under vacuum to give a residue which was purified by flash silica gel chromatography. Benzoic acid, 5-hydroxy-2-methyl-4-nitro- (9CI) (640 mg, 3.25 mmol, 10% yield) was obtained after purification.
