[C:1]1([CH3:8])[C:6]([OH:7])=[CH:5][CH:4]=[CH:3][CH:2]=1.[S-:9][C:10]#[N:11].[Na+].[Br-].[Na+].BrBr.C(=O)(O)[O-].[Na+]>CO>[CH3:8][C:1]1[CH:2]=[C:3]([S:9][C:10]#[N:11])[CH:4]=[CH:5][C:6]=1[OH:7]
To a 500 ml three-necked flask were added sequentially with agitation o-cresol (15 g, 138.7 mmol), sodium thiocyanate (NaSCN, 34 g, 419.3 mmol), sodium bromide (NaBr, 16 g, 155.5 mmol) and methanol (200 ml). The mixture was cooled to 0° C., and then a solution of bromine (8.6 ml, 167 mmol) in methanol (30 ml) was added dropwise thereinto. After 1 hour of stirring at 0° C., the mixture was warmed up to room temperature and then stirred for another 4 hours at room temperature. After the reaction was completed, a 200 ml saturated aqueous solution of sodium bicarbonate (NaHCO3) was added to the reaction mixture and stirred for 10 min. The mixture was extracted with ethyl acetate (2×500 ml). The combined organic layer was dried over anhydrous magnesium sulfate, filtrated, concentrated under reduced pressure to give yellow oil. Silica gel column chromatography purification (silica-gel H: 300-400 mesh; petroleum ether/ethyl acetate=8:1 v/v) was performed to yield 3-methyl-4-hydroxy-phenyl thiocyanic acid as a white solid (16 g, yield: 69.8%).
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