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5-Methylbenzene-1,3-diol (25.0 g, 0.2 mol) was dissolved in N,N-dimethylformamide (100 mL) at 0 °C and slowly added dropwise to a pre-cooled mixture of POCl3 (44.0 g, 0.3 mol) and N,N-dimethylformamide (200 mL). After the dropwise addition was completed, the reaction mixture was stirred at room temperature for 1 hour. Subsequently, the reaction mixture was slowly poured into ice water and the solid product was precipitated. The solid was collected by filtration and washed three times with distilled water to remove residual acid and solvent. Finally, the product was dried to afford 2,4-dihydroxy-6-methylbenzaldehyde (21.0 g, 82.0% yield), which could be used in subsequent reactions without further purification.