1. To a solution of 1,4-dimethoxybenzene (10.0 g, 72.3 mmol) in 1,4-dioxane (30 mL), 38% aqueous formaldehyde (5 mL) and paraformaldehyde (3.0 g, 99.0 mmol) were added sequentially. The reaction mixture was heated to 90°C and concentrated hydrochloric acid (5 mL each) was added in two portions over 30 minutes. The reaction mixture was continued to be heated for 1 hour and then 30 mL of concentrated hydrochloric acid was added. Cooled to room temperature, a white precipitate was precipitated, collected by filtration and dried under vacuum. The crude product was recrystallized from acetone to give 1,4-bis(chloromethyl)-2,5-dimethoxybenzene (4.5 g, 26% yield) as a white solid.
2. 1,4-bis(chloromethyl)-2,5-dimethoxybenzene (15.0 g, 63.8 mmol) and hexamethylenetetetramine (18.0 g, 127.6 mmol) were dissolved in chloroform (50 mL) and refluxed and stirred for 24 hours. After the reaction was completed, it was cooled to room temperature and the light yellow precipitate was collected by filtration. The precipitate was dissolved in water (30 mL), acidified by the addition of acetic acid (10 mL) and stirred at 90 °C for 24 hours. After cooling to room temperature, it was extracted with dichloromethane (200 mL). The organic phase was washed three times with water (200 mL) and dried over anhydrous sodium sulfate. After evaporating the solvent, the residue was recrystallized from ethanol to give 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (5.5 g, 45% yield) as a bright yellow solid.
1H NMR (300 MHz, CDCl3) δ 10.50 (s, 2H), 7.26 (s, 2H), 3.95 (s, 6H).
13C NMR (101 MHz, CDCl3) δ 189.19, 155.73, 129.15, 110.92, 77.33, 77.01, 76.70, 56.23.
FTMS for C10H10O4: calcd. m/z 195.1 [M + 1]+; found 194.1.
