Synthesis
General steps for the synthesis of 4-hydroxy-5-methoxy-2-nitrobenzaldehyde from 4-(benzyloxy)-5-methoxy-2-nitrobenzaldehyde: 4-(benzyloxy)-5-methoxy-2-nitrobenzaldehyde (10g, 0.03mol) was placed in a 500mL round-bottomed flask, and 200mL of trifluoroacetic acid was added to dissolve it, and if dissolution was incomplete, dichloromethane was added to the solution to aid in solvency. Dichloromethane can be added in appropriate amount to aid solubilization. The reaction was carried out at room temperature with continuous stirring overnight. The progress of the reaction was monitored by thin-layer chromatography (TLC with dichloromethane as the unfolding agent). Upon completion of the reaction, the solvent was removed by rotary evaporation and the residue was dissolved in ethyl acetate. Subsequently, the pH was adjusted to 1-10 with 1 mol/L NaOH solution to neutralize the residual trifluoroacetic acid, and then the pH was adjusted to about 5 with 6 mol/L HCl solution to convert sodium phenol to phenol hydroxyl. The reaction solution was extracted with ethyl acetate, the organic phases were combined, dried over anhydrous sodium sulfate, and then concentrated to dryness. Since the product was poorly soluble in hexane and impurities were better soluble, the product was washed with hexane and dried to give 5 g of a yellow solid, 4-hydroxy-5-methoxy-2-nitrobenzaldehyde, in 72.9% yield.
References
[1] Organic Process Research and Development, 2018, vol. 22, # 3, p. 391 - 398
[2] Organic Process Research and Development, 2018, vol. 22, # 9, p. 1241 - 1256
[3] New Journal of Chemistry, 2016, vol. 40, # 3, p. 2601 - 2608
[4] Chemical Communications, 2015, vol. 51, # 52, p. 10431 - 10434
[5] Patent: CN108727177, 2018, A. Location in patent: Paragraph 0082; 0097; 0098
