21606-04-2

67-56-1

603-11-2

21606-04-2

1. 3-Nitrophthalic acid (500 g, 2.37 moles) was slowly added to a pre-cooled mixture of 2500 ml of methanol and 260 ml of thionyl chloride in an ice bath. 2. The reaction mixture was heated to reflux and maintained for about 24 h. 3. Upon completion of the reaction, the reaction solution was concentrated under reduced pressure, followed by removal of excess thionyl chloride under nitrogen protection. 4. 1500 ml of toluene was added to the residue, mixed thoroughly and filtered. 5. The resulting solid product was dried at 60-70°C to give 522.0 g (98% yield) of 2-carboxy-phthalic acid. 6. 4. 1500 ml of toluene was added to the residue, mixed thoroughly and filtered. 5. The resulting solid product was dried at 60-70 °C to give 522.0 g (98% yield) of methyl 2-carboxy-3-nitrobenzoate, which was essentially free of 3-nitrodimethylphthalate. 6. A further 500 g of 3-nitrophthalic acid was taken and mixed with 2.5 liters of methanol in a round-bottomed flask. The mixture was cooled to 5-10°C. 7. 259.5 ml of thionyl chloride was added dropwise under constant stirring for 60-90 minutes. 8. After the dropwise addition, the reaction mixture was heated to 60-65°C and kept reacting for 20-25 hours. 9. After the reaction was completed, all solvents were removed by distillation at 60-65°C. 10. 1500 ml of toluene was added and stirred for 5-6 hours under nitrogen atmosphere. 11. stirred under nitrogen atmosphere for 5-6 h. 11. The solid product was isolated by filtration, washed with 500 ml of toluene and subsequently dried at 55-65 °C for 5-10 h. 525 g of 3-nitrophthalic acid-1-methyl ester (compound of formula II) was obtained in the final product.