To a 3-liter RBF add 175 mL of conc. nitric acid and 185 g of phthalic anhydride, in an ice bath. Start slowly adding 175 mL of conc. sulfuric acid with vigorous stirring. Then reflux under hot water bath for 3 h with stirring, cool down to room temperature. Then add 500 mL of water and stir until the mixture is very fine without any lumps, filter and wash with 100ml of cold water. Collect the crude 3-nitrophthalic Acid. Put the residual solution in the freezer for few days to precipitate all of the 3-nitrophthalic Acid, filter. Recrystallize from glacial acetic acid, crystallization is slow.
Slowly adding the sulfuric acid
Reflux for 3h in steam bath
The mixture solidified after cooling down
Water was added with stirring and the mixture was filtered and washed
Crystallizing out the product out of the residual solution in a freezer
The pure product