[N+:1]([C:4]1[CH:5]=[C:6]([C:13]([OH:15])=[O:14])[C:7](=[CH:11][CH:12]=1)[C:8]([OH:10])=[O:9])([O-:3])=[O:2].S(=O)(=O)(O)O>C(O)C>[N+:1]([C:4]1[CH:5]=[C:6]([C:13]([O:15][CH2:13][CH2:6][CH2:7][CH3:8])=[O:14])[C:7](=[CH:11][CH:12]=1)[C:8]([O:10][CH2:5][CH2:4][CH2:12][CH3:11])=[O:9])([O-:3])=[O:2]4-nitrophthalic acid (2.0 g, 9.5 mmol) was dissolved in 30 ml of absolute ethanol and then 0.3 ml of concentrated sulfuric acid was added. The mixture was heated at 120° C. for 24 hours, and the solvent was evaporated under reduced pressure. The oily residue was dissolved in diethyl ether and washed three times with water and once with 10% Na2CO3 solution. The ether solution was dried over anhydrous sodium sulfate. After evaporation of the solvent, a light yellow crude solid was obtained. The crude product was purified by silica gel column chromatography (n-hexane: acetic acid =10:1) to give 2.1 g (68.4%) of di-n-butyl 4-nitrophthalate (compound 403).
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