[OH:1][C:2]1[CH:7]=[CH:6][C:5]([NH:8][C:9](=[O:15])/[CH:10]=[CH:11]\[C:12](O)=[O:13])=[CH:4][CH:3]=1.[C:16]([O-])(=[O:18])[CH3:17].[Na+].C(OC(=O)C)(=O)C>O>[C:16]([O:1][C:2]1[CH:7]=[CH:6][C:5]([N:8]2[C:9](=[O:15])[CH:10]=[CH:11][C:12]2=[O:13])=[CH:4][CH:3]=1)(=[O:18])[CH3:17]To a three-neck 1 liter reaction vessel equipped with a condenser, a teflon stirring rod and a thermometer, 97 g (0.49 moles) of N-(4-hydroxyphenyl)maleamic acid, 27.7 g (0.38 moles) of sodium acetate and 400 g of acetic anhydride are added and then heated by using silicone oil. When the reaction solution reaches 70° C. for 2 hours with stirring, the solution is poured into a large amount of distilled water and a great amount of precipitates are formed. The precipitate is taken by filtration and washed several times with distilled water to remove acetic acid, followed by recrystallization from ethanol to give the titled compound. Yield 53%. B.P. 155°-158° C.
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