| 摘要 |
PURPOSE:An acid anhydride which has anhydride groups formed with the carboxyls in the same molecule is dipped in acetic anhydride, then almost of the acetic anhydride is removed, and the residue is dried with heat to collect the acid anhydride of good color phase in high recovery yield through simple operations. CONSTITUTION:An acid anhydride which has anhydride groups formed with the carboxyls in the same molecule is crushed as fine as possible, dipped in acetic anhydride and almost of the acetic anhydride is removed by filtration or decantation. The residue is dried by heating at 100-150 deg.C, preferably over 130 deg.C for several hours to give the acid anhydride of good color phase. As the acid anhydride, is cited pyromellitic dianhydride, phthalic anhydride, nitrophthalic anhydride or 2,3,6,7-naphthalenetetracarboxylic dianhydride.
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