CPC C07D 307/89 (2013.01) [C07D 407/10 (2013.01); C07D 407/12 (2013.01)] | 14 Claims |
1. A method for producing an aromatic dianhydride, the method comprising:
reacting an aromatic diimide with a substituted or unsubstituted phthalic anhydride in an aqueous medium in the presence of an amine exchange catalyst under conditions effective to provide an aqueous reaction mixture comprising an N-substituted phthalimide, an aromatic tetraacid salt, and at least one of an aromatic triacid salt and an aromatic imide diacid salt, wherein the reacting is at a reaction temperature that is 140 to 250° C. and a reaction pressure of 1.13 to 2.16 MPa;
removing the N-substituted phthalimide from the aqueous reaction mixture by extracting the aqueous reaction mixture with an organic solvent; and
converting the aromatic tetraacid salt to the corresponding aromatic dianhydride;
wherein the extracting is in an extraction column comprising a metal packing material having a specific surface area of greater than 1500 square meters per cubic meter;
wherein extracting the aqueous reaction mixture comprises passing a dispersed phase comprising the aqueous reaction mixture through a continuous phase comprising the organic solvent; and
wherein an interface between the aqueous reaction mixture and the organic solvent in the extraction column is at a level that is 14 to 85% of the height of the extraction column.
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