Phosphoric Acid → 3-Chlorophthalic acid

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The purpose of this Example was to show that without decantation, a relatively higher level of impurities levels were present in the 4,4′-oxydiphthalic anhydride that was produced, as compared to Examples 4 and 5 where decantation is practiced. 2645 parts of a WC of material consisting of 68.7 wt % 4,4′-oxydiphthalic anhydride, 13.3 wt % of potassium chloride, 18 wt % of ortho-dichlorobenzene based on total weight of the WC, and some minor impurities such as hexaethylguanidinium chloride (1146 ppm) and chlorophthalic anhydride (1591 ppm), was mixed with 528 parts of phosphoric acid (85 wt %) and 11877 parts of water and heated under vacuum until boiling, about 80° C. Under these conditions, 4,4′-oxydiphthalic anhydride and chlorophthalic anhydride react with the water to form 4,4′-oxydiphthalic tetraacid (ODTA) and chlorophthalic acid (CIDA). The oDCB was removed from the mixture as an azeotrope with water. The weight of the reactor was maintained constant by adding the corresponding amount of water back to the reactor. The process took approximately 25 hours. Subsequently, the mixture was cooled to 14° C. and centrifuged. The WC was washed with 10 parts of water per part of 4,4′-oxydiphthalic tetraacid. 1492 parts of the final WC was obtained and it contained 85% of 4,4′-oxydiphthalic tetraacid and less than 30 ppm of hexaethylguanidinium chloride, 464 ppm of chlorophthalic acid and 64 ppm of potassium, with the balance (˜5 wt %) being water.

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