| abstract |
The production of low color polyetherimides, including its intermediates, such as bisimides and diaryl diether dianhydrides, may be affected by producing an improved purity intermediate of 4-nitro-N-alkylphthalimide. A salt, such as alkali metal carbonate or alkali metal hydrogen carbonate, is added to an aqueous mixture of 4-nitro-N-alkylphthalimide and 3-nitro-N-alkylphthalimide to selectively hydrolyze the imide linkage of 3-nitro-N-alkylphthalimide forming a water-soluble acid-amide salt. An organic solvent is added to this salt mixture to phase separate 4-nitro-N-alkylphthalimide having dissolved in the organic solvent from acid-amide salt of 3-nitro-N-alkylphthalimide having dissolved in water. |