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.
This invention is related to a method for making diether dianhydrides by the reaction of halophthalic anhydride and a metal salt of an aromatic dihydroxy compound in the presence of a solvent and a phase transfer catalyst. Typical phase transfer catalyst include guanidium salts, aminopyridinium salts, or phosphazenium salts.
A method for making aromatic ether imides is provided by effecting the displacement of reactive radicals on a phthalimide nucleus with a mono- or bis-alkali metal phenoxide in the presence of a nonpolar solvent and a phase transfer catalyst, such as a triorganoborate. The aromatic ether imide made by the present invention are useful intermediates for making aromatic ether anhydrides and aromatic bis (ether anhydrides).
Branched alkyldiorganoaminopyridinium salts have been found useful as phase transfer catalysts for facilitating nucleophilic aromatic substitution. For example, the 2-ethylhexyl salts of dialkylaminopyridine, can be used as stable phase transfer catalysts for making aromatic etherimides by reacting substituted phthalimides and alkali metal phenoxides in the presence of a non-polar organic solvent.