PURPOSE: To readily obtain the title compound which is a raw material for polyimides, etc., at a low cost without requiring expensive dehydrating agents and using special steps, by thermally dehydrating hydrous wet crystals of diphenyl sulfone-3,3',4,4'-tetracarboxylic acid.
CONSTITUTION: Hydrous wet crystals of diphenyl sulfone-3,3',4,4'-tetracarboxylic acid is dehydrated, preferably at 110W250°C, especially 150W230°C under ordinary or reduced pressure to afford the aimed compound. The above-mentioned raw material diphenyl sulfone-3,3',4,4'-tetracarboxylic acid is obtained by, e.g., oxidizing the corresponding methyl substitution product with nitric acid or dichromic acid or catalytically oxidizing the above-mentioned substitution product with air. The raw material must be used in the form of the hydrous wet crystals. The moisture content in the wet crystals is preferably about 5W80wt.%, especially about 10W66wt.% expressed in terms of the wet basis.
Sanami, Hiroshi
Nakazawa, Mikiro
