Purification of 1, 2, 3, 4-cyclopentanetet-racarboxylic acid and preparation of its anhydride

Claim 1

IN A PROCESS FOR PREPARING AN ANHYDRIDE OF 1,2,3,4CYCLOPENTANETETRACARBOXYLIC ACID WHEREIN THE RESULTANT ANHYDRIDE IS DISCOLORED, THE 1,2,3,4-CYCLOPENTANETETRACARBOXYLIC ACID BEING PREPARED BY A PROCESS COMPRISING NITRIC ACID OXIDATION OF BICYCLO (2,2,1)-5-HEPTENE-2,3-DICARBOXYLIC ANHYDRIDE AND INCLUDING NITROGEN-CONTAINING IMPURITIES PRODUCED DURING THE PREPARATION THEREOF, THE IMPROVEMENT COMPRISING PREPARING THE ANHYDRIDE FROM 1,2,3,4-CYCLOPENTANETETRACARBOXYLIC ACID WHICH HAS BEEN PURIFIED BY A PROCESS COMPRISING CRYSTALLIZING THE 1,2,3,4-CYCLOPENTANETETRACARBOXYLIC ACID INCLUDING IMPURITIES FROM A SOLVENT COMPRISING BY VOLUME ABOUT 10-80 PARTS OF WATER AND ABOUT 90-20 PARTS OF AT LEAST ONE ALKANOIC MONOCARBOXYLIC ACID CONTAINING 1-4 INCLUSIVE CARBON ATOMS TO REDUCE THE IMPURITY CONTENT.