Production of heterocyclic dicarboxylic acids

Claim 1

THE PROCESS OF PRODUCING AROMATIC HETEROCYCLIC DIAND TRICARBOXYLIC ACIDS IN WHICH AT LEAST ONE CARBOXYL GROUP STANDS IN A NEIGHBORING POSITION TO A HETERO-ATOM WHICH COMPRISES HEATING A SUBSTANTIALLY ANHYDROUS ALKALI METAL SALT OF AN AROMATIC HETEROCYCLIC CARBOXYLIC ACID SELECTED FROM THE GROUP CONSISTING OF AROMATIC HETEROCYCLIC DICARBOXYLIC ACIDS HAVING THE CARBOXYL GROUPS ATTACHED TO THE HETEROCYCLIC RING IN OTHER THAN THE POSITIONS OF THE PRODUCTS TO BE PRODUCED AND AROMATIC HETEROCYCLIC MONOCARBOXYLIC ACIDS, THE HETEROCYCLIC NUCLEUS OF SAID AROMATIC HETEROCYCLIC CARBOXYLIC ACIDS COMPRISING CARBON ATOMS, AND AT LEAST ONE HETEROATOM SELECTED FROM THE GROUP CONSISTING OF SULFUR OXYGEN AND NITROGEN, IN AN INERT ATMOSPHERE UNDER ANHYDROUS CONDITIONS TO A TEMPERATURE ABOVE 275* C. AND BELOW THE DECOMPOSITION TEMPERATURE OF THE STARTING MATERIAL UNTIL AT LEAST ONE CARBOXYL GROUP HAS CHANGED POSITION IN COMPARISON WITH THE STARTING MATERIAL, CONVEDRTING THE AROMATIC HETEROCYCLIC CARBOXYLIC ACID ALKALI METAL SALT FORMED THEREBY INTO THE CORRESPONDING FREE AROMATIC HETEROCYCLIC CARBOXYLIC ACID BY ACIDIFYING AND SEPARATING THE FREE AROMATIC HETEROCYCLIC CARBOXYLIC ACID SO PRODUCED FROM THE REMAINING REACTION MIXTURE COMPONENTS.