METHOD OF PREPARING INTRAMOLECULAR ANHYDRIDE OF TRIMELLITIC ACID Russian patent published in 2000 - IPC

FIELD: organic synthesis. SUBSTANCE: product is prepared by single- stage liquid-phase oxidation of pseudocumene with air oxygen into trimellitic acid followed by thermal dehydration of the latter into intramolecular anhydride. First reaction is conducted in presence of manganese catalyst containing heavy metal salts and bromine compounds as promoter in acetic acid at 160-225 C and pressure, heavy metals being Ni, Co, and Zr taken together and/or in the form of binary mixtures (Ni- Co, Ni-Zr, Zr-Co) and bromine compounds being hydrobromic acid and/or its mixture with hydrochloric acid, while manganese-to-metals ratio is 1:(0.1-0.3), Br/Cl ratio 1:(0.5-4.0), summary concentration of catalyst in reaction mixture is 0.05-0.12%, concentration of bromine and/or bromine-chlorine mixture 0.12-0.44%, process is conducted under conditions of countercurrent of oxygen-containing compounds and reaction products. Feed of hydrohalic acid is distributed along the height of reaction zone in such a way that no more than 50% of promoter of its total amount were fed into the top part of reaction zone simultaneously acetic acid solution of pseudocumene and variable-valence metal salts and process proceeds until 25% conversion of pseudocumene into trimellitic acid is attained. The rest of promoter is fed in dispersed mode into bottom part of reaction zone and process is led until 97% concentration of trimellitic acid in reaction product is reached. After that, reaction product is discharged from the bottom part of reaction zone. Product is concentrated into 30-60% suspension of trimellitic acid by distilling off at least half amount of solvent. Suspension is subjected to dehydration in one or two in-series operated apparatuses provided with heating elements and condensers, wherein residual solvent is evaporated at 200-250 C and melt of crude trimellitic anhydride is kept until water vapors stop to release. EFFECT: intensified and simplified process and increased quality of product. 3 dwg, 2 tbl, 17 ex