An Improved Synthetic Approach for Obtaining High‐Quality Terephthalic Acid: Eliminating the Need for Purification

• Published in: ChemistrySelect (Weinheim) 2017-12, Vol.2 (35), p.11815-11820
• Main Authors: Kuznetsova, Nina I., Bal'zhinimaev, Bair S., Bhattacharyya, Alak, Walenga, Joel T.
• Format: Article
• Language: English
• Subjects: ammonium acetate; homogeneous catalysis; ionic liquid; oxidation; oxygen; terephthalic acid
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.201702615

The large‐scale production of terephthalic acid (TPA) is currently based on the two‐step technology, with oxidation of p‐xylene in an acetic acid solution containing a Co/Mn/Br catalyst, followed by the purification of the crude product containing the impurity p‐carboxybenzaldehyde (CBA). Here we offer a simple and robust route to the target product, which makes it possible to avoid the tedious and energy‐consuming hydropurification of TPA to remove CBA. We demonstrate that addition of ammonium acetate and ionic liquids to the acetic acid solution changes the reaction medium to improve solubility of TPA and CBA and accelerates oxidation of CBA to TPA. Efficient combinations of the additives and appropriate oxidation conditions have been selected to attain nearly complete oxidation of CBA to TPA over the reaction time and formation of the oxidation product with content of CBA less than 25 ppm without the hydropurification step. Pure without purifying: Combination of ammonium acetate and ionic liquids serves as solubilizing additive in oxidation of p‐xylene to terephthalic acid to intensify removal of p‐carboxybenzaldehyde intermediate from the reaction mixture. As a result, the oxidation product contains less than 25 ppm of p‐carboxybenzaldehyde without hydro purification conventionally practiced.