PURPOSE: To obtain the high-purity substance by converting biphenyldicarboxylic acid into a dialkali salt, adding a water-soluble organic solvent to the resultant aqueous solution, depositing the dialkali salt, separating and liberating the formed salt.
CONSTITUTION: An alkali and water are added to crude biphenyldicarboxylic acid(BDCA) to provide an aqueous solution of a dialkali salt and a water-soluble organic solvent is then added thereto to provide an aqueous solution of the dialkali salt. Thereby, solubility of the dialkali salt in water is reduced to deposit the dialkali salt. The separated crystals are then dissolved in water and a mineral or organic acid is subsequently added to afford the high-purity BDCA. A solvent (e.g. acetone) having ≥100g/100g-water solubility in water at 20°C and a lower boiling point than that of water with a great difference in the boiling point therefrom is preferred as the water-soluble organic solvent in aspects of recovery. The amount thereof used is preferably such that ≥50% dialkali salt is deposited. The high-purity BDCA is useful as a raw material for polymers.
KAWAMURA MASAYUKI
KAMEI TAKESHI
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