Acid-base behavior and Al3+ complex formation of synthesized 2,3-dihydroxyterephthalic acid (DHTPA) at pH 3 as a model compound of Inogashira fulvic acid (IFA)

作者：Kurisaki Tsutomu^*; Etou Mayumi; Okaue Yoshihiro; Wakita Hisanobu; Yokoyama Takushi

来源：Polyhedron, 2014, 72: 135-139.

DOI：10.1016/jpoly.2014.02.006

• Inogashira fulvic acid
• Al-DHTPA complex
• Coordination mechanism
• Al-27 NMR
• Complex formation

The interaction between the aluminum ion (Al3+) and Inogashira fulvic acid (IFA) at pH 3 was investigated using the calibration curve method for 27Al NMR spectra. The average conditional stability constant (log K) can be calculated to be 2.002.04 (M-1) (bidentatemonodentate) from the results of Al-27 NMR measurements. In addition, because IFA has various coordination sites, including COOH, phenolic and/or alcoholic OH groups, we attempted to synthesize 2,3-dihydroxyterephthalic acid (DHTPA) as a model compound with the functional groups of IFA for the investigation of the microscopic coordination mechanism between Al3+ and IFA by potentiometric titration and Al-27 NMR measurements. The pK(ai) values of DHTPA could be determined successfully (pK(a1) = 2.3, pK(a2) = 3.4 and pK(a3) = 7.2; pKa4 was not determined), and these values indicate that DHTPA can act as a powerful chelating ligand, even at pH 3. DHTPA can interact with Al3+, and it predominantly forms 1:1 and 2:1 AlDHTPA complexes. The calculated average conditional formation constant (log K-1 and K-2) of each complex can be determined as 1.09 (1:1) and 4.81 (M-1) (2:1). The results obtained showed that both the 1:1 and 2:1 AlDHTPA complexes are formed and Al3+ interacts with IFA at pH3.

• 出版日期2014-4-10