Study On The Complex Properties Of Black Wattle Tannin

On the basis of the basic principle for complex chemistry, the complex characters ofblack wattle tannin and its derivatives with some metal ions were studied to make full useof vegetable tannins. Firstly, protonation constants and metal-complex stability constantsof black wattle tannin, valonea tannin and tannic acid were determined by pHpotentiometric titration. The complex selectivity of different structures of tannins withFe³⁺, Cu²⁺, Zn²⁺, Ni²⁺ ions was investigated and factors affecting protonation constant andstability constant were discussed. The results showed that the purification of black wattletannin by gel column chromatography showed little effect on the complex stabilityconstants. The stability constant of black wattle tannin with Fe³⁺ is larger than that ofEDTA. Secondarily, effects of reaction temperature and sodium bisulfite concentration onthe sulfonation degrees of black wattle tannin were investigated by orthogonal test. Therelationships between the sulfonation degrees and the stability constants were analyzed.The results showed the sulfonation improved the complex capability and selection of thetannin to the ions.Thirdly, the etherification of the tannin with chioroactic acid wascarried out, and the complex properties of the modified products were studied. The resultsshowed that the complex capability of the etherified tannin was a little smaller than that ofthe unmodified tannin. Finally, coordination structures and the coordination ratio of metalcomplexes of the black wattle tannin and its derivatives were characterized by means ofFTIR and UV-Vis. The results showed that phenolic hydroxyl and carboxyl groups werethe main coordination groups, and the coordination numbers of the metal complexes wererelated to kinds of metal ions and the tannins, pH value of the solutions, and so on.