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Chemistry and Industry of Forest Products ›› 2021, Vol. 41 ›› Issue (1): 1-6.doi: 10.3969/j.issn.0253-2417.2021.01.001

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Determination of Deprotonation Characteristics of Tannic Acid by Potential Titration Method

Liangliang ZHANG1(), He ZHANG1, Man XU1, Xinyu HU1, Yiwen LIU2   

  1. 1. Institute of Chemical Industry of Forest Products, CAF; National Engineering Lab. for Biomass Chemical Utilization; Key Lab. of Chemical Engineering of Forest Products, National Forestry and Grassland Administration; Key Lab. of Biomass Energy and Material, Jiangsu Province; Jiangsu Co-Innovation Center for Efficient Processing and Utilization of Forest Resources, Nanjing 210042, China
    2. Wufeng Chicheng Biotechnology Co. Ltd., Engineering Techonology Research Center of High-Efficient Cultivation and Deep Processing of Chinese Gall, National Forestry and Grassland Administration, Yichang 443413, China
  • Received:2020-10-28 Online:2021-02-28 Published:2021-03-03


The deprotonation process of a typical tannic acid, 1, 2, 3, 4, 6-penta-O-galloyl-β-D-glucopyranose(PGG), and its parent compound methyl gallate(MeG) was studied by pH potentiometric titration and spectrophotography. The dissociation constants of PGG and MeG were calculated by chemometric methods using the Reactlab Equilibrium software. Concentration profiles of the fully protonated PGG and its two deprotonated forms at different pH values were also predicted by the chemometric method. The results showed that the deprotonation of phenolic hydroxyl of PGG was found with the increasing of pH value, and fully deprotonated forms of PGG existed at pH>11. These formed negative ions of oxygen can further coordinate with metal ions. Spectroscopic studies showed that there were two deprotonated forms of PGG, and the corresponding pKa values were 10.84±0.03 and 10.62±0.02. There was only one deprotonated form of MeG during titration, and the corresponding pKa value was 9.68±0.02.

Key words: tannic acid, deprotonation, dissociation constants, spectrophotography, stochiometry

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