Investigation of the structure changes of tannides acylated derivatives in the process of synthesis using differentiating electronic absorption spectroscopy

Abstract

A number of acylated derivatives of industrial gallotannin and ellagitannin from alder cones with different substitution degrees of phenolic hydroxyls has been synthesized. The synthesis involved the preparation of a mixture of derivatives with different substitution places of phenolic hydroxyls and different number of substitutions. The synthesis of acylated derivatives was carried out under reflux with the mixture of the modifier with tannides in glacial acetic acid, and recrystallization of the derivatives obtained was performed from the water-ethanol mixture. Succinic and maleic anhydrides were used as modifiers. The primary electronic absorption spectrum and its first and second derivatives – differential electronic absorption spectra were studied. As the result of the study of the electronic absorption spectra of tannides with varying degrees of modification it has been found that significant changes in the spectrum shift of the absorption band of aromatic groups (250-270 nm) is observed only for the acylated gallotannins. Thus, it has been shown that the degree of modification correlates with the degree of the shift of the absorption band, and it allows to use this reaction for identification of the combinatorial derivative of gallotannin. The electronic absorption spectra of various acylated ellagitannins derivatives did not actually differ. It indicates a more stable and rigid electronic and spatial structure of digallic acid, which prevents the use of spectroscopy in the UV region to identify individual combinatorial derivatives of ellagitannins. In HPLC the spectrunm of acylated tannins contains additional bands, including the low molecular weight region of the spectrum. It indicates the appearance of new acylated derivatives in the combinatorial mixture of tannides.