Thermal and IR-Fourier transform spectroscopic study of water-soluble carbohydrate-arylamine condensation products in neutral media

Abstract

Production of synthetic analogues of natural compounds, including high-molecular ones, as well as study of processes of their structure formation, is a pressing task of organic substances technology. To a large extent, this applies to synthetic humic substances, important products characterized by plant growth effect, chelating and other important properties. Simple carbohydrates and aromatic amines as oxygen and nitrogen-containing constituents during condensation in ethanol media produce water-fractionated products, the soluble fractions of which are studied herein by thermal degradation in combination with IR-Fourier transform spectroscopy. Spectral band profile is confirmed mainly by aliphatic structure with high degree of functionalization by carboxyl, hydroxyl and amine groups. As the isolated water-soluble solid products are thermally decomposed in the range of 100-180 °С temperatures in an inert atmosphere, the intensity of bands at 1030 and 1090 cm-1 decreases, and the intensity of the first band drops to almost zero at 180 °С. This experimental fact indicates the progress of thermal dehydration processes, indicating the presence of hydroxyl functions in the structure of the products. The latter are both OH-groups of carbohydrate residue and groups, formed during condensation processes. Additionally, the intensity of the absorption band in the region of 1600 cm-1 corresponding to the fluctuations of double bonds resulting from dehydration is increased. It can be assumed that unlike products of insoluble fractions, as well as products of acid-catalyzed condensations, water-soluble products are formed in neutral ethanol media, the main processes of formation of which are processes of direct retro-aldol cleavage of N-glycosylamines with subsequent condensation of decomposition products. Such a set of processes is an alternative to the experimental difficulty of Amadori rearrangement and lead to formation of products structure differ from one for acid catalyzed condensation products.