Thermal destruction of d -mannose condensation products using p -aminoacetanilide in solvent-free systems

Thermal destruction of D-mannose condensation products using p-aminoacetanilide in solvent-free systems, such as paraffinic oil and a KBr-matrix, was studied by the methods of electronic and vibrational spectroscopy. The thermal destruction of mannosylamine in a KBr matrix is accompanied by intense coloration. At the same time, the bands in the IR spectra characterizing the functionalization of aminoacetanilide retain their position and intensity, which indicates the absence of transformation of the amine fragment. The appearance of the 1645, 1680, 1690 cm-1 bands of enone O=C-C=C- fragments is noted, along with the 1750 and 1780 cm-1 bands attributed to the stretching C=O vibrations of esters and lactones likely formed as a result of transformation of the primary mannosylamine degradation products. The thermal destruction of a mannosylamine suspension in paraffinic oil shows a lower transformation of the mannosyla-mine structure in comparison with experimental processes in a KBr matrix. The spectra depict the bands of С = O vibrations in different structural environments, as well as the signal shift of 1280 cm-1 into the low- frequency region characterizing the elimination of arylamine. The reflection spectra of the alcohol solutions of destruction products demonstrate the presence of only the 1750 cm-1 band; the 1780 cm-1 band does not appear probably due to the instability of lactones in solutions, which causes their recyclization. An analysis of vibrational spectra showed the absence of bands characteristic of melanoidin N-heterocycles due to the predominant formation of acyclic conjugated systems and carboxylic acid derivatives in the studied solvent-free systems. In the electronic spectra of the alcohol solutions of destruction products in both systems, maxima of about 260 nm were recorded. These maxima correspond to the absorption of oxyenone chromophores and the continuous absorption region in the visible part of the spectrum, caused by the formation of extended chromophores, i.e. condensation products of the intermediates of mannosylamine decomposition. The obtained results can be useful both when selecting conditions for the Maillard reaction with a given functionalization and when developing methods for the synthesis of antioxidant agents for protecting polymers and oils.

d-mannose, p-aminoacetanilide, lactones, melanoidins, thermal destruction, spectroscopy