Home – Home – Jornals – Chemistry for Sustainable Development 2016 number 1

The effect of mechanochemical action of aqueous alkaline media on the chemical composition and molecular mass distribution of lignin from upland peat was studied. It was shown that mechanochemical action leads both to hydrolytic destruction and to condensation processes in the molecular structure. These transformations are combined with oxidative processes. The accumulation of a noticeable amount of polar groups in lignin causes an increase in its hydrophilic properties and promotes a decrease in molecular mass due to the dissolution of low-molecular fraction in aqueous alkaline solution. As a consequence, complicated and deep lignin transformations combining destructive and condensation processes lead to gradual transformation of its chemical structure into humic substances. Lignin molecules subjected to sonolysis are composed of oxidized guayacyl and hydroquinone fragments connected through ether bonds or carbon bonds of methylene group. Some guayacyl fragments are oxidized to 2,3-dihydroxybenzoic acid. Along with carbon-carbon and ether bonds, they also include insignificant amount of nitrogen-carbon bonds formed as a result of oxidative ammonolysis of lignin during sonolysis. The stability of a part of lignocarbon bonds to hydrolytic action promotes the formation of not only framework but also the peripheral part of humic acids formed from polyose fragments as a result of sonolysis. The intensity of transformation of the lignocarbon complex into humic substances is due to the strength of the base used during sonolysis. It is assumed that the low molecular mass fractions of lignin participate in the formation of the framework part of humic substances during sonolysis of the secondary plant raw material in alkaline media.