FEATURES OF LIGNIN NITRATION BY NITROGEN DIOXIDE

• Published in: Journal of characterization and development of novel materials Vol. 10; no. 4; pp. 207 - 220
• Main Authors: Gaponova, I S, Davydov, E Ya, Pokholok, T V, Lomakin, S M, Pariiskii, G B
• Format: Journal Article
• Language: English
• Published: Hauppauge Nova Science Publishers, Inc 01.10.2018
• Subjects: Aldehydes; Dimers; Hydroxyl groups; Infrared spectroscopy; Lignin; Nitrates; Nitration; Nitric oxide; Nitrogen dioxide; Nitroso compounds; Oxidation; Oximes; Phenols; Radicals
• ISSN: 1937-7975

The mechanism of the stable radical generation in lignin under the action of nitrogen dioxide and NO2 - air mixture is considered. The formation of phenoxyl, iminoxyl and acylaminoxyl radicals has been detected by EPR technique. The proposed mechanism involves a primary oxidative reaction of phenol groups with dimers of NO2 (nitrosyl nitrate) resulting in the formation of phenoxyl radicals and nitric oxide. In the subsequent recombination of phenoxyl radicals and nitric oxide, nitroso compounds and oximes are formed. By reaction of oximes with radicals NO2, stable iminoxyl radicals are formed. This mechanism is confirmed by kinetic dependencies obtained over a wide range of NO2 concentrations. From IR spectroscopy measurements it follows that hydroxyl groups of nonphenolic structures of lignin are oxidised to aldehydes producing in reaction with NO2 acylaminoxyl radicals. The kinetic data show that the adsorption of NO2 on the lignin surface is the rate-determining factor of the stable radical formation.