Demethylation and Nitration of Lignin

Abstract

The formation of methanol during treatment of wood meal with nitrogen dioxide is favored by the presence of oxygen and suppressed by addition of sodium sulfate. With 0.5% of added nitrogen dioxide large amounts of methanol were produced at 70°C when kraft lignin was impregnated with 0.5M nitric acid. A markedly increased formation of methanol and nitro groups in the lignin occurred when sodium nitrate was added. At low acidity the effect of sodium nitrate was insignificant. In a solution which was 0.5 molal with respect to nitric acid and 0.8 molal with respect to sodium nitrate, appreciable amounts of methanol and nitro groups were produced even when no nitrogen dioxide was added. This is explained by a generation of nitrogen dioxide from nitric acid in a autocatalytic process favored by high concentrations of nitrate and hydrogen ions.