Unprecedented catalyst-free lignin dearomatization with hydrogen peroxide and dimethyl carbonate
Lignin can be efficiently dearomatized and oxidized under catalyst-free conditions in dimethyl carbonate as solvent and hydrogen peroxide as oxidant at 20–80 °C. Based on H2O2 loadings, modified fibres with different aromatic content and sizes can be achieved (from 100% to 0% aromatics). At loadings > 0.2 mol H2O2 g lignin−1 almost complete dearomatized lignin can be achieved, resulting in a pale oily gel. Analyses of the derivatives show increase in carbonylic bonds (FTIR) and oxygen (elemental analysis) and smaller size fibres (ESI-MS). Changes were also in-depth monitored by 2D 1H-13C HSQC NMR. Depending on a desired application (e.g. resins, additives, coatings, etc.), tailored dearomatized lignin fibres can be straightforwardly produced. Being a novel reaction with relatively high peroxide concentrations, experiments must be conducted under strong safety conditions to avoid possible explosions and other risks associated to peroxides and/or in situ formed derivatives.