Structural characterization of lignin in the process of cooking of cornstalk with solid alkali and active oxygen
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A novel, efficient, and environmentally friendly technology is used in cornstalk cooking, active oxygen (O2 and H2O2) cooking with solid alkali (MgO). After the cooking, the milled wood lignin in the raw material and pulp and the water-soluble and insoluble lignin in the yellow liquor were all characterized by attenuated total reflectance Fourier transform infrared spectroscopy and two-dimensional heteronuclear single-quantum coherence NMR. The results showed that the cooking procedure with solid alkali and active oxygen had a high selectivity for delignification, which could remove 85.5% of the lignin from the raw material. The syringyl (S/S鈥?S鈥? units could be dissolved preferentially because of their high reactivity, and a novel guaiacyl unit with a carbonyl group (G鈥? was generated in the cooking process. Moreover, during the cooking, the 尾-O-4鈥?(A/A鈥?A) structures as the main side-chain linkages in all the lignins could be partly broken and the 尾-O-4鈥?(A鈥? with a ring-conjugated structure was readily attacked by oxygen, whereas the H unit and 尾-5鈥?and 尾-尾鈥?structures were found to stay stable without characteristic reaction. 漏 2012 American Chemical Society.