Lignins in Alkaline Solutions

The spectra of kraft lignin in KBr pellets and in alkaline solutions show striking differences, as clearly illustrated by the difference spectrum (Fig. 5.2.7). The absorbances at 1560, 1494, 1395, and 1305 cm-1 are more intense, whereas the intensities in the spectral ranges 1710-1603 and 1270-900cm-1, and the aromatic skeletal vibration at 1514cm-1, are lower in NaOH solution. Similar qualitative spectral differences are observed when larch (Larix decidua) MWL is measured in KBr and in aqueous alkaline solutions (Fig. 5.2.8) although the magnitude of the differences is smaller with the hardwood MWL. 

The spectral differences in the solid state (neutral) and solution state spectra (alkaline) are due to the presence of ionizable functional groups in lignin, e.g., 

---

UV Spectrum of Sodium Borohydride-Reduced Lignin in Alkaline Solution... 

Oxidation with Barium Dioxide and Alkali. The alkali lignin was boiled in alkaline solution with an excess of barium dioxide and a little cupric hydroxide under conditions reported to give high yields of vanillic acid (5, 6). Analysis indicated only 13.8% ether extractives and the following yields on the basis of the original alkali lignin 2.8% vanillic acid, 0.4% p-hydroxybenzoic acid, 0.1% vanillin, 0.2% acetovanillone, and a trace of />-hydroxybenzaldehyde. 

Oxidation of Alkali Lignin with Oxygen in Alkaline Solution. 

The reaction mechanism for nitrobenzene oxidation of lignin is still not well understood. Thus, although nitrobenzene in an alkaline solution has been usually regarded as two-electron-transfer oxidant (Chang and Allan 1971), recent investigations on the nitrobenzene oxidation of lignins and related compounds indicate that nitrobenzene in alkaline solution acts as an one-electron-transfer oxidant (Schultz and Templeton 1986). 

TJ McDonough. Peracetic acid decomposition and oxidation of lignin model compounds in alkaline solutions. PhD thesis. University of Toronto, 1972. 

TJ McDonough and H Rapson. Reactions of peracetic acid with lignin model componnds in alkaline solution. Trans. Tech. Sec. CPPA 1 12-17, 1975. 

Like lignin in alkaline NaOH, DBP and MBP can be removed from TBP solvent by forming micellar structures in alkaline sodium carbonate wash solutions. Actinides that were originally com-plexed by DBP and MBP in the TBP organic phase prior to carbonate wash are also transferred from the solvent and are loosely incorporated into the micellar structure of the wash, the aqueous raffinate. 

---