Determination of nitrobenzene oxidation products by GC and1H-NMR spectroscopy using 5-iodovanillin as a new internal standard
The nitrobenzene oxidation method was modified to obtain more reproducible data and more structural information about lignin, not only by gas chromatography (GC) but also by proton nuclear magnetic resonance (1H-NMR) spectroscopy for quantitative determination of the oxidation products and to simplify the procedures. The nitrobenzene oxidation mixture was directly extracted after acidification without preextraction of by-products. The direct extraction made the extractive step easy and gave reproducible data. 5-Iodovanillin was selected as a new internal standard. The reason for this selection was that 5-iodovanillin did not exist in the nitrobenzene oxidation products from any plant species and had an aldehyde group whose peak did not overlap with the other aldehyde peaks on an1H-NMR spectrum. Thus, the use of 5-iodovanillin enabled us to quantifyp-hydroxybenzaldehyde, vanillin, and syringaldehyde in oxidation products on the basis of1H-NMR analysis as well as GC. Furthermore, more information about the condensed structure of lignin was derived by comparing the1H-NMR and GC analyses.
Key wordsLignin 5-Iodovanillin Modified nitrobenzene oxidation 1H-NMR analysis
Unable to display preview. Download preview PDF.
- 4.Chen C-L (1992) Nitrobenzene and cupric oxide oxidations. In: Lin SY, Dence CW (eds) Methods in lignin chemistry. Springer-Verlag, Berlin Heidelberg, pp 301–321Google Scholar
- 7.Dence CW (1992) The determination of lignin. In: Lin SY, Dence CW (eds) Methods in lignin chemistry. Springer-Verlag, Berlin Heidelberg, pp 33–61Google Scholar
- 8.Erdtman H (1935) Phenoldehydrierung. VI. Dehydrierende kupplung einiger guajakol-derivate. Svensk Kem Tidskr 47:223–230Google Scholar