Splitting Of Linkages Research Articles

Pyrolysis-gas chromatography-mass spectrometry of two trimeric lignin model compounds with alkyl-aryl ether structure

Thermal degradation of ω-guaiacoxy-acetoguaiacone-benzylether (A) and ω-syringoxy-acetoguaiacone-benzylether (B) has been investigated for a better understanding of the thermolytic behaviour of lignins. Earlier differential scanning calorimetric studies revealed that degradation starts below 200° C. Direct insertion probe experiments also demonstrated that splitting of linkages between aroxy and acetoguaiacone-benzylether (C) moieties commences at 175° C. As a consequence the presence of the following compounds was observed: guaiacol and C (from A) and syringol and C (from B). Simultaneously to these splitting mechanisms a rearrangement occurs between the ω-carbon of compound C and the phenolic oxygen of the aroxy residues, resulting in the formation of 2-methoxybenzaldehyde and acetovanillone-benzylether (from A) and 2,6-dimethoxybenzaldehyde and acetovanillone-benzylether (from B). Pyrolysis-gas chromatography-mass spectrometry experiments between 240 to 600°C corroborated these results. The higher the pyrolysis temperature the more peaks are displayed in the pyrograms. The pyrograms obtained at 600° C show 40 to 70 major peaks which were evaluated. The relative retention times, M + values and in most cases the assignments to defined compounds are given. Many ‘unknown’ substances could be identified as condensation products derived from benzyl radicals. Flow diagrams illustrate the main splitting mechanisms of compounds A and B.

Mechanism of hydrogenation of coal-derived asphaltene

Use of asphaltene instead of the parent coal as the starting material for hydrogenolysis makes it easier to discuss the reaction mechanism, because the mean chemical structures of both reactant and products can be deduced from structural analysis. In this study asphaltene from Japanese Akabira coal was hydrogenated at 400 or 370 °C under initial pressures of 9.8 or 10.4 MPa using red-mud and sulphur catalyst. The structures of the products (oil and remaining asphaltene) and of the original asphaltene were analysed statistically by n.m.r. data. Most of the conversion of asphaltene to oil was caused by saturation of aromatic rings, decomposition of naphthenic rings, dehydroxylation and the decrease of inert ( O + N + S) elements resulting from the opening of hetero-rings; the splitting of linkages between unit structures did not contribute to the conversion.