SinS - Abstract

Abstract Information :

Bio-oils typically contain thousands of highly oxygenated molecular compositions with a wide variety of functional groups e.g. acids, alcohols, aldehydes, ethers, ethers, furans, phenols, ketones, among others. In general, bio-oils need further processing to reduce their oxygen content, in an effort to improve their quality and miscibility with petroleum fuels and to produce fine chemicals. Bottlenecks in both fundamental knowledge and technological aspects, limit the advances in the chemical processes required for a successful transition to produce chemicals from renewable biological material sources.

Structural elucidation in complex mixtures remains as a key goal in analytical chemistry. Powerful analytical techniques such as ultrahigh resolution mass spectrometers (UHRMS) can deliver the elemental molecular composition profile of a complex mixtures. When coupled to gas chromatography (GC), it is possible to separate volatile isomeric compositions while detecting thousands of co-eluting compounds. The positive identification of the individual isomers is laborious due to the large number of analytes and the lack of authentic standards with known response factors for identification and quantification. As consequence, only a few hundred of chemicals have been confidently identified in bio-oils. An alternative analytical method consisting of chemoselective derivatisations followed by GC-UHRMS can be the key to facilitate structural elucidation at the individual chemical level in complex mixtures. Chemoselective derivatisations aim to tag moieties containing a particular functional group before GC-UHRMS analysis. The comparison of the retention time of the individual chemicals before and after derivatization will reveal those isomers that were transformed through the specific chemical reaction, and thus containing the targeted functional group.

The hydroxyl group is the most abundant functional group in bio-oils and natural product derivatives and can be found in carbohydrates, alcohols, carboxylic acids, and phenols. Here, acetic anhydride (Ac2O) in the presence of acetone and dimethyl sulfoxide (DMSO) was used to derivatise the hydroxyl group in a bio-oil obtained from lignocellulosic material, and various chemical standards. The samples were then characterised by GC coupled to a Fourier transform ion cyclotron mass spectrometry. Our data reveals the extraordinary complexity of the bio-oil and the variety of hydroxyl groups within the bio-oil chemicals. The oxidation of primary and secondary aromatic alcohols and the methylthiomethylation (MTM) in available ortho positions of phenolic compositions were observed exclusively in DMSO-Ac2O mixtures, whereas phenols without saturated side chains were acetylated in acetone-Ac2O. The comparison between the individual chemicals detected in DMSO-Ac2O and acetone-Ac2O then allows the discrimination and semi-quantification of individual chemicals with a phenolic hydroxyl group, from aromatic alcohol (including benzylic and other non-phenolic alcohol) moieties. Phenolic compositions are known as coke precursors in catalytical pyrolysis and upgrading processes. Thus, the combination of chemoselective derivatisations in combination with GC-UHRMS can be a valuable resource to outline the hydroxyl group profile in elemental chemical compositions in complex mixtures.