Characterization of the tetramethylammonium hydroxide thermochemolysis products of carbohydrates

Add time:08/06/2019    Source:sciencedirect.com

The identification of the thermochemolysis products (in the presence of tetramethylammonium hydroxide, TMAH) of carbohydrates is presented. Analysis was carried out using on-line flash pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and off-line flash (vacuum) pyrolysis followed by GC/MS. Standard samples of hexoses, pentoses, deoxyhexoses, lactose, cellulose and starch were treated with 25% aqueous TMAH (100 times excess by weight). Approximately 50 μg (for on-line analysis) or 250 μg (for off-line analysis) of the carbohydrate/TMAH mixture was heated to 700°C (10 s) using a quartz holder and a CDS pyroprobe. From electron and chemical impact mass spectral data, and, from literature on alkaline decomposition of carbohydrates, tentative structures of unique products and the mechanisms of their formation are proposed. A series of permethylated deoxy aldonic acids are tentatively identified as key products. It is postulated that these ‘saccharinic acids’ are initially formed from the action of alkali on reducing sugars which are then subsequently methylated. In addition, thermochemolytic analysis of lactose, cellulose and starch afforded their own unique permethylated deoxy aldonic acids as well producing methoxy benzene products, i.e. 1,2,4-trimethoxybenzene, 2,4-dimethoxyphenol. It is believed that glycosidically-linked saccharides initially degrade under alkaline conditions similar to the so-called ‘peeling reaction’ observed for cellulose under alkaline pulping conditions and then are finally methylated. An algal sample has been analyzed for its carbohydrate composition. The observation of hexose, pentose and polysaccharide thermochemolysis products illustrate the potential of the method to characterize the saccharide composition of more complex biomaterials.

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