- Tin, molybdenum and tin-molybdenum oxides: Influence of Lewis and Bronsted acid sites on xylose conversion
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In this study, tin oxide (SnO2), molybdenum oxide (MoO3) and a mixed oxide based on tin and molybdenum (respectively, Sn100, Mo100 and SnMo25, synthesized by the impregnation method) were applied in xylose conversion. The best results were obtained employing Mo100 and SnMo25. In the presence of SnMo25, after 0.5 h, xylose conversions of 39.5%, 34.1% and 63.4% were obtained, respectively, at 110, 130 and 150 °C. For Mo100, conversions of 49.6%, 71.8% and 85.3% were attained under the same reaction conditions, showing that Mo100 provided the best conversion results. However, with the use of this catalyst there was an increase in the amount of soluble and insoluble polymeric material. In terms of the soluble products formed from xylose, depending on the reaction condition were detected xylulose (X), lyxose (L) and furfural (FUR), glyceraldehyde (GL), pyruvaldehyde (PYR), glycoaldehyde (GLYC), dihydroxyacetone (DHA), lactic acid (AL), levulinic acid (LA) and acetic acid (AA). However, with the use of Sn100 or without a catalyst (systems with low conversions) there was mainly the formation of lyxose. The use of Mo100 and SnMo25 (systems which exhibit high acidity) leads mainly to isomerization, epimerization and dehydration reactions, as in the case of the retro-aldol pathway and furfural conversion, highlighting the importance of Lewis and Bronsted acid sites in relation to modulating the selectivity of the systems.
- Meneghetti, Mario R.,Meneghetti, Simoni M. P.,Pryston, Dhara B. A.,da Silva Avelino, Débora Olimpio,dos Santos, Thatiane V.
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- Insight into Aluminum Sulfate-Catalyzed Xylan Conversion into Furfural in a Γ-Valerolactone/Water Biphasic Solvent under Microwave Conditions
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A simple and efficient biphasic system with an earth-abundant metal salt catalyst was used to produce furfural from xylan with a high yield of up to 87.8 % under microwave conditions. Strikingly, the metal salt Al2(SO4)3 e
- Yang, Tao,Zhou, Yi-Han,Zhu, Sheng-Zhen,Pan, Hui,Huang, Yao-Bing
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p. 4066 - 4079
(2017/10/12)
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- Hemicellulose-derived chemicals: One-step production of furfuryl alcohol from xylose
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One-pot production of furfuryl alcohol via xylose dehydration followed by furfural hydrogenation was investigated over a dual catalyst system composed of Pt/SiO2 and sulfated ZrO2 as metal and acid catalysts, respectively. All samples were characterized by XRD, XRF, N2 physisorption, TG-MS and FTIR regarding their most fundamental properties for the studied process. A systematic study is reported on the effects of the reaction temperature, the composition of the binary solvent and the molar ratio between acid and metal sites in the catalyst system. The results revealed the feasibility of the one-step process for furfuryl alcohol synthesis and showed that the occurrence of both acid and metal sites is compulsory in order to promote the dehydration of xylose to furfural and its further hydrogenation to furfuryl alcohol. Selectivity towards furfuryl alcohol was found to be strongly dependent on the solvent, which can inhibit its polymerization to some extent. This journal is the Partner Organisations 2014.
- Perez, Rafael F.,Fraga, Marco A.
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p. 3942 - 3950
(2014/08/05)
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- Aldose-ketose interconversion in pyridine in the presence of aluminium oxide
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The reaction rate of the Lobry de Bruyn-Alberda van Ekenstein transformation of aldoses to ketoses in boiling pyridine was strongly increased by the addition of aluminium oxide. In addition to aldose-ketose transformation, 2-epimers of the starting aldoses and 3-epimers of the primarily produced ketoses were formed to some extent, as reported also when these reactions are carried out without aluminium oxide. The relative amounts of the primary ketose and the starting aldose in the reaction mixtures may be explained on the basis of their stability, predicted from reported free energy calculations. Isomerisation of ketoses to aldoses was much slower than the reverse reaction. The relative free energies are also in these cases important, the very stable xylo-2-hexulose gave only 7% and 6% of the aldoses gulose and idose, respectively, after boiling for 7 h in pyridine in the presence of aluminium oxide.
- Ekeberg, Dag,Morgenlie, Svein,Stenstrom, Yngve
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p. 1992 - 1997
(2008/02/10)
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- Prebiotic carbohydrate synthesis: Zinc-proline catalyzes direct aqueous aldol reactions of α-hydroxy aldehydes and ketones
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Zn-proline catalyzed aldolisation of glycoladehyde gave mainly tetroses whereas in the cross-aldolisation of glycoladehyde and rac-glyceraldehyde, pentoses accounted for 60% of the sugars formed with 20% of ribose. The Royal Society of Chemistry 2005.
- Kofoed, Jacob,Reymond, Jean-Louis,Darbre, Tamis
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p. 1850 - 1855
(2007/10/03)
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- Base catalysed isomerisation of aldoses of the arabino and lyxo series in the presence of aluminate
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Base-catalysed isomerisation of aldoses of the arabino and lyxo series in aluminate solution has been investigated. L-Arabinose and D-galactose give L-erythro-2-pentulose (L-ribulose) and D-lyxo-2-hexulose (D-tagatose), respectively, in good yields, whereas lower reactivity is observed for 6-deoxy-D-galactose (D-fucose). From D-lyxose, D-mannose and 6-deoxy-L-mannose (L-rhamnose) are obtained mixtures of ketoses and C-2 epimeric aldoses. Small amounts of the 3-epimers of the ketoses were also formed. 6-Deoxy-L-arabino-2-hexulose (6-deoxy-L-fructose) and 6-deoxy-L-glucose (L-quinovose) were formed in low yields from 6-deoxy-L-mannose and isolated as their O-isopropylidene derivatives. Explanations of the differences in reactivity and course of the reaction have been suggested on the basis of steric effects.
- Ekeberg, Dag,Morgenlie, Svein,Stenstrom, Yngve
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p. 779 - 786
(2007/10/03)
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- Rare keto-aldoses from enzymatic oxidation: Substrates and oxidation products of pyranose 2-oxidase
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Pyranose oxidases are known to oxidise D-glucose, D-xylose and L- sorbose to keto-aldoses, biochemically interesting compounds that may also be used for synthetic purposes in a variety of reactions. In this study pyranose oxidase from the basidiomycete Peniophora gigantea was investigated, and it was found that this enzyme is able to oxidise a broad variety of substrates very effectively. In analogy to its natural mode of action, most substrates are oxidised regioselectively in position 2. Certain compounds, however, are converted into 3-keto derivatives, and the enzyme even exhibits transfer potential, that is, disscharides are formed from β-glycosides of higher alcohols. Substrates that may be oxidised at C-2 in yields between 40-98% are D-allose, D-galactose, 6-deoxy-D-glucose, D-gentiobiose, α-D-glucopyranosyl fluoride and the very interesting 3-deoxy-D-glucose. 1,5-Anhydro-D-glucitol (1-deoxy-D-glucose) is very effectively oxidised in position 2 in 98% yield and additionally gives a product of dioxidation at C-2 and C-3 upon prolonged reaction time Selective oxidation at C-3 was found for 2-deoxy-D-glucose in very good yields and for methyl β-D-gluco- and methyl β-galactopyranoside in lower yields. All oxidation products were unequivocally characterised by NMR spectroscopy and/or chemical derivatisation. In addition, the kinetic data of the enzymatic reactions were determined for all substrates. On the basis of these data and the structural characteristics of the substrates, a model for the minimal structural requirements of the enzyme-substrate interaction is suggested. The enzyme presumably uses two different binding modes for the regioselective C-2 and the C-3 oxidations, which are described.
- Freimund, Stefan,Huwig, Alexander,Giffhorn, Friedrich,Koepper, Sabine
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p. 2442 - 2455
(2007/10/03)
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- Synthesis of D-erythro-2-pentulose and D-threo-2-pentulose and analysis of the 13C- and 1H-n.m.r. spectra of the 1-13C- and 2-13C-substituted sugars.
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The pentuloses D-erythro-2-pentulose (1) and D-threo-2-pentulose (2) and their 1-13C- and 2-13C-substituted derivatives were prepared by hydrogenating the corresponding isotopically normal and 13C-substituted D-pentos-2-uloses with a Pd-carbon catalyst. The threo isomer and its labeled derivatives were alternatively prepared from isotopically normal and 13C-substituted D-xyloses with immobilized D-xylose (D-glucose) isomerase (E.C.5.3.1.5). The equilibrium compositions of 1 and 2 (furanose anomers and acyclic keto forms) in 2H2O were determined from 13C-n.m.r. spectra (75 MHz) of the 2-13C-labeled derivatives. The conformational properties of the cyclic and acyclic forms in 2H2O were assessed with the use of 1H-1H, 13C-1H, and 13C-13C spin-coupling constants obtained from 1H-n.m.r. (620 MHz) and 13C-n.m.r. (75 MHz) spectra. Compared with the structurally related aldotetrofuranoses the 2-pentulofuranoses more strongly prefer conformations in which the anomeric hydroxyl group is oriented quasi-axially. The strongly dipolarized carbonyl group in the acyclic keto forms of 1 and 2 appears to stabilize chain conformations having O-1 and O-3 eclipsed with the carbonyl oxygen.
- Vuorinen,Serianni
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- Aldol Reaction between Small Sugars. Preparation of DL-threo-2-Pentulose and DL-lyxo-3-Hexulose and their Isolation as O-Isopropylidene Derivatives
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The improved diastereoselectivity obtained with strongly basic anion-exchange resin as catalyst in aldol condensation between two-, three- and four-carbon "sugars" has been utilised in the preparation of DL-threo-2-pentulose and DL-lyxo-3-hexulose, which were isolated as their O-isopropylidene derivatives.A possible reason for the observe preference of formation of the lyxo-diastereomer in condensation between glycolaldehyde and glycero-tetrulose is suggested.
- Morgenlie, Svein
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p. 745 - 748
(2007/10/02)
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- Kinetics, Catalysis, and Mechanism of the Secondary Reaction in the Final Phase of the Formose Reaction
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In the final phase of the formose reaction sugars are formed by the reaction of glycolaldehyde, glyceraldehyde and dihydroxyacetone.The application of high-pressure liquid chromatography allows for the first time to investigate intermediate and final products quantitatively.The results of kinetical investigations allow to suggest a reaction mechanism for the secondary reaction in the final phase of the formose reaction.This mechanism is compared with that of the starting phase and other known mechanisms.From the results metal ion-catalyzed aldol reactions have to be assumed.
- Harsch, Guenther,Bauer, Hermann,Voelter, Wolfgang
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p. 623 - 635
(2007/10/02)
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