- Effect of carbon chain length on catalytic C–O bond cleavage of polyols over Rh-ReOx/ZrO2 in aqueous phase
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Production of linear deoxygenated C4 (butanetriols, -diols, and butanols), C5 (pentanetetraols, -triols, -diols, and pentanols), and C6 products (hexanepentaols, -tetraols, -triols, -diols, and hexanols) is achievable by hydrogenolysis of erythritol, xylitol, and sorbitol over supported-bimetallic Rh-ReOx (Re/Rh molar ratio 0.5) catalyst, respectively. After validation of the analytical methodology, the effect of some reaction parameters was studied. In addition to C–O bond cleavage by hydrogenolysis, these polyols can undergo parallel reactions such as epimerization, cyclic dehydration, and C–C bond cleavage. The time courses of each family of linear deoxygenated C4, C5, and C6 products confirmed that the sequence of appearance of the different categories of deoxygenated products followed a multiple sequential deoxygenation pathway. The highest selectivity to a mixture of linear deoxygenated C4, C5, and C6 products at 80percent conversion was favoured under high pressure in the presence of 3.7wt.percentRh-3.5wt.percentReOx/ZrO2 catalysts (54–71percent under 80 bar) at 200 °C.
- Besson, Michèle,Da Silva Perez, Denilson,Perret, Noémie,Pinel, Catherine,Sadier, Achraf
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- MECHANISMS OF PYROLYSIS OF POLYSACCHARIDES: CELLOBIITOL AS A MODEL FOR CELLULOSE
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The pyrolysis of cellobiitol has been studied as a model for cellulose.The products were determined from pyrolysis at 350 deg C in vacuo and at 350 deg C and at 171 deg C at atmospheric pressure.In vacuo, a 32percent yield of 1,6-anhydro-β-D-glucopyranose (levoglucosan 5) and a 70percent yield of D-glucitol and its anhydrides were obtained, but under atmospheric pressure these yields were much lower.A mechanism is postulated in which the first step in the pyrolysis is a heterolytic scission of the glucosidic linkage to produce a glucosyl cation and a glucitol anion.The formeryields the volatile levoglucosan by intramolecular attack of O-6 on the C-1 cation and this reaction is favored in vacuo because of the resultant efficient removal of 5.The glucitol is obtained predominantly as anhydrides, which are volatile in the vacuum pyrolysis.Lower tempeature (171 deg C) pyrolysis gave no 5.The glucosyl cation under such conditions is believed to undergo intermolecular nucleophilic substitution with hydroxyl groups from unreacted starting material and from glucitol to produce oligosaccharides.
- Lowary, Todd L.,Richards, Geoffrey N.
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- THE CHEMICAL-TRANSFORMATION PRODUCTS OF 1,6-DIBROMO-1,6-DIDEOXYGALACTITOL AND 1,2:5,6-DIANHYDROGALACTITOL IN AQUEOUS SOLUTION
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After hydrolysis of 1,6-dibromo-1,6-dideoxygalactitol (1) and 1,2:5,6-dianhydrogalactitol (2), 11 compounds were isolated, three of them as tritylated derivatives.Their structures were established on the basis of chemical evidence and, for four compounds, by X-ray diffraction.The main product of the hydrolysis of 1 was 3,6-anhydro-1-bromo-1-deoxy-DL-galactitol; the end-products of the hydrolysis of 2 were 1,5-anhydro-DL-galactitol, 2,5-anhydro-DL-altriol and galactiotol.
- Vidra, Ildiko,Simon, Kalman,Institoris, Laszlo,Csoeregh, Ingeborg,Czugler, Matyas
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- Acid Catalyzed Dehydration of Alditols. Part I. D-Glucitol and D-Mannitol
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The acid catalyzed dehydration of D-glucitol and D-mannitol has been studied using 13C NMR spectroscopy to monitor the reactions.The products formed were identified and rate constants were measured.Dehydration of (1S)-1-2H-D-mannitol with 3 M sulfuric acid was shown to yield (1R)-1-2H-1,4:3,6-dianhydro-D-mannitol, showing that dehydration of D-mannitol to 1,4-anhydro-D-mannitol and, subsequently, to the 1,4:3,6-dianhydride takes place with inversion at the primary carbon atom.
- Bock, Klaus,Pedersen, Christian,Thoegersen, Henning
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p. 441 - 450
(2007/10/02)
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