14233-61-5Relevant articles and documents
Porous Tin-Organic Frameworks as Selective Epimerization Catalysts in Aqueous Solutions
Delidovich, Irina,Hoffmann, Andreas,Willms, Andrea,Rose, Marcus
, p. 3792 - 3798 (2017/06/19)
Epimerization of sugars is a carbon-efficient route not only to produce rare carbohydrates but also to extend the product scope for chemical production in future biorefineries. Industrially available catalysts for epimerization are limited mainly to soluble Mo(VI) species as well as substrate-specific epimerases. Here we report highly active and selective tin-organic frameworks (Sn-OF) as solid catalysts for the epimerization of aldoses at the C-2 position, such as the conversion of glucose to mannose. The reaction proceeds via a carbon skeleton rearrangement, that is, through breaking of a C-2/C-3 carbon bond and formation of a C-1/C-3 bond. Partially hydrolyzed Ph3Sn-OH sites were found to be the catalytically active centers. Our results suggest that the high catalytic activity of Sn-OFs for the epimerization is determined by (1) Lewis acidity of tin; (2) free Sn-OH groups; and (3) the high hydrophobicity of organic linkers applied in the aqueous solutions.
Synthesis of furfural from xylose, xylan, and biomass using AlCl 3·6H2O in biphasic media via xylose isomerization to xylulose
Yang, Yu,Hu, Chang-Wei,Abu-Omar, Mahdi M.
experimental part, p. 405 - 410 (2012/06/16)
Furfural was prepared in high yields (75%) from the reaction of xylose in a water-tetrahydrofuran biphasic medium containing AlCl3· 6H2O and NaCl under microwave heating at 140°C. The reaction profile revealed the formation of xylulose as an intermediate en route to the dehydration product (furfural). The reaction under these conditions reached completion in 45 min. The aqueous phase containing AlCl3· 6H2O and NaCl could be recycled multiple times (>5) without any loss of activity or selectivity for furfural. Extension of this biphasic reaction system to include xylan as the starting material afforded furfural in 64% yield. The use of corn stover, pinewood, switchgrass, and poplar gave furfural in 55, 38, 56, and 64% yield, respectively, at 160°C. Even though AlCl3·6H2O did not affect the conversion of crystalline cellulose, moderate yields of the by-product 5-hydroxymethylfurfural (HMF) were noted. The highest HMF yield of 42% was obtained from pinewood. The coproduction of HMF and furfural from biomass was attributed to the weakening of the cellulose network in the biomass, as a result of hemicellulose hydrolysis. The multifunctional capacity of AlCl3·6H2O (hemicellulose hydrolysis, xylose isomerization, and xylulose dehydration) in combination with its ease of recyclability make it an attractive candidate/catalyst for the selective synthesis of furfural from various biomass feedstocks. Aluminum in microwaves: AlCl3·6H2O successively hydrolyzes biomass hemicellulose to xylose, isomerizes xylose to xylulose, and dehydrates xylulose to furfural under microwave heating at 160°C with yields in the range of 38-64%, depending on the biomass feedstock. The use of a biphasic medium allows the recycling of AlCl 3·6H2O (which remains in the aqueous phase) for multiple cycles without loss of activity or selectivity (see figure). Copyright
Substrate-dependent chemoselective aldose-aldose and aldose-ketose isomerizations of carbohydrates promoted by a combination of calcium ion and monoamines
Tanase, Tomoaki,Takei, Tomoyuki,Hidai, Masanobu,Yano, Shigenobu
, p. 303 - 312 (2007/10/03)
Epimerization of aldoses at C-2 has been extensively investigated by using various metal ions in conjunction with diamines, monoamines, and aminoalcohols. Aldoses are epimerized at C-2 by a combination of alkaline-earth or rare-earth metal ions (Ca2+, Sr2+, Pr3+, or Ce3+) and such monoamines as triethylamine. In particular, the Ca2+ -triethylamine system proved effective in promoting aldose-ketose isomerization as well as C-2 epimerization of aldoses. 13C NMR studies using D-(1-13C)glucose and D-(1-13C)galactose with the CaCl2 system in CD3OD revealed that the C-2 epimerization proceeds via stereospecific rearrangement of the carbon skeleton, or 1,2-carbon shift, and ketose formation proceeds partially through an intramolecular hydrogen migration or 1,2-hydride shift and, in part, via an enediol intermediate. These simultaneous aldose-aldose and aldose-ketose isomerizations showed interesting substrate-dependent chemoselectivity. Whereas the mannose-type aldoses having 2,3-erythro configuration (D-mannose, D-lyxose, and D-ribose) showed considerable resistance to both the C-2 epimerization and the aldose-ketose isomerization, the glucose-type sugars having 2,3-threo and 3,4-threo configurations, D-glucose and D-xylose, are mainly epimerized at C-2 and those having the 2,3-threo and 3,4-erythro configurations, D-galactose and D-arabinose, were mostly isomerized into 2-ketoses. These features are of potential interest in relevance to biomimic sugar transformations by metal ions.
