Mechanism of Brønsted acid-catalyzed conversion of carbohydrates

Potential Brønsted acid-catalyzed glucose and fructose conversion routes to levulinic acid have been studied by DFT calculations. The most favorable mechanisms for sugar transformations initiated by protonation of different OH groups are identified. It is demonstrated that the differences in the rea...

Celý popis

Uloženo v:

Podrobná bibliografie
Vydáno v:	Journal of catalysis Ročník 295; s. 122 - 132
Hlavní autoři:	Yang, Gang, Pidko, Evgeny A., Hensen, Emiel J.M.
Médium:	Journal Article
Jazyk:	angličtina
Vydáno:	Amsterdam Elsevier Inc 01.11.2012 Elsevier Elsevier BV
Témata:	5-Hydroxymethylfurfural Acid catalysis Acids active sites aqueous solutions Biomass biorefining Carbohydrates carbon Catalysis Catalysts Chemical reactions Chemistry condensation DFT calculations Exact sciences and technology fructose General and physical chemistry glucose Hexose humin hydroxymethylfurfural Levulinic acid Reaction mechanism rehydration Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry Hexose Levulinic acid 5-Hydroxymethylfurfural Reaction mechanism Biomass Acid catalysis DFT calculations Water Glucose Potential Dehydration Precursor Acidic solution Brönsted acid Sequential Hydroxyl group Carbohydrate Chemical reactivity Catalytic reaction Condensation reaction Regioselectivity Reaction path Carbon Conversion Fructose Density functional method Rehydration Protonation Aqueous solution
ISSN:	0021-9517, 1090-2694
On-line přístup:	Získat plný text
Tagy:	Přidat tag Žádné tagy, Buďte první, kdo vytvoří štítek k tomuto záznamu!

Popis
Shrnutí:	Potential Brønsted acid-catalyzed glucose and fructose conversion routes to levulinic acid have been studied by DFT calculations. The most favorable mechanisms for sugar transformations initiated by protonation of different OH groups are identified. It is demonstrated that the differences in the reactivity of glucose and fructose in acidic aqueous solutions are dominated by the regioselectivity of the initial protonation step. [Display omitted] ► Regioselectivity of the initial protonation of sugars determines selectivity of their conversion. ► Favorable protonation of fructose opens path to levulinic acid via HMF intermediate. ► Favorable protonation of glucose leads to reversion products and humin precursors. ► Novel direct mechanism of glucose transformation to levulinic acid is reported. A comprehensive DFT study of acid-catalyzed glucose and fructose reactions in water covering more than 100 potential reaction paths is performed with the aim to identify the main reaction channels for obtaining such desirable biorefinery platform products as 5-hydroxymethylfurfural (HMF) and levulinic acid (LA). Characteristic for fructose dehydration by Brønsted acids is the preferred protonation of the O2H group at the anomeric carbon atom, which initiates a sequence of facile reactions toward HMF. Further rehydration to LA is more difficult and competes with condensation reactions leading to humins. A very different result is obtained when glucose is the reactant. The preferred protonation site is the O1H hydroxyl group. The associated reaction paths do not lead to the formation of HMF or LA but result in humin precursors and reversion products. Protonation of other sites occurs at a much lower rate. Nevertheless, when glucose is activated at these less reactive sites, it can lead to LA via a reaction mechanism that does not involve the intermediate formation of fructose and HMF. This direct mechanism is argued to be preferred over the conventional sequential conversion scheme. It is concluded that the differences in the reactivity of glucose and fructose in acidic aqueous solutions are dominated by the regioselectivity of the initial protonation step.
Bibliografie:	http://dx.doi.org/10.1016/j.jcat.2012.08.002 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 14 ObjectType-Article-1 ObjectType-Feature-2 content type line 23
ISSN:	0021-9517 1090-2694
DOI:	10.1016/j.jcat.2012.08.002