Roles of hydroxyls in the noncatalytic and catalyzed formation of levoglucosan from glucose

Seshadri, Vikram; Westmoreland, Phillip R.

doi:10.1016/j.cattod.2015.10.033

Cited by 30 publications

(31 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…First, the formation of a 1,6-acetal ring occurs in a two-step pattern, forming a phosphate intermediate (P1-i1, P3-i3, P4-i4, P5-i3, and P6-i4, as circled in Fig. 3 ), similar to the reported inorganic acid-catalyzed LG or LG end formation by Westmoreland et al [30] and our group [19] . Second, there are two patterns for the H 3 PO 4 -catalyzed breakage of C4-O4 bond, dehydration and carbonyl group shift.…”

Section: The Lgo Formation Mechanism Under H 3 Po 4 -Catalyzed Conditsupporting

confidence: 85%

Insight into the formation mechanism of levoglucosenone in phosphoric acid-catalyzed fast pyrolysis of cellulose

Lü

et al. 2020

Journal of Energy Chemistry

View full text Add to dashboard Cite

Section: The Lgo Formation Mechanism Under H 3 Po 4 -Catalyzed Conditsupporting

confidence: 85%

Insight into the formation mechanism of levoglucosenone in phosphoric acid-catalyzed fast pyrolysis of cellulose

Lü

et al. 2020

Journal of Energy Chemistry

View full text Add to dashboard Cite

“…From a chemical point of view, levoglucosan arises from the intramolecular cyclization of a glucopyranose unit resulting in a bicyclic form structurally similar to glucose, with a bridge between positions 1 and 5 (see Figure ). The mechanism of glucose pyrolysis to levoglucosan (and other substances) has been widely investigated both experimentally and with theoretical methods . This mechanism necessarily involves an intramolecular cyclization and a dehydration process.…”

Section: Introductionmentioning

confidence: 99%

Investigating the Conformation of the Bridged Monosaccharide Levoglucosan

et al. 2018

View full text Add to dashboard Cite

Levoglucosan is one of the main products of the thermal degradation of glucose and cellulose and is commonly used as a tracer for biomass burning. Herein we report a conformational analysis of levoglucosan under isolation conditions, by means of microwave spectroscopy coupled with ultrafast laser vaporization in supersonic expansions. We observed three different conformations of levoglucosan in the gas phase. They all share a common heavy atom rigid bicyclic structure. The difference between the three of them lies in the network of intramolecular hydrogen bonds that arises from the OH groups at positions 2, 3 and 4. The different combinations of H-bonds give richness to the conformational landscape of levoglucosan. The gas phase conformers obtained in this work are compared to the crystal structure of levoglucosan previously reported. Although the heavy atom frame remains unchanged, there are significant differences in the positions of the H-atoms. In addition, the levoglucosan structure can be compared to the related glucose, for which gas phase conformational studies exist in the literature. In this case, in going from glucose to levoglucosan, there is an inversion in the chair conformation of the pyranose ring. This forces the OH groups to adopt axial positions (instead of the more favorable equatorial positions in glucose) and completely changes the pattern of intramolecular H-bonds.

show abstract

“…However, the energetics behind this process remains unknown and, as far as we know, no theoretical investigations on its mechanism are available in literature. Very recently, only computational studies at the Density Functional Theory (DFT) level on the mechanism of formation of the anhydrosugars levoglucosan and levoglucosenone have appeared . Since higher yields of LAC are desirable to place conveniently this chemical platform into biorefinery streams, it becomes crucial to understand in detail the mechanism of this reaction.…”

Section: Introductionmentioning

confidence: 99%

“…Even if in the absence of catalyst only small amounts of LAC are obtained, we believe it is crucial to identify the key species involved in the process, to estimate the energy barriers along the reaction pathway and elucidate the nature and role of the forces that drive the reaction. Recently several examples in literature indicate DFT as a suitable approach to investigate a variety of reactivity problems relevant to sustainability in chemistry . Our model‐system is the starting species 1 (see Scheme ), that is, a molecule formed by two eliminations from a d ‐glucopyranosyl residue of the cellulose chain, namely (2S)‐5‐Hydroxy‐2‐(hydroxymethyl)‐2,3‐dihydro‐4 H ‐pyran‐4‐one (ascopyrone P) .…”

Section: Introductionmentioning

confidence: 99%

The Reaction Pathway of Cellulose Pyrolysis to a Multifunctional Chiral Building Block: The Role of Water Unveiled by a DFT Computational Investigation

et al. 2016

View full text Add to dashboard Cite

LAC (hydroxylactone (1R,5S)-1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one) is one of the most interesting products of the pyrolysis of cellulose and represents a useful chiral building block in organic synthesis. A computational investigation at the DFT level on the mechanism of formation of LAC shows that this species can be obtained following two reaction paths, path A and path B, starting from a well-known pyrolysis product (ascopyrone P). A series of internal rearrangements involving in all cases a proton transfer leads directly to LAC (path B). An alternative path (path A) can be also followed. From this path, via a "gate" connecting the two reaction channels, it is possible to reach path B and form LAC. In both cases, the rate-determining step of the process is the initial keto-enol isomerization. We found that water, which is present in the reaction mixture, "catalyzes" the reaction by assisting the proton transfers present in all the steps of the process. In particular, water lowers the barrier of the rate-determining step that becomes 40.9 kcal mol (79.4 kcal mol in the absence of water). The corresponding computed rate constant is 4.3×10 s at 500 °C, a value which is consistent with the presence of LAC in the absence of metal catalysts. The results of this study on the non-catalyzed process underpin the important role played by water in the formation of pyrolysis products of cellulose where proton transfer is a key mechanistic step.

show abstract

Roles of hydroxyls in the noncatalytic and catalyzed formation of levoglucosan from glucose

Cited by 30 publications

References 33 publications

Insight into the formation mechanism of levoglucosenone in phosphoric acid-catalyzed fast pyrolysis of cellulose

Insight into the formation mechanism of levoglucosenone in phosphoric acid-catalyzed fast pyrolysis of cellulose

Investigating the Conformation of the Bridged Monosaccharide Levoglucosan

The Reaction Pathway of Cellulose Pyrolysis to a Multifunctional Chiral Building Block: The Role of Water Unveiled by a DFT Computational Investigation

Contact Info

Product

Resources

About