(432d) Pyrolysis Kinetics to and from Levoglucosan
Levoglucosan is a major and characteristic product of cellulose pyrolysis, formed catalytically in the absence of metal ions by R-OH molecules like water and other hydroxylated sugar-pyrolysis products [Seshadri and Westmoreland, J. Phys. Chem. A 116:49 (2012) 11997-20013]. No radicals are necessary, although radical chemistry must be important at high temperatures. Other pericyclic unimolecular reactions may also occur, often involving hydroxyl groups. Here, we extend the previous work through quantum-chemistry predictions of transition states for altered glucose structures. Specifically, the OH groups on C1 and C6 that are involved in levoglucosan formation are substituted by NH2 and CH3. Nitrogen has one lone pair of electrons, and the methyl carbon has none; the calculations thus reveal how oxygen's two lone pairs influence the kinetics of glucose pyrolysis, and the results are then applied to cellulose. Added insights result from examining solvation by explicit water molecules, solvations by continuum models, and the effect of ionic acids. Finally, the routes by which levoglucosan may decompose are examined.