Concerted reactions are proposed to be keys to understanding thermal decomposition of
glucose in the absence of ionic chemistry, including molecular catalysis by ROH molecules such as H(2)O, other
glucose molecules, and most of the intermediates and products. Concerted transition states, elementary-reaction pathways, and rate coefficients are computed for pyrolysis of β-
D-glucose (β-D-glucopyranose), the monomer of
cellulose, and for related molecules, giving an improved and elementary-reaction interpretation of the reaction network proposed by Sanders et al. (J. Anal. Appl. Pyrolysis, 2003, 66, 29-50). Reactions for ring-opening and formation, ring contraction, retro-
aldol condensation, keto-enol tautomerization, and
dehydration are included. The
dehydration reactions are focused on bicyclic ring formations that lead to
levoglucosan and 1,6-β-D-anhydrousglucofuranose. The bimolecular ROH-assisted reactions are found to have lower activation energy compared to the unimolecular reactions. The same
dehydration reaction to
levoglucosan should occur for
cellulose going to cellosan (e.g., cellotriosan) plus a shortened
cellulose chain, a hypothesis supported by the very similar activation energies computed when alternate groups were substituted at the C1 glycosidic
oxygen. The principles of Sanders et al. that distinguish
D-glucose, D-
fructose,
sucrose, and
cellulose pyrolysis prove useful in providing qualitative insights into
cellulose pyrolysis.