Maleic acid (MA) and AlCl 3 self-assemble into catalytic complexes (Al-(MA) 2 -(OH) 2 (aq)) with improved selectivity for converting glucose to HMF, and levulinic acid. The calculated activation energy (E a ) of the MA-aluminum catalyzed glucose-to-fructose isomerization is 95 kJ·mol -1 compared to 149 kJ·mol -1 for HCl and AlCl 3 alone. Furthermore, conversion of fructose to HMF is enhanced. The catalytic conversion of fructose to HMF by MA and AlCl 3 at 180 o C is 1.7× faster
A fast-pyrolysis probe/tandem mass spectrometer combination was utilized to determine the initial fast-pyrolysis products for four different selectively (13)C-labeled cellobiose molecules. Several products are shown to result entirely from fragmentation of the reducing end of cellobiose, leaving the nonreducing end intact in these products. These findings are in disagreement with mechanisms proposed previously. Quantum chemical calculations were used to identify feasible low-energy pathways for several products. These results provide insights into the mechanisms of fast pyrolysis of cellulose.
Seven synthesized G-lignin oligomer model compounds (ranging in size from dimers to an octamer) with 5-5 and/or β-O-4 linkages, and three synthesized S-lignin model compounds (a dimer, trimer, and tetramer) with β-O-4 linkages, were evaporated and deprotonated using negative-ion mode ESI in a linear quadrupole ion trap/Fourier transform ion cyclotron resonance mass spectrometer. The collision-activated dissociation (CAD) fragmentation patterns (obtained in MS and MS experiments, respectively) for the negative ions were studied to develop a procedure for sequencing unknown lignin oligomers. On the basis of the observed fragmentation patterns, the measured elemental compositions of the most abundant fragment ions, and quantum chemical calculations, the most important reaction pathways and likely mechanisms were delineated. Many of these reactions occur via charge-remote fragmentation mechanisms. Deprotonated compounds with only β-O-4 linkages, or both 5-5 and β-O-4 linkages, showed major 1,2-eliminations of neutral compounds containing one, two, or three aromatic rings. The most likely mechanisms for these reactions are charge-remote Maccoll and retro-ene eliminations resulting in the cleavage of a β-O-4 linkage. Facile losses of HO and CHO were also observed for all deprotonated model compounds, which involve a previously published charge-driven mechanism. Characteristic "ion groups" and "key ions" were identified that, when combined with their CAD products (MS experiments), can be used to sequence unknown oligomers.
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