The formation of 2-furaldehyde and formic acid from pentoses in slightly acidic deuterium oxide studied by 1H NMR spectroscopy

Furfural formation from d-xylose: the use of different halides in dilute aqueous acidic solutions allows for exceptionally high yields

“…In Scheme 2 a reaction mechanism is proposed based on the results presented here and those of previous works already mentioned. 5,12 In this mechanism more than one option for side reactions is assumed, whereas the formation of furfural (F) entails a distinctive sequence of one enolization followed by three dehydration reactions, always started by protonation at specific positions. Noteworthy, the kinetics for such mechanism can still be described with very good accuracy by Scheme 1, considering k 2 as the sum of the possible side reactions, and considering the intermediates to occur in very low concentrations.…”

The role of xylulose as an intermediate in xylose conversion to furfural: insights via experiments and kinetic modelling

“…16,17 However, most researchers have adopted a reaction mechanism hypothesis that involves the formation of an acyclic xylose form, even though this mechanism is not able to fully explain the formation of some side products. 4, 15 Antal et al 17 have also proposed the formation of both acyclic and cyclic forms of xylose at temperatures above 250 C.…”

“…10,19,20 Several other authors explained the reaction to take place via a 1,2-enediol intermediate with subsequent dehydration. 4,18 More recently, the isomerization of aldopentoses to ketose sugar (luxose 17,21 or xylulose [22][23][24] ) as an intermediate step in furfural formation has been studied intensively. The current developments of bi-functional catalysts [24][25][26][27][28] and other catalytic systems 29 consider an implementation of such two stage process which includes the xylose isomerization as the rst step followed by the second step -the ketose sugar dehydration to furfural.…”

“…It is a pentose which can be formed either by direct degradation of polymeric xylan in lignocellulosic material or by depolymerization of the solubilized oligomeric xylan. 2 In addition, several studies describe the furfural formation from other pentoses [3][4][5][6] or hexoses. 5 Furfural can be also obtained as a by-product of different biomass treatment processes.…”

Efeitos dos produtos de hidrólise de materiais lignocelulósicos sobre a produção de H2 por fermentação

“…A Figura 10. Estrutura de uma hemicelulose evidenciando suas ligações acetil (1 a 4) e grupos acetilados (5) presentes em alguns açúcares (STÅHLBERG et al, 2011 apresenta um mecanismo acíclico e dois mecanismos cíclicos diretos distintos (AHMAD et al, 1995). Ainda não há suporte experimental para esses mecanismos, pois a degradação das pentoses, principalmente xilose, é complexa e certamente não acontece devido apenas a um mecanismo.…”