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Green Chemistry
Page 7 of 8
DOI: 10.1039/C8GC02260G
ARTICLE
Journal Name
precipitation of black materials formed during the reaction 33 wt% xylose and 60% from 50 wt% xylose at a pH of 1.28
which were filtered off. Water was then evaporated and the after 6h of reaction. If the pH was lowered to 0.86 the yield to
recovered residue was dried overnight at 100 °C before furfural was enhanced to 75% after 4h of reaction showing
1
13
analyzing by H and C NMR. It was shown that this solid was that by decreasing the pH, the reaction rate and the yield of
ChCl and that no structural modification was observed after furfural could be increased. ChCl can be recovered after the
the reaction since signals were similar to those obtained when reaction and was recycled successfully which is also of high
commercial ChCl was analyzed (Figures S7, S8). One can interest. The formation of choline xyloside as an intermediate
mention that 95% of ChCl was recovered with high purity. The was found to promote the formation rate of furfural starting
recycling of ChCl was then performed by adding fresh xylose from a highly concentrated feed of xylose. The reaction
(125mg) to an acidic solution of water in the presence of MIBK mechanism was determined, relying first on the genesis of
following the conditions described above. A 69% yield of choline xyloside. This step is followed by the formation of a
furfural was obtained demonstrating the stability of ChCl carbocation on the C2 position and ring con-traction, leading
under our working conditions and the possibility to recycle it.
to furfural after further dehydration. To the best of our
knowledge, it is the first time that such an intermediate is
identified. Overall, the use of ChCl as a component of the
biphasic medium appears as a beneficial approach for the
synthesis of chemicals from highly concentrated feeds of
carbohydrates, which will undoubtedly inspire research in the
future.
Table 3: Effect of ChCl on the furfural yield starting from 50wt% of xylose in a biphasic
media (H
2
O/MIBK = 1/20) at 120°C and a pH of 1.28.
Entry
ChCl
Initial formation rate
Max. yield of
Time (h)
(wt%)
of furfural (mmol/h)
furfural (%)
1
2
3
4
5
0
0.099
0.199
0.316
0.330
0.366
54
57
12
12
12
20
60
56
6
(12)*
12
100
150
60 (60)*
57
Conflicts of interest
There are no conflicts to declare.
*The furfural yield was stable from 6 to 12 h.
We next explored the effect of choline chloride on the
Acknowledgements
dehydration of a higher concentrated xylose solution (50 wt%).
In these experiments, the ChCl concentration was kept at 60
wt%. We were delighted to see that the initial production rate
of furfural was also enhanced (0.316 mmol/h, Table 3, entry 3)
The authors would like to thank the ANR agency for the funding
of FurCab Project ANR-15-CE07-0016.
compared to the rate of the reaction medium without ChCl Notes and references
0.099 mmol/h, Table 3, entry1). The maximum furfural yield
(
‡ For a sake of clarity, all the conversion curves are presented in
the supporting information of the manuscript.
was similar in both cases (60% vs 54%). Regardless on the
concentration, ChCl exhibited a beneficial effect on the initial
production rate of furfural (Table 3, Figure S9) a maximum rate
being obtained for 150 wt% of ChCl (0.366 mmol/h). However,
the highest furfural yield (60%) was achieved at a ChCl ratio of
1
2
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1
00 wt% relative to water corresponding to a xylose : ChCl
5
molar ratio of 0.93.
Based on all these results, it was interesting to see if the
reaction time could be lowered to reach a furfural yield higher
than 70%. A reaction was performed in an acid aqueous
solution of a pH of 0.86 instead of 1.28 using 33.3 wt% of
xylose at 120°C. We were pleased to see that after 3 h of
reaction, 73% of furfural were obtained, for a total conversion
of xylose and that after 4h of reaction the yield of furfural was
2
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7
5% (Figure S10). This last result showed that by lowering the
pH we could increase the reaction rate and the yield to
furfural. The recycling of ChCl was also performed and similar
yield to furfural (75% after 4h) was obtained with the
recovered ChCl demonstrating again its recyclability.
1
1
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1
1
Conclusions
Along this study, we have demonstrated that choline chloride
can enhance the formation rate of furfural from a highly
concentrated solution of xylose with a yield around 70% from
4 S. Lima, M. M. Antunes, A. Fernandes, M. Pillinger, M. F.
Ribeiro and A. A. Valente, Appl. Catal., A, 2010, 388, 141.
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| J. Name., 2012, 00, 1-3
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