NJC
Paper
very interesting for these kinds of reactions involving one-pot the gas atmosphere was quickly evacuated under vacuum. The
transformations of cellulose. We reported for the first time this autoclave was heated (3 1C minÀ1) up to the desired temperature
reaction in the presence of solid catalysts namely Cs2HPW12O40 and left for the desired time under autogenous pressure.
and sulfated zirconia which led to much lower yields. While the Pressure can be tuned by choosing the adequate amount of
first one showed deactivation, the second one could be partly solvent. Reaction time was started when the stabilized temperature
regenerated retaining some reactivity. This confirms that bio- was obtained (1 hour). After reaction, the reactor was cooled using
mass transformation in organic solvents at high temperatures a water/ice bath. The reaction mixture consisted of a homogeneous
with reusable solid acid catalysts is a challenge still as in the liquid phase and a solid phase. The solid phase was filtered over
case of water.31 Besides butyl levulinates, no other identifiable micropore Teflons filters (0.45 mm), washed with acetone until a
products from cellulose have been formed in significant amounts. colorless filtrate was recovered, and dried at room temperature.
Water that inevitably formed in situ by alcohol dehydration had Cellulose liquefaction was determined by the ratio of the mass
an ambivalent influence by enhancing the cellulose reactivity of the recovered solid (whatever its nature) and the mass of
and limiting the esterification step. The latter is less favored introduced cellulose. In the presence of a solid catalyst, the
when secondary and tertiary alcohols are used.
estimated recovered mass of the catalyst was subtracted from
the mass of the recovered solid. Different procedures were
applied to recover the catalysts: for HPA: no treatment, drying
in oven at 100 1C, or calcination at 450 1C under air flow saturated
with water (2 hours); for ZrS: calcination at 450 1C under air flow
Experimental part
Microcrystalline cellulose (particle size 20 mm, crystallinity degree (2 hours). The liquid phase was analyzed on a Shimadzu GC
70%, water content 4 wt%) was used as received from Sigma. ACS 2010 (DB-1 column) and a Shimadzu GC-MS QP202S for detecting
grade 1-butanol, 2-butanol, iso-butanol and concentrated sulfuric butyl-levulinates and dibutyl ethers by comparison with authentic
acid were obtained from Sigma. Tert-Butanol was obtained from samples. Quantification was performed using 1-octanol as standard.
Fluka Analytical with a purity of 99.7%. The considered super-
critical coordinates of butanol isomers were from the Handbook of
Product yields are molar yields and were calculated as follows:
For butyl levulinates: (mol of product)/(mol of C6H10O5 units
Chemistry and Physics:32 1-butanol: 290 1C, 4.4 MPa; 2-butanol: in charged cellulose) Â 100.
262 1C, 4.2 MPa; iso-butanol: 275 1C, 4.3 MPa; tert-butanol: 233 1C,
For di-butyl ethers: (mol of product) Â 2/(mol of butanol) Â 100.
3.9 MPa. Samples of non-commercially available butyl levulinates
Solid-state CP-MAS NMR spectra were recorded on an AVANCE
were prepared for the calibration purpose and isolated by distillation: III 500WB spectrometer. References were TMS for 13C (2000 scans)
iso-butyl and sec-butyl levulinates were obtained by reacting levulinic and 85% H3PO4 for 31P (160 scans).
acid in alcohol in the presence of Amberlyst-15 (reflux, 4 h); tert-butyl
X-ray diffraction spectra were obtained on a Bruker D5005
levulinate was prepared according to Chen et al.25 Cs acidic salt spectrometer. Before XRD analysis the HPA samples were
of 12-tunsgtophosphoric acid and sulfated zirconia were synthe- calcined at 800 1C to form the WO3 phase that could be
sized following procedures previously optimized in our group.33,34 differentiated from the Cs phase, known to be stable upon
CsxH3ÀxPW12O40 was synthesized as follows: H3PW12O40 (10.23 g) treatment at high temperatures.35
was dissolved in 6.4 mL of water. Adjusted equivalents of CsCl
(e.g. 1.07 g for Cs2HPW12O40) were dissolved in 1.3 mL of water.
The two solutions were mixed and a white precipitate formed
Acknowledgements
immediately. The mixture was centrifuged for 30 min to separate
A. D. thanks the University of Lyon 1 for a PhD fellowship. We
the liquid and solid phases. The solid was dissolved in a minimum
warmly thank C. Lorentz (IRCELYON) for help with solid-state
amount of water and this method of centrifugation was repeated
NMR analysis.
2 times to completely wash the white solid from the remaining
salt. The white precipitate was cooled in a freezer overnight and
then lyophilized (sublimation of water under vacuum to avoid
structural damage). Sulfated zirconia was prepared as follows: a
References
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catalyst (40 wt%/cellulose). The reactor was cooled to 0 1C and
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