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mic acid, etc.) or heterogeneous (sulfated ZrO2, Nafion, Amber-
lyst-15, sulfonated carbon, zeolites, etc.) catalysts.[7] Yields of
methyl glycosides of about 50–60% were claimed. However,
the reaction temperatures (200–2758C) are still high and under
these conditions the formation of dimethylether is possible in
large quantities. In 2010, de Vos,[8] Corma,[9] and co-workers re-
ported the conversion of cellulose to alkyl glycosides in ionic
liquids (ILs). ILs are capable of dissolving cellulose, thus in-
creasing its reactivity and allowing reaction temperatures to be
decreased to 110 8C. Starting from C4–C8 alkyl alcohols, more
than 80% mass yield of alkyl glycosides were obtained in 1-
butyl-3-imidazolium chloride using a catalytic amount of Am-
berlyst-15. Although ILs are considered as promising solvents
for cellulose processing, their price, toxicity, and long-term re-
cycling are still important shortcomings.
mass (wheat straw) from which butyl glycosides and butyl xy-
losides are produced in high yields. As mentioned above, butyl
glycosides and xylosides are important compounds not only
because they can be used as hydrotropes but also because
they are key intermediates in the production of amphiphiles.
Results and Discussion
Avicel (Avicel PH-200, FMC BioPolymer) microcrystalline cellu-
lose (MCC) was first selected in this study owing to its high
purity, which facilitates analytical procedures. Inspired by the
previous works of Schüth, Rinaldi,[10] and co-workers, the MCC
was first ball milled in the presence of H2SO4. Typically, cellu-
lose was impregnated with 10.7 wt% of H2SO4 prior to ball
milling in a planetary ball mill (Retsch PM 100) at 200 rpm for
24 h. Under these conditions, size-exclusion chromatography
revealed that the degree of polymerization (DP) of the recov-
ered cello-oligomers was lower than 6, which is consistent
with previous works.[10,11] Next, the recovered cello-oligomers
containing H2SO4 (1 g) were suspended in n-butanol and
heated at 1178C without any intermediate purification. The
cello-oligomer content in n-butanol was 6.7 wt%. The yields of
butyl glycosides were determined by using GC–MS analysis
(relative to the initial amount of anhydroglucose introduced in
the planetary ball mill). At the beginning of the reaction, the
reaction media was heterogeneous owing to the insolubility of
cello-oligomers in n-butanol. As the reaction proceeded, the
reaction mixture became homogeneous, indicating conversion
of the cello-oligomers. The results are illustrated in Figure 1.
Analysis of the reaction media by GC–MS (using standards
provided by Agro-industrie Recherches et DØveloppements,
ARD) confirmed the formation of butyl glycosides. Data on the
characterization of butyl glycosides can be found in the exist-
ing literature.[9a] Based on the kinetic profile of the reaction
(Figure 1), the yield of butyl glycosides reached a maximum of
62% after 2 h. At prolonged reaction times, the yield of butyl
glycosides dropped to 42% presumably owing to their degra-
dation in the reaction media. Note that after 2 h (62% yield),
only 50 mg of a solid black residue was recovered. Considering
that 1 g of cellulose was initially introduced in the reactor, this
suggests that the conversion of cellulose was at least
Recently, Rinaldi, Schüth, and co-workers developed the
acid-assisted ball milling of cellulose and even lignocellulosic
biomass as an efficient pretreatment process for the produc-
tion of bio-based chemicals.[10] Notably, ball milling of cellulose
in the presence of an acid catalyst allowed cellulose to be de-
polymerized to form water-soluble cello-oligomers under dry
conditions.[11] Mechanical constraints were proposed to force
a conformational change of the anhydroglucose rings, a pivotal
step for the “dry” acid-catalyzed hydrolysis of the 1,4-b-glycosi-
dic bonds. As ball milling does not destroy the acid catalyst,
water-soluble cello-oligomers can then be directly hydrolyzed
in water after the milling process under very mild conditions
(1308C, 1 h) to obtain glucose in 91% yield.
Here, we show that the mechanical treatment of cellulose in
the presence of an acid is a promising technology to produce
butyl glycosides directly from microcrystalline cellulose. Cello-
oligomers obtained after the acid-assisted ball-milling treat-
ment readily undergo Fischer glycosylation when suspended
in boiling n-butanol to afford the targeted butyl glycosides in
high yields (Scheme 1). Importantly, acid-assisted ball-milled
cellulose does not recrystallize in n-butanol (contrary to the
case with water); therefore, it is more prone to glycosylation
than to hydrolysis, allowing the ball-milling treatment time
(energy-consuming step) to be drastically reduced. This pro-
cess was also successfully transposed to lignocellulosic bio-
95%. As generally observed in the chemistry of car-
bohydrates, it was difficult to identify with accuracy
the chemical structure of side products. Formation of
HMF-derived chemicals were observed by GC–MS.
However, their amount in the reaction stayed below
1%, suggesting that other side products were also
concomitantly produced. Among them, the forma-
tion of glycosylated oligoglucosides was observed by
GC–MS, but not quantified. This observation is in ac-
cordance with previous works where it is established
that glycosylation of glucose affords glucosides that
contain on average one alkyl chain for every 1.1 to
1.5 glucose units.
Analysis of the crude mixture by performing 13C
1
and H NMR spectroscopy brings useful information.
Scheme 1. General scheme of the glycosylation of acid-assisted ball-milled cellulose.
The 13C NMR analysis of the crude is very similar to
ChemSusChem 2015, 8, 3263 – 3269
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