Efficient production and separation of biodegradable surfactants from cellulose in 1-butyl-3-methylimidazolium chloride

Article abstract of DOI:10.1002/cssc.201402722

Alkyl glycoside biodegradable surfactants were produced from cellulose and 1-octanol or 1-dodecanol in a one-pot, two-step (hydrolysis-glycosidation) process in 1-butyl-3-methylimidazolium chloride. Both surfactant productivity and separation efficiencies have been strikingly enhanced compared to other previously reported ionic liquid processes. Production temperatures were decreased to limit the extent of glucose dehydration and further degradation processes, but the conversions remained high. Surfactant molar yields up to 72% were achieved by operating at 70°C. Several separation procedures were tested to achieve high recoveries of both surfactant and ionic liquid. The use of a silica stationary phase was useful for isolation of the surfactant, whereas crystallization of the ionic liquid improved its separation efficiency. Finally, the precipitation of dodecyl glycosides in aqueous media was highly efficient for their isolation and for the recovery (> 99 %) of the ionic liquid by using only water as the solvent for separation.

Full text of DOI:10.1002/cssc.201402722

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DOI: 10.1002/cssc.201402722
Efficient Production and Separation of Biodegradable
Surfactants from Cellulose in 1-Butyl-3-Methylimidazolium
Chloride
Alberto V. Puga and Avelino Corma*[a]
Alkyl glycoside biodegradable surfactants were produced from
cellulose and 1-octanol or 1-dodecanol in a one-pot, two-step
(hydrolysis–glycosidation) process in 1-butyl-3-methylimidazoli-
um chloride. Both surfactant productivity and separation effi-
ciencies have been strikingly enhanced compared to other pre-
viously reported ionic liquid processes. Production tempera-
tures were decreased to limit the extent of glucose dehydra-
tion and further degradation processes, but the conversions re-
mained high. Surfactant molar yields up to 72% were achieved
by operating at 708C. Several separation procedures were
tested to achieve high recoveries of both surfactant and ionic
liquid. The use of a silica stationary phase was useful for isola-
tion of the surfactant, whereas crystallization of the ionic liquid
improved its separation efficiency. Finally, the precipitation of
dodecyl glycosides in aqueous media was highly efficient for
their isolation and for the recovery (>99%) of the ionic liquid
by using only water as the solvent for separation.
Introduction
Long-chain alkyl glycosides are nonionic surfactants that are
composed of a saccharide as the hydrophilic head and an alkyl
chain as the hydrophobic tail. They exhibit excellent detergen-
cy, good cleansing performance over wide pH ranges, low tox-
icity (including good skin compatibility), and high biodegrada-
bility.[1] Owing to these favorable properties, alkyl glycosides
are becoming increasingly popular for applications in laundry
detergents, cleaners, cosmetics, personal care products, food
emulsifiers, pharmaceutical formulations, and agrochemicals.[1a]
Glucose derivatives comprise the most important group of
alkyl glycosides; this group consists of alkyl glucosides togeth-
er with certain amounts of alkyl oligoglucosides (CnGm with n=
1 or n>1, respectively, see structure in Figure 1), which are
routes, such as the Koenigs–Knorr method,[1a,3] and less-selec-
tive acid-catalyzed reactions that proceed under equilibrium
conditions, such as the Fischer glycosidation.[1a,3d,e,4] The latter
procedure is simple and has been successfully implemented
for the industrial production of long-chain alkyl glucosides,
either directly or in a two-step process, whereby the sugar
molecule is first reacted with a short-chain alcohol and the re-
sulting glycoside is then transacetalized with a longer alkan-
ol.[1a,2] Direct methods involve less equipment than two-stage
transacetalization processes. In a typical commercial direct pro-
cess, glucose is reacted with long-chain alkanols (preferably 1-
dodecanol/1-tetradecanol mixtures derived from vegetable
oils) in the presence of an acidic catalyst at moderately high
temperatures (100–1258C) under reduced pressure (0.5–
4.0 kPa), and water is continuously removed from the mixture
by distillation.[5] This shifts the equilibrium towards the alkyl
glucosides. The catalysts are usually sulfonic acids operating
under homogeneous regimes, and thus, neutralization at the
end of the reaction is required. The use of heterogeneous
(solid) acids that can be efficiently separated by filtration and
recycled, such as ionic-exchange resins,[4] zeolites,[6] and Al-
MCM-41 mesoporous materials,[7] has also been reported.
Furthermore, Lewis acid-catalyzed Fischer glycosidation reac-
tions between various monosaccharides and alcohols have
been performed in an ionic liquid, that is, 1-butyl-3-methylimi-
dazolium trifluoromethanesulfonate ([C4mim][OTf]);[8] in all
cases, noticeable increases in the yields were observed in the
presence of the ionic liquid relative to the yields obtained
under neat reactions.[8a] In a more recent report, another ionic
compound, [NH4]Cl, proved extremely active as a catalyst for
the reaction.[9]
currently produced worldwide on a scale of about 85 ktaÀ1 [2]
.
Several synthetic procedures using sugar feedstocks and
leading to alkyl glycosides are known, including stereospecific
Figure 1. Generic structure of the biodegradable surfactant products (CnGm,
n=8 or 12), namely, alkyl glucosides (m=1) and alkyl oligoglucosides
(m>1, mostly 2 or 3), obtained directly from cellulose in this work.
[a] Dr. A. V. Puga, Prof. A. Corma
Instituto de Tecnologꢀa Quꢀmica (UPV-CSIC)
Universitat Politꢁcnica de Valꢁncia
Avda. dels Tarongers s/n, 46022 Valencia (Spain)
E-mail: acorma@itq.upv.es
The carbohydrate source for the industrial production of
alkyl glucosides can be either monomeric (anhydrous or mono-
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201402722.
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hydrate) or polymeric (e.g., syrups) forms of glucose.[1a,3e] Nev-
ertheless, these are edible feedstocks, and it would be conven-
ient to replace them with nonedible counterparts, such as
lignocellulosic biomass. In this context, the transformation of
cellulose into alkyl glucosides by using 1-butyl-3-methylimida-
zolium chloride ([C4mim]Cl) as the ionic liquid solvent in a one-
pot, two-step process that couples cellulose hydrolysis and
Fischer glycosidation was recently developed in our laborato-
ries.[10] The efficiency of the process is enhanced by conducting
the first (hydrolysis) step with a controlled reaction time (1.5 h)
and a controlled amount of water, and subsequently, by per-
forming the second (glycosidation) step under reduced pres-
sure. Furthermore, successful alkyl glucoside production was
observed even for long-chain alcohols such as 1-dodecanol.[10d]
This is in contrast to the one-step experiments reported by
de Vos and co-workers,[11] for which no products were obtained
from cellulose and 1-dodecanol, though the reaction worked
well with shorter chain alkanols.
to the production of alkyl glycosides in [C4mim]Cl.[10c,d] Given
that both reactions can be catalyzed by acids, this two-step,
one-pot process was made feasible by carefully adjusting the
hydrolysis and glycosidation times and by using the same cata-
lyst (Amberlyst 15) throughout the entire transformation. First,
cellulose was dissolved in [C4mim]Cl, and then the catalyst and
water were added. The hydrolysis reaction was allowed to pro-
ceed at 1008C for 1.5 h (optimized time), and subsequently,
the alkanol was added and the glycosidation reaction was per-
formed under reduced pressure at 908C for 24 h.
To maximize production, it was mandatory to increase the
amount of cellulose, and in this line, we observed that 1:10
ratios also proved successful. Thus, all the reactions presented
herein were done at a cellulose/[C4mim]Cl weight ratio of 1:10
with the aim to achieve higher productivity relative to the
total amounts of ionic liquid and alcohol used. The higher the
cellulose concentration in the starting reaction mixture, the
higher the viscosity of the initial solution. This affects stirring
efficiency. In addition, cellulose precipitation was observed if
water was added too rapidly at that stage. To prevent this, the
addition of water was done slowly with incremental amounts
(see the Experimental Section). The yields of the main products
upon reacting with 1-octanol or 1-dodecanol are listed in
Table 1 (procedures 1 and 2, see the Experimental Section).
After catalyst and alkanol separation, the corresponding octyl
and dodecyl glycosides were formed in 46.5 and 32.3% molar
yields (83.8 and 69.5% mass yields, respectively). This repre-
sents a slight improvement in the case of the octyl derivative
relative to our previous studies (39.7% molar yield, 71.5%
mass yield for an almost identical reaction procedure),[10c] but
a noticeable, almost threefold increase in dodecyl glucoside
production was observed (only 12.7% molar yield combined
glucoside/xyloside yield in an experiment with xylan-contain-
ing a-cellulose).[10d] Therefore, it seems reasonable to conclude
that water addition rates are crucial and can have a significant
impact on the outcome of the reaction, especially at high cel-
lulose concentrations. However, at this point molar balances,
taking into account all the identified products in solution, only
reached 59.0 and 45.7% of the initial cellulose for octyl and
dodecyl, respectively. To improve yields further, a thorough
study of the reaction network and kinetics of the different
transformations occurring was undertaken, as detailed below.
We will show now the procedure followed to further in-
crease the yields of alkyl glycosides through the knowledge of
the reactions involved and the role played by the reaction con-
ditions on the rate of formation of the products and byprod-
ucts. As we will discuss below, the control of reaction tempera-
tures is a key factor to minimize the extent of dehydration of
the saccharides to furanic compounds and of subsequent deg-
radation leading to polymeric material. A plausible reaction
mechanism is depicted in Scheme 1. As suggested, glucose
(and higher oligomers such as cellobiose, cellotriose, and so
forth) would be produced by cellulose hydrolysis in the first
step. Then, alkyl glycosides would be formed by Fischer glyco-
sidation of the resultant saccharides. Acetalization of glucose
would lead to alkyl monoglucosides (CnG1) as major products,
whereas higher (especially di- and tri-) saccharides would be
In the technical processes using glucose as the starting ma-
terial, product isolation involves neutralization of the acidic
catalyst (if homogeneous), distillation of both the alkanol and
water formed during neutralization, and bleaching of the dis-
colored crude.[1a,5] In the ionic liquid process using cellulose as
the feedstock, as presented herein, the solid acidic catalyst (a
sulfonic acid resin) can be readily separated by filtration, and
the alkanol can be removed by distillation to leave a mixture
of products and ionic liquid. The main drawback of this pro-
cess is the separation of the alkyl glycoside products from this
mixture with the ionic liquid. On a laboratory scale, this can be
overcome by using a silica gel fixed bed through which the
mixture can be eluted with mobile phases composed of, for
example, ethyl acetate and methanol.[8,10c,d] This procedure, al-
though efficient for the isolation of alkyl glucosides, requires
the use of large amounts of volatile organic solvents, which
have a negative impact on both the economics and the envi-
ronmental footprint of the process. Moreover, given the high
cost of the ionic liquid, its recovery and reutilization is of
utmost importance.
In this work, besides achieving an important increase in the
yields of alkyl glucosides (CnG1) and alkyl oligoglucosides
(CnGm) by process optimization, we put particular emphasis on
the steps for separation and recovery of both the product and
the ionic liquid. Several separation methodologies, including
extraction, short-path chromatography, crystallization of
[C4mim]Cl, and precipitation of the alkyl glycosides in aqueous
media, have been studied. Product analyses and quantification
of the environmental footprint of each separation method
have been performed to discern which approaches are most
suited for a possible implementation of the process at a larger
scale.
Results and Discussion
Production of alkyl glucosides from cellulose
As previously reported, coupling the hydrolysis of cellulose
with the Fisher glycosidation of the glucose thus formed leads
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Scheme 1. Conversion of cellulose into alkyl glycosides in a one-pot, two-step process in an ionic liquid ([C4mim]Cl), for which the first step is the hydrolysis
of cellulose and the second step is the Fischer glycosidation of the formed glucose and glucose oligomers. The major products are alkyl glucosides [top
right: CnG1 =alkyl monoglucosides, CnGm =alkyl oligoglucosides (m>1)]; the structures of the identified minor dehydration products are also shown [bottom:
HMF=5-(hydroxymethyl)furfural, LG=levoglucosan, CnMF=5-(alkoxymethyl)furfural].
balance, as reported elsewhere
Table 1. Product yields[a–c] for the one-pot hydrolysis and Fischer glycosidation of cellulose in [C4mim]Cl in the
presence of Amberlyst 15.
for the Fischer glycosidation of
glucose and other sugars.[1a,4] In
[a]
[a]
Reaction
procedure
Alkanol
Th
[8C]
Tg
t[a]
[h]
Yield [%]
CnG1
Molar
balance[d]
fact, dark insoluble solids were
recovered from aqueous HPLC
samples and from several frac-
tions during the separation pro-
cedures (see details below). Ele-
mental analyses of such solids
revealed that their carbon con-
tents were higher than those of
the starting cellulose (typically
56–63%, compared to 44% for
cellulose). Furthermore, they
were amorphous, and their FTIR
fingerprint regions indicated
they were noticeably different to
the starting cellulose, in particu-
lar because they lacked the
strong CÀO stretching band cen-
tered at n˜ =1060 cmÀ1 (see
Figure 2). Therefore, it seems
clear that such solid materials
[8C]
total CnGm
glucose
HMF
1[e]
2[e]
2[f]
3[f]
4[f]
5[f]
6[f]
7[f,h]
1-octanol
100
90
25.5
25.5
25.5
21.5
21.5
46.5
48.2
48.5
46.5
32.3
33.4
43.6
48.0
46.9
57.4
62.1
46.5
32.3
34.5
45.5
49.7
51.9
65.9
71.8
1.6
2.0
2.9
5.5
2.9
2.0
2.0
1.5
7.5
7.5
12.0
11.8
9.6
6.0
7.0
7.4
76.0
58.3
50.7
64.1
64.5
61.7
76.6
88.1
1-dodecanol
1-dodecanol
1-dodecanol
1-dodecanol
1-dodecanol
1-dodecanol
1-dodecanol
100
100
90
90
90
90[g]
90[g]
80[g]
80
70
70
70
80
80, 70
[a] General reaction conditions: A mixture of cellulose (0.6 g, 3.7 mequiv glucose) in [C4mim]Cl (6 g), Amber-
lyst 15 (0.35 g, 1.64 mequiv H+), and H2O (0.76 g, 42 mmol, slowly added) was stirred at the specified hydrolysis
temperature (Th) for 1.5 h; then, the alkanol (ꢀ43 mmol) was added, and the resulting mixture was stirred at
the specified glycosidation temperature (Tg) under a pressure of 0.7 kPa until the total reaction time (t).
1
[b] Based on H NMR spectroscopy, HPLC, and GC data. [c] See Scheme 1 for product abbreviations. [d] Consid-
ering the specified products, several byproducts including insoluble degradation material and unreacted cellu-
lose; see the Supporting Information for further details. [e] Catalysts and excess amounts of alkanol were sepa-
rated by filtration and distillation from the final mixtures, respectively; the listed yields are based on analyses
of the resulting products/ionic liquid mixtures. [f] Yields are based on direct analyses of reaction mixture sam-
ples. [g] Glycosidation reaction pressure=4.0 kPa. [h] Hydrolysis performed at 808C for 1.5 h, and then at 708C
for further 2.5 h, at which point, 1-dodecanol was added.
converted into alkyl oligoglucosides (CnGm, m>1). Levogluco-
san and 5-(hydroxymethyl)furfural (HMF) would be produced
through glucose dehydration reactions, which in turn result in
a decrease in surfactant yields and in the formation of poly-
mers from HMF. Small amounts of 5-(alkoxymethyl)furfural
(CnMF) are also formed by either dehydration of alkyl gluco-
sides or etherification of HMF under acidic catalysis.[12]
are not composed of unreacted cellulose to any relevant
extent but that they most likely result from condensation and
dehydration processes involving furanic byproducts (mostly
HMF, see Scheme 1) as precursors.[13] Considering the amount
of carbon in those solids, molar balances reach 76.0 and 58.3%
for octyl and dodecyl, respectively (Table 1, procedures 1 and
2). On the basis of this hypothesis, a kinetic study of the dode-
cyl glycoside reaction will be presented to track the formation
of HMF during the course of the transformations. This would
enable the design of further experiments to reduce the
In the reactions under consideration herein, we first focused
on analyzing possible polymeric degradation products that
could make up a considerable portion of the remaining molar
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spectively, which thus reveals that some product decomposi-
tion was taking place. The amounts of glucose and other sac-
charides were very low at long reaction times (2.9% glucose at
25.5 h), whereas HMF was present at 10–15% yields through-
out the reaction, although the amounts did not increase signif-
icantly. Our hypothesis is that HMF—and possibly other dehy-
drated sugars and furanic derivatives—may also undergo irre-
versible condensation and further dehydration processes to
give oligomeric and/or polymeric species. If these are not
taken into account, molar balances of identified products are
low at long reaction times. Such undesired processes might be
favored if working with more concentrated reaction mixtures,
unless the reaction variables are reoptimized. Therefore, opti-
mization of the reaction outcome was attempted first by low-
ering the temperatures, whilst maintaining cellulose feed con-
centrations.
Figure 2. Transmission FTIR spectra of starting fibrous cellulose (a) and
the insoluble solid product from the cellulose into C12Gm transformation
(c, reaction 2; for further details see the Experimental Section).
Both steps in the reaction sequence were then performed at
lower temperatures, that is, hydrolysis at 908C and glycosida-
tion at 808C (reaction procedure 3), under otherwise analo-
gous conditions. The evolution of the reaction products is plot-
ted in Figure 4. As expected as a result of the lower tempera-
ture, cellulose depolymerization proceeded at a slower rate
(glucose yield after 1.5 h was 34.9%, compared to 45.6% for
the reaction at 1008C, see above), and interestingly, HMF pro-
duction was also much lower at this stage (3.5 and 6.9% at 90
and 1008C, respectively). After 1-dodecanol addition, glycosi-
dation at 808C took place also at slower rates, as can be clearly
observed by tracking the slower decrease in the amount of
glucose (and higher oligosaccharides) in Figure 4 relative to
that depicted in Figure 3. The slower production of C12Gm was,
however, compensated by a sustained increase up to 8 h, after
which a plateau was achieved (45.5% yield for C12Gm after
21.5 h, see Table 1). Although HMF production was lower at
lower temperatures, prolonged reaction led to considerable
amounts of HMF (11.8% at 21.5 h), together with lower molar
balances (from 80.4% at 8 h down to 64.1% at 21.5 h, see the
Supporting Information). According to these data, it seems
that the persistence of saccharides in solution results in both
amounts or furanic and polymeric byproducts. First, the reac-
tion were conducted as previously reported,[10d] that is, by per-
forming the hydrolysis step at 1008C for 1.5 h and then the
glycosidation step at 908C and 4.0 kPa for 24 h (reaction pro-
cedure 2). The time profile of the transformation is shown in
Figure 3 (full set of data shown in the Supporting Information).
Under these conditions, depolymerization of cellulose is evi-
denced by the formation of glucose and glucose oligomers,
which build up in the mixture during the hydrolysis step (up
to a total 45.6% molar yield for glucose after 1.5 h). Further-
more, glucose dehydration also took place, which resulted in
noticeable amounts of HMF and levoglucosan (6.9 and 0.9%,
respectively, after 1.5 h). At that point, 1-dodecanol was added
and the reaction was continued at 908C under reduced pres-
sure (4.0 kPa), which resulted in rapid C12Gm production and
concomitant glucose (and oligosaccharide) consumption. After
4 h, the molar yield of C12Gm was 37.9% (35.6% for C12G1),
whereas that of glucose dropped to 21.8%. At longer reaction
times, glucose and higher oligomers were further consumed,
but the amounts of C12Gm did not increase accordingly at 8
and 25.5 h, and total surfactant yields were 39.6 and 34.5%, re-
Figure 3. Time profile for the conversion of cellulose into C12Gm, for which
the hydrolysis and glycosidation steps were performed at 1008C and 908C/
Figure 4. Time profile for the conversion of cellulose into C12Gm, for which
the hydrolysis and glycosidation steps were performed at 908C and 808C/
*
*
4.0 kPa, respectively (reaction procedure 2, Experimental Section). : total
4.0 kPa, respectively (reaction procedure 3, Experimental Section). : total
~
~
~
~
~
~
&
&
*
*
*
*
C12Gm; : C12G1; : C12G2; : glucose; : cellobiose; : cellotriose; : HMF.
C12Gm; : C12G1; : C12G2; : glucose; : cellobiose; : cellotriose; : HMF.
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C12Gm and HMF production, which in turn leads to slightly
higher surfactant production at 808C but also to a noticeable
extent of side reactions.
Given that the glycosidation reaction is favored by reduced
pressures, we sought to optimize the reaction by decreasing
the pressure under otherwise identical conditions (reaction
procedure 4). The outcome of the reaction, for which the
second step was performed at 0.7 kPa, was improved in terms
of C12Gm yield (49.7% after 21.5 h, see Table 1) because of
faster glycosidation, as graphically shown in Figure 5. The
Figure 6. Time profile for the conversion of cellulose into C12Gm, for which
the hydrolysis and glycosidation steps were performed at 908C and 708C/
*
0.7 kPa, respectively (reaction procedure 5, Experimental Section). : total
~
~
~
&
*
*
C12Gm; : C12G1; : C12G2; : glucose; : cellobiose; : cellotriose; : HMF.
In an additional experiment, the temperature of hydrolysis
was reduced down to 808C in the attempt to minimize the
amount of HMF formed during the initial stages of the reaction
(reaction procedure 6). Indeed, this strategy was successful,
and the molar yield of HMF before the addition of alcohol
(1.5 h) was only 1.6% (see Figure 7); this yield is considerably
Figure 5. Time profile for the conversion of cellulose into C12Gm, for which
the hydrolysis and glycosidation steps were performed at 908C and 808C/
*
0.7 kPa, respectively (reaction procedure 4, Experimental Section). : total
~
~
~
&
*
*
C12Gm; : C12G1; : C12G2; : glucose; : cellobiose; : cellotriose; : HMF.
extent of undesired dehydration leading to HMF was also
smaller (9.6%). Therefore, working at lower temperatures and
higher vacuum proves beneficial for the production of surfac-
tants from cellulose hydrolysates in [C4mim]Cl, although further
optimization to obtain higher yields and to minimize HMF for-
mation was still pursued. In this line, conditions were carefully
modified in subsequent experiments. In a first reaction, the
same experimental variables for hydrolysis were used, whereas
the glycosidation temperature was reduced by 108C, that is,
hydrolysis at 908C and glycosidation at 708C; this latter step
was extended up to a total time of approximately 45 h (reac-
tion procedure 5). The time profile of this reaction is shown in
Figure 6. During the first stages after the hydrolysis step, the
formation of C12Gm was slower than that at 808C. For example,
the yield of C12G1 was 21.2% after approximately 8 h (23.3%
for all C12Gm), whereas for the former reaction, it was above
46% (see above and Figure 5). At longer reaction times, the
global surfactant yield increased up to 51.9% (46.6 h, see
Table 1). Interestingly, at short reaction times, glucose yields
kept increasing even after the addition of 1-dodecanol, where-
as HMF production was lower than that for the reactions de-
scribed above (up to a maximum 7.4% molar yield at 8 h). This
indicates that, under such mild conditions, hydrolysis still takes
places to some extent and glucose dehydration to HMF is re-
duced.
Figure 7. Time profile for the conversion of cellulose into C12Gm, for which
the hydrolysis and glycosidation steps were carried out at 80 and 708C/
*
0.7 kPa, respectively (reaction procedure 6, Experimental Section). : total
~
~
~
&
*
*
C12Gm; : C12G1; : C12G2; : glucose; : cellobiose; : cellotriose; : HMF.
lower than that for hydrolysis at 908C, which was above 3%.
Cellulose depolymerization was also slower (19.3% glucose
after 1.5 h), but this did not affect surfactant production. In
fact, the C12G1 yields increased noticeably up to a reaction time
of 24 h (56.6%), together with a considerable amount of dode-
cyl oligoglucosides (8.8%), and then these yields remained on
a plateau to give a total surfactant yield of 65.4%. Under these
conditions, the molar balance, considering all identified prod-
ucts in solution, was 81.3%. These results indicate that HMF
formation is reduced at 808C during hydrolysis, which results
in an increase in the saccharide/HMF ratio; these results also
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indicate that the glycosidation of the preferentially formed sac-
charides predominates at lower temperatures (708C) over deg-
radation processes.
Separation of octyl glycosides
After the one-pot process leading to alkyl glycosides from cel-
lulose in [C4mim]Cl and subsequent separation of the sulfonic
acid resin catalyst (by filtration) and most of the alkanol (by
distillation), a mixture of products and ionic liquid is obtained.
The second main objective of this work, after the yield en-
hancements described above, is the separation of the alkyl gly-
cosides from the ionic liquid with the aim to achieve both effi-
cient product isolation and ionic liquid recovery for further
reuse. Unfortunately, such a separation is challenging, as it is
for other cellulose-derived saccharides. In the case of glucose,
efficient separation has only been achieved by chromatograph-
ic techniques, albeit at the expense of using enormous
amounts of solvents and only recovering 92% of the ionic
liquid.[14] As opposed to the difficult separation of two ex-
tremely hydrophilic substances, such as glucose and
[C4mim]Cl, it should be more straightforward to partition the
amphiphilic long-chain alkyl glycosides produced in the stud-
ied reactions if the appropriate procedure and conditions were
found. As a starting point, we studied the separation of C8Gm
produced in [C4mim]Cl by a chromatographic method through
a short-path silica bed. Several alternative procedures, such as
extractions and crystallizations, were also tested with the pur-
pose of achieving efficient separation with reduced use of re-
sources, chiefly solvents. A summary of data illustrating the ef-
ficiency of each separation procedure is presented in Table 2.
The efficiency of each method was quantified as the amounts
of solvents used (for separation) relative to the amounts of
products. Such ratios are similar to the well-known E factors
(waste/product ratios)[15] and are used here for comparison
purposes and to assess environmental footprints.
Aiming at maximizing the productivity of surfactants, a final
experiment was performed, for which the hydrolysis step was
conducted at decreasing temperatures, that is, at 808C for
1.5 h (as in reaction 6) and then at 708C for a total of 4 h (reac-
tion procedure 7). Glucose yields increased up to 25.5% at that
stage, whereas HMF formation remained low (1.9%), which
thus improved the saccharide/HMF ratio. This proved beneficial
for surfactant production. After the subsequent glycosidation
step, after a total time of 48.5 h, C12Gm yields reached high
values (71.8%), with 9.7% oligoglucosides in addition to the
major C12G1 products (62.1%, see Figure 8). Molar balances
were close to 90%, which thus reflects the success of this opti-
mization strategy and the importance of limiting HMF forma-
tion.
Separation by short-path chromatography through a silica
bed with ethyl acetate/methanol mixtures was successful for
the isolation of C8Gm (procedure 1a in the Experimental Sec-
tion). Similar methods have been previously adopted for the
separation of alkyl glycosides in processes starting from glu-
cose[8] and cellulose.[10c,d] Herein, we quantified the efficiency
of this separation procedure (Table 2), including the recovery
of both the surfactant products and the ionic liquid. The yield
and purity of the isolated C8Gm products were 40.8 and 96.6%,
respectively; consequently, efficient separation of the surfac-
tant can be achieved by this method. Less-polar products
(mainly HMF and C8MF) were eluted in earlier fractions (for de-
tails see the Experimental Section and the Supporting Informa-
Figure 8. Time profile for the conversion of cellulose into C12Gm, for which
the hydrolysis step was performed at 808C (1.5 h) and then at 708C (up to
t=4 h) and the glycosidation step was performed at 708C/0.7 kPa (reaction
~
*
*
*
procedure 7, Experimental Section). : total C12Gm; : C12G1; : C12G2; : glu-
~
~
&
cose; : cellobiose; : cellotriose; : HMF.
In conclusion to the alkyl glycoside production process from
cellulose in [C4mim]Cl, we achieved yield improvements by
carefully adjusting the rates of addition of water and the alka-
nol and, more importantly, the temperature of each step. In
the case of C12Gm, optimization efforts led to yields above 70%
and mass balances approaching 90%.
Table 2. Summary of separation data[a] for the product/ionic liquid mixtures in the transformation of cellulose into octyl glycosides.
Separation
procedure[b]
Method
Isolated C8Gm
yield [%]
C8Gm purity
[%]
[C4mim]Cl recovered
[%]
[C4mim]Cl purity[c]
[%]
Mass(solvents)/
mass(products)
1a
1b
1c
1d
short-path chromatography
extraction with ethyl acetate
crystallization of [C4mim]Cl
precipitation of [C4mim]Cl
40.8
–
2.9
2.2
96.6
–
5.3
10.7
92.9
98.3
95.9
98.4
99.6
88.1
95.1
92.3
6222
–
2554
1971
1
[a] Based on H NMR spectroscopy and GC data. [b] Related to the corresponding reaction listed in Table 1; see procedure details in the Experimental Sec-
tion. [c] Dry basis.
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tion). Levoglucosan could be partitioned in later fractions with
some [C4mim]Cl contamination. Despite the facile operation
and efficient surfactant isolation of short-path chromatography
on silica, the recovery of [C4mim]Cl is low from a practical
point of view (92.9%). Furthermore, the amount of solvents
used for the separation is rather large (see Table 2).
hydrogen bonding. In summary, elution through silica proved
to be the only successful method for the separation of C8Gm,
although at the expense of a low recovery of the ionic liquid.
Separation of dodecyl glycosides
Given the amphiphilicity of the alkyl glucoside surfactants,
they can be dissolved to some extent in organic solvents such
as ethyl acetate (48 and 31 gLÀ1 for b-C8G1 and b-C12G1, re-
spectively, as measured in this work), whereas the [C4mim]Cl
ionic liquid is highly hydrophilic and does not generally dis-
solve in low-polarity media. However, extraction with the use
of ethyl acetate resulted in negligible C8Gm recoveries, owing
to their preference to remain in the ionic-liquid phase (see pro-
cedure 1b in the Experimental Section and Table 2).
The length of the alkyl chain has a marked influence on the
detergency of alkyl glycosides, especially on their critical mi-
celle concentrations.[1a,3c,17] Furthermore, the longer the alkyl
chain, the more nonpolar the surfactant. In principle, this
should be advantageous for the separation of long-chain alkyl
glycosides from [C4mim]Cl. Our subsequent investigations
were thus focused on the direct conversion of cellulose into
C12Gm in the ionic liquid and on the subsequent separation.
First, short-path chromatography and, second, the [C4mim]Cl
crystallization method, both in an analogous manner as per-
formed for the C8Gm reactions, were tested. Moreover, we will
present herein a distinct method consisting in the precipitation
of the surfactant product in aqueous media. A summary of the
relevant separation efficiency data is listed in Table 3.
A second separation approach was then considered on the
basis of the fact that [C4mim]Cl is a crystalline solid at room
temperature, and it can, therefore, be purified by crystallization
under anhydrous conditions. A first crystallization experiment
was done by dissolving the ionic liquid/products mixture in an-
hydrous acetonitrile, which was followed by the addition of an-
hydrous ethyl acetate in the presence of a seed crystal of
[C4mim]Cl. Although the ionic liquid could be separated in its
solid form by this procedure, the recovery of the surfactant in
the supernatant was not successful (molar yield ꢀ2.9%, see
procedure 1c in the Experimental Section and Table 2). Then,
an alternative crystallization methodology was adopted. This
consisted in slowly adding a concentrated solution of acetoni-
trile to ethyl acetate containing a seed crystal of [C4mim]Cl
under Schlenk techniques.[16] Such a procedure resulted in the
precipitation of 98.4% of the initial [C4mim]Cl ionic liquid from
the mixture (see Table 2 and procedure 1d in the Experimental
Section) although at a purity of only 92.3%. In addition to the
ionic liquid, a substantial amount of the octyl glucosides pro-
duced in the reaction were also found in the solid (correspond-
ing to a yield of 41.3%), whereas only a small proportion of
them were partitioned into the liquor phase (corresponding to
a 2.2% molar yield, see Table 2). As a general conclusion of the
attempted extraction and crystallization methodologies, it is
clear that despite the high solubility of octyl glucosides in or-
ganic solvents such as ethyl acetate, the surfactant products
partitioned preferentially in the ionic-liquid phases, most likely
due to the high affinity of glucoside derivatives towards the
imidazolium chloride ionic liquid through efficient and strong
In the case of short-path chromatography, the partitioning
efficiency of the dodecyl glucosides was similar to that ach-
ieved for the octyl glycosides discussed above. As seen in
Table 3, the isolated C12Gm yield was 25.2% for a product of re-
markable purity (97.7%, procedure 2a). However, the ionic
liquid recovery was far from ideal, as only 87.5% of the initial
amount was recovered with good purity. As in the case of
C8Gm, this chromatographic procedure can be successfully em-
ployed for laboratory-scale purposes. Nonetheless, it does not
comply with the stringent requirements of a potential com-
mercial process with regard to ionic-liquid recovery and
amounts of solvents used (see Table 3), despite the high purity
of the fractionated surfactant material.
The [C4mim]Cl precipitation procedure, although proven to
be of low efficiency for C8Gm, was also tested for the analogous
C12Gm mixture (procedure 2b). It was expected that the longer
hydrophobic (dodecyl) moiety in the surfactant would improve
its partitioning into the organic supernatant liquor. The results
listed in Table 3 show that the recovery of C12Gm was slightly
better than that of C8Gm (yields of isolated products were 8.9
and 2.2%, respectively). However, the crude product obtained
was of very low purity (22.2%), and most of the surfactant re-
mained in the solid [C4mim]Cl fraction. Therefore, this method
is not suitable for the recovery of alkyl glycosides and ionic liq-
Table 3. Summary of separation data[a] for of product/ionic liquid mixtures in the transformation of cellulose into dodecyl glycosides.
Separation
procedure[b]
Method
Isolated C12Gm
yield [%]
C12Gm purity
[%]
[C4mim]Cl recovered
[%]
[C4mim]Cl purity
[%][c]
Mass(solvents)/
mass(products)
2a
2b
2c
2d
7a
7b
short path chromatography
precipitation of [C4mim]Cl
precipitation of C12Gm
precipitation of C12Gm and recrystallization
precipitation of C12Gm
precipitation of C12Gm and bleaching
25.5
8.9
33.8
23.3
69.7
64.8
97.0
22.2
61.1
95.0
66.9
92.4
87.5
97.4
99.5
–
99.5
–
99.5
94.9
98.9
–
99.2
–
9413
1876
175
409
78
86
1
[a] Based on H NMR spectroscopy and GC data. [b] Related to the corresponding reaction listed in Table 1; see procedure details in the Experimental Sec-
tion. [c] Dry basis.
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uids, even in the case of long dodecyl chains as the hydropho-
bic part.
thin-film evaporators, is not uncommon for commercial alkyl
glycoside production processes starting from glucose.[1a,5c,18] In
the present case, the use of a short-path (Kugelrohr) apparatus
proved efficient and yielded a crude product containing very
low amounts (<1%) of the alkanol. The resulting crude surfac-
tant was still strongly discolored. A bleaching treatment[1a,5b]
led to a pale yellow paste essentially composed of C12Gm
(>92% by dry weight, see procedure 7b in Table 3), which
could be dissolved in water at low concentrations (dictated by
its low solubility) to give solutions with noticeable foam forma-
tion and stability (see picture in Figure 9).
Also on the basis of the different hydrophilicity of C12Gm and
[C4mim]Cl, we will show another separation method in aque-
ous media. It is known that long-chain alkyl glycosides show
low critical micelle concentrations and low cloud points (and
hence, low solubilities) in aqueous solutions.[3c,17] Moreover,
[C4mim]Cl is extremely hygroscopic and miscible with water in
all proportions. Therefore, we expected that, in the presence
of appropriate amounts of water, the ionic liquid would be
solubilized, whereas C12Gm would precipitate out of the solu-
tion. Indeed, by adding water to an ionic liquid/products mix-
ture obtained for reaction procedure 2, an insoluble solid was
formed. After separation by filtration, washing and drying, this
solid was analyzed and found to consist mostly of C12Gm
(61.1% by weight, corresponding to a 33.8% molar yield; pro-
cedure 2c, see Table 3) and, consequently, almost quantitative
separation was achieved. The main impurities were residual 1-
dodecanol, which remained after the distillation step, and
minor amounts of C12MF and [C4mim]Cl (this residual ionic
liquid content could be minimized by additional washings with
water). The ionic liquid was efficiently recovered from the
aqueous liquors (99.5% of the initial amount, purity=98.9%).
Minor substances in the recovered ionic liquid were HMF, resid-
ual C12Gm, and levoglucosan. This method involved the use of
smaller amounts of solvents than either chromatography or
[C4mim]Cl crystallization/precipitation. Furthermore, no organic
solvents were employed. Given the success of this procedure,
it was also used for reaction 7, for which the best surfactant
yields were achieved. Despite the higher proportion of dodecyl
oligoglucosides (C12Gm, m>1) and, hence, higher hydrophilic
character of the surfactant, the method also proved extremely
efficient. The recovery of C12Gm was almost quantitative (yield
of isolated product=69.7%, comprising both C12G1 and higher
C12Gm, m>1; see procedure 7a in Table 3). On the other hand,
[C4mim]Cl was recovered from the aqueous liquors with no-
ticeably high efficiency (99.5% of the initial amount, purity=
99.2%). This separation procedure, for which no volatile organ-
ic compounds are used, leads to almost quantitative recovery
of both C12Gm and [C4mim]Cl in a remarkably clean method, as
only water is involved in the separation process. In addition, it
involves the use of considerably smaller amounts of solvents
(two orders of magnitude reduction, see Table 3) relative to
the amounts used for other methods, such as elution through
silica. In conclusion, this method holds promise for its practical
applicability in cellulose transformation processes in ionic liq-
uids beyond the laboratory scale.
Figure 9. Photograph of a foamy aqueous solution of the bleached crude
surfactant product obtained by separation procedure 7a.
For laboratory-scale operation, recrystallization was also suc-
cessful for the purification of dodecyl glycosides. Thus, by
treating a crude product (after the removal of 1-dodecanol,
see procedure 2d in the Experimental Section) with a mixture
of hexane and ethyl acetate under refluxing conditions, a dark
solution was obtained. After removing a small amount of in-
soluble solids by hot filtration, a pale brown solid crystallized
from the clear liquor. This recrystallized product was composed
of highly pure C12Gm (purityꢀ95%, see Table 3).
Conclusions
The production of alkyl glycosides from cellulose in a one-pot,
two-step (hydrolysis and glycosidation) process in the 1-butyl-
3-methylimidazolium chloride ([C4mim]Cl) ionic liquid proceed-
ed efficiently. Yields were enhanced and selectivities for alkyl
glucosides, which are generally moderate because of sugar de-
hydration and further degradation reactions towards a number
of byproducts including 5-(hydroxymethyl)furfural and insolu-
ble polymeric material, were improved by optimizing the oper-
ation variables. In the optimized procedure, the molar yield of
1-dodecyl glycosides reached a maximum of 72%. The extent
of degradation was thus reduced and molar balances were ap-
proximately 90% under remarkably mild conditions.
Surfactant refining
The crude C12Gm products isolated by precipitation in aqueous
media were obtained as dark solids or pastes containing some
1-dodecanol remaining from the previous vacuum distillation.
Therefore, the product needed refining to meet the required
specifications for surfactant formulations. The residual 1-dodec-
anol could be removed by an additional distillation step. In
fact, the use of two distillation steps, by using short-path or
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reaction products were quantified by 1H NMR (300.13 MHz) spec-
troscopy at 258C with a Bruker Avance-300 spectrometer by using
[D6]DMSO as the solvent. Phases and baselines were corrected as
appropriate, and integrals of selected signals were measured;
yields were calculated by relating such integrals to those of bi-
phenyl as an external standard. Saccharides, octyl glucosides, and
HMF were quantified by HPLC analyses of samples diluted with ul-
trapure water, acidified by the addition of a 1.4m aqueous H2SO4
solution, by using a Coregel 87H column (Waters 1525 Binary HPLC
Pump, injection volume=10 mL, column temperature=708C,
eluent=4 mm aqueous H2SO4, flow rate=0.7 mLminÀ1) and a re-
fractive index detector (Waters 2410). Alkyl mono- and oligogluco-
sides were quantified by GC analyses after silylation of samples
(ꢀ20 mg) with N,O-bis(trimethylsilyl)trifluoroacetamide (ꢀ0.1 g) in
pyridine (ꢀ0.9 g) by using a Varian CP-3800 gas chromatograph
[on-column injection, injection volume=0.6 mL, Varian Select Bio-
diesel column for glycerides with the following temperature pro-
gram: 508C (1 min), 50–1808C (158CminÀ1), 180–2308C (78C
minÀ1), 230–3708C (108CminÀ1), 3708C (5 min), carrier gas: N2,
flow=2.5 mLminÀ1, flame ionization detector]. XRD measurements
were performed by means of a PANalytical Cubix’Pro diffractome-
ter equipped with an X’Celerator detector and automatic diver-
gence and reception slits by using CuKa radiation (0.154056 nm).
Elemental analyses were performed by using a Euro EA Elemental
Analyzer. Fourier transform infrared (FTIR) spectra were recorded
with a Nicolet is10 Thermo Scientific spectroscope from samples
milled with potassium bromide and pressed into pellets.
Despite being extremely challenging, the separation of the
surfactants from the ionic liquid was attempted by several
methods and good results regarding the possible practical im-
plementation of the process were obtained. In this context,
the ionic liquid should be recovered well in excess of 99% and
reused. At the laboratory scale, chromatographic separations
with the use of silica gel as the stationary phase proved to be
an excellent method for the isolation of the surfactants. How-
ever, [C4mim]Cl could not be recovered quantitatively (maxi-
mum recoveryꢀ90%) by these methods owing to strong ad-
sorption of the ionic liquid onto silica. Alternatively, crystalliza-
tion of [C4mim]Cl, although possible, did not lead to efficient
separation of the surfactant into the supernatant liquor. Finally,
we found that the best method was the separation of long-
chain alkyl glucosides in aqueous media. In the case of dodecyl
glycosides, the product could be well separated by precipita-
tion after the addition of water. The ionic liquid remained in
solution, and it could be almost quantitatively recovered
(>99%). In addition, the surfactant products were isolated in
high yields (up to a 70% molar yield) and refined to yield tech-
nical-grade products with good color and surfactant proper-
ties. This method is inherently clean, owing to the use of water
as the only separation solvent. Therefore, the presented pro-
cess holds promise for the manufacture of this class of special-
ty chemicals (biodegradable surfactants) from a readily avail-
able and inexpensive biomass-derived feedstock such as cellu-
lose.[10a,b]
Cellulose conversion into alkyl glycosides: Reaction optimi-
zation
Experimental Section
Cellulose into C8Gm: Hydrolysis at 1008C, glycosidation at
908C (procedure 1)
Materials
In a typical experiment, cellulose (0.6054 g, 3.734 mequiv, calculat-
ed as anhydroglucose) and [C4mim]Cl (6.0442 g) were heated in an
oil bath at 1058C for 30 min and then at 1208C for another 30 min
with gentle stirring and vacuum (1.0–2.0 kPa); a pale-yellow clear
solution (9.1% cellulose weight) was obtained. At this stage, the oil
bath temperature was decreased to 1008C and Amberlyst 15
(0.3501 g, 1.645 mequiv, calculated as H+ equivalents) was added;
after 3 min, the viscosity of the solution decreased noticeably and
stirring efficiency improved. Then, incremental amounts of water
(0.06, 0.10, 0.10, 0.20, and 0.30 mL) were slowly dispensed drop-
wise, so that thorough mixing was ensured before the next addi-
tion to prevent precipitation of cellulose or cellulose oligomers at
different time intervals (t=0–3, 5–8, 10–13, 15–20, and 30–35 min,
respectively, taking t=0 min as the start of water addition). The
mixture was stirred until the desired hydrolysis end time (t=1.5 h).
1-Octanol (5.546 g, 42.59 mmol) was added to this cellulose hydro-
lysate, and the mixture was stirred at 908C under reduced pressure
until most of the water was separated by distillation into a Dean–
Stark apparatus. Then, the reaction was continued at 908C and ap-
proximately 0.7 kPa for 24 h under vigorous stirring. The catalyst
beads were then separated from the liquid mixture by filtration
through a sintered glass funnel (pore size=0), and they were
washed with methanol (5ꢂ2 mL). After removal of the volatiles
under reduced pressure (2.0–4.0 kPa, 608C), a major part of the ini-
tial 1-octanol (4.7 g) was separated from the resulting combined
liquids by using vacuum distillation (0.01–0.02 kPa, 808C). The resi-
due (dark brown syrup, ꢀ6.58 g) contained [C4mim]Cl (91.8 wt%)
and the following products (molar yields): C8Gm (46.5%), HMF
(7.5%), C8MF (1.5%), levoglucosan (1.9%), and glucose (1.6%).
Cellulose (fibrous, long) was supplied by Sigma–Aldrich and was
dried under reduced pressure (0.7 kPa) at 1008C for 30 min before
use; weight loss after drying was 3–5% (attributed to adsorbed
water). Amberlyst 15 (hydrogen form, dry, 4.7 mequivgÀ1), 1-dodec-
anol (98+% ACS reagent), 1-octanol (Chromasolv, for HPLC,
ꢁ99%), octyl b-d-glucopyranoside (ꢁ98%), n-dodecyl b-d-malto-
side (ꢁ98%), hydrogen peroxide solution (stabilized, 30 wt% in
H2O), molecular sieves (3 ꢁ, 1.6 mm pellets), phosphorus pentoxide
(dessicant), and biphenyl (ReagentPlus, 99.5%) were supplied by
Sigma–Aldrich and were used as received. Acetonitrile (Chroma-
solv, for HPLC, ꢁ99%) was supplied by Sigma–Aldrich and was de-
hydrated by means of an MBRAUN SPS-800 system. The ionic
liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl, >95%)
was supplied by Fluka and was handled quickly under a stream of
dinitrogen. Dodecyl b-d-glucopyranoside (99.9%) was supplied by
Calbiochem. Sulfuric acid (95–97%, synthesis grade), hexane (96%,
ACS analytical grade), ethyl acetate (Multisolvent HPLC grade), and
silica gel 60 (0.04–0.06 mm for flash chromatography, mesh 230–
400 ASTM) were supplied by Scharlau. N,O-Bis(trimethylsilyl)trifluor-
oacetamide (ꢁ98%) and pyridine (99+%) were supplied by Acros
Organics and were used as received.
Analytical methods
Analyses of reaction mixtures, crude materials, and partitioned frac-
tions for product identification and quantification were performed
by a combination of 1H NMR spectroscopy, ion-exclusion HPLC,
and GC of silylated samples. Alkanols, [C4mim]Cl, and most of the
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C12Gn (n>2, 0.8%), glucose (2.0%), levoglucosan (1.1%), HMF
(7.0%), and C12MF (0.5%).
Cellulose into C12Gm: Hydrolysis at 1008C, glycosidation at
908C (procedure 2)
Dodecyl glycosides were produced by a procedure similar to pro-
cedure 1 from cellulose (0.5913 g, 3.647 mequiv), [C4mim]Cl
(5.9035 g, 9.1% cellulose weight), Amberlyst 15 (0.3477 g,
1.634 mequiv, calculated as H+ equivalents), water (0.76 mL), and
1-dodecanol (7.992 g, 42.89 mmol). At that stage, the dark amber
mixture contained the following products (molar yields): C12G1
(33.4%), C12G2 (1.1%), glucose (2.9%), cellobiose (0.1%), levogluco-
san (1.1%), and HMF (12.0%). After separation of Amberlyst 15 and
1-dodecanol (ꢀ7.43 g), the resulting residue (dark brown syrup,
ꢀ6.63 g) contained [C4mim]Cl (91.1 wt%), 1-dodecanol (2.1 wt%),
and the following products (molar yields): C12G1 (32.3%), glucose
(2.0%), levoglucosan (2.2%), HMF (7.5%), and C12MF (1.7%).
Cellulose into C12Gm: Hydrolysis at 808C for 1.5h, then at
708C for 2.5h (procedure 7)
Dodecyl glucosides were produced by a procedure similar to pro-
cedure 4 from cellulose (0.5833 g, 3.598 mequiv), [C4mim]Cl
(5.1660 g, 10.1% cellulose weight), Amberlyst 15 (0.3528 g,
1.654 mequiv), water (0.76 mL), and 1-dodecanol (7.899 g,
42.39 mmol). The hydrolysis step was performed at 808C until t=
1.5 h and then at 708C until t=4.0 h, whereas the glycosidation
step was continued until t=48.5 h, which led to a mixture that
contained (molar yields) C12G1 (62.1%), C12G2 (8.6%), C12Gn (n>2,
1.1%), glucose (1.5%), levoglucosan (1.1%), HMF (7.4%), and
C12MF (1.4%).
Cellulose into C12Gm: Hydrolysis at 908C, glycosidation at
808C (procedure 3)
Separation of alkyl glycosides and ionic liquid
Dodecyl glycosides were produced by a procedure similar to pro-
cedure 2 from cellulose (0.6416 g, 3.957 mequiv), [C4mim]Cl
(5.9902 g, 9.7% cellulose weight), Amberlyst 15 (0.3484 g,
1.637 mequiv), water (0.06, 0.10, 0.10, 0.20, and 0.30 mL added at
t=0–3, 4–8, 9–12, 13–16, and 17–20 min intervals), and 1-dodeca-
nol (7.883 g, 42.30 mmol). The hydrolysis step was performed at
908C until t=1.5 h, whereas the glycosidation step was performed
at 808C until t=21.5 h, which led to a mixture that contained
(molar yields) C12G1 (43.6%), C12G2 (1.9%), glucose (5.5%), cello-
biose (0.3%), levoglucosan (1.1%), and HMF (11.8%).
Separation of C8Gm by short-path chromatography (procedure
1a)
A portion (1.2900 g) of the distillation residue obtained after the
reaction (procedure 1) was fractionated by elution through a short-
path (diameter=4.5 cm, length=3 cm) silica gel bed (ꢀ21 g). The
eluent used initially was an ethyl acetate/methanol mixture
(82:18 v/v, 356 g). The collected pale-yellow fractions (10ꢂꢀ5 mL,
#1–10, and 6ꢂꢀ25 mL, #11–16) were concentrated to dryness by
removing the solvents under reduced pressure, and the resulting
residues were analyzed for product identification. Elution was then
continued by consecutively passing methanol (79 g) and water
(100 g) through the column. The collected fractions (5ꢂꢀ40 mL,
#17–21) were concentrated and analyzed in the same fashion as
that described above. Product yields and ionic liquid recoveries are
listed in the Supporting Information for selected fractions. Frac-
tion #1 yielded a dark amber paste (10.9 mg) that contained C8MF.
Fraction #2 yielded a dark amber oil (21.8 mg) that was composed
of HMF, C8MF, and trace amounts of 1-octanol. Fraction #3 yielded
a dark amber oil (11.7 mg) that was composed of HMF and C8MF.
Fraction #4 yielded a dark amber oil (19.4 mg) consisting of a mix-
ture of HMF, C8G1, and trace amounts of C8MF. Fractions #5–8 yield-
ed a dark brown solid (87.3 mg) that was composed mainly of
C8Gm (yield=40.8%, purity=96.6%). In addition to minor amounts
of unidentified substances and trace amounts of [C4mim]Cl, levo-
glucosan was found in fractions #11–14. Finally, [C4mim]Cl
(1.0797 g, 92.9% of initial, purity=99.6%) was recovered from frac-
tions #15–20 as a dark amber syrup.
Cellulose into C12Gm: Glycosidation at 0.7kPa (procedure 4)
Dodecyl glycosides were produced by a procedure similar to pro-
cedure 3 from cellulose (0.6404 g, 3.950 mequiv), [C4mim]Cl
(5.9204 g, 9.8% cellulose weight), Amberlyst 15 (0.3488 g,
1.639 mequiv), water (0.76 mL), and 1-dodecanol (7.834 g,
42.04 mmol). The glycosidation step was performed at 0.7 kPa,
which led to a mixture that contained (molar yields) C12G1 (48.0%),
C12G2 (1.6%), glucose (2.9%), cellobiose (0.3%), levoglucosan
(1.2%), HMF (9.6%), and C12MF (0.9%).
Cellulose into C12Gm: Glycosidation at 708C (procedure 5)
Dodecyl glycosides were produced by a procedure similar to pro-
cedure 4 from cellulose (0.6655 g, 4.104 mequiv), [C4mim]Cl
(6.4760 g, 9.3% cellulose weight), Amberlyst 15 (0.3513 g,
1.650 mequiv), water (0.76 mL), and 1-dodecanol (7.935 g,
42.58 mmol). The glycosidation step was performed at 708C until
t=46.6 h, which led to a mixture that contained (molar yields)
C12G1 (46.9%), C12G2 (4.4%), C12Gn (n>2, 0.6%), glucose (2.0%), lev-
oglucosan (1.2%), HMF (6.0%), and C12MF (0.6%).
Separation of C8Gm by extraction with ethyl acetate (proce-
dure 1b)
A portion (0.60 g, ꢀ8.5% of the total) of the distillation residue ob-
tained by following procedure 1 was mixed with ethyl acetate
(4.61 g), and the resulting mixture was stirred at room temperature
for 30 min and then allowed to settle. After several minutes, a yel-
lowish liquid phase separated as the top layer from the dark
amber viscous bottom phase. The top layer was separated by de-
cantation, and the volatiles were removed under reduced pressure
at 608C to leave a yellowish oil (96 mg), mostly composed of 1-do-
decanol (87%) and [C4mim]Cl (9%); the amount of C8Gm in this
layer was below the detection limit of the techniques. In contrast,
Cellulose into C12Gm: Hydrolysis at 808C (procedure 6)
Dodecyl glycosides were produced by a procedure similar to pro-
cedure 4 from cellulose (0.6435 g, 3.969 mequiv), [C4mim]Cl
(6.0293 g, 9.6% cellulose weight), Amberlyst 15 (0.3504 g,
1.647 mequiv), water (0.76 mL), and 1-dodecanol (7.947 g,
42.65 mmol). The hydrolysis step was performed at 808C, whereas
the glycosidation step was continued until t=48.2 h, which led to
a mixture that contained (molar yields) C12G1 (57.4%), C12G2 (7.7%),
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the bottom layer did contain essentially the total expected amount
of C8Gm (19.2 mg, molar yield ꢀ40%).
liquid recoveries are listed in the Supporting Information for select-
ed fractions. Fraction #1 yielded a dark amber paste (9.9 mg) that
contained C12MF. Fractions #2 and 3 yielded dark amber pastes
(23.0 and 16.9 mg, respectively) composed of C12MF, HMF, and 1-
dodecanol. Fraction #4 yielded a dark amber paste (9.2 mg) con-
sisting of a mixture of HMF and C12Gm. Fractions #5–8 yielded
a brown solid (47.2 mg) that was mainly composed of C12Gm
(yield=25.5%, purity=97.0%). Minor amounts of unidentified sub-
stances and trace amounts of [C4mim]Cl and levoglucosan were
found in fractions #15–17. Finally, [C4mim]Cl (0.7455 g, correspond-
ing to 87.5% of the initial amount, purity=99.5%) was recovered
from fractions #18 and 19 as a dark amber syrup.
Separation of C8Gm by crystallization of [C4mim]Cl (procedure
1c)
A portion (ꢀ6.0 g) of ionic liquid/products mixture obtained by
following procedure 1 was dissolved in anhydrous acetonitrile
(3.6 g) and then a seed crystal of [C4mim]Cl and anhydrous ethyl
acetate (7.2 g, dropwise) were added with gentle stirring. By keep-
ing the temperature below 158C, a pale brown solid started to
crystallize. After a few minutes, a slurry was formed. More ethyl
acetate (60 g) was added, and the supernatant liquor was separat-
ed by filtration and concentrated to dryness to yield an oil that
contained only a small amount of C8Gm (30.1 mg, representing
a 2.9% yield) mixed with 1-octanol, HMF, and residual [C4mim]Cl,
among other substances. The crystallized material was dried under
reduced pressure (ꢀ1.0 kPa) at 608C to yield a pale brown solid
(5.755 g) containing [C4mim]Cl (95.1 wt%, representing 95.9% of
the initial amount) and C8Gm (2.5%, yield=28.0%), among other
substances.
Separation of C12Gm by precipitation of [C4mim]Cl (procedure
2b)
A portion (2.2677 g) of the distillation residue obtained after the
reaction (procedure 2) was fractionated by a procedure similar to
procedure 1c by using acetonitrile (0.8 mL) and ethyl acetate
(75 mL). After evaporation of the volatiles from the liquors, a dark
amber syrup (0.1730 g) containing C12Gm (22.2%, yield=8.9%), 1-
dodecanol (35.4%), [C4mim]Cl (16.7%), HMF (5.8%, yield=5.0%),
C12MF (1.9%, yield=2.0%), and minor amounts of other unidenti-
fied compounds was obtained. The dried crystallized solid
(2.0655 g) contained [C4mim]Cl (94.9%, representing 97.4% of the
initial amount), C12Gm (4.8%, yield=23.0%), levoglucosan (0.2%,
yield=1.7%), and HMF (0.1%, yield=0.9%). Product yields and
ionic liquid recoveries are listed in the Supporting Information for
each fraction.
Separation of C8Gm by precipitation of [C4mim]Cl (procedure
1d)
A portion (3.86 g) of the distillation residue obtained after the reac-
tion (procedure 1) was dissolved in anhydrous acetonitrile (1.4 mL),
and the resulting mixture was added dropwise to anhydrous ethyl
acetate (30 mL) containing a small amount of [C4mim]Cl (ꢀ5 mg,
as a seed for crystallization) under vigorous stirring at room tem-
perature (25–308C) and under Schlenk techniques, upon which
bulk precipitation was observed. The resulting suspension was
stirred for another 20 min and then allowed to settle. The mother
liquor was separated by filtration under an atmosphere of argon
from the brown solid formed. The solid was then washed with an-
hydrous ethyl acetate (10 mL). The combined mother and washing
liquors were concentrated under reduced pressure to yield a dark
amber syrup (0.1334 g) that was composed of (weight percentag-
es) C8G1 (10.7%, yield=2.2%), [C4mim]Cl (23.7%), 1-octanol
(14.7%), HMF (7.7%, yield=3.6%), C8MF (3.0%, yield=0.7%), and
minor amounts of other unidentified compounds. On the other
hand, the precipitated solid was dried under high vacuum
(ꢀ0.01 kPa) at 308C for 2 h; the pale brown solid thus obtained
(3.9111 g) contained [C4mim]Cl (92.3%, representing 98.4% of the
initial amount) and the following products (molar yields): C8G1
(41.3%), HMF (3.9%), glucose (1.9%), cellobiose (0.2%), and levo-
glucosan (1.8%). Product yields and ionic liquid recoveries are
listed in the Supporting Information. Furthermore, an insoluble ma-
terial was isolated by centrifugation–decantation from an HPLC
sample of the ionic liquid fraction. After washing and drying,
a brown solid (3.2 mg; C 60.1, H 6.1, N 1.4, S 0.8%; carbon content
equivalent to a 17.0% molar carbon yield relative to the initial cel-
lulose) was obtained.
Separation of C12Gm by precipitation in water (unoptimized re-
action outcome, procedure 2c)
A portion (3.1114 g) of the distillation residue obtained after the re-
action (procedure 2) was mixed with water (20.65 mL). The result-
ing suspension was stirred in an oil bath at 1008C for 30 min, al-
lowed to cool down to 30–408C, and then filtered through a sin-
tered glass funnel (pore size=4). The dark brown solid thus col-
lected was washed with water (3ꢂ5 mL) and dried under a stream
of air. The crude product was recovered by dissolving the collected
material in methanol (3ꢂ5 mL) and decanting the resulting sus-
pension, whereby a residual insoluble solid was separated (see
below). The combined solutions were concentrated to dryness by
removing the solvents under reduced pressure to yield a dark
amber sticky solid (0.3383 g) that contained C12Gm (61.1%, yield=
34.4%), 1-dodecanol (34.2%), C12MF (3.7%, yield=2.5%), [C4mim]Cl
(1.9%, representing 0.2% of the initial amount), and minor
amounts of HMF and other unidentified compounds. The residual
insoluble material was dried under reduced pressure to yield
a dark brown solid (27.5 mg) that was analyzed by FTIR, XRD (no
diffraction peaks observed), and elemental analysis (C 56.4, H 5.3,
N 1.6, S 1.0%; the carbon content represents a 12.6% molar yield
relative to the initial cellulose). To recover the ionic liquid, the com-
bined aqueous layer (see above) was concentrated under reduced
pressure to yield a dark amber viscous liquid (2.8093 g) that con-
tained [C4mim]Cl (98.9%, representing 99.5% of the initial
amount), HMF (0.6%, yield=7.1%), C12Gm (0.4%, yield=1.9%), and
levoglucosan (0.1%, yield=1.1%). Product yields and ionic liquid
recoveries are listed in the Supporting Information for each frac-
tion.
Separation of C12Gm by short-path chromatography (proce-
dure 2a)
A portion (0.9596 g) of the distillation residue obtained after the
reaction (procedure 2) was fractionated by a procedure similar to
that described for C8Gm (procedure 1b) through silica gel (ꢀ24 g)
and eluted with an ethyl acetate/methanol mixture (84:16 v/v,
352 g) and then with methanol (79 g). Product yields and ionic
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Separation of C12Gm by precipitation in water (optimized reac-
tion outcome, procedure 7a)
Acknowledgements
Financial support by the Spanish Ministry of Economy and Com-
petitiveness (Severo Ochoa and CTQ2012–32315) is gratefully ac-
knowledged. A.V.P. is grateful to both the Consejo Superior de In-
vestigaciones Cientifꢀcas (CSIC) and the European Social Fund
(ESF) for a JAE-Doc postdoctoral grant.
A portion (6.0560 g, representing 95.7% of the original mixture) of
the distillation residue obtained after the reaction (procedure 7)
was treated in a manner analogous to that outlined in procedur-
e 2c by using water (40.0+5ꢂ5 mL for washing), which yielded
a dark amber sticky solid (1.4297 g) that contained C12Gm (68.0%,
yield=69.7%), 1-dodecanol (29.4%), [C4mim]Cl (1.9%, representing
0.5% of the initial amount), C12MF (0.5%, yield=0.7%), and HMF
(0.1%, yield=0.4%). An insoluble material was recovered from
a sample of the crude in [D6]DMSO, which was washed with ace-
tone and dried under vacuum to yield an off-white solid (C content
ꢀ40%, corresponding to a 4.6% of the initial cellulose). The dark
amber viscous liquid (5.4421 g) obtained from the aqueous liquors
contained [C4mim]Cl (90.4%, representing 99.5% of the initial
amount), HMF (0.2%, yield=2.4%), C12Gm (0.2%, yield=0.9%), glu-
cose (0.2%, yield=1.7%), levoglucosan (0.1%, yield=1.1%), and
minor amounts of other saccharides.
Keywords: biomass · cellulose · ionic liquids · separation ·
surfactants
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Crude refining by distillation and recrystallization (procedure
2d)
A crude product (0.55 g) obtained in a manner analogous to that
outlined in procedure 2c after removal of the residual 1-dodecanol
by distillation was recrystallized from hot hexane/ethyl acetate
(20:1 v/v, 7 mL). A small amount of insoluble material was removed
by filtration (after washing with ethyl acetate and acetone and
drying, a black solid was obtained, ꢀ 0.06 g). This solid was ana-
lyzed by XRD and elemental analysis (C 62.9, H 6.9, N 1.9, S 0.6%).
Crystallization from the filtrate was observed upon cooling. The re-
crystallized solid was collected by filtration, washed with hexane/
ethyl acetate (20:1 by volume, 5 mL), and dried under reduced
pressure to yield a brownish solid (0.25 g, 95 wt%, C12Gm yield=
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A portion (1.3328 g) of the crude product obtained after procedur-
e 7a (89.2% of the original reaction 7 mixture) was refined by first
performing a distillation under high vacuum (0.1–0.02 kPa, 1258C)
by using a Kugelrohr apparatus. The distillate (0.31 g) was essen-
tially composed of 1-dodecanol. The dark brown solid residue
(0.9168 g) was bleached by mixing with aqueous H2O2 (30%,
0.25 g) and H2O (1.17 g), and the pH of the solution was main-
tained at approximately 9 by the addition of an aqueous NaOH so-
lution (40%). The resulting suspension was stirred at 908C for 2 h
and then concentrated to dryness under reduced pressure (1.0 kPa,
658C) to yield a pale yellow paste (1.4623 g) that contained mostly
C12Gm (48.7%, 92.4% on a dry basis, yield=64.8%) and H2O
(ꢀ45%), together with minor amounts of 1-dodecanol (<1%) and
[C4mim]Cl (<1%, representing <0.5% of the initial amount).
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Received: July 22, 2014
Published online on October 10, 2014
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2014, 7, 3362 – 3373 3373