Cellulose conversion into alkylglycosides in the ionic liquid 1-butyl-3-methylimidazolium chloride

Article abstract of DOI:10.1039/c0gc00192a

The conversion of cellulose into alkylglycosides is carried out in the ionic liquid 1-butyl-3-methylimidazolium chloride in the presence of an acidic catalyst. Primary alcohols like n-butanol and n-octanol were used as alkylating reagents. The acidic resin Amberlyst 15DRY proved to be the optimum heterogeneous catalyst: it catalyzes the hydrolysis of the β(1→4) links in the cellulose polymeric chain as well as the alkylation of the hydroxyl groups at the C1 position of the glucose intermediate. The cellulose was fully converted under mild conditions; in a reaction with n-butanol, the obtained yield of butylglucopyranoside isomers was 86%.

Full text of DOI:10.1039/c0gc00192a

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www.rsc.org/greenchem | Green Chemistry
Cellulose conversion into alkylglycosides in the ionic liquid
1-butyl-3-methylimidazolium chloride
Igor A. Ignatyev,a Pascal G. N. Mertens,a Charlie Van Doorslaer,a Koen Binnemansb and Dirk E. de Vos*a
Received 8th June 2010, Accepted 27th July 2010
DOI: 10.1039/c0gc00192a
The conversion of cellulose into alkylglycosides is carried out in the ionic liquid
1-butyl-3-methylimidazolium chloride in the presence of an acidic catalyst. Primary alcohols like
n-butanol and n-octanol were used as alkylating reagents. The acidic resin Amberlyst 15DRY
proved to be the optimum heterogeneous catalyst: it catalyzes the hydrolysis of the b(1→4) links in
the cellulose polymeric chain as well as the alkylation of the hydroxyl groups at the C1 position of
the glucose intermediate. The cellulose was fully converted under mild conditions; in a reaction
with n-butanol, the obtained yield of butylglucopyranoside isomers was 86%.
in a one-pot process into more stable compounds such as
alkylglycosides. We have recently reported that addition of
hydrogen and hydrogenation catalysts allows the conversion
Introduction
Alkylglycosides are a class of biodegradable nonionic surfac-
tants with a broad application scope, e.g. in the cosmetic,
in one pot of the intermediately formed glucose into polyols,
detergent, food and pharmaceutical industries.1 One of their
but the poor solubility of hydrogen in BMimCl is a serious
interesting features is their ability to form liquid crystals.2
handicap for efficient hydrogenation.16 This urged us to consider
The conventional alkylglycoside synthesis was first described
hexose acetalization as an alternative reaction. Not only does
by E. Fischer as the formation of a glycoside by the reaction
this allow us to use the most abundant carbohydrate source
of an aldose or ketose with an alcohol in the presence of
available for alkylglycoside production; the alkylation may in
acid species,3a and since then numerous homogeneous and
addition suppress the undesired pyrolysis of glucose. There is
heterogeneous catalysts have been proposed and applied for
an apparent compatibility between hydrolysis and alkylation
their synthesis.3–6 Typical drawbacks of this reaction, such as
reactions as they both require acid catalysis. In this work, we
the necessity for functional group protection and deprotection,6
demonstrate an effective one-pot transformation of cellulose in
or the formation of oligomeric species, can be avoided by using
the presence of Amberlyst 15DRY to butylglucopyranosides and
specific heterogeneous acidic catalysts like sulfonated resins,7
octylglucopyranosides in 1-butyl-3-methylimidazolium chloride
acid clays 8 and zeolites.9–10
Ionic liquids (ILs), and in particular chloride-containing ones,
as the solvent under relatively mild conditions. Similar work on
BMimCl, cellulose and alcohols appeared when our paper was
can be suitable solvents for cellulose. They disrupt the hydrogen
ready for submission.17
bonds and dissolve the cellulose chains at the molecular level.11
For instance, 1-butyl-3-methylimidazolium chloride (BMImCl)
Experimental
can dissolve up to 25 wt% of cellulose.12 There are already
multiple examples of successful cellulose transformations in ILs,
such as derivatization of the cellulose chains,13 or production of
composite materials that besides cellulose also contain carbon
nanotubes or inorganic materials.14 Cellulose hydrolysis was
successfully conducted in the IL BMImCl with glucose as the
major product in the presence of homogeneous acids, or of
the heterogeneous acidic catalyst Amberlyst 15DRY.15 However,
prolongation of the reaction time can cause pyrolysis of glucose,
and when homogeneous acids are used, a ceiling yield of 50%
is reached at which hexose degradation starts to decrease the
overall process yield.15b
1-Butyl-3-methylimidazolium chloride (99%), ethyltributyl-
phosphonium diethyl phosphate (>95%) and tetrabutyl-
phosphonium chloride (>95%) were obtained from
IoLiTec Ionic Liquids Technologies GmbH. 1-Ethyl-3-
methylimidazolium diethyl phosphate (≥98.0% (HPLC/T))
and 1-ethyl-3-methylimidazolium acetate (97%) were obtained
from Sigma-Aldrich. The cellulose used was Avicel PH 101
(DP 215–240). a-D-glucopyranoside (min 98%), butyl a-D-
gluco-pyranoside and butyl b-D-glucopyranoside (min 98%)
were obtained from Carbosynth Limited. Amberlyst 15DRY
was purchased from Sigma-Aldrich. The H-b zeolite was a
commercial sample from the PQ corporation (CP 811 BL-25).
The H-MCM-22 was prepared in-house based on a literature
recipe.18 Reactions were conducted in sealed glass vials (10 mL)
with continuous stirring.
It is worthwhile to investigate whether glucose, formed
through acid hydrolysis of cellulose, can be further transformed
aCentre for Surface Chemistry and Catalysis, K.U. Leuven, Kasteelpark
Arenberg 23 – box 02461, BE-3001, Heverlee, Belgium. E-mail: dirk.
devos@biw.kuleuven.be; Fax: +32 16321998; Tel: + 32 16321610
Other chemicals were obtainedfrom commercial suppliers and
were used as received. For reactions with methanol and ethanol,
10 ml stainless steel batch pressure reactors were employed under
0.8 MPa of argon. After reaction, samples were derivatized using
bDepartment of Chemistry, Coordination Chemistry, K.U. Leuven,
Celestijnenlaan 200F – box 02404, BE-3001, Heverlee, Belgium
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Table 1 Initial experiments on glucose alkylation in ionic liquids
Entry
Solvent
n-Butanol (mL)
Catalyst
Yield of a-BGP (%)
Yield of b-BGP (%)
1
2
3
4
—
1
0.3
1
0.01 g Hb zeolite
45
31
48
17
30
26
32
10
1 g BMImCl
—
1 g BMImCl
0.005 g PTSA
0.01 g Amberlyst 15DRY
0.01 g Amberlyst 15DRY
0.3
Reaction conditions: 0.01 g glucose, 90 ◦C, 4 h.
Table 2 Initial experiments with cellulose
Yield of a-BGP Yield of b-BGP
Yield of glucose Yield of
Total conversion
Entry Catalyst
(%)
(%)
Yield of BGF (%) (%)
levoglucosan (%) of cellulose (%)
1
2
3
0.01 g H-b
0
0
29
0
0
16
0
0
5
0
0
10
0
0
7
0
0
67
0.01 g H-MCM-22
0.01 g Amberlyst
15DRY
Reaction conditions: 0.05 g cellulose, 1 g of BMImCl, 20 ml of water, 0.3 mL n-butanol, 110 ◦C, 24 h.
MSTFA (N-(trimethylsilyl)-N-methyltrifluoroacetamide) and
injected onto a 30 m HP-1 column in a GC (HP 5890) or a GC-
MS (Agilent 6890 GC and 5973 MS) instrument. Typically, a ca.
four-fold excess of MSTFA with respect to the –OH groups was
added to 0.3 mL of sample mixed with 0.3 mL of pyridine, and
the mixture was stirred for 3 h at 80 ◦C. Derivatized compounds
were then extracted into 0.5 mL of dibutylether and analyzed.
The procedure was verified and made quantitative using known
amounts of reference compounds such as glucose, butyl-a-D-
glucopyranoside, butyl-b-D-glucopyranoside, and others. The
water content of the ILs was determined with a coulometric
Karl–Fischer titrator (Mettler Toledo DL39).
bond, and thus represents a dimeric model for the cellulose poly-
mer. Just like glucose, cellobiose is readily soluble in BMImCl.
In the reaction with this dimeric substrate, the acid catalyst
should not only be capable of alkylation but also of hydrolysis
of the b(1→4) bond. This also implies that some water should be
available in the reaction medium. Minor contamination of the
hydrophilic BMImCl by water is hard to avoid; Karl–Fischer
titration showed that the level of contamination was ca. 0.1 wt%
of water. To ensure that at least a stoichiometric amount of water
is available, 20 ml of water was added per g of IL. We applied
Amberlyst 15DRY, a catalyst previously reported to hydrolyze
cellulose in BMImCl.15a Cellobiose (0.05 g) was successfully
hydrolyzed and butylated by using 0.01 g of Amberlyst 15DRY
and 0.3 mL of n-butanol in 1 g of water-enriched BMImCl at
110 ◦C for 24 h. a-BGP and b-BGP were obtained with yields of
43% and 24%, respectively. By-products were glucose (31%) and
levoglucosan (2%). The detection of the latter product indicates
that under certain conditions alkylation in the presence of an
acidic catalyst can lead to degradation reactions, as will be
demonstrated below. 110 ◦C has previously been reported as
an optimal temperature for glucose butylation.9–10
Results and discussion
In a first phase, glucose was used as a substrate for the alkylation
in ILs. Multiple interesting procedures for glucose alkylation
have been reported.7–10 In order to investigate the effect of the IL
solvent on the alkylation, we performed alkylation reactions
with or without BMImCl in n-butanol, without adding any
other solvent. All catalysts tested, including Amberlyst 15DRY,
showed significant activity for butylation of glucose at 90 ◦C
(Table 1, entries 1–4). Amberlyst 15DRY is a macroporous
Brønsted acid resin.
The main products were butyl-a-D-glucopyranoside (a-BGP)
and butyl-b-D-glucopyranoside (b-BGP). Yields in the presence
of BMimCl are considerably lower than in pure BuOH. This
is simply a thermodynamic and kinetic consequence of the
three-fold lower n-BuOH concentration when the reaction was
carried out in the presence of the IL. Nevertheless, the result in
the presence of para-toluene-sulfonic acid shows that a >50%
yield of butylglucosides can be achieved easily, even in an IL
(Table 1, entry 2).
Next, cellulose was employed in the form of the micro-
crystalline commercial product Avicel. The cellulose reagent
may contain some additional water which can be consumed
in the hydrolysis (typically 4–7 wt% based on cellulose).19 In
our first attempt, H-b zeolite (Si/Al = 13) and H-MCM-22
zeolite (Si/Al = 30) were applied besides Amberlyst 15DRY7c for
reactions with n-butanol. The zeolite materials that were chosen
are both strong heterogeneous acids with ample access to the
acid sites, due to the small crystal size, in the case of H-b, or due
to the flaky morphology, in the case of H-MCM-22. Moreover,
9
zeolites like H-b have been reported to be suitable catalysts
for alkylation of monomeric carbohydrates. However, when the
zeolites were tested, no products of cellulose depolymerization
were detected at all, not even after a 24 h reaction time (Table 2,
entries 1 and 2). Significantly better results were obtained with
Amberlyst 15DRY (Table 2, entry 3). This suggests that the
As a step-up towards cellulose, cellobiose was investigated as
a reaction substrate, in view of its molecular structure being
an intermediate between those of glucose and cellulose. This
compound consists of two glucose units linked by a b(1→4)
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Scheme 1 Splitting of cellulose with formation of a-BGP, b-BGP, glucose and levoglucosan.
dissolved polymer chains can only interact with well-accessible
acid sites in macropores.
at ~2, which is close to the value observed in the IL mediated
reaction. This suggests that the IL facilitates the b-BGP to a-
BGP conversion in the alkylglycoside fraction.
Detailed product identification by comparison with reference
compounds, by comparison with results of reported reactions
and by GC-MS identification showed that the major product
was BGP in its a- and b-forms, with the a-anomer as the
dominant product. A smaller amount of butylglucofuranosides
(BGF) was also detected, as well as of glucose (Table 2, entry
3; Scheme 1). Levoglucosan, a pyrolysis product, has also been
identified. It is worth noting that the pyrolysis of glucose and
similar compounds can also lead to dehydrated compounds such
as furans;15 however, these were not detected here by means of
GC or GC-MS.
Fig. 1 shows that glucose is the major primary product of
the reaction. At 110 ◦C and under the conditions specified,
its concentration passes through a maximum at 1 h and then
decreases with time. The total yield of alkylated carbohydrates
is more or less constant in the 2–4 h time interval. The BGPs are
the major products, and in this fraction, a-BGP is dominant.
However, the selectivity slowly changes. The a-BGP to b-BGP
ratio increases from 1.5 at the first sampling point, to 1.7 at
maximal product yield, and eventually evolves towards 2 at
long reaction times. Between reaction times of 2 h and 4 h, the
furanosides are gradually isomerized into pyranosides. a-BGP
is indeed thermodynamically more stable than b-BGP and the
BGFs.10 This variation of the a-BGP to b-BGP ratio early in the
reaction has also been reported by Moreau for the alkylation
of D-glucose with n-butanol. Remarkably, in a zeolite-catalyzed,
solventless reaction of glucose, b-BGP is the kinetically favored
product, and the initial a-BGP to b-BGP ratio is as low as
0.5. Only at over 90% conversion does the a/b ratio stabilize
While attempting to reach the equilibrium by extending the
reaction time up to 24 h, it was observed that the product
yield starts to decrease slowly. In order to understand this phe-
nomenon, pure a-BGP and glucose were dissolved in BMImCl
in the presence of the acid resin, and the mixture composition
was monitored versus time. This clearly showed that at 110 ◦C, a-
BGP is more resistant to acidic hydrolysis caused by Amberlyst
15DRY than glucose, as is shown in Fig. 2. Especially initially,
the concentration of glucose falls faster than that of a-BGP. We
observed that under the same conditions but without the
acidic catalyst, concentrations of glucose and a-BGP remained
virtually unchanged during the same periods of time. The fact
that even the a-BGP concentration decreases is likely due to
the dynamic nature of the equilibrium between glucose and a-
BGP: as glucose starts to disappear, the equilibrium shifts to
glucose and a-BGP is transformed back into glucose, even in
the presence of n-butanol.
Fig. 2 Stability of a mixture of glucose and a-BGP in BMImCl (1 g)
in the presence of Amberlyst 15DRY (0.01 g) at 110 ◦C.
In order to maximize the yield of butylated products two
approaches were used. First, it was attempted to shift the
equilibrium via the law of mass action. This was achieved by
adding an additional volume of n-butanol after some time of
cellulose hydrolysis, when the extra solvent no longer causes
precipitation of the polymeric material (Table 3, entries 2–3).
Indeed, addition of a large excess of n-butanol right from the
start could impede smooth cellulose dissolution. In a second
approach, part of the Amberlyst 15DRY particles were removed
after some reaction time. It was speculated that the amount
of acid catalyst required for the hydrolysis may be higher than
the amount needed for the alkylation (Table 3, entries 4–7).
Fig. 1 Run profile of reaction between cellulose (0.05 g) and n-butanol
(0.3 mL) in BMImCl (1 g) in the presence of Amberlyst 15DRY (0.01 g)
at 110 ◦C.
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Table 3 Conversion of cellulose to butylglycosides over Amberlyst 15DRY in various conditionsa
Yield of
Yield of
Yield of
Yield of
Yield of
Total yield of butylated
Entry Solvent
Co-reagent a-BGP (%) b-BGP (%) BGF (%) glucose (%) levoglucosan (%) products (%)
1
1 g BMImCl
1 g BMImCl
1 g BMImCl
1 g BMImCl
1 g BMImCl
1 g BMImCl
1 g BMImCl
1 g [EMIm][Et2PO4]
1 g [EMIm][AcO]
1 g [EMIm][AcO]
1 g [Bu3PEt][Et2PO4]
1 g [Bu3PEt][Et2PO4] 4 mL H2O
1 g [Bu4P][Cl]
1 g [Bu4P][Cl]
—
—
29
53
61
37
33
28
24
0
0
0
12
14
0
16
30
25
20
16
12
10
0
0
0
12
14
0
5
3
0
13
12
11
9
0
0
0
0
0
0
10
9
7
6
4
12
12
8
9
0
0
0
5
0
0
0
50
85
86
70
61
51
43
0
0
0
24
28
0
2b
3b
4c
5d
6e
7f
3 mL H2O
—
—
—
—
—
—
11
18
27
15
18
0
0
0
19
22
0
8
9
10
11
12
13
14
4 mL H2O
—
—
4 mL H2O
0
0
0
0
0
a General reaction conditions: 0.05 g cellulose, 0.3 mL n-butanol, 0.01 g Amberlyst 15DRY, 110 ◦C, 24 h. b After 4 h 1.2 mL of n-butanol was added
to the reaction mixture. c 95% of the Amberlyst 15DRY particles were removed after 4 h. d 70% of the Amberlyst 15DRY particles were removed after
4 h. e 95% of the Amberlyst 15DRY particles were removed after 2 h. f 70% of the Amberlyst 15DRY particles were removed after 2 h.
Particularly the first approach was successful in raising the
alkylglycoside yield, and using an overall n-BuOH to glucose
monomer ratio of 50, the yield climbed up to 86%. Note that
this is much higher than the ~50% maximal yield of glucose
from cellulose that is obtained when no secondary reaction
is performed in the same pot.15b The same experiment was
also performed on a five-fold increased scale, with otherwise
identical ratios of reactants and ionic liquid solvent. A summed
84% maximal yield of alkylated compounds was retrieved,
using the same overall 50 : 1 ratio of butanol to carbohydrate
monomeric units. Regarding the partial removal of the acid
catalyst, the best effect was noted when 95% of the particles
were removed after 4 h (Table 3, entries 4–5), with finally a
yield of 70% butylated products at the relatively low molar
n-BuOH to glucose monomer ratio of 10. Such a procedure
constitutes a compromise between a sufficient catalyst contact to
allow smooth hydrolysis and alkylation, and on the other hand,
prevention of acid-catalyzed degradation late in the reaction.
We also tried to use alternative ILs that dissolve cellu-
lose, such as 1-ethyl-3-methylimidazolium diethylphosphate, 1-
ethyl-3-methylimidazolium acetate, ethyltributyl-phosphonium
diethylphosphate or tetrabutylphosphonium chloride (Table 3,
entries 8–14). Note that some of these ILs are considerably
more hydrophobic than BMImCl. Therefore, these IL solvents
were also tested with the addition of an amount of water
that is stoichiometric with respect to the cellulose. Only ethyl-
tributylphosphonium diethylphosphate showed some suitability
for the reaction (Table 3, entries 11–12). Using other anions than
chloride may be problematic, since some anions that have been
reported as suitable for cellulose dissolution, e.g. acetate, may
actually act as a buffer and consequently quench the acidity of
the resin. This could account for the lack of product formation
in the presence of 1-ethyl-3-methylimidazolium acetate. One of
the factors contributing to the suitability of ethyltributylphos-
phonium diethylphosphate could be the asymmetric nature of its
cation, which decreases the viscosity of the IL medium and thus
increases diffusivities and reaction rates.20 While the addition of
a minute amount of water (0.25 or 0.33 wt%) did not hinder
the dissolution of the cellulose, it had no significant effect in
this type of reaction (Table 3, entries 2, 10, 12, 14). None of the
assessed alternative ILs matched the performance of BMImCl.
Besides n-butanol, n-octanol was also used as an alkylating
agent. Using the same 10 to 1 molar ratio of alcohol with
respect to the glucose monomer, a similar kinetic profile was
observed. Fig. 3 shows that a-OGP (octylglucopyranoside) is
the major product of the reaction after 30 min. Its concentration
passes through a maximum at 4 h and then decreases with
time. Again, the b-isomer and the furanosides are the prevalent
by-products. By analogy with the alkylation with butanol,
the predominance of a-OGP can be explained by its higher
thermodynamic stability in comparison with b-OGP and OGF
(octylglucofuranoside).21 Control experiments showed that a-
OGP is again more resistant to acidic degradation caused by
Amberlyst 15DRY than the intermediate glucose. Reaction
between 0.05 g of cellulose and 0.5 mL of n-octanol in 1 g
of ethyltributylphosphonium diethyl phosphate, in the presence
of 0.01 g of Amberlyst 15DRY at 110 ◦C during 24 h gave
the following product yields: 20% of a-OGP, 5% of b-OGP,
22% of glucose and 5% of levoglucosan. This confirms that
Fig. 3 Run profile of reaction between cellulose (0.05 g) and n-octanol
(0.5 mL) in BMImCl (1 g) in the presence of Amberlyst 15DRY (0.01 g)
at 110 ◦C.
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Table 4 Transalkylation of a-BGP with n-octanol
Amberlyst 15DRY Yield of
Entry mass (g)
Yield of
Yield of
Yield of
Yield of Yield of Yield of
Total yield of octylated
a-OGP (%) b-OGP (%) OGF (%) glucose (%) BGF (%) BGP (%) levoglucosan (%) compounds (%)
1
2
3
4
0.020
0.010
0.001
0
38
30
6
21
10
4
5
4
8
3
15
12
0
6
4
0
0
5
10
8
0
64
44
18
10
10
80
90
0
0
0
0
Reaction conditions: 0.05 g a-BGP, 1 g BMImCl, 0.5 mL n-octanol, 110 ◦C, 24 h.
other ILs than BmimCl are also potential solvents in these
reactions.
In solvent-free systems, the rate of glucose alkylation de-
creases with increasing length of alcohol alkyl chain.22 This
is due to the decreasing solubility of glucose in more apolar
alcohols. We have observed a different situation when cellulose
dissolved in BMimCl is the carbohydrate source: octylation is
initially faster than butylation. On the other hand, using shorter
alcohols negatively affected the reaction. Thus, when methanol
or ethanol were applied in the same molar ratio with respect to
the glucose monomers, the cellulose was not visibly dissolved,
and no products of etherification or hydrolysis could be detected.
It seems that the short alcohols compete more successfully
than the cellulose for the hydrogen bond formation with the
chloride anions. As the chain length of the alcohol reagent
increases, its hydrogen bond donor capacity decreases, and this
Fig. 4 Run profile of reaction between cellulose (0.05 g), n-butanol
(0.3 mL) and subsequently n-dodecanol (two loads of 0.611 g, indicated
by arrows) in BMImCl (1 g) in the presence of Amberlyst 15DRY
(0.01 g) at 110 ◦C.
allows a better solvation of the cellulose by the IL and a faster
reaction.
However, an alkyl chain that is too long, as in 1-dodecanol,
again decreases the product yields. Thus, no products were
obtained from a 24 h reaction of cellulose and n-dodecanol in
BMImCl at 110 ◦C, even if a visually homogeneous reaction
mixture was formed. Apparently, BMimCl is not a suitable
solvent to effect the reaction between dissolved glucose and n-
dodecanol, which have widely different polarities.
Conclusions
The results prove that when the cellulose structure is unfolded
in an ionic liquid, the depolymerization becomes rather easy,
and can be carried out under moderate conditions. Two ionic
liquids were identified that allow to dissolve the cellulose and
to perform the acid-catalyzed hydrolysis and alkylation. While
the use of an acid catalyst could cause degradation of the
formed hexoses, it was demonstrated here that this problem
can be alleviated by in situ conversion of the glucose to
alkylglycosides. When an excess of the alcohol was offered, or
when part of the acid catalyst was removed during the alkylation
phase, the yield of alkylglycoside could be maximized. The
direct synthesis of alkyl glycosides with longer chains, such
as dodecylglycopyranosides, is less easy, but can be achieved
via transalkylation. To separate the reaction products from the
ionic liquid, supercritical antisolvent precipitation with carbon
dioxide could be a promising technique.23
In an alternative approach to prepare the long-chain alkylgly-
cosides, it was attempted to perform a transalkylation, starting
from a short-chain alkylglycoside. The data in Table 4 prove that
this transalkylation can easily be performed in an IL: reaction
of a-BGP and n-octanol gave up to 64% yield of octylated
compounds within 24 h. The acidic catalyst concentration
required for this transalkylation is similar to the amount of
catalyst typically used in the cellulose depolymerization, i.e. at
least 10 mg of catalyst per g of IL (Table 4, entries 1–4). In
order to synthesize dodecylglucosides, a reaction was performed
using 0.05 g of cellulose (0.31 mmol monomers), 0.3 mL of n-
butanol, 10 mg of Amberlyst 15DRY and 20 mL of water in 1 g of
BMImCl. After 1 h of stirring at 110 ◦C, 0.611 g o◦f n-dodecanol
(3.2 mmol) was added. After another 3 h at 110 C, n-butanol
was evaporated from the reaction mixture in a rotary evaporator,
and an extra portion of 0.611 g of n-dodecanol was added. As is
shown in Fig. 4, equilibrium was apparently reached after 10 h.
At this point, the yield of DGP is 45% (29% a-DGP and 16%
b-DGP), with the a-glucopyranoside isomers dominating over
the b-isomers during the whole course of the reaction (DGP =
dodecylglucopyranoside). This proves that hydrolysis followed
by alkylation and transalkylation is a viable route in forming the
long-chain alkylglycosides from cellulose.
Acknowledgements
Financial support by K.U. Leuven (project IDO/05/005) is
gratefully acknowledged. This work is supported by IAP project
Functional Supramolecular Systems (Belgian Science Policy)
and by the CASAS Metusalem Grant. IAI thanks the Leuven
Arenberg Doctoral School for a PhD fellowship (DBOF). This
work is also supported by IoLiTec (Denzlingen, Germany).
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