Transformation of cellulose into biodegradable alkyl glycosides by following two different chemical routes

Article abstract of DOI:10.1002/cssc.201000371

The transformation of cellulose into long-chain alkyl glycoside surfactants has been carried out following two different routes: (1) Direct transformation of cellulose to butyl-, hexyl-, octyl-, decyl- and dodecyl-α,β- glycosides in an ionic liquid media and Amberlyst-15Dry as catalysts, with mass yield of up to 82%; and (2) two steps reaction with transformation of cellulose into methyl glucosides, with a procedure described by Zhang et al., followed by transacetalation with 1-octanol and 1-decanol in the presence of Amberlyst-15Dry. A kinetic study for the direct transformation of cellulose using 1-octanol has shown that depolymerisation of cellulose continues during the Fischer glycosidation. Increasing the chain length of the alcohol decreases the global reaction rate owing to an increase in the lipophilicity of the alcohol that decreases its contact with the carbohydrates. Finally, several acid catalysts were tested and the best results were obtained with Amberlyst-15Dry.

Full text of DOI:10.1002/cssc.201000371

DOI: 10.1002/cssc.201000371
Transformation of Cellulose into Biodegradable Alkyl
Glycosides by Following Two Different Chemical Routes
Nicolas Villandier and Avelino Corma*[a]
The transformation of cellulose into long-chain alkyl glycoside
surfactants has been carried out following two different
routes: (1) Direct transformation of cellulose to butyl-, hexyl-,
octyl-, decyl- and dodecyl-a,b-glycosides in an ionic liquid
media and Amberlyst-15Dry as catalysts, with mass yield of up
to 82%; and (2) two steps reaction with transformation of cel-
lulose into methyl glucosides, with a procedure described by
Zhang et al., followed by transacetalation with 1-octanol and
1-decanol in the presence of Amberlyst-15Dry. A kinetic study
for the direct transformation of cellulose using 1-octanol has
shown that depolymerisation of cellulose continues during the
Fischer glycosidation. Increasing the chain length of the alco-
hol decreases the global reaction rate owing to an increase in
the lipophilicity of the alcohol that decreases its contact with
the carbohydrates. Finally, several acid catalysts were tested
and the best results were obtained with Amberlyst-15Dry.
Introduction
Long-chain alkyl glycosides are non-ionic compounds with ex-
cellent surfactant properties, low toxicity, and good biodegrad-
ability.[1] These carbohydrate derivates have several applica-
tions in cosmetics, detergents, food emulsifiers and pharma-
ceutical dispersing agents.[1,2]
to make the biodegradable surfactants. Almost at the same
time, we reported that it was possible to transform cellulose
into hexyl- and octyl-a,b-glycosides with yields of up to 82%,
using 1-butyl-3-methylimidazolium chloride as the solvent and
Amberlyst-15Dry (A15) or heteropolyacid (H3PW12O40) as the
catalyst.[13]
Generally, the alkyl glycosides are prepared by using two
main procedures: (1) Fischer glycosidation and (2) the Koen-
ings–Knorr method. The Fischer glycosidation is simpler and
less costly than the Koenings–Knorr method, and involves the
direct acid-catalysed acetalisation of a carbohydrate, usually
glucose, in the presence of an alcohol. Several homogeneous
or heterogeneous acid catalysts, such as ion-exchange resins,
amorphous silica–alumina, zeolites, Al-MCM-41 mesoporous
materials and mineral or organic acids, can be used
to catalyse this reaction.[3–7] The Fischer glycosidation
was also performed in 1-butyl-3-methylimidazolium
trifluoromethanesulfonate in the presence of a metal
triflate as a catalyst.[8]
Herein, we have expanded the scope of the method devel-
oped in our laboratory by studying the kinetics of the direct
glycosidation with longer-chain alcohols and have also devel-
oped a process for the synthesis of alkyl glucosides by transa-
cetalation of methyl glucosides, derived from the cellulose,
without further separation and purification, with different fatty
alcohols (Scheme 1).
Alkyl glucosides with alkyl chains containing 8 to
20 carbon atoms can be prepared by the Fischer re-
action, but owing to the low solubility of glucose in
a long-chain fatty alcohol the common approach in-
volves a two-step process.[9–11] In the first step, gluco-
sides containing a shorter alkyl chain are prepared
and then they are transformed into long-chain alkyl
Scheme 1. Procedure for the transformation of cellulose into alkyl glycosides by follow-
ing two routes.
glucosides by means of a transacetalation reaction.
In a recent communication, it has been reported
that it is possible to perform the direct transforma-
tion of cellulose into methyl glucoside in reasonable yields.
Thus, cellulose was converted into methyl-a,b-glucoside in
methanol with 50–60% yield in the presence of several acid
catalysts at 468 K and 30 bar.[12] However, this procedure,
which requires high pressure and temperature, gives very low
yields of alkyl glucosides when reacting longer-chain alcohols
[a] Dr. N. Villandier, Prof. A. Corma
Instituto de Tecnologꢀa Quꢀmica (UPV-CSIC)
Universidad Politꢁcnica de Valencia
Consejo Superior de Investigaciones Cientꢀficas
Avenida de los Naranjos s/n.46022 Valencia (Spain)
Fax: (+34)9638-77809
E-mail: acorma@itq.upv.es
508
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Transformation of Cellulose into Alkyl Glycosides
Results and Discussion
Synthesis of alkyl-a,b-glycoside from cellulose
In the first stage of the work, 1-octanol was selected as the
model alcohol. The Fischer glycosidation was studied between
this alcohol and the monosaccharides derived from cellulose
hydrolysis. After 24 h reaction time, the results obtained show
(Figure 1) that the conversion of cellulose was 98% and that
~
*
Figure 2. Time versus evolution plot of mono- (*), di- ( ), tri- ( ), tetra- (+)
&
and polysaccharides ꢀ5(ꢁ); the total amount of carbohydrates ( ) and the
~
time formation plot of HMF ( ) during the direct transformation of cellulose
into octyl-a,b-glycosides.
from degradation of glucose, was very low (1.8%). After the
addition of 1-octanol and 1 h of Fischer glycosidation, the con-
version of cellulose, the total amount of carbohydrate and the
monosaccharide yield increased to 81, 59, and 21.6% respec-
tively. At the same time, the octyl-a,b-glycoside molar yield
was already 10.6%. Then, between 1 and 7 h of Fischer glycosi-
dation, the conversion of cellulose reached 90% and the rate
of octyl-a,b-glycoside formation was faster than the rate of
monosaccharide transformation. Finally, after reaction for
25.5 h, the carbohydrate yield remaining was 5.4%, the yield of
HMF was 6.1% and the molar yield in octyl-a,b-glycoside was
46.1% (mass yield of 81.7%). These results show that, after the
addition of alcohol, the hydrolysis of cellulose continues
during Fischer glycosidation and the process strongly limits
the degradation of monosaccharide, converting most of it into
octyl glycosides.
~
Figure 1. Time versus conversion plot of a-cellulose ( ) to octyl-a,b-gluco-
&
*
side ( ) and octyl-a,b-xyloside ( ) at 373 K during 1.5 h. Then, after addition
of n-octanol (NO), the reaction was carried out at 363 K under a vacuum of
40 mbar in the presence of A15 and a molar ratio NO/cellulose of 23. The
&
*
molar ( ) and mass ( ) yields of octyl-a,b-glycosides that would be obtained
during the process.
anomeric mixtures of two octyl glycosides, octyl-a,b-glucoside
and -xyloside, were formed with a total mass yield of 81.7%.
Both glycosides appear as primary products, and consequently,
the global reaction can be written as shown in Scheme 2.
By taking into account the evolution of cellulose conversion
and the formation of octyl-a,b-glycosides, different carbohy-
drates derived from cellulose hydrolysis and 5-hydroxymethyl
furfural (HMF) (Figures 1 and 2), we can observe that during
cellulose hydrolysis the total amount of carbohydrate increases
to 55% and at the end of the first step the conversion of cellu-
lose is already 71%. After reaction for 1.5 h, the monosacchar-
ide molar yield was 19.6% and the formation of HMF, derived
Influence of the chain length of the alcohol
The alkyl chain linked to the carbohydrate in the alkyl gluco-
side is compatible with non-polar environments, whereas the
hydroxyl groups are responsible for the high solubility in
water. The length of the alkyl chain has a direct influence on
the alkyl glycoside solubilising ability and has the most pro-
nounced effect on the critical
micelle concentration (CMC).[14]
Even if it is known that short-
chain alkyl glucosides do not
provide any detergency bene-
fits, they can be used to synthe-
sise long-chain alkyl glucosides
that have better detergency
properties.[3b] It is then of inter-
est to have a process flexible
enough to produce alkyl glyco-
sides with different alkyl chains.
By following the process de-
scribed above, the reaction was
Scheme 2. Synthesis of octyl-a,b-glucoside and -xyloside from a-cellulose. [BMIM][Cl]=1-butyl-3-methylimidazoli-
um chloride.
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509

A. Corma and N. Villandier
a,b-glucopyranoside. Then, by
changing the operation condi-
tions and in the presence of
longer-chain alcohols, alkyl-a,b-
glucoside surfactants could be
produced (Scheme 3).
Table 1. Conversion and yields for the one-pot hydrolysis and Fischer glycosidation of cellulose in the presence
of A15, 1-butyl-3-methylimidazolium chloride, and a series of 1-alcohols.[a]
1-Alcohol
Conversion
[%][b]
Yield[c] [mol%] ([wt%])
Alkyl-a,b-glucoside
Alkyl-a,b-xyloside
Surfactant
1-butanol[d]
1-hexanol
1-octanol
1-decanol
1-dodecanol
97
95
98
95
96
46.1 (67.2)
36.9 (60.1)
38.8 (70.0)
28.3 (55.9)
11.6 (25.0)
7.1 (9.0)
8.5 (12.3)
7.3 (11.7)
4.0 (7.2)
1.1 (2.1)
53.2 (76.2)
45.4 (72.4)
46.1 (81.7)
32.3 (63.1)
12.7 (27.1)
Direct transformation of cellu-
lose into methyl-a,b-glucopyra-
nosides
[a] Reaction conditions: a-cellulose (0.3 g, 1.85 mmol unity of glucose), [BMIM][Cl] (6 g), H2O (315 mL) at 373 K
then, after 1.5 h and addition of alcohol (43 mmol), at 363 K under a vacuum of 40 mbar for 24 h. [b] Calculated
by the weight difference of cellulose before and after reaction. [c] Determined by HPLC. [d] Fischer glycosida-
tion was carried out under a vacuum of 400 mbar.
The reaction between cellulose
and methanol was carried out in
the presence of H3PW12O40 at
468 K. The results obtained
(Figure 3) show that after 30 min
carried out by using 1-butanol, 1-hexanol, 1-decanol or 1-do-
decanol in a molar ratio of alcohol to cellulose of 23. The re-
sults obtained after reaction for 25.5 h are presented in Table 1
and show that when the alkyl chain increases, the molar yields
in alkyl-a,b-glycosides decreases. In fact, the order of activity is
1-butanol>1-hexanolꢁ1-octanol>1-decanol>1-dodecanol.
This order of activity can be explained by the hydrophilic–lipo-
philic interactions that exist between the carbohydrates and
the 1-alcohol. Indeed, by increasing the chain length of the al-
cohol, the lipophilic properties of the alcohol increase, and
consequently, the contact between the carbohydrates and the
alcohol is increasingly difficult. Nevertheless, one can always
prepare the corresponding alkyl glucoside with 1-butanol and
then perform the transacetalation with a longer-chain alcohol
within the same reactor. Therefore, the transacetalation pro-
cess could be another solution to transform, in a one-pot oper-
ation, glucose+methanol+long chain alcohol into an alkyl glu-
coside surfactant (see Scheme 1).
the conversion of the cellulose was 87% and two methyl glu-
coside isomers were formed in a total yield of 64.6%. Then,
the methyl glucoside decreased progressively. The presence of
HMF from the possible dehydration reaction of glucose was
not detected in the products. After the reaction, the heteropo-
lyacid solid was eliminated by precipitation and the methyl
glucoside produced could be used to carry out the transaceta-
lation reaction.
Transacetalation of methyl-a,b-glucopyranoside into alkyl-
a,b-glucoside
To develop the transacetalation process, we began by follow-
ing the procedure reported by Zhang et al.[12] to carry out in a
first step: the direct transformation of cellulose into methyl-
~
Figure 3. Time versus conversion plot of cellulose ( ) into methyl-a-gluco-
*
*
side ( ) and -glucoside ( ) at 468 K in the presence of H3PW12O40. The total
amount of a and b isomers of methyl glucoside ( ) is also shown.
&
The transacetalation process
When the reaction between an isomeric a,b mixture of methyl
glucosides (MG) and 1-octanol (NO) was carried out at 378 K,
on A15, with an MG/NO ratio of 15 and under a vacuum of
40 mbar, the results obtained (Figure 4) showed that, after re-
action for 240 min, an anomeric mixture of two octyl glucoside
isomers, octyl-a,b-glucofuranoside and -glucopyranoside, was
formed.
Octyl-a, b-glucofuranoside appears as a primary, unstable
product, whereas the behaviour of octyl-a-,b-glucopyranoside
corresponds to a secondary, stable product. These results sup-
port a reaction mechanism involving the fast formation of the
five-membered ring compound, followed by isomerisation to
Scheme 3. Transacetalation of methyl-a,b-glucopyranoside, derived from cel-
lulose, into alkyl-a,b-glucoside.
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Transformation of Cellulose into Alkyl Glycosides
during the acetalisation of different monosaccharides in the
presence of methanol by using an acid resin or liquid acids as
catalysts.[15–18] Therefore, a new reaction scheme can be estab-
lished (Scheme 4) in which during the conversion of cellulose,
the glucose derived from cellulose hydrolysis reacts with meth-
anol to give two methyl glucoside isomers. Then, transacetala-
tion in the presence of 1-octanol and A15 leads to the forma-
tion of octyl-a,b-glucofuranoside and -glucopyranoside.
When the reaction was performed at 393 K in the presence
of H-Beta zeolite with a Si/Al ratio of 13, octyl-a,b-glucofurano-
side and -glucopyranoside were also formed, but the yields ob-
tained, after 4 h, were only of 15.8 and 9.0% respectively
(Figure 5). If the reaction was prolonged to 22 h, the total yield
of octyl glucosides increased to 38.9%.
~
Figure 4. Time versus conversion plot of methyl-a,b-glucoside ( ) into octyl-
*
*
a,b-glucofuranoside ( ) and -glupyranoside ( ) at 378 K in the presence of
A15. The total amount of octyl-a,b-glucoside isomers of furanose and pyra-
&
nose ( ) are also shown.
the pyranoside product, which is thermodynamically more
stable.
The above reaction scheme has been observed during the
acetalisation of monosaccharide with an alcohol in the pres-
ence of a resin acid catalyst and during the transacetalation of
butyl glucosides.[11,15–17] This last study has also shown that, to
obtain the furanose isomer in high amounts, the reactant for
the transacetalation has to contain a high ratio of furanose to
pyranoside isomers. In fact, when the transacetalation reaction
was performed from a solution with an initial butyl glucofura-
noside/butyl glucopyranoside ratio of 10/90 the formation of
octyl gluofuranoside was minor. To confirm this result, the
transacetalation of methyl glucopyranosides was carried out
from a commercial product. In this case, only octyl-a,b-gluco-
pyranoside was formed with a yield of 70% after 4 h.
~
Figure 5. Time versus conversion plot of methyl-a,b-glucoside ( ) into octyl-
*
*
a,b-glucofuranoside ( ) and -glupyranoside ( ) at 378 K in the presence of
H-beta zeolite. The total amount of octyl-a,b-glucoside isomers of furanose
&
and pyranose ( ) are also shown.
Taking into account all of the above results, we can say that
during the transformation of cellulose into methyl glucoside,
methyl glucofuranoside and methyl glucopyranoside isomers
were formed. This reactivity has also been found to exist
Starting from methyl glucosides derived from cellulose, the
reaction was carried out by using 1-decanol (ND) as the transa-
cetalating alcohol at 378 K with a molar ratio of MG/ND=15.
The results obtained (Figure 6)
show the formation of the two
expected isomers, decyl-a,b-glu-
cofuranoside and -glucopyrano-
side, with an initial rate and a
total yield of decyl-a,b-glucoside
lower than that obtained in the
presence of 1-octanol. This
lower reactivity is due, as ex-
plained above, because of the
increase in lipophilicity of the
fatty alcohol.
Conclusion
We have shown that it possible
to obtain short- and long-chain
alkyl glycoside surfactants from
cellulose with good conversions
Scheme 4. Synthesis of octyl-a,b-glucofuranoside and octyl-a,b-glucopyranoside from methyl-a,b-glucofuranoside
and methyl-a,b-glucopyranoside derived from cellulose.
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511

A. Corma and N. Villandier
(0/100 and then 5/95) to afford the desired alkyl-a,b-glycoside as
an anomeric mixture. The purity of the alkyl glycosides was con-
1
firmed by H and 13C NMR spectroscopy.
Synthesis of methyl-a,b-glucopyranoside from cellulose: The reac-
tion was performed in a 25 mL autoclave (Autoclave Engineers).
After cellulose (0.5 g, 3.09 mmol calculated as anhydroglucose
C6H10O5) and H3PW12O40 (50 mg, 0.017 mmol) were added to the
autoclave pre-charged with methanol (20 mL), N2 (30 bar) was in-
troduced. Then, the reaction mixture was heated at 468 K (ramp:
8 Kminꢂ1) and left at this temperature for the desired reaction
time. To follow the evolution of the reaction, samples were taken
at regular time intervals and diluted with water (2 mL). After filtra-
tion, the different samples were analysed by HPLC. At the end of
the reaction, the unreacted cellulose was filtered and the reaction
solution was neutralised with a solution of Cs2CO3 in methanol
(6 mg in 5 mL). The H3ꢂxCsxPW12O40 precipitate was removed by fil-
tration and the solution was concentrated under vacuum to form a
solid. The solid obtained was weighed, analysed by HPLC and used
as starting material for carrying out the second step, that is, the
transacetalation reaction.
~
Figure 6. Time versus conversion plot of methyl-a,b-glucoside ( ) into
*
*
decyl-a,b-glucofuranoside ( ) and to -glupyranoside ( ) at 378 K in the pres-
ence of A15. The total amount of decyl-a,b-glucoside isomers of furanose
&
and pyranose ( ) are also shown.
Transacetalation of methyl-a,b-glucoside in the presence of fatty
alcohol: The methyl-a,b-glucoside derived from cellulose (0.3 g,
1.54 mmol, 1 equiv), 1-alcohol (23 mmol, 15 equiv) and the catalyst
(50 mg) were heated with stirring at the temperature desired
under a vacuum of 40 mbar so that methanol formed during trans-
acetalation was continuously removed. With the aim of following
the evolution of the reaction, samples were taken at regular time
intervals, diluted in DMSO (5 mL), filtered and analysed by HPLC.
At the end of the reaction, the reaction mixture was treated as de-
scribed above for the preparation of alkyl-a,b-glycoside.
and selectivities by following two different procedures, namely,
direct glycosidation and transacetalation. Furthermore, we
have found that during the direct transformation of cellulose
into alkyl-a,b-glycosides, the hydrolysis of cellulose continues
during Fischer glycosidation and the selectivity decreases with
alcohol chain length. Moreover, we have established that the
furanose and pyranose isomers were formed when cellulose
was converted into methyl glucoside. Methyl glucoside is then
transformed into alkyl glucosides with C8 and C10 alkyl chains;
these are excellent biodegradable surfactants.
HPLC analysis procedure
Experimental Section
Analysis of the samples was performed at 333 K with an HPLC
system composed of a Waters pump (model 1525) and a Waters
2410 differential refractometer. The sugars (glucose, xylose and cel-
lobiose), the dehydration products (HMF and furfural) and alkyl gly-
cosides were analysed by using an ion-exclusion column (Aminex
HPX-87H, Bio-Rad) eluting with an aqueous solution of sulfuric
acid (0.004 mol.lꢂ1) as the mobile phase. This analysis was operat-
ed at a flow rate of 0.6 mLminꢂ1. The analysis of oligosaccharides
was carried out by using a gel permeation chromatography
column (SB-802.5 HQ, Shodex) and DMSO as the eluent
(0.3 mL.minꢂ1). Peak identification was established by comparison
of the sample peak retention times with the standard solution of
the pure compound. The calibration of the peaks was performed
by using standard solutions of varying concentrations to develop a
linear relationship between the peak area and the corresponding
concentration.
Materials
a-Cellulose (Sigma, relative crystallinity of about 75% as estimated
by XRD analysis according to the method reported by Hilmioglu
and Dogan)[19] dried under vacuum at 1008C for 24 h before use.
Microcrystalline cellulose (Alfa-Aesar, relative crystallinity of about
85%), 1-butyl-3-methylimidazolium chloride (Fluka, Basionic ST 70,
ꢀ95% BASF), A15 (Aldrich), H3PW12O40·xH2O (HPW, Fluka, reagent
for microscopy), Cs2CO3 (Aldrich, 99%) and the different 1-alcohols
(Aldrich) were used as received. Zeolite beta CP811 (Si/Al=13, Zeo-
lyst International) was activated at 353 K for 3 h under vacuum
before use.
Reaction procedure
The molecular product yield (Y in mol%) was defined by Equa-
tion (1), in which n0 and ni were the number of moles of C6H10O5
units in the charged cellulose introduced and the number of moles
of product analysed, respectively:
Synthesis of alkyl-a,b-glycoside from cellulose: a-Cellulose (0.300 g,
1.85 mmol calculated as anhydroglucose C6H10O5, 1 equiv) and the
ionic liquid (6 g) were heated with stirring at 373 K under ambient
pressure until a clear solution was formed (about 30 min). Water
(315 mL) and A15 (160 mg, 0.74 mmolH+) were added to this solu-
tion. After reaction for 1.5 h, n-alcohol (43 mmol, 23 equiv) was
added and the reaction media was stirred at 363 K for 24 h under
vacuum (40 mbar except for n-butanol, when the pressure was
400 mbar). Then, the catalyst was filtered and the unreacted alco-
hol was removed by distillation or extracted with heptane. A
sample of the solution obtained was diluted water or DMSO (5 mL)
and was analysed by HPLC. Finally, the crude reaction mixture was
filtered through silica gel eluted with a mixture of MeOH/AcOEt
ni
n0
Yi ðmol %Þ ¼ ꢃ 100
ð1Þ
In the case of kinetic studies carried out on the evolution of differ-
ent carbohydrates, n0 was the number of moles of (C6H10O5)m units
in cellulose introduced, in which m was the number of C6H10O5
units present in the product i. For example, for a disaccharide
m=2. In the case of transacetalation, n0 represented the initial
number of moles of methyl glucoside used in the reaction.
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Transformation of Cellulose into Alkyl Glycosides
[4] a) A. Corma, S. Iborra, S. Miquel, J. Primo, J. Catal. 1996, 161, 713–719;
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[5] M. J. Climent A. Corma, S. Iborra, S. Miquel, J. Primo, F. Rey, J. Catal.
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The mass product yield (Y in wt%) was defined by Equation (2), in
which m0 and mi are the weights of cellulose added to the reaction
and of component i respectively.:
mi
Yi ðwt %Þ ¼
ꢃ 100
ð2Þ
[6] D. D. Harris, European Patent 1983/0096917.
m0
[7] M. H. K. Mao, L. E. Miller, J. M. Weeman, US Patent 1983/4393203.
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[10] F. E. Boettner, U.S. Patent 1965/3219656.
Acknowledgement
[11] A. Corma, S. Iborra, S. Miquel, J. Primo, J. Catal. 1998, 180, 218–224.
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[14] W. J. De Grip, P. H. W. Bovee-Geurts, Chem. Phys. Lipids 1979, 23, 321–
335.
We thank project Consolider Ingenio 2009CDS00050 for financial
support. N.V. thanks the ITQ for a fellowship.
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Keywords: cellulose · glycosidation · reaction mechanisms ·
surfactants · transacetalation
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Received: October 29, 2010
Revised: December 22, 2010
Published online on March 9, 2011
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
513