One pot catalytic conversion of cellulose into biodegradable surfactants

Article abstract of DOI:10.1039/c0cc00031k

Cellulose has been directly converted into environmentally friendly alkyl glycoside surfactants in a one pot transformation. By working in ionic liquid media with Amberlyst 15Dry (A15) as catalyst and coupling the rate of cellulose hydrolysis and the rate of glycosidation of the monosaccharides formed with C₄ to C₈ alcohols, it was possible to obtain 82% mass yield of octyl-α,β-glucoside plus octyl-α,β-xyloside.

Full text of DOI:10.1039/c0cc00031k

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One pot catalytic conversion of cellulose into biodegradable surfactantsw
Nicolas Villandier and Avelino Corma*
Received 19th February 2010, Accepted 15th April 2010
First published as an Advance Article on the web 18th May 2010
DOI: 10.1039/c0cc00031k
Cellulose has been directly converted into environmentally
friendly alkyl glycoside surfactants in a one pot transformation.
By working in ionic liquid media with Amberlyst 15Dry (A15) as
catalyst and coupling the rate of cellulose hydrolysis and the rate
of glycosidation of the monosaccharides formed with C4 to C8
alcohols, it was possible to obtain 82% mass yield of octyl-a,b-
glucoside plus octyl-a,b-xyloside.
Very recently the transformation of cellulose into methyl-
a,b-glucoside in methanol with 50–60% yield in the presence
of several acid catalysts at 468 K and 30 bar has been
reported.20 However, this procedure, which requires high
pressure and temperature, gives low yields of alkyl glycosides
when reacting longer chain alcohols.20
In this work, we present that it is possible to transform
cellulose into alkyl-a,b-glycoside surfactants under very mild
conditions in a one-pot reaction by finding the appropriate
catalyst and reaction conditions that allow coupling of the
hydrolysis of the cellulose with the Fischer glycosidation with
C4 to C8 alcohols. A general procedure to perform the reaction
is as follows (see experimental in ESI for a detailed procedurew).
a-Cellulose (Sigma, 20–100 mm, 75% crystallinity) was stirred
in the presence of an ionic liquid (BMIMCl) at 373 K. A small
amount of water was introduced, and adjusted to fulfil the
requirements of cellulose hydrolysis and to limit the formation
of HMF. Then the catalyst was added and the reaction
proceeded at atmospheric pressure during an optimized time
during which the hydrolysis started to occur. After this initial
period, the alcohol (n-butanol, n-hexanol or n-octanol) was
added and the reaction temperature set to 363 K, under
stirring at 40 mbar pressure, and the process followed with
time. At the end of the reaction the catalyst was filtered out
and the products analysed as indicated in the ESI.w
Both reactions, i.e. cellulose hydrolysis and monosaccharide
glycosidation, are catalysed by acid catalysts. The results given
in Table 1 indicate that H3PW12O40 is active for performing
the hydrolysis of cellulose (see Table 1, entry 2). However, for
practical reasons, it would be desirable to use a solid catalyst
and the heteropolyacid was supported (33 wt%) on silica
(209 m2 gÀ1) following ref. 21 and calcined at 423 K for 2 h
in a vacuum (SiO2-HPW). An insoluble heteropolyacid
Long-chain alkyl glycosides are non-ionic compounds with
excellent surfactant properties, low toxicity and good
biodegradability.1 These carbohydrate derivatives have several
applications in cosmetics and detergents,1 food emulsifiers,
and pharmaceutical dispersing agents.2
Alkyl glycosides can be prepared by two main procedures:
(i) the Fischer glycosidation and (ii) the Koenigs–Knorr method.
The Fischer glycosidation is simpler and less costly than the
Koenigs–Knorr method, and involves the direct acid catalyzed
acetalization of a carbohydrate, usually glucose, in the presence
of an alcohol. Several homogenous or heterogeneous acids such
as ion exchange resins,3 amorphous silica-alumina,3a zeolites4
and Al-MCM-41 mesoporous materials,5 mineral6 and organic
acids7 have been used as catalysts.
One important source of glucose is the acid hydrolysis of
cellulose. The cellulose, which can be an important source
of biofuels8 and chemicals,9 is a crystalline polymer of
D-glucopyranoside units linked together by b-1,4 glycosidic
bonds. The cohesion between the different chains is ensured by
hydrogen bonds and van der Waals interactions10 which
confer to cellulose a high stability, making the hydrolysis
process difficult.
Most hydrolysis processes to convert cellulose into glucose
have been developed in water. The reaction can be carried
out in the presence of mineral acids,11 enzymes12 or under
hydrothermal conditions.13 Recently, heterogeneous catalytic
processes using carbon materials bearing SO3H groups14
H
0.5Cs2.5W12PO40 was also prepared following ref. 22
(see ESIw). None of the two solid heteropolyacid catalysts
was active for the hydrolysis (see Table 1, entries 3 and 4).
para-Toluenesulfonic acid (PTSA), gave reasonable results
(Table 1, entry 6), indicating that sulfonic groups are active
for performing the hydrolysis reaction. Therefore, a solid
catalyst was used in which the sulfonic groups are accessible
through the external surface (Amberlyst 15Dry, A15). Results
from Table 1 entries 7 and 8, indicate that this catalyst is active
and reasonably selective for performing the first step of the
reaction, i.e. the hydrolysis of cellulose. As could be expected,
the amount of water in the reaction medium is an important
variable to control the rate and extension of hydrolysis.23 In
our case it has been observed that an increase in water content
decreases the initial rate of monosaccharide formation from
15
or layered metal oxides such as HNbMoO6 have been
developed, but the yield of glucose is very low. To favour
the cellulose transformation into glucose, Onda et al. have
used a cellulose which was previously pretreated to decrease its
crystallinity.16 Several authors have shown that it is possible to
dissolve cellulose in ionic liquids17 and when in the presence of
mineral18 or solid acid catalysts,19 the cellulose can even be
depolymerized.
Instituto de Tecnologı´a Quı´mica (UPV-CSIC), Universidad
´
Politecnica de Valencia, Consejo Superior de Investigaciones
´
Cientıficas, Avenida de los Naranjos s/n.46022, Valencia, Spain.
E-mail: acorma@itq.upv.es; Fax: +34 9638 77809;
Tel: +34 9638 77800
0.57 to 0.25 mmol gÀ1
h
À1, though the maximum yields
w Electronic supplementary information (ESI) available: Experimental
details and product characterization. See DOI: 10.1039/c0cc00031k
of total reduced saccharides (TRS) and monosaccharides
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Table 1 Hydrolysis of cellulose in the presence of different acid catalystsa
Yield (mol%)c
d
Cellobiose
Glucose
Xylose
4.4
TRS yieldmax
HMF
2.5
Furfural
0.7
Entry
Catalyst
Conversion (%)b
1
2
3
4
5
6
7
8
Blank
H3PW12O40
H0.5Cs2.5PW
SiO2-HPW
C-SO3H
PTSA
No reaction
98
No reaction
No reaction
No reaction
99
98
98
e
3.3
9.2
39.2 (120)
4.2
2.2
3.5
15.3
7.9
10.2
4.9
4.2
6.4
45.3 (120)
30.0 (180)
39.8 (300)
4.3
2.3
2.3
1.0
0.6
0.7
A15
A15f
a
b
Reaction conditions: cellulose (300 mg, 1.85 mmol by glycosidic unit), BMIMCl (6 g), water (80 ml), catalyst (80 mg), 373 K. After 6 h of
reaction. Calculated by the weight difference of cellulose before and after reaction. Determined by HPLC. Total reducing sugars maximum
c
d
obtained (time in min). Determined by DNS dosage. H3PW12O40 (355 mg, 0.37 mmol H+), time (240 min). Water (315 ml).
e
f
(glucose + xylose) were higher when increasing the water
content (Table 1, entries 7 and 8).
when increasing the amount of catalyst (Table 2, entry 5) total
conversion was 98% and the mass yield of octyl-a,b-glycoside
was already 43.8 wt%. Unfortunately the yield of HMF was
15%. Since HMF is formed by degradation of the glucose
formed during the hydrolysis process before it reacts with
the alcohol, the alcohol was added after a shorter time of
hydrolysis to avoid the accumulation and degradation of the
glucose formed, by reacting this with the alcohol. In that way,
the initial reaction times were set to 5, 2.5, 1.5 and 1 h and the
results in Table 2 (entries 5–9) show an optimum at 1.5 h with
98% total conversion, 82 wt% yield of alkyl-a,b-glycosides
and 6% of HMF. These are excellent results that show the
possibility of converting cellulose into surfactants in one pot
under very mild reaction conditions. Under the optimised
conditions the H3PW12O40 also gives good results with 95%
conversion and 74.9% mass yield of octyl-a,b-glycosides
(Table 2, entry 13). Product separation can be made by using
a fixed bed column with silica gel with a mixture of methanol
and ethyl acetate to recover the alkyl-a,b-glycosides and to
recycle the ionic liquid. The Amberlyst 15Dry should be
reused after regeneration of the acidic sites with a H2SO4
solution. In fact, as has been shown by Rinaldi et al.24
studying the hydrolysis of cellulose in the presence of A15,
Nevertheless, it has to be considered that while the water
present in the reaction medium will favour the extent of
hydrolysis and reduction of the HMF formed,23 it will have
a negative effect on the first step of the Fischer glycosidation,
i.e., the formation of the hemiacetals between the aldehyde
group of the monosaccharide and the n-alcohol (see Scheme 1).
At this point the coupling of both reactions, i.e. cellulose
hydrolysis and Fischer glycosidation was attempted using
A15 as catalyst allowing the hydrolysis reaction to proceed
at 373 K for 5 h. After 5 h, which corresponds to the time
required to obtain a maximum yield of TRS, the alcohol was
added and the temperature was set to 363 K. Under this
condition conversion of cellulose and the yields of mono-
saccharides and cellobiose were high, but the yields of alkyl-
a,b-glucoside and alkyl-a,b-xyloside were low regardless of the
alcohol used (see Table 2, entries 1 and 2). This result suggests
that there is still too much water present to perform the
glycosidation reaction efficiently. Therefore the experimental
set-up was modified in such a way that when the alcohol
was added, the pressure of the system was reduced to 40 mbar
(see Table 2, entries 3 and 4). In the case of n-octanol, and
Scheme 1 One step conversion of cellulose into alkyl-a,b-glycoside surfactants.
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Table 2 One pot transformation of cellulose into alkyl glycoside surfactantsa
Yield (mol%)c
Alkyl-a,b- glucoside Alkyl-a,b-xyloside Total yield of
Entry Alcohol
Conversion (%)b
Butanold 96
Cellobiose Glucose Xylose HMF (Yield wt%)
(Yield wt%)
surfactant (wt%)
1
2
3
4
5
6
7
8
5.8
7.1
4.8
4.4
Traces
0.7
0.6
0.5
1.5
1.0
0.8
0.2
0.8
16.4
18.7
9.7
8.1
3.4
3.4
3.1
3.0
4.4
17.4
3.2
1.8
1.1
6.9
6.9
2.7
2.7
3.2
3.2
2.3
2.1
2.8
4.3
2.8
0
3.8
5.3
5.2
3.8
15.1
8.0
7.4
6.1
4.8
10.1
5.8
1.6
4.1
5.0 (7.2)
5.8 (9.4)
Traces
7.2
Hexanold 96
1.2 (1.7)
4.8 (6.9)
5.4 (8.7)
2.8 (4.5)
4.1 (6.7)
5.4 (8.8)
7.3 (11.7)
6.6 (10.7)
4.7 (7.6)
8.5 (12.3)
0
11.1
34.7
40.0
48.3
63.8
70.0
81.7
60.7
52.8
72.4
71.5
74.9
Hexanole 95
Octanole 95
17.1 (27.8)
17.3 (31.3)
24.3 (43.8)
31.7 (57.1)
33.9 (61.2)
38.8 (70.0)
27.7 (50.0)
25.1 (45.2)
36.9 (60.1)
39.7 (71.5)
35.5 (64.0)
Octanolf
98
Octanolg 96
Octanolh 94
Octanoli
Octanolj
98
96
9
10
11
12
13
Octanolk 98
Hexanoli 95
Octanoll
99
Octanolm 95
1.1
6.7 (10.9)
a
a-Cellulose (300 mg, 1.85 mmol unity of glucose), A15 (160 mg, 0.74 mmol H+), ionic liquid (6 g), water (315 ml), at 373 K. Then for the
hydrolysis, the alcohol (43 mmol) was added to the solution and the temperature was decreased to 363 K. The reaction was carried out at 40 mbar
b
c
d
for 24 h. Calculated by the weight difference of cellulose before and after reaction. Determined by HPLC. A15 (80 mg, 0.37 mmol H+),
hydrolysis time: 5 h and Fischer glycosidation carried out at atmospheric pressure. A15 (80 mg, 0.37 mmol H+). Hydrolysis time: 5 h.
e
f
g
h
Hydrolysis time: 2.5 h. Hydrolysis time: 2 h. Hydrolysis time: 1.5 h. Hydrolysis time: 1 h. Fischer glycosidation carried out at atmospheric
i
j
k
l
pressure. Cellulose fibres (600 mg, 3.70 mmol unity of glucose, 67% crystallinity), water (760 ml), A15 (350 mg, 1.64 mmol H+), hydrolysis time:
40 min. H3PW12O40 (710 mg, 0.74 mmol H+), hydrolysis time: 1 h.
m
the H3O+ species was progressively released in the ionic liquid
phase. The regenerated resin allows the production of octyl-
a,b-glycoside with a mass yield of 77.8%.
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In conclusion, we have shown that by working in ionic
liquid media, with a sulfonic resin as catalyst it is possible to
transform cellulose into alkyl glucoside surfactants in a one
pot reaction with a mass yield of 82%. This could be achieved
by properly coupling the hydrolysis of cellulose with the
Fischer glycosidation reaction of the monosaccharide formed
during the first step. The amount of water present in the
reaction medium and its evolution during the reaction time
is a key variable for the success of the global process.
The authors thank project MAT 2006-14274-C02-01,
Consilider Ingenio 2009 CDS 00050 Multicat and Prometeo
2008 GV for financial support. NV thanks ITQ for a fellowship.
15 A. Takagaki, C. Tagusagawa and K. Domen, Chem. Commun.,
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This journal is The Royal Society of Chemistry 2010
4410 | Chem. Commun., 2010, 46, 4408–4410