Selective synthesis of alky poly-β-d-glucopyranoside over mixed metal oxide

Article abstract of DOI:10.1016/j.molcata.2006.11.024

Glycosylation reactions are most commonly encountered in nature. Synthetically, glycosylation is carried out with Lewis acid catalyst, HF, AlCl₃ or mineral acids. However environmental threat associated with such catalysts has encouraged process modification and the development of solid catalyzed glycosylation reactions, which are commercially viable as well. In this contribution comparative study of glycosidic bond formation of simple d-glucose with several fatty alcohols (C₈-C₁₄) over variety of mixed metal oxidic spinels (CuFe₂O₄, ZnFe₂O₄, CoFe₂O₄ and NiFe₂O₄, 10% (w/w) ZnFe₂O₄ supported on SiO₂ and ZrO₂) is taken up to evaluate the performance of this potential catalysts system. Effect of catalyst preparation was evaluated. This replacement of homogeneous acid catalyst by oxidic spinels shows alkyl poly β-d-glucopyranoside as major product at comparatively low temperature range. The effects of variety of parameters were studied in a batch reactor. The mechanism of the reaction over mixed metal oxidic spinels at 363 K is put forth.

Full text of DOI:10.1016/j.molcata.2006.11.024

Journal of Molecular Catalysis A: Chemical 267 (2007) 157–164
Selective synthesis of alky poly-␤-d-glucopyranoside
over mixed metal oxide
Nivedita S. Chaubal, Vishal Y. Joshi, Manohar R. Sawant∗
Department of Chemistry, Institute of Chemical Technology (Autonomous), University of Mumbai,
Matunga, Mumbai 400 019, India
Received 20 September 2006; accepted 14 November 2006
Available online 19 November 2006
Abstract
Glycosylation reactions are most commonly encountered in nature. Synthetically, glycosylation is carried out with Lewis acid catalyst, HF,
AlCl3 or mineral acids. However environmental threat associated with such catalysts has encouraged process modification and the development
of solid catalyzed glycosylation reactions, which are commercially viable as well. In this contribution comparative study of glycosidic bond
formation of simple d-glucose with several fatty alcohols (C8–C14) over variety of mixed metal oxidic spinels (CuFe2O4, ZnFe2O4, CoFe2O4 and
NiFe2O4, 10% (w/w) ZnFe2O4 supported on SiO2 and ZrO2) is taken up to evaluate the performance of this potential catalysts system. Effect of
catalyst preparation was evaluated. This replacement of homogeneous acid catalyst by oxidic spinels shows alkyl poly β-d-glucopyranoside as
major product at comparatively low temperature range. The effects of variety of parameters were studied in a batch reactor. The mechanism of the
reaction over mixed metal oxidic spinels at 363 K is put forth.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Alkyl poly-␤-d-glucopyranoside; Poly-glucose; Spinel; Glycosidic bond formation
1. Introduction
out, in only moderate yield (40–50%). This problem in syn-
thesis has promoted the development of cost effective and less
toxic promoter based synthetic route. Toshima and coworkers
[7] used montmorillonite K-10 as a heterogeneous solid cata-
lyst for glycosidation of olivoses. Later on, same research group
used montmorillonite K-10 with benzyl-protected glucopyra-
nosyl phosphate and several alcohols to get ␤-O-glycosidic
linkages in more than 80% Yield [8]. In previous studies [9], we
have demonstrated stereoselective ␤-d-glucopyranosylation of
2,3,4,6-tetra-o-acetyl-␣-d-glucosyl bromide and fatty alcohols
over LiCO3 as reaction promoter. Such reaction promoter has
limited activity and catalytic life. Highly effective and recyclable
glycosidation methods without halogenations have attracted our
attention. Hence in this work, the glycosylation of d-glucose
with several fatty alcohols in liquid phase has been investi-
gated on a series of mixed metal oxides catalyst prepared by
co-precipitation method, crystallizing with spinel lattice such
as, CuFe2O4, ZnFe2O4, CoFe2O4, NiFe2O4 and 10% (w/w)
ZnFe2O4 supported on SiO2 and ZrO2. The choice of catalyst as
a spinel system is due to two reasons; first, spinel lattice imparts
extra stability to the catalysts under various reaction conditions.
Secondly, mixed metal oxides do not lose their catalytic activ-
Alkyl poly-␤-d-glucopyranoside act as a novel class of sur-
factants, whichareusefulasfoodbulkingagents, reducedcalorie
sweeteners, fat replacement agents for food products, stabi-
lizing agents for food and beverage products, thickening and
emulsifying agents for food products, adhesives, biodegrad-
able plastic and films, sizing agents for paper and textile,
ethical pharmaceuticals and new fibers. The development of
stereo selective methods for the synthesis of glycosidic link-
ages presents a considerable challenge to synthetic chemists
[1–3]. Although well developed chemical synthesis of glyco-
side involves selective protection, deprotection and coupling
using a metal catalyst. Glycosylation of simple alcohols with
d-glucose can be performed by strong acids like BF3-etherate
[4], HCl [5], para toluene sulphonic acid and H2SO4 [6] to
give both ␣- and ␤-anomer with high degree of polymeriza-
tion of glucose unit. Such glycosylation are normally carried
∗
Corresponding author. Tel.: +91 22 2414 5616; fax: +91 22 2414 5614.
E-mail address: mrsawant2@rediffmail.com (M.R. Sawant).
1381-1169/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2006.11.024

158
N.S. Chaubal et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 157–164
ity due to aging and formation of carbon over the surface so
these systems have sustained activity for longer duration [10].
The best catalyst for the selective preparation of alky poly-
␤-d-glucopyranoside was 10% (w/w) ZnFe2O4 supported on
ZrO2. A10%(w/w)ZnFe2O4/ZrO2 preparedbyco-precipitation
method was compared with 10% (w/w) ZnFe2O4/ZrO2 pre-
pared by template route for the selective formation alkyl
poly-␤-d-glucopyranoside. The major product was alkyl poly-
␤-d-glucopyranoside with some poly glucose formation as a side
product.
2.3. Characterization of 10% (w/w) of ZnFe2O4 on ZrO2
prepared by co-precipitation and templated approach
Catalysts were characterized by X-ray diffraction, BET sur-
face area measurement, FT-IR and SEM.
2.4. Reaction methodology and product analysis
The reactor consisted of a standard flat bottom cylindri-
cal vessel of 5 cm, i.e. of 100 ml capacity equipped with four
equi-spaced baffles, a pitched-bladed turbine impeller and a
condenser. The assembly was kept in an isothermal oil bath
at a known temperature and mechanically agitated with an
electric motor. Melting points were determined using capil-
lary method. Specific rotations were recorded on a manual
polarimeter. Infrared spectroscopy was recorded on Model 500
Spectrophotometer, Buck Scientific Inc. 1H NMR were recorded
on model of Hitachi Inc. and operated at 300 MHz. All the
data are uncorrected. Each catalyst was studied for its catalytic
behavior towards glycosidic bond formation with several fatty
alcohols at the 363 K. In a typical reaction d-glucose (10 mmol)
in toluene (16 ml) was stirred for 15 min at room temperature.
Then catalysts and fatty alcohols (C8–14, 20 mmol) was added,
the reaction carried at 363 K for stipulated time depending upon
the nature of substrate. Reaction mass was cooled and filtered
over celite. Filtrate was evaporated in vacuum and the resulting
material was purified by column chromatography (toluene/ethyl
acetate = 15/5) to afford alkyl poly ␤-d-glucopyranoside.
2. Experimental
2.1. Materials and chemicals
Nitrates of zinc, copper, iron and zirconium oxychloride of
analytical reagent were used for catalyst preparation. A 30%
H2O2, SiO2 of mesh size 200 were used; d-glucose and fatty
alcohols (in range from C8 to C14) of analytical grade were used
with out further purification. The catalyst was prepared using
co-precipitation technique and template route.
2.2. Synthesis of catalysts
2.2.1. Co-precipitation technique [10–12]
To prepare the catalyst an aqueous solution containing the
desired ions in the required molar proportions was prepared
by dissolving the salts in the stoichiometric proportion in
distilled water. It was precipitated by sodium hydroxide and
the pH of the solution was maintained 9–9.5. The precipi-
tate was digested at 353 K in water bath for 3 h and then
oxidized by drop wise addition of required amount of 30%
H2O2 with constant stirring for obtaining single phase spinel.
After completion of reaction the resultant precipitate was dried
at 383 K for 3 h then calcined at 1173 K for 9 h. Similarly
ZrO2 was prepared by co-precipitation procedure from ZrOCl2·
7H2O. SiO2 of mesh size 200 was taken as available in the
market.
3. Results and discussion
3.1. Catalyst characterization
3.1.1. XRD of catalysts samples prepared by
co-precipitation method
As shown in Fig. 1 XRD of ZnFe2O4 (a) showed crystalline
˚
single-phase spinel structure with d (Scherrer equation) = 10 A,
˚
a = 8.398 A which is comparable to the authentic ZnFe2O4 in
A 10% ZnFe2O4 catalyst supported on SiO2 and ZrO2 was
prepared by incipient wetness method by impregnating the aque-
oussolutionofnitratesofrequiredioninastoichiometricamount
on the support; they were dried at 393 K for removal of water
and other volatile material and subsequently calcined at 1173 K
for 9 h.
JCPDS file. XRD of ZrO2 (b) shows intense peaks indicating
crystalline nature of ZrO2. XRD of ZnFe2O4/ZrO2 (c) shows
the formation of ZnFe2O4 on the surface of ZrO2, but the crys-
tallinity of the sample was decreased by 60% compared to
unsupported ZnFe2O4 (a). A d-value was 12 A, a = 8.233 A, this
slight decrease in a value and increase in nanocrystallite size
indicates the interaction of ZnFe2O4 and ZrO2. XRD of catalysts
samples prepared by templated method: XRD of ZnFe2O4/ZrO2
(d) in Fig. 1 indicates amorphous nature of the catalyst. Crystal-
lite size is calculated by Scherrer formula (Fig. 1, Table 1).
˚
˚
2.2.2. Templated approach [13]
In a typical preparation, Fe and Zn nitrates were taken in,
stoichiometric amounts (2:1) and were dissolved in 10 ml of
methanol to this 10 ml of decyl polyglycoside (50%) aqueous
solution was added with vigorous stirring for 1 h. The result-
ing solution was gelled at 303 K for 20 h (catalyst preparation
is optimized). Similarly ZrOCl2·7H2O was treated with decyl
polyglycoside (50%) aqueous solution and gelled at 303 K for
20 h. Both, Fe + Zn and Zr gel were mixed together aged for 5 h,
dried at 373 K. This as made bulk sample was calcined at 1173 K
for 9 h in air to remove the surfactant to obtain 10% (w/w) of
ZnFe2O4 on ZrO2.
3.1.2. BET surface area measurement
Results obtained from BET surface area measurement are
tabulated in Table 1 shows the interaction of ZnFe2O4 and
ZrO2. Nanocrystallite size increases in ZnFe2O4/ZrO2 (CP).
Due to amorphous nature of ZnFe2O4/ZrO2 (T) nanocrystal-
lite size cannot be found out. Pore size of ZnFe2O4/ZrO2 (CP)
decreases as compared to individual ZnFe2O4 and ZrO2 and
˚
pore size of ZnFe2O4/ZrO2 (T) is very high; 30 A due to tem-

N.S. Chaubal et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 157–164
159
Fig. 2. Hysteresis of N2 adsorption/desorption over the surface of ZnFe2O4/
ZrO2 (T).
Fig. 1. X-ray diffraction pattern. (CP): co-precipitation method, (T): templated
method.
plated assisted route. Similar trend is observed in surface area
which is very high for ZnFe2O4/ZrO2 (T). From Fig. 2 the
nitrogen adsorption–desorption isotherm shown in Fig. 2 is
a type-IV isotherm, as defined by the IUPAC, with a sharp
step at intermediate relative pressures with an H2 hysteresis
loop due to capillary condensation. The isotherm, shows three
well-defined stages can be identified: (a) a slow increase in
nitrogen uptake at 0.0–0.15 relative pressures, corresponding to
monolayer–multilayer adsorption on the pore walls, (b) a sharp
step at 0.15–0.70 relative pressures indicative of capillary con-
densation in mesopores and (c) a plateau at 0.70–0.95 relative
pressures associated with multilayer adsorption on the external
surface. As observed from pore size distribution, a major part of
the surface area is contributed by pores with a diameter charac-
Fig. 3. Pore size by N2 adsorption/desorption of ZnFe2O4/ZrO2 (T).
3.1.3. FT-IR measurement
Pyridine adsorbed FT-IR of ZnFe2O4/ZrO2 (T) the bands
observed at ∼1635, ∼1493 and ∼1541 cm−1 are assigned to
¨
pyridinemoleculesboundtoBronstedacidsitesandshowspeaks
at ∼1612, ∼1490, and ∼1448 cm−1 that are due to pyridine
˚
teristic of pores ranging from 20 to 37 A, as shown the pore size
distribution (Fig. 3) the catalyst is mesoporous in nature.
molecules bound to Lewis acid sites (Fig. 4).
Table 1
Characterization of catalysts
a
b
BET surface area (m2/g)
Physical properties
˚
˚
Oxide
Precursor
Nanocrystallite size (A)
Pore size (A)
ZnFe2O4(CP)
ZrO2(CP)
ZnFe2O4/ZrO2 (CP)
ZnFe2O4/ZrO2 (T)
Zn(NO3)3 and Fe(NO3)3
ZrOOCl
Zn(NO3)3, Fe(NO3)3 and ZrOOCl
Zn(NO3)3, Fe(NO3)3 and ZrOOCl
10
8
12
–
3.8
6.2
4.7
30
17
24
20
Semiconductor
Dielectric
Semiconductor
Semiconductor
180
a
Scherrer equation.
BET measurement.
b

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Table 2
Effect of various catalysts prepared by co-precipitation method
Catalyst
Room temperature
resistivity
Time (h)
% conversion
to APG
CuFe2O4
NiFe2O4
CoFe2O4
ZnFe2O4
0.19
0.37
0.27
0.59
6
10
11
4
50
55
52.5
60
[Catalyst]: 0.0088 g/cm3; d-glucose: 10 mM; n-meristyl alcohol: 20 mM; speed
of agitation: 900 rpm; temperature: 363 K.
Fig. 4. Pyridine adsorbed FT-IR of ZnFe2O4/ZrO2 (T).
be the energy required for electronic transition resulting in the
decrease in the activity of the catalyst. Hence, from energy of
activation values CuFe2O4 (0.19), ZnFe2O4 (0.59), CoFe2O4
(0.27) and NiFe2O4 (0.37), CuFe2O4 should exhibit highest
and ZnFe2O4 lowest catalytic activity at the reaction temper-
ature. To our surprise the trend is exactly reversed. ZnFe2O4
showed the highest conversion towards glycosidic bond forma-
tion to give alkyl poly-␤-d-glucopyranoside. The most probable
reasons to these observations are: (1) In ZnFe2O4, tetrahedral
site is occupied by Zn2+ ions and octahedral site is occu-
pied by Fe3+. In Zn2+, d10 orbital are more contracted than
any other transition metal ion d-orbital. The decreased over-
lap of the oxygen 2p, 3d and 4s with the Fe3+ at octahedral
site has an indirect but appreciable effect on the hopping pro-
cess. Catalytic activity is mainly due to the hopping of Fe3+
from octahedral site to tetrahedral site. Thus in spinel lat-
tice cation distribution plays an important role in the reaction.
Also it is well known that p-type of semiconductors is active
and selective towards dehydrogenation owing to rapid migra-
tion of holes. From thermoelectric power measurements it can
be concluded that in CuFe2O4 concentration of holes is less
hence dehydrogenation selectivity decreases from ZnFe2O4 to
CuFe2O4 so the selective formation of the product is more. (2)
In ZnFe2O4 as Zn2+ and O2− overlap is poor, Zn–O bond is
weak hence lattice oxygen can be easily exchanged with the
substrate molecule, resulting in the increasing dehydrogenation
activity.
3.1.4. SEM measurement
SEM of ZnFe2O4/ZrO2 (CP) shows the aggregates of crys-
tallites which indicate that due aggregation of the catalyst
particles active sites are less accessible for the reaction to occur
on the surface of the ZnFe2O4/ZrO2 (CP). Whereas SEM of
ZnFe2O4/ZrO2 (T) shows the rod like morphology of the cat-
alyst particles indicating the increase in the surface area of the
catalyst with more access to the active sites for the formation of
glycosidic linkage, hence more and more product is favored on
ZnFe2O4/ZrO2 (T) compared to ZnFe2O4/ZrO2 (CP) (Fig. 5a
and b).
It was thought desirable to study various reaction parameters
under otherwise similar experimental conditions to establish the
reaction mechanism.
3.2. Choice of catalysts for glycosylation reaction
To check effect of various catalysts for glycosidic bond for-
mation, reaction between fatty alcohol and d-glucose were taken
as model reaction. CuFe2O4, ZnFe2O4, CoFe2O4, NiFe2O4 and
10% (w/w) ZnFe2O4 supported on SiO2 and ZrO2 were used
to assess their efficacy in glycosylation reaction (see Table 2).
As per the trend Cu containing spinels show low room temper-
ature resistivity compared to Zn containing spinels that can be
explained on the basis of a valency exchanged mechanism [14].
It is believed that, greater the energy of activation, greater will
Fig. 5. (a) SEM of ZnFe2O4/ZrO2 (CP) and (b) of ZnFe2O4/ZrO2 (T).

N.S. Chaubal et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 157–164
161
Table 3
(1) and (2) Effect of support and preparation procedure
1
2
Catalyst/support
% conversion
to APG
Preparation procedure
of ZnFe2O4/ZrO2
% conversion
to APG
ZnFe2O4/SiO2
ZnFe2O4/ZrO2
66.0
70.0
Co-precipitation (CP)
Templated route (T)
70.0
83.0
[Catalyst]: 0.0088 g/cm3; d-glucose: 10 mM; n-meristyl alcohol: 20 mM; speed
of agitation: 900 rpm; temperature: 363 K.
3.3. Effect of support (catalysts are prepared by
co-precipitation)
Fig. 6. Effect of solvents. Catalyst: ZnFe2O4/ZrO2 (T); [Catalyst]: 0.0088 g/
cm3;d-glucose:10 mM; n-meristylalcohol:20 mM;speedofagitation:900 rpm;
temperature: 363 K.
To study the effect of support 10% (w/w) ZnFe2O4 was
supported on SiO2 and ZrO2. ZnFe2O4/ZrO2 was found to
be the best catalyst with 70% conversion of n-decanol lead-
ing to the formation of alkyl poly-␤-d-glucopyranoside. This
may be due to increased in surface area and nature of the sup-
port. ZrO2 is amphoteric in nature whereas SiO2 is acidic.
It was observed that when ZnFe2O4/SiO2 were used forma-
tion of alkyl poly-␤-d-glucopyranoside was suppressed and
polyglucose that is; glucose–glucose condensation was favoured
product. When ZnFe2O4/ZrO2 were used formation of alkyl
poly-␤-d-glucopyranoside was the main product and polyglu-
cose formation was suppressed. Thus acidity of ZnFe2O4 was
tuned by supporting it with ZrO2 for further study 10% (w/w)
ZnFe2O4/ZrO2 was used (Table 3 (1)).
dimethylformamide and tetrahydrofuran were used as solvent,
though degree of polymerization was in range but separation
of the major product from the reaction mass and solvent recov-
ery was difficult. In dimethyl sulfoxide the product obtained
had undesirable odor. Polar surface area of solvents increase
from toluene < THF < DMSO < DMF < acetic acid, this increase
in polar surface area, increases the formation of polyglucose
suppressing the formation of alkyl poly-␤-d-glucopyranoside.
Hence the formation of alkyl poly-␤-d-glucopyranoside was
more in toluene and product obtained was yellowish with degree
of polymerization in desirable range, also the solvent recovery
was easy. All further reactions were taken in toluene as reaction
media.
3.4. Effect of preparation procedure
3.6. Effect of temperature
A 10% (w/w) ZnFe2O4/ZrO2 was prepared by two differ-
ent methods, viz, co-precipitation and templated approach. It
was seen that catalyst prepared by templated approach showed
83% formation of alkyl poly-␤-d-glucopyranoside (Table 3 (2)).
Increase in the surface area and pore size leads to increase in
more product formation. In co-precipitation method hydrolysis
of the salts takes place very fast so there is no chance for the cat-
alyst to increase the surface area, while in templated approach
hydrolysis of the metal salt takes place very slowly in controlled
manner due to presence of the template, decly poly-glucoside.
The formation of metal template complex followed by hydrol-
ysis leads to the formation of mesopores in the catalyst which
is retained after calcinations. Hence increases the surface area
leading to increasing product formation.
The effect of temperature on conversion under otherwise
similar conditions was studied in the range of 323–373 K as
shown in the Fig. 7. It was seen that the initial conversion
increased up to 363 K and there after decreased due to charring
of glucose with increasing temperature. At 373 K alkyl poly-␤-
d-glucopyranoside was also charred which gave dark color and
3.5. Effect of solvent
Variety of solvents was used for the reaction as shown in
Fig. 6. It was seen that in case of acetic acid due to its acidic
nature degree of polymerization of glucose was more and the
colour of the product also suffered which is undesirable. We
have also checked the reaction without catalyst in acetic acid,
in this case we failed to obtain alkyl poly-␤-d-glucopyranoside,
and instead we obtained only poly glucose. Thus it was con-
firmed that catalysts plays the major role in the formation
of alkyl poly ␤-d-glucopyranoside. When dimethyl sulfoxide,
Fig. 7. Effect of temperature. Catalyst: ZnFe2O4/ZrO2 (T); [Catalyst]:
0.0088 g/cm3; d-glucose: 10 mM; n-meristyl alcohol:20 mM; speed ofagitation:
900 rpm; solvent: toluene.

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N.S. Chaubal et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 157–164
Table 4
Product analysis
Alcohol chain
length
Conversion
to APG (%)
MP (◦C) [α]2D5 1H NMR data of
␤-d-glycoside
IR KBr (cm−1
)
Elemental analysis
Calculated
Observed
C
H
O
C
H
O
n-Octanol
n-Decanol
n-Dodecanol
75.0
78.0
80.0
62.0
135.6
144.5
–
33.8
27.8
22.7
–
4.09 (d, J = 7.8 Hz) 3412, 2928, 2831, 1075, 1030 57.53
9.58 32.89 57.50
9.60 32.90
4.09 (d, J = 7.8 Hz) 3386, 2925, 2829, 1080, 1036 60.75 10.12 29.13 60.78 10.15 29.07
4.09 (d, J = 7.8 Hz) 3390, 2935, 2821, 0851, 1040 65.85 10.36 23.79 65.83 10.35 23.82
4.09 (d, J = 7.8 Hz) 3412, 2928, 2831, 1075, 1030 70.58 13.52 15.94 70.57 13.50 15.93
n-Meristyl alcohol 87.2
Catalyst: ZnFe2O4/ZrO2 (T); [Catalyst]: 0.0088 g/cm3; d-glucose: 10 mM; fatty alcohol: 20 mM; speed of agitation: 900 rpm; temperature: 363 K.
odor to the final product. While at 363 K said problems was not
encountered so further studies were done at 363 K.
3.7. Effect of alcohols
To investigate the effect of chain length of fatty alcohols, gly-
cosylation was also carried out with C8, C10, C12 and C14 under
otherwise similar conditions. Table 4 summarizes the optimized
results of alkyl poly-␤-d-glucopyranosides of several alcohols
over ZnFe2O4/ZrO2 (T) catalyst. It was found that the increase
in the carbon chain length increases the rate of alkyl poly-␤-
glycosylation reaction. The possible reason may be the faster
generation of alkoxide due to increase in carbon number. All
further reaction parameters were optimized using n-meristyl
alcohol (C14).
Fig. 9. Effect of catalyst concentration. Catalyst: ZnFe2O4/ZrO2 (T); speed of
agitation: 900 rpm; d-glucose: 10 mM; n-meristyl alcohol: 20 mM; temperature:
363 K; solvent: toluene.
3.8. Effect of speed of agitation
3.9. Effect of catalyst concentration
The effect of speed of agitation was studied in the range of
600–1500 rpm and is shown in the Fig. 8. It was found that there
was practically no change in the conversion. This shows that
the influence of external resistance to the transfer of substrates
to the catalyst surface was absent, therefore further experiment
were conducted at 900 rpm.
Rate of reaction is directly proportional to concentration of
catalyst based on the entire liquid phase volume. The catalyst
concentration was varied from 0.006 to 0.011 g/cm3 on the basis
of total volume of the reaction mixture keeping all other condi-
tions similar. Fig. 9 shows the effect of concentration of catalyst
on the formation of alkyl poly-␤-d-glucopyranoside. The con-
Fig. 10. Catalyst reusability and stability. Catalyst: ZnFe2O4/ZrO2 (T); [Cata-
lyst]: 0.0088 g/cm3; speed of agitation: 900 rpm; d-glucose: 10 mM; n-meristyl
alcohol: 20 mM; temperature: 363 K; solvent: toluene.
Fig. 8. Effect of speed of agitation. Catalyst: ZnFe2O4/ZrO2 (T); [Catalyst]:
0.0088 g/cm3; d-glucose: 10 mM; n-meristyl alcohol: 20 mM. temperature:
363 K; solvent: toluene.

N.S. Chaubal et al. / Journal of Molecular Catalysis A: Chemical 267 (2007) 157–164
163
Scheme 1. Reaction of glucose and fatty alcohol.
version increased with increase in concentration of catalyst,
which is due to the proportional increase in the number of active
sites. However, beyond 0.0088 g/cm3 concentration of catalyst,
there was no significant increase in the conversion and hence all
further experiments were carried out at this catalyst loading.
five cycles (see Fig. 10). The catalyst was easily recovered
by filtration and could be reused five times for the alkyl
poly-␤-glycosylation reaction without affecting the activity or
selectivity of the process. After fifth run the activity of the cat-
alyst decreases, the XRD pattern of the used catalyst shows
no structural deterioration. The decrease in activity can be
attributed to pore blockage by deposition due to which active
sites becomes inaccessible. The catalysts can be easily reacti-
vated after washing it with acetone and treating it at 373 K for
24 h.
3.10. Catalyst reusability and stability
ZnFe2O4/ZrO2 (T) catalyst has good reusability and with-
out pretreatment it can shows selective conversion up to
Scheme2. ReactionofglucoseandfattyalcoholoverthesurfaceoftheZnFe2O4/ZrO2 (T)catalysttoaffordpoly-␤-d-alkylglucopyranosideandpoly-glucopyranoside.

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4. Reaction and reaction mechanism
5. Conclusion
The ␤-glycosidic bond formation of d-glucose with alcohol is
one-step reaction as shown in Scheme 1 (see glycosidic bond for-
mation in the circle, R = C8–C14 alcohols). In the above reaction
(3) is the major product whereas (4) is side product. Formation
of (4) alters the physico-chemical property of polyglycosides so
product (4) is undesirable, hence reaction suffers and application
of the product is restricted.
The efficacy of different catalysts was evaluated at 363 K
with 0.0088 g/cm3 catalyst loading and toluene as a reaction
solvent at 900 rpm. ZnFe2O4/ZrO2 (T) prepared by template
route shows excellent conversion and selectivity towards alkyl
poly-␤-d-glucopyranosides due to increase in surface area of
the catalyst. C14 fatty alcohol shows maximum formation of
alkyl poly-␤-d-glucopyranosides because of the ease of alkoxide
formation. The catalyst could be reused five times and was easily
recoveredbyfiltrationwithoutaffectingtheactivityorselectivity
of the process.
The most satisfactory mechanism for Fischer glycosylation
was proposed by Levene et al. [15], in which aldoses or ketones
on treatment with alcohols containing acid catalysts yield glyco-
sides as a major product. The major reaction takes place usually
via ␣-furanoside or ␤-furanoside formation. Such intermediates
further convert to pyranosides. For present catalytic system we
suggest following mechanism. d-Glucose (A) shows anomer-
ization of pyranose form which presumably is occurring rapidly
under acidic conditions [16]. This anomerization occurs through
via ring opening followed by addition of fatty alcohol (B) to
form unstable intermediate (C) and lost of water molecule to
form ␣-furanoside or ␤-furanoside (D). Presently we are not
sure about the exact anomeric form of furanoside; however the
major product is alkyl poly-␤-d-glucopyranoside. Another alco-
holmoleculeadditionandeliminationinfuranose(D)givesalkyl
poly-␤-d-glucopyranoside as a major product as shown in (G).
The formation of alkyl poly-␤-d-glucopyranoside occurs due to
attack of –OH of C1 of d-glucose (A) on –OH of C4 of alkyl
␤-d-glucopyranoside (G). The alkyl poly-␤-d-glucopyranoside
shows inside the rectangular box (Scheme 2).
References
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During the course of the reaction, as the catalyst surface is
acidic, formation of polyglucose (H) takes place. Polyglucose
formation occurs due to attack of –OH of C1 of d-glucose (A) on
–OH of C4 of another d-glucose (A). After the formation of the
product on the surface of the catalyst, desorption of the product
takes place and the surface of the catalyst again starts the new
reaction cycle with the adsorption of glucose and fatty alcohol.
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(b) V. Smirnyagin, C. Bishop, Can. J. Chem. 46 (1968) 3085.
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