Polyvinyl trisulfonate ethylamine based solid acid catalyst for the efficient glycosylation of sugars under solvent free conditions

Article abstract of DOI:10.1039/c5ra20300g

Heterogeneous Bronsted solid acid catalysts have the potential to decrease the environmental impact related to chemical production. Herein, we have synthesized polyvinyl bound trisulfonate ethylamine chloride (PV-THEAC) and polyvinyl bound disulfonate ethylamine (PV-DSEA) as Bronsted solid acid catalysts which exhibited effective catalytic activity for acid catalyzed glycosylation reactions with sugar derivatives. In particular, 0.3 equiv. of the PV-THEAC catalyst was found to be the most efficient and a reusable catalyst for glycosylation reactions. A high density of the trisulfonic group (-OSO₃H) contributed to the excellent catalytic activity during glycosylation. Moreover, glycosylation reactions with d-mannose, d-xylose and d-glucose have been studied with alcohol. Remarkable acceleration of the glycosylation reaction using a glycosyltrichloroacetimidate donor was obtained with the selective production of β-glycoside.

Full text of DOI:10.1039/c5ra20300g

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Polyvinyl trisulfonate ethylamine based solid acid
catalyst for the efficient glycosylation of sugars
under solvent free conditions†
Cite this: RSC Adv., 2015, 5, 104715
*
Avinash A. Chaugule, Amol R. Jadhav and Hern Kim
Heterogeneous Brønsted solid acid catalysts have the potential to decrease the environmental impact
related to chemical production. Herein, we have synthesized polyvinyl bound trisulfonate ethylamine
chloride (PV-THEAC) and polyvinyl bound disulfonate ethylamine (PV-DSEA) as Brønsted solid acid
catalysts which exhibited effective catalytic activity for acid catalyzed glycosylation reactions with sugar
derivatives. In particular, 0.3 equiv. of the PV-THEAC catalyst was found to be the most efficient and
a reusable catalyst for glycosylation reactions. A high density of the trisulfonic group (–OSO3H)
contributed to the excellent catalytic activity during glycosylation. Moreover, glycosylation reactions with
D-mannose, D-xylose and D-glucose have been studied with alcohol. Remarkable acceleration of the
glycosylation reaction using a glycosyltrichloroacetimidate donor was obtained with the selective
production of b-glycoside.
Received 1st October 2015
Accepted 18th November 2015
DOI: 10.1039/c5ra20300g
www.rsc.org/advances
monomers have been studied broadly for the construction of
desired solid acids,13 such materials are expensive and their
1. Introduction
activity is still much lower than that of sulfuric acid, so their
effectiveness is limited.14,15 However, previous work has
explored the development of solid acid catalysts such as
sulfated zirconium,16,17 Cs-exchanged heteropoly acids,14 acidic
polymers17 and zeolites.18 In recent years, the use of sulfonated
carbon based solid acids as efficient catalysts for a variety of
acid catalyzed reactions has been reported. This type of solid
acid is usually prepared through carbonization and sulfonation
reactions using renewable biomass as a carbon source.19,20
These solid acids have proven their worth as catalysts for some
important chemical transformations like biodisel production
and hydrolysis of the cellulose acetylation of glycerol etc.21
In inorganic solid acids, the acid strength depends on
several factors such as the crystallinity, topology of the struc-
ture, morphology and most importantly the chemical compo-
sition. For example, microporous zeolites through their
crystalline nature demonstrate stronger acid strength than
mesoporous A1-MCM-42, although they are both composed of
aluminosilicates.22,23 Moreover, polystyrene sulphonic acid
resins are among the very important solid acids used in industry
and have been widely used in acid catalysed reactions such as
etherication, olen hydration, and the alkylation of
phenols.24,25 In the case of polymer based solid acids great
challenges still remain in improving the acid strength via
factors beyond the chemical composition, which are probably
due to a lack of morphology and structural controls of poly-
mers.26 In this paper, we report the synthesis and performance
of a polyvinyl bonded Brønsted trisulfonic group (–OSO3H) solid
acid as a novel, strong and stable solid acid catalyst with a high
Homogeneous Brønsted acid catalysts such as H2SO4 are
remarkable catalysts for the production of fuels and are very
important chemicals for industry.1,2 However, the use of these
catalysts needs energy-efficient processes for the recycling,
separation and treatment of spent acids.3,4 Moreover, the
neutralization of homogeneous acids generates sulfate waste
and thus, the acid does not satisfy the requirement of a catalyst
that can be reused for accelerating reactions. The development
in chemistry toward green chemical processes has been initi-
ated with the use of recyclable strong solid acids as replace-
ments for such unrecyclable liquid acid catalysts.5,6 However,
the main disadvantage to such progress is the lack of solid acids
that are as active, stable and inexpensive as the liquid acid
catalysts.
Solid acid catalysts have received much attention in the eld
of green catalysis with the advantages of being non-polluting,
easily separated and reusable.7,8 Thus, an ideal solid acid
material for such applications should have high stability and
many strong protonic acid sites.9,10 In this regard, researchers
around the world have been committed to improving the acid
density, strength and stability of solid acids.11,12 Although
organic or inorganic solid oxide hybrids and strong acidic
cation exchangeable resins such as peruorosulfonated
Department of Energy Science and Engineering, Energy and Environment Fusion
Technology Center, Myongji University, Yongin, Gyeonggi-do 17058, Republic of
Korea. E-mail: hernkim@mju.ac.kr; Fax: +82 31 336 6336; Tel: +82 31 330 6688
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra20300g
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density of sulfuric acid groups. A new strategy is adopted for the solid was dried under vacuum at 60 ꢁC for 12 h and afforded PV-
development of new types of solid acids: polyvinyl bound tri- DEA as the product. The loading of diethanol amine attached to
sulfonate ethyl amine chloride. This simple approach of PVC was 3.89 mmol gꢀ1, determined through the nitrogen
a polyvinyl bound trisulfonic group through triethanol amine content from elementary analysis. From the calculation 88% of
exhibits remarkable catalytic activity for the glycosylation of the Cl had reacted. The chloroethanol (160.12 mmol, 17.35 g)
unprotected sugars/glycosyl trichloroacetimidate.
with PV-DEA (10.0 g) and acetonitrile (40 mL) were added into
a round bottom ask and the mixture was heated at 80 ꢁC for 24
h. Aer which the reaction mixture was cooled down to room
temperature. The liquid phase was poured off and the solid
residue was washed with acetone. Then, the solid was dried
under vacuum at 60 ꢁC and polyvinyl triethanol amine chloride
(PV-THEAC) was obtained.
The PV-THEAC (5 g, 80 mmol) and chlorosulphonic acid
(27.88 g, 240 mmol) were added into a round bottom ask and
this reaction mixture was vigorously stirred for 48 h. Aer this,
the solid residue was collected by ltration and washed sepa-
rately with water and acetone. The formation of PV-TSEAC was
conrmed through the sulphur content using elemental anal-
ysis and IR.
Elemental analysis: PV-DEA calcd: N 8.41%, C 43.25%, H
7.80%, observed; N 7.35%, C 48.25%, H 7.45%. PV-THEAC
calcd: N 6.63%, C 45.49%, H 8.50%, observed; N 5.58%, C
45.48%, H 8.85%. PV-TSEAC calcd: N 3.63%, C 21.28%, H
3.99%, S 21.30%, observed; N 3.23%, C 45.48%, H 8.85%, S
60.30%. PV-DSEA calcd: N 3.63%, C 25.70%, H 4.28%, S 15.42%,
observed; N 3.27%, C 30.45%, H 3.13%, S 15.81%.
2.3.2. General procedure for glycosylation. A mixture of
unactivated, unprotected sugars/glycosyl trichloroacetimidate
donor (1 mmol), alcohol (5 mmol) and 15 wt% PV-TSEAC was
stirred at 60 ꢁC for 4 h. Aer consumption of the glycosyl donor,
shown using TLC, the reaction mixture was diluted with ethyl
acetate and the catalyst was separated by ltration. The ltrate
was evaporated in a rotary evaporator and further puried using
column chromatography to obtain the desired glycosides.
2. Experimental procedure
2.1. Materials
Polyvinyl chloride (99% pure) with an average Mw ¼ 48 000 g
molꢀ1, diethanol amine (99% pure), triethanol amine (99%
pure), chloromethane (99% pure) and sodium sulfate (99%),
Amberlyst 15, sulfamic acid (99.3% pure) and all of the
substrates used for the glycosylation reactions were purchased
form Aldrich and Acros (with 99% purity) and were used without
further purication. The glycosyltrichloroacetimidate donor
was prepared using a previously reported procedure in the
literature using D-glucose, acetic anhydride (99% pure) and
trichloracetanitrile (99% pure).37 TLC analysis was performed
on silica-gel (SIL G/UV 254) plates to monitor the reaction.
2.2. Characterization
The FTIR spectra of the samples were obtained through
pelletizing the dried samples with potassium bromide (KBr)
and were recorded using a Varian 2000 (Scimitar series) spec-
trophotometer. A spectrum was recorded from 4000 to 500 cmꢀ1
maintaining a resolution of 4 cmꢀ1 with 32 scans in trans-
mittance mode. Mass spectra for the samples were obtained
using a Waters Micromass ZQ LC/MS 2000 (Scimitar series)
spectrophotometer. Thermogravimetric analysis (Scinco TGA N-
100) was used to check the thermal stability of the samples.
Heating of the samples was carried out from room temperature
to 600 ꢁC, at a heating rate of 10 ꢁC minꢀ1 under the continuous
purge of nitrogen (50 mL minꢀ1), and spectra were collected
using Q600 Soware (TA Instruments). The specic surface
area, pore volume and pore diameter were determined based on
physical adsorption of nitrogen on the solid surface of the
Brønsted solid acid catalyst through the Brunauer–Emmett–
Teller (BET) approach, using a BELSORP-Max (MP) from BEL
Propargyl 2,3,4,6-tetra-O-acetyl-b-D-galactopyranoside
(a).
1
White solid; yield 97%; Rf ¼ 0.3 (EtOAc–Pet ether ¼ 1 : 2); H
NMR (CDCl3, 400 MHz) d 2.01 (s, 3H), 2.03 (s, 3H), 2.06 (s, 3H),
2.09 (s, 3H), 2.48 (t, J ¼ 2.2 Hz, 1H), 3.71–3.75 (m, 1H), 4.11–4.17
(m, 1H), 4.26–4.30 (m, 1H), 4.37 (d, J ¼ 2.7 Hz, 2H), 4.78 (d, J ¼
7.8 Hz, 1H), 5.0–5.04 (m, 1H), 5.11 (t, J ¼ 10.0 Hz, 1H), 5.25 (t, J ¼
9.6 Hz, 1H); 13C NMR (CDCl3, 50 MHz) d 20.5, 20.6, 29.6, 55.8,
60.3, 61.6, 68.1, 70.8, 71.8, 72.6, 75.4, 78.0, 98.0, 169.3, 169.4,
170.2, 170.6; HRMS (ESI) m/z [M + Na]+ calcd for C17H22O10Na
409.11, found 407.12.
ꢁ
Japan. NMR spectra were recorded in CDCl3 at 25 C on either
a Bruker 400 (400 MHz) or Bruker 200 spectrometer (200 MHz).
For 13C NMR spectra, carbon chemical shis were internally
referenced to the deuterated solvent signal of CDCl3 (77.16
ppm).
2-Propyl 2,3,4,6-tetra-O-acetyl-b-D-galactopyranoside (c). White
crystals; mp – 87 ꢁC; yield 97%; Rf ¼ 0.2 (EtOAc–Pet ether ¼
1 : 2); 1H NMR (CDCl3, 400 MHz) d 5.84 (dddd, 1H, J ¼ 17.1 Hz,
10.5 Hz, 6.1 Hz, 5.0 Hz) 5.27 (dq, 1H, J ¼ 17.1 Hz, 1.6 Hz), 5.25–
2.3. Typical synthesis procedure for the solid acid catalysts
2.3.1. Preparation of trisulfonate solid acid catalyst (poly- 5.18 (m, 1H), 5.21 (app t, 1H, J ¼ 9.3 Hz), 5.09 (app t, 1H, J ¼ 9.6
vinyl bound trisulfonate triethyl amine chloride). In a typical Hz), 5.02 (dd, 1H, J ¼ 9.4 Hz, 7.9 Hz), 4.55 (d, 1H, J ¼ 7.9 Hz),
synthesis procedure for polyvinyl bound diethanol amine (PV- 4.32 (ddt, 1H, J ¼ 13.2 Hz, 5.0 Hz, 1.6 Hz), 4.25 (dd, 1H, J ¼ 12.2
DEA), a mixture of PVC (10.0 g, 160.10 mmol, 53.57% Cl Hz, 4.7 Hz), 4.12 (dd, 1H, J ¼ 12.2 Hz, 2.5 Hz), 4.08 (ddt, 1H, J ¼
content), diethanolamine (16.81 g, 160.12 mmol) and acetoni- 13.2 Hz, 6.1 Hz, 1.3 Hz), 3.67 (ddd, 1H, J ¼ 9.8 Hz, 4.7 Hz, 2.5
trile (50 mL) was heated at 80 C for 48 h in a 125 mL round Hz), 2.07 (s, 3H), 2.03 (s, 3H), 2.00 (s, 3H), 1.99 (s, 3H); 13C NMR
ꢁ
bottom ask with stirring. Aer cooling this reaction mixture to (63 MHz, CDCl3): d 170.2, 169.9, 169.1, 168.9, 133.1, 117.2, 99.3,
room temperature, the solid residue was collected by ltration 72.6, 71.5, 71.0, 69.7, 68.2, 61.7, 20.4, 20.32, 20.26 (2C); HRMS
and washed successively with water and acetone. Then, the (ESI+): m/z calcd for [C17H24O10Na] 411.12, found 411.12.
104716 | RSC Adv., 2015, 5, 104715–104724
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2-Butene-1-ol 2,3,4,6-tetra-O-acetyl-b-D-galactopyranoside (d).
RSC Advances
Benzoyl 2,3,4,6-tetra-O-acetyl-b-D-galactopyranoside (i). Yield
White solid; yield 94%; Rf ¼ 0.3 (EtOAc–Pet ether ¼ 1 : 1); H 93%; Rf ¼ 0.2 (EtOAc–Pet ether ¼ 1 : 2); 1H NMR (400 Hz,
NMR (CDCl3, 400 MHz) d 2.01 (s, 3H), 2.03 (s, 3H), 2.06 (s, 3H), CDCl3): d ¼ 8.07 (d, 2H, J ¼ 7.2 Hz), 7.61 (t, 1H, J ¼ 7.6 Hz), 7.47
2.10 (s, 3H), 3.69–3.70 (m, 1H), 4.15–4.21 (m, 3H), 4.24 (d, J ¼ 4.5 (t, 2H, J ¼ 7.6 Hz), 5.94 (d, 1H, J ¼ 8.0 Hz), 5.55 (dd, 1H, J1 ¼ 8.4
Hz, 1H), 4.28 (t, J ¼ 5.9 Hz, 1H), 4.32 (bs, 1H), 4.35–4.39 (m, 1H), Hz, J2 ¼ 10.4 Hz), 5.50 (d, 1H, J ¼ 3.2 Hz), 5.21 (dd, 1H, J1 ¼ 3.6
4.58 (d, J ¼ 7.7 Hz, 1H), 4.98–5.03 (m, 1H), 5.09 (t, J ¼ 9.6 Hz, Hz, J2 ¼ 10.8 Hz), 4.24–4.14 (m, 3H), 2.20 (s, 3H), 2.05 (s, 3H),
1H), 5.21 (t, J ¼ 9.6 Hz, 1H), 5.6–5.67 (m, 1H), 5.83–5.89 (m, 1H); 2.03 (s, 3H), 2.00 (s, 3H) ppm. 13C NMR (125 Hz, CDCl3): d ¼
13C NMR (CDCl3, 50 MHz) d 20.6, 20.7, 20.73, 58.5, 61.9, 64.3, 170.1, 170.0, 169.7, 169.3, 164.4, 133.8, 130.0, 128.6, 128.4, 92.6,
68.4, 71.2, 71.7, 72.7, 99.2, 126.7, 133.3, 169.4, 169.4, 170.3, 71.6, 70.5, 67.7, 66.8, 60.9, 20.42, 20.35 ppm. HRMS (ESI) m/z
170.8; HRMS (ESI) m/z [M + Na]+ calcd for C18H26O11Na 441.13, [M + Na]+ calcd for C21H24NaO11 475.11. Found 474.80.
1
found 441.10.
Cyclohexyl 2,3,4,6-tetra-O-acetyl-b-D-galactopyranoside (j).
1
1-Decyl 2,3,4,6-tetra-O-acetyl-b-D-galactopyranoside (e). White White solid; yield 93%; Rf ¼ 0.2 (EtOAc–Pet ether ¼ 1 : 2); H
solid; yield 98%; Rf ¼ 0.6 (EtOAc–Pet ether ¼ 1 : 2); 1H NMR NMR (CDCl3, 400 MHz) d 1.24–1.26 (m, 4H), 1.38–1.48 (m, 2H),
(CDCl3, 400 MHz) d 0.87 (t, 3H), 1.24 (m, 18H), 1.5–1.59 (m, 2H), 1.64–1.77 (m, 3H), 1.83–1.86 (m, 1H), 1.99 (s, 3H), 2.01 (s, 3H),
2.0 (s, 3H), 2.2 (s, 3H), 2.4 (s, 3H), 2.8 (s, 3H), 3.43–3.49 (m, 1H), 2.02 (s, 3H), 2.07 (s, 3H), 3.58–3.63 (m, 1H), 3.64–3.69 (m, 1H),
3.67–3.71 (m, 1H), 3.84–3.89 (m, 1H), 4.11–4.14 (m, 1H), 4.26 4.10 (dd, J ¼ 11.9 and 2.3 Hz, 1H), 4.25 (dd, J ¼ 11.9 and 4.5 Hz,
(dd, J ¼ 7.8 and 4.6 Hz, 1H), 4.49 (d, J ¼ 7.8, 1H), 4.97 (dd, J ¼ 8, 1H), 4.57 (d, J ¼ 7.8 Hz, 1H), 4.95 (dd, J ¼ 9.6 and 8.2 Hz, 1H),
1.4 Hz, 1H), 5.08 (t, J ¼ 9.7, 9.5 Hz), 5.2 (t, J ¼ 9.5, 9.2 Hz, 1H); 5.07 (t, J ¼ 9.6 Hz, 1H), 5.19 (t, J ¼ 9.6 Hz, 1H); 13C NMR (CDCl3,
13C NMR (CDCl3, 100 MHz) d 14.2, 20.5, 22.5, 25.7, 29.2, 29.5, 50 MHz) d 20.6, 20.65, 20.68, 20.7, 23.5, 23.6, 25.4, 31.5, 33.1,
31.7, 61.8, 68.3, 70.2, 71.2, 71.5, 72.7, 100.7, 169.3, 169.4, 170.3, 62.0, 68.5, 71.4, 71.5, 72.8, 78.0, 99.3, 169.2, 169.4, 170.3, 170.7;
170.7; HRMS (ESI) m/z [M + Na]+ calcd for C25H42O10Na 525.26, HRMS (ESI) m/z [M + Na]+ calcd for C20H30O10Na 453.1737,
found 524.80.
found 452.20.
2-Isopropyl-5-methyl cyclohexyl 2,3,4,6-tetra-O-acetyl-b-D-gal-
actopyranoside (f). White solid; yield 94%; Rf ¼ 0.5 (EtOAc–Pet
3. Results and discussion
3.1. FT-IR analysis and acidity determination of the solid
1
ether ¼ 1 : 2); H NMR (CDCl3, 400 MHz) d 0.73 (d, J ¼ 4.6 Hz,
3H), 0.85 (s, 3H), 0.89 (d, J ¼ 1.7 Hz, 3H), 0.91–0.93 (m, 2H),
1.14–1.41 (m, 4H), 1.55–1.72 (m, 5H), 2.01 (s, 3H), 2.03 (s, 3H),
2.06 (s, 3H), 2.08 (s, 3H), 3.25–3.45 (m, 1H), 3.63–3.76 (m, 1H),
4.07–4.28 (m, 2H), 4.56 (d, J ¼ 7.9 Hz, 1H), 4.97 (dd, J ¼ 9.7 and
3.6 Hz, 1H), 5.07 (dd, J ¼ 8.9 and 2.2 Hz, 1H), 5.21 (t, J ¼ 9.4 Hz,
1H); 13C NMR (CDCl3, 50 MHz) d 15.4, 15.9, 20.5, 20.6, 20.7,
20.9, 21.0, 22.3, 22.8, 25.0, 31.4, 31.6, 34.0, 34.1, 40.8, 42.8, 47.4,
48.0, 62.4, 68.7, 68.9, 71.5, 71.6, 73.0, 79.1, 83.1, 98.7, 101.9,
169.3, 169.5, 170.4, 170.2; HRMS (ESI) m/z [M + Na]+ calcd for
acid catalysts
The Fourier transform infrared spectra of PV-THEAC, PV-DEA
and PVC are shown in Fig. 1. The absorption bands in pure
polyvinyl chloride are identied by the vibration bands at 750
cmꢀ1, 1398 cmꢀ1 and 3137 cmꢀ1 for C–Cl, C–C and C–H,
respectively. When diethanol amine is bound to polyvinyl
chloride, the C–Cl vibration band at 750 cmꢀ1 disappears. In
additon, the C–N, –OH and C–O vibration bands at 1247 cmꢀ1
,
3409 cmꢀ1 and 957 cmꢀ1 appeared in the FT-IR spectra (Fig. 1A).
Moreover, polyvinyl chloride bound to triethanol amine is
identied by vibration bands at 1247 cmꢀ1, 957 cmꢀ1 and 3409
cmꢀ1 for C–N, C–O and –OH functionalized groups, respec-
tively.27 The spectra for PV-TSEAC and PV-DSEA have vibration
bands at 1169 cmꢀ1 and 1038 cmꢀ1, which are associated with
C
24H38O10Na 509.23, found 508.80.
1-Adamantanylmethyl 2,3,4,6-tetra-O-acetyl-b-D-galactopyrano-
side (g). White solid; yield 97%; Rf ¼ 0.6 (EtOAc–Pet ether ¼
1 : 1); 1H NMR (CDCl3, 400 MHz) d 1.48–1.52 (m, 3H), 1.58–1.74
(m, 12H), 2.02 (s, 3H), 2.03 (s, 3H), 2.06 (s, 3H), 2.10 (s, 3H), 2.97
(d, J ¼ 9.4 Hz, 1H), 3.51 (d, J ¼ 9.4 Hz, 1H), 3.63–3.71 (m, 1H),
4.16 (dd, J ¼ 9.4 Hz, 1H), 4.28 (dd, J ¼ 7.7 and 4.5 Hz, 1H), 4.43
(d, J ¼ 7.7 Hz, 1H), 5.01 (dd, J ¼ 9.4 and 4.8 Hz, 1H), 5.09 (t, J ¼
9.47 Hz, 1H), 5.21 (t, J ¼ 9.3 Hz, 1H); 13C NMR (CDCl3, 50 MHz)
d 20.6, 20.68, 20.7, 28.0, 33.8, 37.0, 39.2, 61.9, 68.4, 71.2, 71.6,
72.7, 80.9, 101.7, 169.2, 169.4, 170.3, 170.7; HRMS (ESI) m/z [M +
Na]+ calcd for C25H36O10Na 519.22, found 519.01.
(Z)-Octadec-9-enyl 2,3,4,6-tetra-O-acetyl-b-D-galactopyranoside
(h). White solid; yield 82%; Rf ¼ 0.3 (EtOAc–Pet ether ¼ 1 : 2); 1H
NMR (CDCl3, 400 MHz) d 0.89 (t, 3H), 1.26 (bs, 24H), 1.5–1.67
(m, 4H), 2.01 (s, 3H), 2.03 (s, 3H), 2.05 (s, 3H), 2.09 (s, 3H), 3.44–
3.5 (m, 1H), 3.67–3.72 (m, 1H), 3.85–3.90 (m, 1H), 4.14 (dd, J ¼
9.7 and 2.4 Hz, 1H), 4.5 (d, J ¼ 8 Hz, 1H), 4.99 (dd, J ¼ 7.8 and 1.4
Hz, 1H), 5.1 (t, J ¼ 9.7 Hz, 1H), 5.21 (t, J ¼ 9.5 Hz, 1H), 5.34–5.37
(m, 1H); 13C NMR (CDCl3, 100 MHz) d 14.2, 20.1, 20.68, 21.7,
28.0, 33.8, 37.5, 39.2, 61.9, 68.4, 71.2, 71.6, 72.7, 80.9, 103.7,
169.2, 169.4, 170.5, 170.1.
ꢀ
the stretching frequency of O]S]O and the SO3 stretching
mode in the SO3H group respectively (Fig. 2).
Yang and Kou et al. determined the Lewis and Brønsted
acidity of solid acids through monitoring the shi of the IR
absorption bands at 1438 cmꢀ1 and 1540 cmꢀ1 in pyridine.28
Generally, pyridine adsorbed complexes show two major
absorption peaks at 1438 cmꢀ1 and 1548 cmꢀ1 analogous to
Lewis and Brønsted acidity, respectively. This method implies
that the presence of a band occurring at 1437 cmꢀ1 in pure
pyridine is shied nearly to 1450 cmꢀ1 which indicates that
pyridine is coordinated to Lewis acid sites. Meanwhile, the new
band which appeared near 1541 cmꢀ1 is an indication of pyr-
idinium ions resulting from the presence of Brønsted acidic
sites. In this regard, the results of the pyridine adsorption
spectra of the PV-TSEAC and PV-DSEA catalysts and pure pyri-
dine are shown in Fig. 3. It can be seen that the results for the
PV-TSEAC and PV-DSEA catalysts show the new vibration band
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Fig. 1 FT-IR analysis of PVC (A), polyvinyl bound diethanol amine (B),
and polyvinyl bound triethanol amine chloride (C).
Fig. 3 Acidity determination using IR spectroscopy based on pyridine:
pyridine (A), PV-TSEAC (B), PV-TSEAC with pyridine (C) and PV-DSEA
with pyridine (D).
shows a continuous weight loss of approximately 54% from 100
ꢁC to 300 ꢁC due to the corresponding loss of the –OSO3H groups
and the second weight loss form 300 ꢁC to 600 ꢁC corresponds to
the decomposition of polyvinyl chloride. Based on the results of
the TGA analysis, it can be conrmed that PV-TSEAC and PV-
DSEA are stable up to 100 ꢁC, therefore they can be used in
a wide variety of acid catalyzed reactions (Scheme 2).
Fig. 5a and b show the nitrogen adsorption desorption
isotherms of PV-TSEAC and PV-DSEA. The nitrogen adsorption
desorption isotherms of PV-TSEAC and PV-DSEA exhibit a well
dened type-II isotherm pattern. This shows evidence for
monolayer–multilayer adsorption up to high P/P0. Moreover, the
existence of the H5 type hysteresis loop starts from the relative
pressure P/P0 at 0.26, which indicates that macropores are
present on the outer surface of the catalyst. The pore sizes of PV-
TSEAC and PV-DSEA are shown to be 95.28 nm and 95.21 nm
respectively. Moreover, the BET surface area of PV-TSEAC and
PV-DSEA was recorded as 2 m2 gꢀ1. However; this result
suggests a homogeneous distribution of the chelating group
(–OSO3H) in the macroporous polymer framework, which
probably provides a good density of acidic sites and activity for
acidic reaction.
Fig. 2 FI-IR spectra of PV-TSEAC (A) and PV-DSEA (B) showing the
–OSO3H group vibration band.
positioned at 1541 cmꢀ1, which conrms that the prepared
solid acids are strictly Brønsted acidic. Further evidence for
their Brønsted acidity is the presence of a protonated pyridine
band for the individual N–H bending and C–C stretching modes
in both catalyst spectra (Scheme 1).
3.2. TGA and BET analysis of the solid acid catalysts
TGA thermograms of PV-TSEAC and PV-DSEA are shown in
Fig. 4. The results show that both catalysts are stable up to 100
ꢁC. In the case of the PV-TSEAC catalyst, 55% continuous weight
ꢁ
loss was recorded from 100 to 305 C. Indeed, this weight loss
corresponds to the three –OSO3H groups from PV-TSEAC.
Aerwards, the second weight loss observed from 305 ꢁC to
3.3. Catalytic activity
500 ꢁC is because of polyvinyl chloride decomposition which has Fischer glycosylation always presents a useful method for the
been previously reported in the literature.29 The TGA of PV-DSEA preparation of simple alkyl or aryl glycosides from unprotected,
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Scheme 1 Synthesis procedure of the PV-TSEAC and PV-DSEA solid acid catalysts.
unactivated reducing sugars. Moreover, the Fischer glycosyla-
tion reaction has been enhanced using heterogeneous solid
acid catalysts.7,8 We sought to explore the catalytic activity of our
prepared catalysts as probable heterogeneous Brønsted acid
catalysts for glycosylation reactions using different sugar
derivatives. In the preliminary set of reactions, unprotected D-
glucose (1 equiv.) was allowed to react with 1-octanol (5 equiv.)
under solvent and catalyst free conditions at 60 ꢁC and the
reaction progress was monitored continuously, with no reaction
during a period of 8 h (Scheme 3). Aerwards, the same reaction
was conducted in 0.3 equiv. of PV-TSEAC and PV-DSEA catalyst
under solvent free conditions at 60 ꢁC. Aer 4 h, total utilization
of the D-glucose was veried using TLC for the PV-TSEAC cata-
lyst, whereas in 6 h total utilization of the D-glucose was
observed for the PV-DSEA catalyst. The reaction mixture was
then separated from the catalysts by ltration, puried through
1
1
column chromatography and subjected to H NMR. In the H
NMR spectra it was observed that the reaction of D-glucose with
Fig. 4 Thermogravimetric analysis of the synthesized PV-TSEAC and
PV-DSEA solid acid catalysts.
Scheme 2 Structure of PV-DSEA and PV-TSEAC.
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Fig. 5 BJH cure (A) and pore size distribution cure (B) for the synthesized PV-TSEAC and PV-DSEA solid acid catalysts.
1-octanol using PV-TSEAC afforded a high (96%) yield of the a glycosylation reaction. Glycosyl trichloroacetimidates are one
glycoside product (Table 1). Meanwhile, the PV-DSEA catalyst of the most reliable, applicable classes of glycosyl donors and
provided only an 88% yield of glycoside. These results indicate are easily activated by catalytic quantities of Brønsted acid.30
that the prepared catalysts are active for the glycosylation of Therefore, we sought to investigate the glycosylation of a glyco-
glucose and comparing the PV-TSEAC and PV-DSEA catalysts, syltrichloracetimidate donor (Scheme 4) using PV-TSEAC as the
the PV-TSEAC catalyst shows the highest activity for the glyco- Brønsted acid catalyst. When a glycosyltrichloroacetimidate
sylation reaction of glucose. Therefore, we considered PV- donor (1) was used for glycosylation under solvent free condi-
TSEAC as a Brønsted acid catalyst for further catalytic studies. tions, an excellent yield of b-glycoside as the major product was
Stereochemical control of glycosylation reactions is the most obtained (Table 2). The b-glycoside product selectivity was
recent area of synthesis to be entirely resolved. In this context, probably obtained via the reaction proceeding through an SN2
we initiated an investigation to see if these Brønsted acid reaction (nucleophilic attack of –OR from the b side) which
catalysts could be used for the stereochemical control of depends on good leaving groups and solvent free reaction
conditions which has been previously reported.31 In this
fashion, we observed that glycosylation of the glycosyltri-
chloroacetimidate donor (1) with cyclohexanol in the presence
of the PV-TSEAC catalyst at 60 ꢁC led to the formation of b-
cyclohexyl glycoside in 93% yield (Table 2 entry j). Thus, the
reaction conditions were generalized through treatment of a set
of alcohols with the glycosyltrichloroacetimidate donor (1) and
very good yields of the b-alkyl glycoside were obtained. A series
of primary alcohols such as 1-pentanol and 1-decanol also
demonstrated 94% and 98% (Table 2 entries b & e) yields of the
Scheme 3 Reaction of D-glucose with 1-octanol in the presence of
catalyst at 60 ꢁC.
b-alkyl glycoside under similar conditions via the PV-TSEAC
Brønsted acidic catalyst. Moreover, from cyclic alcohols such
Table 1 Fischer glycosylations under reflux conditionsa
as 2-isopropyl-5-methyl cyclohexanol and cyclohexanol excellent
yields of 2-isopropyl-5-methyl cyclohexyl glycoside and
Entry
Heating time [h]
Reactant [%]
Yield [%]
1b
2
3
8
1
2
3
4
6
100
<22
10
<6
0
0
40
60
90
96
88
4
5
6c
0
a
All reactions were carried out using the PV-TSEAC catalyst with D-
glucose and 1-octanol under solvent free conditions at 60 ꢁC.
b
Reaction was carried out under catalyst free conditions with the
c
other conditions the same. Reaction was carried out with the PV-
Scheme 4 Reaction of a glycosyltrichloroacetimidate donor with
DSEA catalyst under the same conditions.
alcohol in the presence of the PV-TSEAC catalyst.
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Table 2 Catalytic activity of the synthesized PV-TSEAC for glycosylation from a glycosyltrichloroacetimidate donor in various alcohols
Time Yield
b
Entry Alcohol
Product
[h]
[%]
ratio
a
Propargyl alcohol
3.5
97
96
98
b
1-Pentanol
3
94
c
2-Propenol
4.2
4
97
94
98
98
99
96
d
e
2-Butene-1,4-diol
1-Decanol
4
f
2-Isopropyl-5-methyl cyclohexanol
3.5
94
96
98
90
g
1-Adamantane methanol
3
h
(Z)-Octadec-9-enol
4.3
82
88
96
90
i
Benzoic acid
4
j
Cyclohexanol
2.5
93
99
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Table 2 (Contd.)
Time Yield
b
Entry Alcohol
Product
[h]
[%]
ratio
K
Propargyl alcohol
3.5
95
94
91
(2R,4aR,6S,7R,8S,8aS)-8-Hydroxy-6-methoxy-2-phenylhexahydropyrano
[3,2-d][1,3]dioxin-7-yl benzoate
l
3.8
3.5
88
86
(2R,4aR,6S,7R,8S,8aS)-8-Hydroxy-6-methoxy-2-phenylhexahydropyrano
[3,2-d][1,3]dioxin-7-yl benzoate
m
90
cyclohexyl glycoside, respectively, were obtained (Table 2 entries further established via disaccharide synthesis. We examined
f & j). In the case of an aromatic and secondary alcohol excellent the reactivity of acceptor 4 with donor 2 and donor 1. In these
stereoselective yields of the b-glycoside products were also ob- cases, the coupling reactions occurred smoothly under mild
tained. NMR spectral analysis of the acetylated products conditions and afforded the desired b-linked disaccharides
revealed the formation of the products as b-anomers. Moreover, (Table 2 entries l & m).
the activity of the catalyst was also demonstrated using the O-
Additionally, glycosylation reactions using other mono-
benzylated glycosyl donor 2 (Scheme 3). Donor 2 in the presence saccharides such as D-mannose, D-xylose and D-galactose were
of the PV-TSEAC catalyst was tested with a propyl alcohol also allowed to react with 1-octanol under similar conditions
acceptor, which provided a high yield with 94% selectivity of the using the PV-TSEAC Brønsted acidic catalyst.33 As expected,
b-glycoside product (Table 2 entry k). On the other hand, the these reactions also proceeded smoothly and provided 95%,
noteworthy activating power of the PV-TSEAC catalyst was 88% and 91% yields of the glycoside product from D-mannose,
D-fructose and D-xylose respectively (Table 3). The acid density in
PV-TSEAC is the vital aspect for glycosylation through the
formation and breakage of the hydrogen bond interaction.32
Table 3 Catalytic activity of synthesized PV-TSEAC for glycosylation
using different sugar derivatives with cyclohexanol
The ratio of the anomeric products was determined through
1
comparing the integral values of the peaks in the H NMR and
Carbohydrate
Alcohol
Time [h]
Yield [%]
a : b
13C NMR spectra. A comparative study of the catalytic perfor-
mance of PV-TSEAC with other catalysts is shown in Table 4. In
comparative studies, the PV-TSEAC catalyst obtained a high
yield of product compared to that of the sulfamic acid and triic
acid catalysts. Under the same optimal conditions commonly
D-Glucose
D-Mannose
D-Fructose
D-Xylose
1-Octanol
1-Octanol
1-Octanol
1-Octanol
3.5
3.6
4
97
95
88
91
<25 : >75
<45 : >55
<23 : >77
<18 : >82
4
Table 4 Comparison of the catalytic activity of different catalysts for the glycosylation of D-glucose using 1-octanol at 60 ꢁ
C
Entry
Catalyst
Catalyst load
Time [h]
Yield [%]
Ref.
1
2
3
4
5
6
7
Sc(OTf)3
Sulfamic acid
TfOH
0.1 equiv.
0.2 equiv.
0.2 equiv.
1.0 equiv.
0.3 equiv.
0.3 equiv.
0.3 equiv.
24
5
5
16
4
4
55
81
77
52
97
65
78
34
35
36
37
BF3$OEt2
PV-TSEAC
Amberlyst 15
Sulfated zirconia
In this study
In this study
In this study
4
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Table 5 Comparison of the Hammett acidity functions of different
Amberlyst 15 catalysts (ꢀ4.59) are comparatively lower than that
of the PV-TSEAC catalyst (ꢀ5.18) (Table 5). Hence, we can
demonstrate that PV-TSEAC is the best heterogeneous Brønsted
acid catalyst for the glycosylation reaction (Scheme 5).
acids with the PV-TSEAC catalysta
Acid
Amax
[I] (%)
[IH+] (%)
H0 (ꢂ0.05)
Reusability is a very signicant factor in the case of solid acid
catalysts. The innovative accomplishment of a new ecofriendly,
mild, advanced and reusable catalyst for glycosylation is one of
the major ambitions of this study. To study the reusability of the
catalyst it was collected at the end of reaction, washed three
times with distilled water and reused. The catalytic activity of
the recycled PV-TSEAC catalyst was studied under similar
conditions with 1-octanol and D-glucose for ve successive
cycles (Fig. 6). Excellent yields of 1-octyl glycoside were obtained
for up to ve cycles without any signicant loss of activity.
Hence, the catalyst is capable of being recycled ve times
without any loss of catalytic activity.
Sulfonted zirconia
Sulfamic acid
HOTf
Amberlyst 15
PV-TSEAC
0.65
0.66
0.58
0.71
0.30
41.8
43.2
38.2
46.4
19.6
58.1
56.7
61.7
53.5
80.3
ꢀ4.67
ꢀ4.64
ꢀ4.73
ꢀ4.59
ꢀ5.18
a
Indicator: 2, 4 dinitroaniline (pK(I)aq ¼ ꢀ4.53).
4. Conclusion
In conclusion, the new Brønsted solid acid catalysts PV-TSEAC
and PV-DSEA were synthesized via sulfonate group ctional-
ization on a polyvinyl polymer. We characterized the sulfonate
group (–OSO3H) moiety on the polyvinyl polymer using FT-IR
spectroscopy and elemental analysis. TGA analysis also
showed the stability of the catalyst up to 100 ꢁC and the
distribution of the –OSO3H groups was proven through BET
analysis. The synthesized PV-TSEAC catalyst showed excellent
catalytic activity for glycosylation reactions with alcohol and
sugar derivatives. We also investigated the b-glycoside selec-
tivity using a glycosyltrichloracetimidate donor as a reactant.
From the results, we can conclude that the high density of
–OSO3H groups contributed to the catalytic activity of the
catalyst during glycosylation. Overall the results revealed that
the synthesized PV-TSEAC catalyst exhibited excellent activity
for glycosylation reactions.
Scheme
5 Different glycosyl donors and acceptor used for the
glycosylation of sugars using PV-TSEAC as the catalyst.
used acid catalysts such as Amberlyst 15 and sulfonated
zirconia were screened and the afforded results clearly show
that PV-TSEAC is an excellent catalyst for the glycosylation
reaction. Moreover, the Hammett acidities of these catalysts
using 2,4 dinitroaniline as an indicator in UV-spectroscopy were
compared. The Hammett acidity (Ho) of the sulfamic acid
(ꢀ4.64), HOTf (ꢀ4.73), sulfonated zirconia (ꢀ4.67) and
Acknowledgements
This work was supported by the 2015 research fund of Myongji
University in Korea.
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