S.S. Poly, et al.
MolecularCatalysis479(2019)110608
The aforementioned studies demonstrate the high potential of Hβ for
the acetalization of glycerol with carbonyl compounds. However,
quantitative studies, which focus on the effects of surface properties/
acidity and substrate scope for carbonyl compounds, have not been
reported, hitherto. Such studies would help elucidate zeolite catalysis
including Hβ.
Table 1
Catalyst screening for the acetalization of glycerol (1) with 3-pentanone (2a).
Our research group has previously developed efficient hetero-
geneous catalyst systems using Hβ zeolites for ester hydrolysis [40] and
the hydration of alkynes/epoxides [41]. Furthermore, we have also
quantitatively reported how this type of catalysis is influenced by acid
site concentration and the catalyst surface hydrophobic/hydrophilic
properties based on various adsorption experiments and kinetic studies.
In this work, we investigated the glycerol acetalization efficiency of Hβ
as a function of Si/Al ratio by comparing with other heterogeneous and
homogeneous catalysts, and observed that Hβ, with relatively high Si/
Al ratio of 75 (Hβ-75), showed the highest efficiency. The substrate
scope for carbonyl compounds and the reusability of Hβ-75 were also
examined. Furthermore, the effect of hydrophobicity and acid site
concentration on the acetalization efficiency is discussed to provide
insight into the high efficiency of Hβ-75.
Entry
Catalyst
1
none
0
2
Hβ-12.5
Hβ-20
44
48
96
77
43
46
68
62
58
61
48
61
43
67
54
65
16
13
62
2
3
4
Hβ-75
5
Hβ-255
6
HZSM5-11
HZSM5-20
HZSM5-75
HZSM5-150
HY-50
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
24
25
HMOR-45
Al2O3
ZrO2
TiO2
SnO2
Nb2O5
2. Experimental
Nb2O5.nH2O
SiO2
2.1. General
CeO2
Cs2.5H0.5PW12O40
Amberlyst-15
Montmorillonite K10
H2SO4
Commercial compounds (Tokyo Chemical Industry or Kanto
Chemical Company) were used without further purification. GC–MS
(Shimadzu GCMS-QP2010) analyses were performed using an Ultra
ALLOY+-1 capillary column (Frontier Laboratories Ltd.) with N2 and
He as the carrier gases. 1H NMR analyses were performed using a JEOL-
ECX 600 spectrometer operating at 600.17 MHz.
56
25
44
28
PTSA
Sc(OTf)3
a
b
Yields of 3a were determined by 1H NMR spectroscopy.
40 wt.% aqueous solution.
2.2. Catalyst preparation
3. Results and discussion
Hβ-75 (JRC-Z-HB150, originally supplied from Clariant), Hβ-12.5
(JRC-Z-HB25), HMOR-45 (JRC-Z-HM90, originally supplied from
Clariant), TiO2 (JRC-TIO-4), CeO2 (JRC-CEO-3), and amorphous SiO2-
Al2O3 (JRC-SAL-2) were provided by the Catalysis Society of Japan. Hβ-
20 (HSZ-940HOA), Hβ-255 (HSZ-980HOA), HZSM5-20 (HSZ-840HOA)
and HY-50 (HSZ-385HUA) were purchased from Tosoh Co. As-synthe-
sized Hβ-5 (HSZ-940HOA), based on a previous report [42], was sup-
plied from UniZeo Co., Ltd. HZSM5-11 was obtained by calcination of
NH4-ZSM5 having a Si/Al ratio of 11 (HSZ-820NHA, purchased from
Tosoh Co.), at 550 °C for 3 h. HZSM5-75 and HZSM5-150 were obtained
from N.E. CHEMCAT Co. Niobic acid (Nb2O5∙nH2O, HY-340) was kindly
provided by CBMM. Nb2O5 was synthesized by calcination of the niobic
acid (500 °C for 3 h). SiO2 (Q-10) was provided by Fuji Silysia Chemical
Ltd. ZrO2 and SnO2 were obtained by calcination of ZrO2∙nH2O and
H2SnO3 (Kojundo Chemical Laboratory Co., Ltd.), at 500 °C for 3 h.
Sulfonic acid-functionalized resin (Amberlyst-15) was commercially
purchased from Sigma-Aldrich.
3.1. Comparison of Hβ zeolites with various acid catalysts
Initially, the acetalization of glycerol (1) with 3-pentanone (2a) was
investigated using a wide matrix of 24 heterogeneous and homogenous
catalyst types, by refluxing in toluene for 20 h. The results are sum-
marized in Table 1. Under these conditions, the reaction does not
proceed in the absence of any catalyst (entry 1). Among the catalysts
tested, Hβ-75 afforded the highest yield (96%) of the five-membered
cyclic acetal (3a) (entry 4), without the formation of the corresponding
six-membered cyclic acetal. The Si/Al ratio of Hβ is observed to influ-
ence the 3a yield, which increased as a function of increased Si/Al ratio
from 12.5 to 75 (entries 2–4), while the use of Hβ-255 resulted in a
lower yield compared with Hβ-75 (entry 5). A similar dependency on
the Si/Al ratio was observed using a series of proton-exchanged ZSM5
(HZSM5) zeolites having Si/Al ratios between 11 and 150 (entries 6–9).
HZSM5-75 exhibited a higher yield compared with the other HZSM5
catalysts (entry 8), although HZSM5-75 was inferior to Hβ-75. The
zeolites possessing a relatively high Si/Al ratio of 75 exhibited high
catalytic performance. The performance of Hβ-75 with other hetero-
geneous acid catalysts was compared, including other proton-ex-
changed zeolites (HY-50 and HMOR-45), metal oxides (Al2O3, ZrO2,
TiO2, SnO2, Nb2O5, Nb2O5∙nH2O, SiO2, and CeO2), a heteropoly acid
(Cs2.5H0.5PW12O40), and commercially-available solid acid catalysts
(Amberlyst-15 and Montmorillonite K10). Moderate-to-good yields
(43–67%) of 3a were obtained in the presence of Al2O3, ZrO2, TiO2,
SnO2, and Nb2O5 (entries 12–16). Nb2O5∙nH2O, known as a water-tol-
erant solid acid [43], also exhibited an acceptable yield of 65% (entry
17). However, all 3a yields were lower when compared with the yield
for Hβ-75. Conversely, the yields for SiO2 and CeO2 were significantly
lower (entries 18 and 19). Cs2.5H0.5PW12O40 and montmorillonite K10
exhibited moderate activity, forming 3a in 62% and 56% yields (entries
2.3. Catalytic tests
For a typical catalytic reaction, glycerol (1 mmol) was subjected to
acetalization with aldehydes or ketones (1.5 mmol) in the presence of a
catalyst (25 mg) and toluene (1 mL). The reaction mixture was added to
a reaction tube (cylindrical Pyrex glass tube, 17 cm3), containing a
magnetic stirrer bar and placed in a heated reactor, at reflux conditions,
under a nitrogen atmosphere with stirring at 400 rpm. After completion
of the reaction, methanol (2 mL) was added and catalyst was removed
by filtration. The solvent was evaporated from the reaction mixture,
and the acetal/ketal product yield and glycerol conversion in the crude
mixture determined by 1H NMR analysis (JEOL-ECX 600 spectrometer
operating at 600.17 MHz, solvent CD3OD) using mesitylene as an in-
ternal standard.
2