Chemoselective Synthesis of Dithioacetals from Bio-aldehydes with Zeolites under Ambient and Solvent-free Conditions

Article abstract of DOI:10.1002/cctc.201601687

Dithioacetals are an important class of versatile compounds extensively applied in pharmaceuticals, separations, electrochemistry, and organic synthesis, but few heterogeneous catalytic systems are reported to be generally applicable for their synthesis f

Full text of DOI:10.1002/cctc.201601687

Accepted Article
Title: Chemoselective synthesis of dithioacetals from bio-aldehydes
with zeolites under ambient and solvent-free conditions
Authors: Saravanamurugan Shunmugavel, Hu Li, Tingting Yang,
Anders Riisager, and Song Yang
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10.1002/cctc.201601687
ChemCatChem
FULL PAPER
Chemoselective synthesis of dithioacetals from bio-aldehydes
with zeolites under ambient and solvent-free conditions
Hu Li,[a] Tingting Yang,[a] Anders Riisager,[b] Shunmugavel Saravanamurugan,[c]* Song Yang[a]*
Abstract: Dithioacetals are an important class of versatile
compounds extensively applied in pharmaceuticals, separations,
electrochemistry and organic synthesis, but few heterogeneous
catalytic systems are reported to be generally applicable for their
synthesis from a wide range of substrates. Herein, a series of
commercial and modified zeolites were demonstrated to be excellent
catalysts for thioacetalization of different thiols with carbonyl
compounds, including biomass-derived aldehydes, at room
temperature under solvent-free conditions. Thus a near quantitative
yield of dithioacetal was obtained over H-beta(19) at room
temperature with a low catalyst to substrate ratio of 1:19, and a
methodology to follow the reaction progress by ex situ UV-Vis
absorption analysis was demonstrated. Recycling experiments with
H-beta(19) in five consecutive runs resulted in slight loss of activity,
but the original activity could be fully restored after calcination at 550
ºC. Combined the reaction results and physicochemical properties of
the zeolites revealed that relatively large pores and moderate acidity
with an appropriate distribution of Brønsted/Lewis acid sites
contributed to the pronounced performance in the dithioacetal
formation.
dimethylfuran) [3]. Besides the above transformation routes
involving the participation of hydrogen and oxygen atoms,
efficient synthesis of nitrogen-containing cyclic compounds from
biomass-derived furanics has also been developed in recent
years [4]. For instance, catalytic reductive amination of furfural or
HMF over metal nanoparticles (e.g., Rh, Ru, Ir, Pt and Au)
afforded the corresponding furfuryl amines in high selectivities
(up to ~90%) [4a-c], while acidic catalysts, such as H-ZSM-5(Si/Al
= 25) and formic acid, were able to produce indoles and N-alkyl-
[4d-e]
pyridinium salts from furfural and HMF, respectively
.
However, few studies can be found on the synthesis of biofuran-
derived sulfur-containing cyclic compounds with zeolites [4f]
.
Among various organic sulfides, dithioacetals are extensively
applied in pharmaceutical and pesticidal production [5], toxicant
[8]
separation [6], electrochemistry [7], and organic syntheses
.
Dithioacetals are formed by either Brønsted or Lewis acid-
catalyzed condensation of thiols with ketones and aldehydes in
a similar way as acetals are formed with alcohols, but dithiols
have also been used to protect carbonyl groups [9]. However,
unlike alcohols thiols have the possibility to form intermolecular
disulfides via oxidative coupling [10] and drawbacks such as need
of volatile organic solvents (e.g., dichloromethane and
acetonitrile), and use of homogeneous and unrecoverable acids
or metal salts [11] have been entailed in previous studies.
Introduction
To alleviate the reliance of industrial production of chemicals
and fuels from fossil resources, a great deal of attention has
been placed on catalytic valorization of lignocellulosic biomass
derivatives to potential replacements [1]. 5-Hydroxymethylfurfural
(HMF) and furfural are two primary platform molecules, which
can be produced from acid-catalyzed dehydration of hexoses
and pentoses, respectively [2]. Through different upgrading
processes such as rehydration, oxidation, etherification and
hydrogenation, HMF and furfural can be further converted to a
variety of value-added chemicals (e.g., levulinic acid, 2,5-
furandicarboxylic acid and maleic anhydride) and biofuel
additives (e.g., γ-valerolactone, 5-ethoxymethylfurfural and 2,5-
Common heterogeneous acid catalysts such as H3PW12O40/SiO2,
Montmorillonite K-10 clay, and Amberlyst-15 are easy to
separate and reuse, but their applicability is often limited for
[12]
different substrates
. In addition, thioacetals are quite
sensitive to acidic sources due to the occurrence of reversible
reactions, limiting the efficacy of their preparation. Developing
alternative and efficient solid catalysts for chemoselective
synthesis of dithioacetals through thioacetalization of carbonyl
compounds
- especially biomass-derived carboxides - is
therefore desirable. Zeolites are thermally stable, microporous
crystalline aluminosilicates where acidity and regular pore
[13]
architecture can be controlled by varying the Si/Al ratio
.
Zeolites have been demonstrated to be versatile catalysts for a
wide range of organic reactions in both the petrochemical
industry and in biomass refinery in the past decades, combining
excellent catalytic performance with facile recovery and reuse [14]
[a]
Dr. H. Li, T. Yang, Prof. S. Yang
State-Local Joint Engineering Lab for Comprehensive Utilization of
Biomass, State Key Laboratory Breeding Base of Green Pesticide
and Agricultural Bioengineering (Ministry of Education), Center for
R&D of Fine Chemicals, Guizhou University
Guiyang, Guizhou 550025, China
.
In the present study, a variety of commercially available zeolites,
including Y, beta, mordenite and ZSM-5, have been exploredas
catalysts for thioacetalization of biomass-derived carboxides
with different alkyl and aromatic thiols to the corresponding
dithioacetals under mild reaction conditions. H-beta(19) was
further modified by calcination at high temperature, treatment
with ammonium hydroxideor co-used with a neutral ionic liquid to
investigate the role of acidity and pore size of the zeolite in the
reaction.
E-mail: jhzx.msm@gmail.com
Prof. A. Riisager
Centre for Catalysis and Sustainable Chemistry, Department of
Chemistry, Technical University of Denmark
DK-2800 Kgs. Lyngby, Denmark
Dr. S. Saravanamurugan
Center of Innovative and Applied Bioprocessing (CIAB)
Mohali 160 071, Punjab, India
[b]
[c]
E-mail: saravana@ciab.res.in
Supporting information for this article is given via a link at the end of
the document.
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10.1002/cctc.201601687
ChemCatChem
FULL PAPER
Results and Discussion
thioacetalization of furfural (8% yield, TOF of 0.2 h-1; entry 5),
indicating occurrence of mass transfer hindrance due to its
relatively narrower pore size (~5.5 Å) than furfural (ca. 5.6 Å)
and ethyl-2-mercaptoacetate (ca. 5.8 Å) [16]. Compared to H-
Y(30), H-mordenite(10) possessed more acidity but gave a
relatively lower dithioacetal yield of 69% and TOF of 1.2 h-1
(entry 6), indicating that a higher molar ratio of B/L acid sites and
smaller crystal size (Table S2) were more favorable for
dithioacetal formation. Likewise, the catalytic results of beta
In
a
sustainable transformation approach, furfural was
predominantly used as a crucial platform chemicalfor producing
C4 and C5 compounds [15]. In this context, the selective
thioacetalization of furfural with ethyl-2-mercaptoacetate to
furfuryl dithioacetal was conducted at room temperature (23 ºC)
under solvent-free conditions. The results obtained with various
zeolites for the reaction are shown in Table 1. It can be seen
that no significant amount of furfural was converted and
dithioacetal formed in the absence of a catalyst (entry 1).
zeolites
H-beta(12.5),
H-beta(19)
and
H-beta
(150)
demonstrated a concerted role of pore/crystal size, total acidity,
and B/L acid ratio for the thioacetalization (entries 7-9; Figures
S1-S3), wherein H-beta(19) having superior activity with respect
to product yield (98%) and selectivity (99%) seems to be a better
candidate for further experimental optimization. It should be
noted that the mass balance of carbon and sulfur is close to
100%, with hemiacetals (1-12%) and disulfides (1-9%) via
oxidative coupling of thiols as major byproducts in all reactions
performed with zeolites (Table 1).
Intriguingly,
Y
type zeolites effectively catalyzed the
transformation of furfural to dithioacetal with moderate to
excellent yields up to 95% (entries 2-4). It is worth mentioning
that H-Y(2.6) despite possessing a higher acidity (2.1 mmol/g,
Table S1) exhibited a lower catalytic performancethan the other
Y zeolites, yielding 51% of dithioacetal with a TOF of 0.8 h-1,
which can be ascribed to its lower Brønsted to Lewis (B/L) acid
ratio of 1.4 and the relatively high crystal size (ca. 162 nm; Table
S2). A very poor activity was found with H-ZSM-5(15) for
Table 1. Catalytic thioacetalization of furfural with ethyl 2-mercaptoacetate over different zeolites[a]
Total acidity
(mmol/g)[b]
-
Furfural conv.
Dithioacetal
yield/[selec.] (%)
1/[33]
TOF
(h-1)[d]
-
Disulfide yield /
[selec.](%)[e]
<0.1/[>99]
Entry
Catalyst
B/L ratio[c]
(%)
3
1
2
3
4
5
-
-
H-Y(2.6)
2.1
1.4
0.9
1.2
1.4
2.3
2.9
0.2
63
99
90
18
51/[81]
95/[96]
83/[92]
8/[44]
0.8
2.3
3.1
0.2
1.3/[97]
0.8/[99]
1.0/[99]
8.9/[95]
H-USY(6)
H-USY(30)
H-ZSM-5(15)
6
7
8
9
H-mordenite (10)
H-beta(12.5)
H-beta(19)
1.9
1.3
1.5
0.5
0.3
2.7
2.1
0.2
77
97
99
48
69/[90]
95/[98]
98/[99]
40/[83]
1.2
2.4
2.2
1.9
5.6/[97]
1.6/[>99]
1.3/[>99]
4.8/[98]
H-beta(150)
10[f]
H-beta(19)-700
0.8
1.0
74
68/[92]
2.8
5.9/[>99]
11[g]
12[h]
13
H-beta(19)-NH3
H-beta(19)
-
-
-
-
-
93
86
97
87/[94]
80[93]
89/[92]
-
-
2.1/[>99]
0.6/[99]
0.3/[98]
Amberlyst-15
4.7
0.6
[a] Reaction conditions: 1 mmol furfural, 2.2 mmol ethyl 2-mercaptoacetate, 50 mg catalyst, 6 h, 23 C. [b] Total content of acid sites was determined by NH3-
TPD. [c] The molar ratio of Brønsted/Lewis acid sites was determined by pyridine-adsorbed FT-IR. [d] Turnover frequency TOF = (mole of dithioacetal) /
[(catalyst amount × total acidity) × time]. [e] Disulfide yield and selectivity were obtained by excluding the mole of ethyl-2-mercaptoacetate reacted with furfural.
[f] Prepared by calcination of H-beta(19) at 700 ºC for 3 h with a heating rate of 5 ºC/min. [g]Treated by aq. NH3 (0.02 M, 200 mL/g) for 1 h, washed with water,
and calcined at 350 ºC for 0.5 h. [h] 50 μL water was added prior to the reaction.
In order to examine the influence of acid type on product
formation, H-beta(19) was modified by calcination at a high
temperature of 700 ºC and by treatment with aq. NH3,
respectively. The calcination greatly increased the amount of
Lewis acid sites at the expense of Brønsted acid sites in the
catalyst, and the aq. NH3 treatment enlarged the pore diameter
but had little effect on the acid site distribution. In addition, both
catalysts obtained a reduced total acid contentby the treatments
(entries 10-11; Figure 1). For H-beta(19)-700 a slight increase in
disulfide formation and a lower dithioacetal yield compared to
the parent zeolite H-beta(19) under identical conditions can be
correlated with the content of Lewis acid sites, indicating the
dominant role of an appropriate ratio of B/L acid sites in
enhancing the selectivity toward dithioacetal. H-beta(19) treated
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10.1002/cctc.201601687
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with aq. NH3 further substantiated the predominant role of Lewis
acid sites on the yield of dithioacetal, as also previously reported
[17]. In addition, dithioacetal yield (80%) decreased when adding
water prior to the reaction over H-beta(19), suggesting that
Lewis acid sites were inhibited by water (entry 12). When
Amberlyst-15 (entry 13) - containing only Brønsted acid sites -
amount of H-beta(19) (50 mg) was used (entry 2). Trace
amounts of furfural condensation products and disulfide were
observed by subjecting the sample to GC-MS analysis. In
addition, partial adsorption of the product into the pore channel
of the zeolite with relatively high dosage could also lead to a
slight decrease in selectivity. When further reducing the catalyst
amount to 30, 15 or 5 mg, no significant decrease in the
selectivity towards dithioacetal was observed, although the
corresponding yields were significantly descended (entries 3-5).
Interestingly, comparable product yields (89-91%) could be
achieved by prolonging the reaction time to 12 or 24 h with lower
catalyst amounts. An experiment with a high concentration of
furfural (10 mmol) was also performed (entry 6), and here an
excellent yield of dithioacetal (88%) with high selectivity (91%)
was also achieved.
was applied as catalyst, a slightly lower yield of dithioacetal
[18]
(89%) compared to H-beta-19
(98%) was observed
,
demonstrating that the thioacetalization seems to take place
more smoothly with the assistance of Lewis acid sites, which is
consistent with the results reported for the acetalization of
aldehydes with methanol [19]
.
The influence of reaction time on the thioacetalization of furfural
with ethyl 2-mercaptoacetate with H-beta(19) was further studied
at room temperature under solvent-free conditions, and the
results are presented in Figure 2. The yield of dithioacetal
significantly increased as the reaction proceeded from 0.5 to 4 h,
and reached near quantitative furfural conversion after 6 h.
However, when the reaction time was extending to 10 h, a small
decline in dithioacetal yield was observed, and more of the
byproduct disulfide (4.2%) was formed at this elevated time
period. These results clearly demonstrate that dithioacetal can
be synthesized in excellent yields with H-beta(19).
Table 2. Thioacetalization of furfural with ethyl 2-mercaptoacetate using
different amounts of H-beta(19)[a]
H-beta(19)
(mg)
Time
(h)
Furfural
conv. (%)
Dithioacetal
yield (%)
Dithioacetal
selec. (%)
Entry
1
2
3
70
50
30
6
6
6
100
99
94
98
90
94
99
98
92
4
15
6/[12]
80/[96]
78/[91]
98/[95]
5
6[b]
5
12/[24]
54/[97]
97
52/[89]
88
96/[92]
91
50
20
[a] Reaction conditions: 1 mmol furfural, 2.2 mmol ethyl-2-mercaptoacetate,
23C. [b] Reaction conditions: 10 mmol furfural, 22 mmol ethyl-2-
mercaptoacetate, 23C.
Recyclability is an important parameter in heterogeneous
catalysis to evaluate long term catalyst activity. Hence, the
reusability of H-beta(19) was examined for the thioacetalization
of furfural as well. After each reaction cycle, the H-beta(19)
zeolite was separated by centrifugation, washed with
dichloromethane and methanol, and dried at 80 ºC overnight.
The amount of substrates (furfural and ethyl 2-mercaptoacetate)
was scaled with respect to the amount of recovered catalyst in
subsequent reaction cycles, and the obtained results are
compiled in Figure 3. During five consecutive reaction runs, the
yield of dithioacetal gradually decreased to 85% with an almost
constant selectivity of >97%. N2 adsorption-desorption isotherms
and pyridine-adsorbed FT-IR spectra of fresh and recovered H-
beta(19) zeolites demonstrated a small decrease in specific
surface area from 685 to 593 m2/g (Figure S4) and acidity from
1.5 to 1.2 mmol/g, which could be partially responsible for the
activity loss (Figure 4). TG analysis further substantiated
deactivation of active sites located in the H-beta(19) zeolite by
adsorption of organic species during the reaction by comparing
the weight loss of fresh and used catalyst (Figure S5).
Importantly, the catalyst activity was re-established after
calcination at 550 ºC for 3 h after the fifth run, and the
dithioacetal yield attained to 96% (Figure 3) which was almost
the same as for the fresh zeolite (98%).
Figure 1. NH3-TPD profile (A) and pyridine-adsorbed FT-IR spectra (B) of
different treated and parent H-beta(19) zeolites.
Figure 2. Influenceof reaction time on thioacetalization of furfural with ethyl-2-
mercaptoacetate over H-beta(19). Reaction conditions: 1 mmol furfural, 2.2
mmol ethyl-2-mercaptoacetate, 50 mg H-beta(19), 23C.
Table 2 illustrates the effect of H-beta(19) dosage on the
thioacetalization of furfural with ethyl-2-mercaptoacetate. Full
conversion of furfural was achieved with a relatively large
amount of H-beta(19) zeolite (70 mg) with slightly lower
selectivity towards dithioacetal (entry 1) compared to when lower
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The reaction progress of the H-beta(19) catalyzed
thioacetalization was followed by monitoring a reaction solution
diluted with methanol by ex-situ UV-Vis in the wavelength range
of 190-350 nm (Figure 5). Apparently it is seen that the substrate
peaks centered at ~275 nm (furfural) and ~210 nm (ethyl 2-
mercaptoacetate) (Figure S6) gradually disappeared with the
progression of reaction time from 0.5 to 6 h. Concurrently, the
dithioacetal product peak at 225 nm gradually increased in
intensity over the reaction time, as expected. This clearly
indicates that UV-Vis is a simple and effective technique to
monitor the reaction progress, and the approach could likely be
extended to analogues thioacetalization reactions of aldehydes.
Figure 3. Catalytic recycling study of H-beta(19) in thioacetalization of furfural
with ethyl 2-mercaptoacetate. Reaction conditions: furfural to ethyl-2-
mercaptoacetate = 1:2.2 mmol, mass ratio of furfural to H-beta(19) = 1.92:1, 6
h, 23 C.
Figure 5. Reaction progress study of thioacetalization of furfural with ethyl-2-
mercaptoacetate over H-beta(19) with UV-Vis spectrophotometry. Reaction
conditions: 1 mmol furfural, 2.2 mmol ethyl 2-mercaptoacetate, 50 mg H-beta(19),
23 ºC.
Figure 4. Pyridine-adsorbed FT-IR spectra of fresh and recovered H-beta(19).
Table 3. Catalytic thioacetalization of furfural with different thiols over H-beta(19)[a]
To examine the applicability of H-beta(19) zeolite in
thioacetalization, the substrate scope was expanded to other
thiolating agents (Table 3) and aldehydes including biomass-
derived carboxides (Table 4). Facile transformation of both
aliphatic thiols and aldehydes to the corresponding dithioacetals
took place in high yields (>90%) in 2-6 h of reaction time (Table
3, entries 1-4; Table 4, entries 1-2), while disulfides was only
formed in small amount (6-10%) via Lewis acid-catalyzed
oxidative coupling of the thiols [10]. Conversely, the aromatic
counterparts, especially mercaptobenzene (kinetic diameter: 6.2
Å), veratraldehyde (6.9 Å) and vanillin (6.2 Å) were more
reluctant to dithioacetal formation (Table 3, entries 5-8; Table 4,
entries 3-8). However, use of longer reaction time (e.g. 9-12 h)
Dkinetic
(Å)[b]
Time
(h)
Yield
(%)
Entry
Thiol
Product
1
5.8
6
98
2
3
5.4
6.0
2
6
>99
97
and enlargement of the pores in H-beta(19) by treatment with aq.
[17]
ammonia
was demonstrated to increase the dithioacetal
4
5
6
7
5.7
5.5
5.4
5.9
6
12
12
9
93
82
86
yields (Table 3, entries 7-8), most likely as a result of more easy
access and availability of the relatively steric hindered
substrates to the acidic sites in the zeolite. Alternatively, co-
addition of the ionic liquid 1-butyl-3-methylimidazolium chloride
([BMIM][Cl]) substantially increased the yields of dithioacetals
(>71%) formed by phenyl thiols and aldehydes (Table 3, entries
7 / (54)[c] 7-8; Table 4, entries 5-8), possibly by facilitating release of
/ [76][d]
protons inside the H-beta(19) zeolite [20]. Combined, these
results confirmed the necessity of having large pore size and
moderate acidity with an appropriate distribution of Brønsted and
Lewis acidic sites to achieve a pronounced yield of dithioacetal.
10 / (67)[c]
[85][d]
/
8
6.2
9
[a] Reaction conditions: 1 mmol furfural, 2.2 mmol thiol, 50 mg H-beta(19), and 23 ºC.
[b] Kinetic diameter σ was estimated from 0.84 × (Vc)1/3 or 2.44 × (Tc/pc)1/3; Vc
(cm3/mol) = critical volume, Tc (K) = critical temperature, and pc (bar) = critical
pressure.[16] [c] H-beta(19) treated with aq. NH3(0.02 M, 200 mL/g) for 1 h, followed
by washing with water and calcination at 350 ºC for 0.5 h. [d] 1-Butyl-3-
methylimidazolium chloride (100 mg) was added.
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10.1002/cctc.201601687
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Table 4. Catalytic thioacetalization of ethyl 2-mercaptoacetate with different
aldehydes over H-beta(19)[a]
Dkinetic
(Å)[b]
Time
(h)
Yield
(%)
Entry
1
Aldehyde
Product
5.7
5.6
5.6
4
4
6
93
95
98
2
3
4
5
5.9
5.9
9
9
96
Scheme 1. Plausible reaction mechanisms for catalytic thioacetalization of
furfural with zeolites containing Brønsted and Lewis acid sites
29 /
[85][c]
Conclusions
21 /
[73][c]
6
7
6.0
6.9
9
9
A series of aliphatic and aromatic dithioacetals were synthesized
in moderate to quantitative yields over commercial and modified
zeolites at room temperature (23 ºC) under solvent-free
conditions. It was demonstrated that H-beta(19) showed
superior catalytic performance to other employed zeolites in
thioacetalization of different carbonyl compounds, including
biomass-derived carboxides, to give corresponding dithioacetals
in near quantitative yields (>99%). A relatively large average
pore size and moderate total acidity with an appropriate
Brønsted/Lewis acid site ratio of the zeolite evidently played a
promotional effect for the dithioacetal formation. During
recyclability the H-beta(19) exhibited a small loss of activity
towards dithioacetal formation after five consecutive runs.
However, the parent catalytic performance of H-beta(19) to
achieve near quantitative yield of dithioacetal could be regained
by a simple calcination at 550 ºC, thus revealing the structural
integrity of the used zeolite. In summary, commercially available
zeolites are established as attractive and versatile catalysts for
synthesizing dithioacetals of interest for the chemical industry.
20 /
[75][c]
18 /
[71][c]
8
6.2
9
[a] Reaction conditions: 1 mmol aldehyde, 2.2 mmol ethyl-2-mercaptoacetate, 50 mg
H-beta(19), and 23 ºC. [b] Kinetic diameter σ was estimated from 2.44 × (Tc/pc)1/3; Tc
(K)
methylimidazolium chloride (100 mg) was added.
= critical temperature, and pc (bar) =
critical pressure.[16] [c]1-Butyl-3-
Aldehyde acetalization is normally reversible when catalysed
with strong Brønsted acids, and a great excess of alcohol
relative to aldehyde is thus used to promote the formation of the
corresponding acetal [14a]. For thioacetalization, the reaction
pathway with Brønsted acid sites alone might involve the
activation of carbonyl groups as shown in Scheme 1A. On the
other hand, Lewis acid sites could simultaneously activate both
aldehyde and thiol groups of the substrates [18b]. With respect to
the present zeolite system operated by both Brønsted and Lewis
acid sites, it is speculated that the reaction most likely proceed
through formation of a thiocarbenium ion, followed by external
addition of R-SH to give the dithioacetal (Scheme 1B). Therefore
it is proposed that the dissociation of the Lewis acid centre (i.e.
Al species) from the anion by a proton (Brønsted acid) could
stabilize the thiocarbenium ion, thus facilitating the
thioacetalization reaction in an efficient way.
Experimental Section
Catalyst preparation
All the commercially available zeolites in NH4-form used throughout the
study were supplied by Zeolyst International. The acidic zeolites were
prepared by calcination at 550 ºC in air for 6 h with a ramp of 1.2 ºC/min,
while the dealuminated zeolite H-beta(19)-700 was obtained by
calcination at 700 ºC in air for additional 6 h. To increase the pore size of
the zeolite, H-beta(19) was treated with aq. NH3 (0.02 M, 200 mL/g) for 1
h, followed by washing with water and calcination at 350 ºC for 0.5 h [17]
.
Catalyst characterization
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The number of acid sites present in the zeolites was measured by NH3
temperature-programmed desorption (TPD) using an AutoChem II 2920
pore analyzer, wherein the ammonia desorption was determined every
547-597; c) X. Zhang, K. Wilson, A. F. Lee, Chem. Rev. 2016, 116, 12328-
12368; d) R. Mariscal, P. Maireles-Torres, M. Ojeda, I. Sádaba, M. L.
Granados, Energy Environ. Sci. 2016, 9, 1144-1189; e) B. Liu, Z. Zhang,
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a heating ramp of 10 ºC/min.
Thermogravimetric (TG) analysis was conducted by use of
a
NETZSCHSTA 429 instrument under N2 atmosphere (30 mL/L) in the
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All catalytic batch experiments were performed in an Ace pressure tube
at room temperature under vigorously stirring. All reagents were obtained
from J&K Scientific Ltd. (Beijing) in analytical gradeand used as received.
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Acknowledgements
HL, TTY and SY wish to acknowledge the financial support from
the National Natural Science Foundation of China (21576059,
21666008) and the Key Technologies R&D Program of China
(2014BAD23B01). SS thanks the Department of Biotechnology
(Government of India), New Delhi, India for support.
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Keywords: zeolites • biomass • dithioacetal • value-added
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Table of Contents
FULL PAPER
Benign biorefinery route: Various
value-added dithioacetals are
H. Li, T. Yang, A. Riisager,
S.Saravanamurugan,* S. Yang*
catalytically synthesized in near
quantitative yields from solvent-free
thioacetalization of biomass-derived
aldehydes at room temperature. The
pronounced performance is obtained
with large pore zeolites having
moderate acidity with an appropriate
distribution of Brønsted/Lewis acid
sites. The robust and controllable
catalytic system shows great potential
for large-scale production of
Page No. – Page No.
Chemoselective synthesis of
dithioacetals from bio-aldehydes with
zeolites under ambient and solvent-
free conditions
dithioacetals.
This article is protected by copyright. All rights reserved.