One-pot Synthesis of Acetals by Tandem Hydroformylation-acetalization of Olefins Using Heterogeneous Supported Catalysts

Article abstract of DOI:10.1007/s10562-020-03504-5

Abstract: A green route for one?pot synthesis of acetals by tandem hydroformylation?acetalization of olefins using supported Rh?based?catalysts was developed. Experimental results demonstrated that suitable Rh loading (1 wt%) with appropriate reaction temperature (120?°C) and reaction time (8?h) were favorable for the formation of acetals, and a high acetals selectivity of 94.6% was achieved. More importantly, the selectivity to valuable linear products was enhanced in this tandem catalysis. Based on the catalytic mechanism study, highly dispersed RhO_x nanoparticles and abundant acid sites on the supports were responsible for the hydroformylation and acetalization, respectively. Graphical abstract: One-pot synthesis of acetals directly from olefins with high selectivity was achieved over heterogeneous bifunctional catalysts via tandem hydroformylation-acetalization. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-020-03504-5

Catalysis Letters
https://doi.org/10.1007/s10562-020-03504-5
One‑pot Synthesis of Acetals by Tandem
Hydroformylation‑acetalization of Olefns Using Heterogeneous
Supported Catalysts
Xiao Li1,2 · Tingting Qin1,2 · Liusha Li1,2 · Bo Wu1,2 · Tiejun Lin1 · Liangshu Zhong1,3
Received: 31 October 2020 / Accepted: 16 December 2020
© The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
A green route for one−pot synthesis of acetals by tandem hydroformylation−acetalization of olefns using supported Rh−
based catalysts was developed. Experimental results demonstrated that suitable Rh loading (1 wt%) with appropriate reaction
temperature (120 °C) and reaction time (8 h) were favorable for the formation of acetals, and a high acetals selectivity of
94.6% was achieved. More importantly, the selectivity to valuable linear products was enhanced in this tandem catalysis.
Based on the catalytic mechanism study, highly dispersed RhOx nanoparticles and abundant acid sites on the supports were
responsible for the hydroformylation and acetalization, respectively.
Graphical abstract
One-pot synthesis of acetals directly from olefns with high selectivity was achieved over heterogeneous bifunctional catalysts
via tandem hydroformylation-acetalization.
Keywords One-pot synthesis · Tandem hydroformylation-acetalization · Acetals · Heterogenous catalyst
1 Introduction
Supplementary Information The online version contains
Hydroformylation of olefins is an important industrial
supplementary material available at https://doi.org/10.1007/s1056
process for the production of versatile aldehydes. The as-
obtained aldehydes are raw chemical intermediates and
widely used to synthesize alcohols, aliphatic amines, car-
boxylic acids, acetals and other fne chemicals via various
2-020-03504-5.
* Liangshu Zhong
zhongls@sari.ac.cn
Extended author information available on the last page of the article
Vol.:(0123456789)
1 3

X. Li et al.
reactions with the active aldehyde group [1]. From an eco-
nomical and environmental point of view, combination of
other reactions with olefns hydroformylation to form tan-
dem catalysis process, such as hydroformylation-reduction,
hydroaminomethylation and hydroformylation-acetalization,
will provide a green and efcient route for the production of
many fne chemicals. Among the various down-stream prod-
ucts derived from aldehydes, acetals are valuable chemicals,
which can be widely applied for the synthesis of perfumes,
pharmaceuticals and agricultural chemicals [2–4]. Though
mature procedures have been developed for the synthesis of
acetals from aldehydes, strong mineral acids, such as HCl,
solid acids, Lewis acids or organic acids were always used as
catalysts in the current methodologies, which sufered from
serious drawbacks including corrosive conditions and gen-
eration of acidic waste (Scheme 1) [5–7]. With the gradu-
ally strict requirements of environmental protection, it is
urgent to develop an alternative green route for the acetals
synthesis. Tandem hydroformylation-acetalization of olefns
by bifunctional catalysts, which endows active metal sites for
olefns hydroformylation to produce aldehydes and Lewis/
Brønsted acid sites for the subsequent acetalization of alde-
hydes with alcohols to form acetals, will provide a sustain-
able and promising route for the acetals synthesis [8–12].
More importantly, one-pot synthesis of acetals directly
from olefns by tandem hydroformylation-acetalization will
greatly suppress the byproduct formation and simplify the
operation process compared with the traditional routes [13].
The application of tandem hydroformylation-acetalization
catalyst mainly focused on the optimization of homogene-
ous Rh-based catalysts [1, 8, 14–16]. At early stage, the
catalysts were prepared by simply physical mixing transi-
tion metal complexes and Lewis/Brønsted acid [17–19].
However, this method sufered from serious drawback as
the acidity of phosphonium would be quenched once the
Lewis basic phosphines was added. With the improvement
of ligands for homogeneous Rh-based catalysts, bifunctional
ligands containing phosphino-fragments and Lewis acidic
moieties (such as phosphonium) were developed. For exam-
ple, Liu and coworkers had successfully synthesized some
bifunctional phosphines ligands simultaneously containing
phosphino fragments and phosphonium fragments for Rh-
based catalysts [20–22]. The yield of acetals varied in the
percentage of 45–89% when diferent ligands were used.
Except Rh-based catalysts, ruthenium complexes containing
chloride, pyridine, phosphine and CO ligands developed by
Norinder et al. also showed a satisfactory yield of undecanal
dimethylacetal (65%) for 1-decene as substrate [23, 24]. The
aforementioned homogeneous catalysts consisting of bifunc-
tional ligands have achieved superior catalytic activity and
selectivity towards the desired products. However, separa-
tion and recycle of the expensive homogeneous catalysts are
still in the development stage.
In order to overcome the disadvantages of homogene-
ous catalysis, biphasic catalytic system and heterogeneous
catalysts have been developed for various catalytic reac-
tions. Karakhanov et al. used water-soluble trisodium salt
of tris(sulfonatophenyl)phosphine as a ligand of Rh-based
catalysts for oct-1-ene hydroformylation in the presence of
polyols. The selected ligand not only ensured the excellent
selectivity to targeted acetals but also favored the easy sepa-
ration of products from the reaction mixture [25, 26]. Jin
et al. also synthesized a Brønsted acid–Rh bifunctional cata-
lyst for the tandem hydroformylation-acetalization of ole-
fns in ionic liquid-alcohol systems and the catalytic system
showed excellent efciency and durability [17]. However,
the ligands for catalysts in biphasic conditions may increase
the cost. Heterogeneous catalysts with the merits of easy
separation and cost efectiveness were potential choices and
attracted lots of attention. Gorbunov et al. used a catalyst
system including rhodium complex, phosphine ligand, and
cation-exchange resins for hydroformylation-acetalization
of 1-octene in the presence of ethylene glycol and glycerol.
Though the cation-exchange resins can be easily separated,
the separation of homogeneous ligand from the reaction
mixture was still difcult [27]. Ali et al. prepared MCM-
41 supported Rh-based catalysts for the hydroformylation-
acetalization of aryl olefn [13]. However, additives such
as heteropolyacids, phosphite or phosphine ligands, were
essential. As far as hydroformylation was concerned, Lang
et al. found that the ZnO nanowires supported single-atom
Rh catalysts demonstrated similar efficiency as that of
homogeneous Wilkinson’s catalyst and can be reused for
four times without an obvious decline in activity [28]. Wang
et al. also developed Rh1/CoO catalysts with remarkable
activity and selectivity towards propene hydroformylation
[29]. Early published reviews also summarized the strategies
×
×
multiple steps
acidic conditions
× complicated separation and purification processes
atomic economy
easy separation
short process
green
Scheme 1 Comparison of the traditional route and the method pre-
sent herein for the production of acetals from olefns
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One‑pot Synthesis of Acetals by Tandem Hydroformylation‑acetalization of Olefns Using…
for the heterogenization of traditionally homogenous cata-
lysts for hydroformylation [30, 31]. However, to the best of
our knowledge, few eforts have been done to the develop-
ment of heterogeneous catalysts for the tandem hydrofor-
mylation-acetalization of olefns.
phases of samples were identifed by comparing the obtained
patterns with JCPDS standard fles.
Nitrogen adsorption measurements were performed on
a Micromeritics TriStar 3020 instrument. Approximate
50 mg samples were frstly degassed at 200 °C in vacuum
for 6 h then transferred to the analysis station for the adsorp-
tion–desorption at −196 °C. The specifc surface area was
calculated using the Brunauer–Emmett–Teller (BET) equa-
tion. The total pore volume and average pore size were deter-
mined by the Barrett–Joyner–Halenda (BJH) method.
The loading of Rh elements was measured on the induc-
tively coupled plasma optical emission spectrometer (ICP-
OES, Optima 8000, Perkins Elmer) after the catalysts were
dissolved according to the standard in-house procedures.
X-ray photoelectron spectroscopy (XPS) measurements
for the catalysts were carried out on a Thermo Scientifc
K-Alpha spectrometer using the Al Kα (hν=1486 eV) radia-
tion. The binding energy of Rh 3d photoelectron peaks were
corrected based on the binding energy of the C 1 s neutral
carbon peak at 284.8 eV.
Herein, we developed various supported Rh-based cata-
lysts for the hydroformylation-acetalization of olefns under
mild condition. The acetals selectivity over 1Rh/SiO2 cata-
lyst could be up to 94.6%, which was comparable with the
results of homogeneous catalysts [4, 32]. The efects of Rh
loading, reaction temperature and reaction time on catalytic
performance were studied in detail. Moreover, the scope of
olefn or alcohol substrates and catalytic mechanism were
also investigated.
2 Experimental
2.1 Materials and Reagents
Al2O3 and TiO2 supports were purchased from Sasol
Chemicals (Shanghai) Co. LTD. and ACROS ORDANIC,
respectively. SiO2 support was bought from Shanghai
Aladdin Biochemical Technology Co. LTD. RhCl3·xH2O
(35.0–42.0%), methanol (99.5%), ethyl alcohol (99.5%),
and toluene (99.5%) were obtained from Sinopharm Chemi-
cal Reagent Co. LTD. 1-hexene (99.5%), 1-octene (97%),
1-decene (95%), styrene (95%) and heptanal (97%) were
bought from Shanghai Aladdin Biochemical Technology
Co. LTD. All reagents were used as received without any
further pretreatments.
Temperature-programmed reduction (TPR) experiments
were conducted using a Micromeritics Autochem-II 2920
instrument equipped with a thermal conductivity detector
(TCD) and a MKS Cirrus 2 mass spectrometer. The catalysts
were pretreated under a helium fow at 200 °C for 2 h. Once
the TCD signals became stable, the gas stream was switched
to 5% (v/v) H2/Ar, and the temperature was then increased
from 50 °C to 800 °C at a rate of 10 °C per minute.
NH3-TPD measurements were carried out to study the
surface acidity. Typically, about 50 mg samples were pre-
treated at 200 °C for 30 min and cooled to 50 °C in a He
fow. Then, NH3 (30 mL/min, 60 min) fow was provided
for adsorption saturation. After purging with He for 2 h, the
temperature was raised from 50 °C to 700 °C at a ramp of
10 °C/min.
2.2 Catalyst Preparation
The supported Rh-based catalysts were prepared by tra-
ditional wet impregnation method. Typically, appropriate
RhCl3•xH2O was frstly dissolved in deionized water to
form uniform solution by continuous stirring and then SiO2
support was added into the solution. After 4 h continuous
stirring, excess water was evaporated by water bath at 80 °C.
The as-obtained powders were frstly dried at 120 °C over-
night, then calcined at 350 °C for 4 h. The samples with
diferent Rh loading were denoted as xRh/SiO2 (x=0.5, 1
and 2 in wt%). For comparison, TiO2 and Al2O3 supports
were also used, and 1Rh/TiO2 and 1Rh/Al2O3 catalysts were
prepared according to the same procedure.
For transmission electron microscopy (TEM) measure-
ments, the samples were analyzed on a JEOL-JEM 2011
electron microscope with 200 kV accelerating voltage. The
samples were prepared by dispersing the catalyst powder
in ethanol followed by ultrasonication. One droplet of the
suspension was dropped onto carbon-coated copper grids
for measurements.
2.4 Catalytic Test
The tandem hydroformylation-acetalization of olefns was
carried out in a Tefon-line steel batch reactor (50 mL).
Typically, 0.1 g catalysts, 6 mL of methanol and 0.7 mL of
1-hexene were added into the reactors in sequence. Then
the reactor was sealed and flled with 4 MPa syngas (CO/
H2 =1:1, v/v) after the reactor was purged with syngas for
fve times. The reaction were conducted at 60~140 °C with
desired time. After the reaction fnished, the residual syngas
2.3 Characterization
X-ray difraction (XRD) patterns were obtained on a Rigaku
Ultima IV X-ray powder difractometer using Cu Kα radia-
tion with the wavelength of 1.54056 Å at 40 kV and 40 mA
with a scanning angle (2θ) ranging from 20 ° to 90 °. The
1 3

X. Li et al.
was released and the liquid was withdrawn for analysis. The
products were qualitatively analyzed by the gas chromatog-
raphy-mass spectrometry (GC–MS) equipped with an HP-
5MS column (30 m length, 0.25 mm in diameter). The prod-
uct selectivity was determined by the gas chromatography
(GC) equipped with a fame ionization detector (FID) with
dodecane as internal standard.
of weak acidic sites. The broad peaks located at 280–680 °C
can be attributed to the medium-to-strong acidic sites. It
was obvious that the concentration of surface acidic sites
decreased with following order of SiO2 >Al2O3 >TiO2.
Then a series of characterizations were carried out to
study various supported Rh-based catalysts. The composi-
tion and structural properties of the as-prepared catalysts
were summarized in Table S1. According to the ICP-AES
results, the actual loading of Rh on these supports was basi-
cally close to the theoretical value. The specifc surface areas
of SiO2 supported catalysts were all close to 460 m2/g. With
the increase of Rh loading from 0.5 wt% to 2 wt%, the spe-
cifc surface area slightly decreased. Compared with the
SiO2 supported catalysts, 1Rh/Al2O3 and 1Rh/TiO2 catalysts
exhibited smaller specifc surface area with 189.4 m2/g and
199.1 m2/g, respectively. Nitrogen absorption–desorption
isotherms of these catalysts were shown in Fig. S1. All the
samples displayed type V isotherms with a steep N2 hyster-
esis, indicating non-uniform mesoporous structure.
2.5 Reusability and Sheldon’s Hot Filtration
Recycling experiments: After the reaction was completed
under typical condition, the used catalysts was collected by
centrifugation and washed with water and ethanol to remove
the adsorbed reactant/products. Then the obtained sample
was dried at 80 °C for 5 h to regain 1Rh/SiO2 catalyst.
Sheldon’s hot fltration: The hot fltration test was con-
ducted referred to the precious reports. The evaluation was
done following the regular steps for the catalytic test except
with shorter reaction time (2 h). After the reactor was cooled
to room temperature, the residual syngas was released. Then
the catalyst was separated from the reaction mixture via a
syringe flter. Afterwards, the reaction mixture was stirred
at the catalytic conditions as usual for further catalytic
evaluation.
According to the XRD patterns in the Fig. 1b, no obvi-
ous difraction peaks belonged to Rh species were observed
for all catalysts, indicating that the Rh species were highly
dispersed on these supports. As shown in the Fig. S2, TEM
measurements also confrmed that the RhOx nanoparticles
were highly dispersed on the SiO2 support. The average size
of RhOx nanoparticles increased from 1.6 nm to 2.6 nm
when the Rh loading amount increased from 0.5 wt% to
2 wt%. As for 1Rh/Al2O3 and 1Rh/TiO2 catalysts, RhOx
nanoparticles were also highly dispersed though the specifc
surface areas of these two supports were smaller than SiO2
support (Fig. S3).
3 Results and Discussion
3.1 Catalyst Characterization
Before impregnation, the surface acidic sites of SiO2, Al2O3
and TiO2 supports were measured by NH3-TPD. As dis-
played in the Fig. 1a, SiO2 and Al2O3 supports have two
obvious NH3 desorption peaks while TiO2 support only
showed one weak peak at low temperature. The peaks
located at about 100 °C can be assigned to the contributions
XPS measurements were conducted to further determine
the valence states of Rh species. As shown in Fig. S4, the
Rh binding energies of the as-prepared catalysts were all
at about 309 eV, suggesting the Rh species were mainly in
oxidized state after calcination. Slight diferences for the
Fig. 1 NH3-TPD (a) of the supports and XRD patterns (b) of the as-prepared catalysts
1 3

One‑pot Synthesis of Acetals by Tandem Hydroformylation‑acetalization of Olefns Using…
binding energies were attributed to the diferent interaction
between oxide supports and Rh species. H2-TPR results (Fig.
S5) revealed that there was an obvious peak located at 80 °C
for 1Rh/SiO2 catalyst, indicating that the RhOx nanoparti-
cles on SiO2 support can be sufciently reduced to metallic
Rh at reaction temperature [33]. In contrast, the peaks of
1Rh/Al2O3 and 1Rh/TiO2 catalysts were located at higher
temperature, suggesting stronger metal-support interaction.
and 2Rh/SiO2 catalysts. For instance, the selectivities to
2-ethyl-1-pentanol and heptanal over 0.5Rh/SiO2 catalysts
were 12.4% and 10.7%. As for the 2Rh/SiO2 catalyst, a high
selectivity of 8.6% for aldehydes was obtained, which was
only 3.0% for 1Rh/SiO2 catalyst. For comparison, the cata-
lytic performances of Al2O3 and TiO2 supported catalysts
were also investigated as displayed in the Table 1, entries
5–6. Though all the catalysts were active for this tandem
hydroformylation-acetalization of olefns, diferent products
distributions were obtained. The acetals selectivity over
1Rh/Al2O3 and 1Rh/TiO2 catalysts were 81.2% and 83.4%
respectively, which were much lower than that of 1Rh/SiO2
catalyst (94.6%). For 1Rh/Al2O3 catalyst, the byproducts
included hexane (0.6%), 2-ethyl-1-pentanol (3.6%) and hep-
tanal (14.6%). For 1Rh/TiO2 catalyst, the selectivities for
hexane, 2-ethyl-1-pentanol and heptanal were 1.2%, 7.0%
and 8.4%, respectively. However, for 1Rh/SiO2 catalyst, the
selectivities to various byproducts were extremely low with
1.4% for hexane, 1.0% for 2-ethyl-1-pentanol and 3.0% for
heptanal. These results suggested that 1Rh/SiO2 catalyst was
the most efcient for the one-pot synthesis of acetals by tan-
dem hydroformylation-acetalization of olefns.
3.2 Hydroformylation‑acetalization of 1‑Hexene
Catalytic performances of the as-prepared catalysts for tan-
dem hydroformylation-acetalization of 1-hexene were sum-
marized in Table 1. The reactions were carried out at 120 °C
and 4 MPa syngas (CO/H2 = 1, v/v). The chromatograms
and mass spectrums of the main products were given in the
Fig. S6. No aldehydes or acetals were found in the fnal
products when the reaction was carried out at the absence
of heterogeneous catalyst (Table 1, entry 1) (Fig. S7). In
addition, the hot fltration results showed that no increase
of the acetals was observed in the fltrate, suggesting that
the tandem hydroformylation-acetalization of olefns was
heterogeneously catalyzed. We frstly studied the catalytic
performances of SiO2 supported catalysts with diferent Rh
loading. All the catalysts exhibited complete olefns conver-
sion (>99%). The acetals selectivity over 1Rh/SiO2 catalyst
(94.6%) was higher than that over 0.5Rh/SiO2 (74.6%) and
2Rh/SiO2 (86.8%) catalysts (Table 2, entries 2–4). Except
acetals, some byproducts including hexane, heptanal and
2-ethyl-1-pentanol were also generated (Fig. S8). An obvi-
ous increase of byproducts was found over 0.5Rh/SiO2
To gain more insights about the tandem catalysis, hydro-
formylation of 1-hexene was carried out using methylben-
zene as solvent (Table 1, entry 7). In this case, aldehydes
were the dominant products with a selectivity of 78.2%,
which was much lower than the selectivity to correspond-
ing acetals (94.6%) in tandem hydroformylation-acetaliza-
tion (Fig. S9). Moreover, the selectivity to internal olefns
(21.8%) in the hydroformylation far exceeded the selec-
tivity of all byproducts (5.4%) including hexane, heptanal
Table 1 Catalytic results of diferent catalysts for hydroformylation-acetalization of 1-hexene
Entry
Catalyst
Conversion (%)
Selectivity (%)a
L/Bd
Internal olefns
Hexane
Otherb
Heptanal
Acetals
Lc
Bc
L+B
1e
2
3
4
5
–
>99
>99
>99
>99
>99
>99
>99
100.0
–
–
12.4
1.0
2.9
3.6
7.0
–
–
10.7
3.0
8.6
14.6
8.4
–
38.2
42.0
40.8
39.5
42.0
–
–
–
74.6
94.6
86.8
81.2
83.4
–
–
0.5Rh/SiO2
1Rh/SiO2
2Rh/SiO2
1Rh/Al2O3
1Rh/TiO2
1Rh/SiO2
–
–
–
–
–
2.3
1.4
1.7
0.6
1.2
–
36.4
52.6
46.0
41.7
41.4
–
1.1
0.8
0.9
0.9
1.0
0.6
6
7f
21.8
78.2
Reaction conditions: catalyst (0.1 g), 1-hexene (0.7 mL), CH3OH (6 mL), syngas (CO/H2 =1, v/v; 4 MPa), 120 °C, 8 h
aThe selectivity is determined by the GC analysis with dodecane as internal standard
bOther refers to 2-ethyl-1-pentanol
cL and B represent the linear products and branched products, respectively
dL/B is the ratio of linear to branched products
eNo catalyst is added during the reaction
fMethylbenzene is used as solvent
1 3

X. Li et al.
Table 2 Scope of olefns
and alcohols in the tandem
hydroformylation–acetalization
reaction
Entry Olefns
Alcohols Olefn
Selectivity (%)a
L/Bc
conversion
Alkanes Others Aldehydes
Acetals
Lb Bb
(%)
L+B
>99
1d
2
21.2
>99
–
–
–
–
–
–
–
3.2
1.5
34.8 60.5 95.3 0.6
27.8 67.2 95.0 0.4
45.8 41.5 87.3 1.1
3
4
>99
>99
5.0
–
–
–
–
12.7
5e
>99
5.1
4.1
13.5
37.1 40.2 77.3 0.9
Reaction conditions: catalyst (0.1 g), olefn (0.7 mL), alcohol (6 mL), syngas (CO/H2 =1, v/v; 4 MPa),
120 °C, 10 h
aThe products selectivity is determined by the GC analysis with dodecane as internal standard
bL and B represent the linear products and branched products, respectively
cL/B is the ratio of linear to branched products
dReaction conditions: ethylene (1.2 MPa), syngas (CO/H2 =1, v/v; 2.4 MPa), 120 °C, 4 h
e Reaction temperature: 100 °C
and other byproducts in the tandem catalysis. In addition,
the ratio of linear products to branched products (0.6) in
hydroformylation was lower than that (0.8) in the tandem
hydroformylation-acetalization. These experimental results
strongly indicated that tandem hydroformylation-acetal-
ization process not only greatly promoted the conversion
of 1-hexene, but also enhanced the selectivity to valuable
linear product. The aldehydes produced from the frst step
hydroformylation can be further in-situ converted to the cor-
responding acetals. The continuous removal of aldehydes
as intermediates can drive the hydroformylation reaction
[34, 35]. In addition, steric hindrance was weaker for linear
aldehydes than that of branched aldehydes. As a result, the
acetalization of linear aldehydes with methanol was faster
than the acetalization of branched aldehydes, which led to
the higher selectivity to linear acetals.
3.3 Efects of Reaction Temperature and Reaction
Time
To systematically study the efects of reaction tempera-
ture, the tandem reactions were carried out at 60 °C, 80 °C,
100 °C, 120 °C and 140 °C, respectively. As shown in
Fig. 2a, the highest selectivity towards acetals (94.6%) was
obtained when the reaction was conducted at 120 °C. The
acetals selectivity gradually increased from 87.6% to 94.6%
as the reaction temperature increased from 60 °C to 120 °C.
It was worthy to note that the internal olefns, which were
Fig. 2 Hydroformylation-acetalization of 1-hexene over 1Rh/SiO2
catalyst at diferent reaction temperature (60 °C, 80 °C, 100 °C,
120 °C and 140 °C) for 8 h (a) and with diferent reaction time (1 h,
2 h, 4 h, 8 h) at 120 °C (b). Reaction conditions: catalysts (0.1 g),
1-hexene (0.7 mL), CH3OH (6 mL), syngas (CO/H2 =1, v/v; 4 MPa)
1 3

One‑pot Synthesis of Acetals by Tandem Hydroformylation‑acetalization of Olefns Using…
less active than terminal olefns, can be converted to the cor-
responding aldehydes or acetals with the temperature rais-
ing. When the reaction was carried out at 60 °C, the selec-
tivity to internal olefns can be up to about 10%. However,
almost no internal olefns were found in the fnal products
when the reaction temperature exceeded 80 °C. When the
reaction temperature was further increased from 120 °C to
140 °C, the acetals selectivity sharply declined to 61.4%
accompanied with the rapid increase of 2-ethyl-1-pentanol.
This was caused by the enhanced hydrogenation of 2-ethyl-
1-pentanal at high reaction temperature. These results indi-
cated that appropriate reaction temperature was critical to
ensure the high acetals selectivity. In addition, the catalytic
performances of 1Rh/SiO2 catalyst with time-on-stream
were also tested. As shown in Fig. 2b, the acetals selectivity
increased sharply at the frst four hours and then gradually
stabilized as the reaction time increasing. By contrast, the
selectivity to internal olefns showed completely opposite
trends. This phenomenon indicated that the internal olefns
can be further converted into acetals and appropriate extend-
ing reaction time was benefcial for the formation of acetals.
of acetals gradually declined while the yield of aldehydes and
internal olefns increased with the recycling. The spent cata-
lyst was carefully studied with diferent characterization tech-
niques. The acidity of spent catalyst was similar to the fresh
catalyst according to the results of NH3-TPD (Fig. S16). Based
on TEM characterization, the average size of RhOx nanopar-
ticles on the spent catalyst was larger than that on the fresh
catalyst (Fig. S17). Furthermore, ICP-OES characterization
showed that the Rh content on SiO2 support decreased from
0.95 wt% to 0.52 wt% after three times uses (Table S2). The
leaching Rh element was also found in the solution (Table S3).
Based on these results, it was reasonable to conclude that the
deactivation of catalyst was attributed to the growth of RhOx
nanoparticles and Rh leaching though formation of homoge-
neous Rh-carbonyls species. In addition, the formed homo-
geneous Rh-carbonyls species may also participate into the
hydroformylation step. For the further study, more eforts are
needed to improve the stability of 1Rh/SiO2 catalyst for tan-
dem hydroformylation-acetalization of olefns.
In this study, heterogeneous Rh-based catalysts were
successfully applied for the one-pot synthesis of acetals by
tandem hydroformylation-acetalization of olefns. Com-
pared with the traditional route which consisted of multiple
steps, high atomic economy and easy separation of catalyst/
products were the most obvious advantages of this tandem
catalytic system. For this tandem process, bifunctional
catalyst including diferent active sites was needed. In our
study, Rh was frstly chosen due to its excellent catalytic
performance for olefns hydroformylation to produce alde-
hydes. Almost 100% olefns conversion was obtained over
various supported catalysts, suggesting high hydroformyla-
tion activity of RhOx nanoparticles. As for the following
acetalization reaction, strong mineral acids, such as HCl,
solid acids, Lewis acids or organic acids were always used
[36, 37]. Several supports including SiO2, Al2O3 and TiO2
were selected in our study, and the NH3-TPD measurements
showed that there were surface acidities over all the three
supports while SiO2 supports exhibited the highest acid con-
centration among the three studied supports (Fig. 1a). The
catalytic test results indicated that SiO2 supported Rh-based
catalysts exhibited the highest acetals selectivity mainly due
to its higher acid concentration. Based on the experimen-
tal results, it is reasonable to speculate that the synergistic
efects between the active RhOx nanoparticles and the sur-
face acid sites were critical for one-pot synthesis of acetals
as shown in Scheme 2.
3.4 Investigation of the Scope of Olefns
and Alcohols Substrates
The scope of olefn and alcohol substrates for tandem hydro-
formylation-acetalization of olefns over 1Rh/SiO2 catalyst
was also examined and the results were listed in the Table 2.
A family of aliphatic and aromatic terminal olefns, includ-
ing ethylene, 1-hexene, 1-octene and styrene can be con-
verted into the corresponding acetals with high selectivity.
The mass spectrums of various acetals were given from the
Fig. S10 to Fig. S13. As for ethylene, 1,1-dimethoxypropane
was the only product. The selectivities to the correspond-
ing acetals can be up to 95% and almost no intermediate
aldehyde was left when 1-octene and 1-decene were used as
substrates (Table 2, entries 2–3). When styrene was chosen
as substrate, the selectivity to the corresponding acetals was
87.3% (Table 2, entry 4). Compared with the reported val-
ues in precious literature, higher ratio of linear to branched
acetals was obtained over 1Rh/SiO2 catalysts in the tandem
hydroformylation-acetalization of styrene (Table S4), sug-
gesting that the combination of acetalization with hydro-
formylation can enhance the selectivity to valuable linear
acetal. In addition, when methanol was replaced by ethanol,
high selectivity to acetals (77.3%) can still be achieved over
the 1Rh/SiO2 catalyst (Table 2, entry 5).
3.5 Stability and Catalytic Mechanism Discussion
4 Conclusion
From the viewpoint of practical application, the reusability
of catalyst is an important indicator. So the durability of 1Rh/
SiO2 catalyst was investigated. As shown in Fig. S14, the yield
In summary, we have demonstrated an efcient and green
route for one-pot synthesis of acetals directly from olefns
by tandem hydroformylation-acetalization of olefns over
1 3

X. Li et al.
Scheme 2 Reaction paths for
the tandem hydroformylation-
acetalization of olefns
4. Khan SR, Bhanage BM (2013) Tetrahedron Lett 54:5998
heterogeneous catalysts under mild condition. Compared
with the traditional routes, simplifed procedure with easy
catalyst/products separation can be achieved over the het-
erogeneous Rh-based catalysts. The experimental results
showed that a suitable Rh loading with appropriate reaction
temperature and reaction time was benefcial for the acetals
formation. 100% olefins conversion and a high acetals
selectivity of 94.6% can be obtained over 1Rh/SiO2 cata-
lyst under the optimal reaction conditions (120 °C and 8 h).
More importantly, the selectivity toward desired valuable
linear products was enhanced in this tandem catalysis com-
pared with the hydroformylation reaction alone. Based on
the mechanism study, highly dispersed RhOx nanoparticles
and surface acidic sites on the supports were responsible for
the hydroformylation and acetalization, respectively. Fur-
thermore, various corresponding acetals can be produced
with satisfactory yields when diferent olefns or alcohols
were used as substrates.
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Acknowledgements This work was supported by the Ministry of Sci-
ence and Technology of China (2017YFB0602202), Natural Science
Foundation of China (91945301), Key Research Program of Frontier
Sciences, CAS (Grant No. QYZDB-SSW-SLH035), and the “Transfor-
mational Technologies for Clean Energy and Demonstration”, Strategic
Priority Research Program of the Chinese Academy of Sciences (Grant
No. XDA21020600) and the Youth Innovation Promotion Association
of CAS.
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Compliance with Ethical Standards
24. Rodrigues C, Delolo FG, Norinder J, Börner A, Bogado AL,
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Conflict of interest The authors declare that they have no known com-
peting fnancial interests or personal relationships that could have ap-
peared to infuence the work reported in this paper.
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Afliations
Xiao Li1,2 · Tingting Qin1,2 · Liusha Li1,2 · Bo Wu1,2 · Tiejun Lin1 · Liangshu Zhong1,3
1
2
3
CAS Key Laboratory of Low-Carbon Conversion Science
and Engineering, Shanghai Advanced Research Institute,
Chinese Academy of Sciences, Shanghai 201203, PR China
School of Physical Science and Technology, ShanghaiTech
University, Shanghai 201203, PR China
University of the Chinese Academy of Sciences,
Beijing 100049, PR China
1 3