RhCl(TPPTS)3 encapsulated into the hexagonal mesoporous silica as an efficient heterogeneous catalyst for hydroformylation of vinyl esters

Article abstract of DOI:10.1016/j.apcata.2011.09.028

RhCl(TPPTS)₃ (TPPTS = m-trisulphonato triphenyl phosphine) was in situ encapsulated into the mesopores of hexagonal mesoporous silica (HMS) by in situ method. The catalyst was characterized by P-XRD, ³¹P-CPMAS NMR, FT-IR, N₂ adsorption, TGA, TEM and ICP techniques. These characterization confirmed the encapsulation and heterogenization of RhCl(TPPTS)₃. The synthesized heterogeneous catalyst evaluated for hydroformylation of vinyl esters gave 100% conversion and high selectivity to iso-aldehyde. Vinyl acetate was subjected as a representative vinyl ester for detailed investigations. The performance of the catalyst in terms of conversion and selectivity depended on the studied parameters: amount of the catalyst, substrate, partial pressure of CO and H₂, and temperature. Recyclability aspects of the heterogenized catalyst are investigated.

Full text of DOI:10.1016/j.apcata.2011.09.028

Applied Catalysis A: General 409–410 (2011) 99–105
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Applied Catalysis A: General
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RhCl(TPPTS)3 encapsulated into the hexagonal mesoporous silica as an efficient
heterogeneous catalyst for hydroformylation of vinyl esters
N. Sudheesh, Amit K. Chaturvedi, Ram S. Shukla∗
Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research (CSIR), G. B. Marg,
Bhavnagar 364 021, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 January 2011
Received in revised form 26 August 2011
Accepted 25 September 2011
Available online 1 October 2011
RhCl(TPPTS)3 (TPPTS = m-trisulphonato triphenyl phosphine) was in situ encapsulated into the meso-
pores of hexagonal mesoporous silica (HMS) by in situ method. The catalyst was characterized by P-XRD,
31P-CPMAS NMR, FT-IR, N2 adsorption, TGA, TEM and ICP techniques. These characterization confirmed
the encapsulation and heterogenization of RhCl(TPPTS)3. The synthesized heterogeneous catalyst evalu-
ated for hydroformylation of vinyl esters gave 100% conversion and high selectivity to iso-aldehyde. Vinyl
acetate was subjected as a representative vinyl ester for detailed investigations. The performance of the
catalyst in terms of conversion and selectivity depended on the studied parameters: amount of the cata-
lyst, substrate, partial pressure of CO and H2, and temperature. Recyclability aspects of the heterogenized
catalyst are investigated.
Keywords:
Hexagonal mesoporous silica
Hydroformylation
Vinyl esters
© 2011 Elsevier B.V. All rights reserved.
Recycling
Heterogeneous catalyst
1. Introduction
hydroformylation was done in homogeneous conditions [9–12].
Hydroformylation of vinyl esters using heterogeneous catalysts are
Hydroformylation is one of the most important methods for the
functionalization of olefinic double bond [1]. The most important
application of hydroformylation is in the conversion of propanal
to butanal, for the manufacture of 2-ethyl hexanol [2]. However,
a number of potential applications are also being developed for
the synthesis of substituted or functionalized aldehydes using
hydroformylation [3–5]. Hydroformylation of vinyl esters is such
a reaction which is important because the route is versatile for
the synthesis of commercially important products [4,6]. The prod-
uct 2- and 3-acetoxypropanal obtained from the hydroformylation
of vinyl acetate is the intermediate in the production of 1,2-
and 1,3-propane diols. The application of 1,2-propane diol is as
a heat transfer fluid and anti-freezing agents in the pharmaceu-
tical and food industries, and also as solvents in many chemical
industries. Whereas 1,3-propane diol is a valuable chemical for
the polyurethane, adhesive and resin industry. Lactic acid, a food
ingredient, can be synthesized by the oxidation followed by hydrol-
ysis of 2-acetoxypropanal obtained from hydroformylation of vinyl
acetate [7]. Also the asymmetric hydroformylation of vinyl acetate
can be used to obtain chiral 2-acetoxypropanal which is used in
the synthesis of threonine amino acid [8]. Most of the vinyl acetate
scanty [13–15] and need to pay attention. Hence development of
a heterogeneous catalyst system for the hydroformylation of vinyl
esters has a potential concern to overcome the drawbacks of the
homogeneous counterpart.
Previously we have reported hydroformylation of olefins cat-
alyzed by in situ encapsulated HRh(CO)(PPh3)3 into the pores of
hexagonal mesoporous silica (HMS) [16,17]. We had approached a
new technique of encapsulation by entrapping the rhodium com-
plex into the hexadecyl reverse micelles present inside the pores
of HMS. The HRh(CO)(PPh3)3 was insoluble in the water medium
during the catalyst synthesis procedure. Hence in the present
paper we have attempted the in situ encapsulation of RhCl(TPPTS)3
(TPPTS = m-trisulphonato triphenyl phosphine) into the pores of
HMS. The rhodium complex will be soluble in water enhancing
better encapsulation and stability of the catalyst. The catalyst was
evaluated for the hydroformylation of vinyl esters and detailed
parametric investigations were performed on vinyl acetate.
2. Experimental
2.1. Materials
Carbon monoxide (CO, 99.8%) and hydrogen (H2, 99.98%) were
procured from Ami Traders, Bhavnagar, India. The rhodium com-
plex RhCl(TPPTS)3, different vinyl esters, tetraethylorthosilicate
∗
Corresponding author. Tel.: +91 278 2567760; fax: +91 278 2566970.
E-mail address: rshukla@csmcri.org (R.S. Shukla).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.09.028

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N. Sudheesh et al. / Applied Catalysis A: General 409–410 (2011) 99–105
(TEOS) and dodecyl amine were purchased from Sigma–Aldrich,
USA. Toluene was bought from Qualigen, India. All chemicals were
used without any further purification. The double distilled milli-
pore deionised water was always used during synthesis.
2.2. Synthesis of HMS
HMS was synthesized by the reported procedure [16], where the
hexadecyl amine was replaced by dodecyl amine.
2.3. Synthesis of Rh-TPPTS-HMS
The synthesis of RhCl(TPPTS)3 encapsulated HMS was done by
dissolving 0.0027 mol of dodecyl amine in a mixture of 0.0909 mol
of ethanol and 0.296 mol of deionised water. The solution was
stirred on a magnetic stirrer. To this stirring solution 0.07 mmol of
the RhCl(TPPTS)3 was added followed by the addition of 0.01 mol
TEOS in drops. Stirring was continued for 1 h and a pale yellow pre-
cipitate formed was kept for 18 h for aging. The yellow precipitate
was filtered and washed with 1:1 (v/v) ethanol–water mixture and
dried in vacuum. The catalyst was denoted as Rh-TPPTS-HMS.
Fig. 1. P-XRD of HMS and Rh-TPPTS-HMS.
2.4. Characterization techniques
by the single low angle diffraction pattern [19,20]. The intensity of
peak was higher for HMS and was decreased when the Rh-TPPTS
was encapsulated, indicating that the pores have been filled with
the complex.
Powder X-ray diffraction (P-XRD) of the samples were recorded
with Phillips X’Pert MPD system equipped with XRK 900 reaction
chamber, using Ni-filtered Cu K␣ radiation (ꢀ = 1.54050 A) over
The 31P NMR was taken to observe the encapsulation of the com-
plex without decomposition. The 31P NMR in solution and solid
state were analyzed for RhCl(TPPTS)3 and Rh-TPPTS-HMS respec-
tively and were given in Fig. 2. RhCl(TPPTS)3 showed (Fig. 2A) the
peaks at 53.61 ppm corresponding to the phosphorous trans to the
chlorine and a doublet at 29.87 ppm corresponding to the two cis
phosphorous and a doublet of doublet at 36.05 ppm due to the cis
coupling. The peak at 35.72 ppm corresponds to the unavoidable
formation of the TPPTS oxide. The ratio of the doublet and dou-
blet of doublet in the NMR spectra is found to be 1:2 (peak ratio of
peak at 36.05:29.87 ppm). Rh-TPPTS-HMS showed (Fig. 2B) peaks
at 31.13 and 26.04 indicating that the complex has been encapsu-
lated without decomposition. The shift in the peak towards lower
ppm for Rh-TPPTS-HMS was observed. This was due to geometri-
cal constraints of the complex in the mesopores of HMS [16]. The
ratio of these two peaks after encapsulation was determined by
doing deconvolution applying Gaussian non-linear fit using Ori-
gin 6.0 software. The ratio of the peaks at 31.13:26.04 ppm are
found to be ∼1.2:2. The slight change in ratio may be due to the
dissociation of some TPPTS (evidenced by the peak at −14.54 ppm
corresponding to the free TPPTS) which affects the cis coupling of
these phosphorous. Similar observations of dissociation of ligand
during heterogenization were reported [21,22]. The presence of
unavoidable TPPTS oxide is represented by the peak at 27.98 ppm.
Surface area of HMS and Rh-TPPTS-HMS were determined using
nitrogen adsorption at 77 K and isotherm is shown in Fig. 3. The
volume adsorbed was higher for the HMS. The surface area of HMS
and Rh-TPPTS-HMS were 136.54 and 59.85 m2/g, respectively. The
surface area got decreased when the pores were occupied with the
encapsulated RhCl(TPPTS)3.
˚
a 2␪ range of 1–10◦ at a step time of 0.05◦ s−1. The FT-IR spec-
tra of the samples were recorded from 400 to 4000 cm−1 with
a PerkinElmer Spectrum GX FT-IR system using KBr pellets. The
NMR, 31P-CPMAS was recorded by a Bruker 500 Ultrashield sys-
tem. Thermogravimetric analysis (TGA) was carried out in a Mettler
TGA/DTA 851e, in nitrogen flow rate at 50 mL/min. The TEM and
Rh mapping of the catalysts were carried out with a TEM instru-
ment (JEOL, JEM 2100) equipped with EDX facility. Inductively
coupled plasma atomic emission spectroscopy (ICP-AES) analysis
(Optima 2000DV, PerkinElmer instruments) was used to determine
the rhodium content in the catalyst. The surface area analysis and
pore size distribution of the samples were measured by nitrogen
adsorption at 77.4 K using a Sorptometer (ASAP-2010, Micromerit-
ics). All the samples were degassed at 80 ◦C for 4 h prior to the
measurements.
2.5. Hydroformylation of vinyl esters
Hydroformylation of vinyl esters were carried out in a 100 mL
stainless steel autoclave reactor (Autoclave Engineers, USA). The
experimental setup, safety precautions and procedures were simi-
lar to that described elsewhere [16]. The weighed amount of vinyl
ester and catalyst were taken in the SS-autoclave with 50 mL of
toluene. The autoclave was raised to desired temperature and then
syngas (CO:H2; 1:1; p/p) was pressurized to the required level.
Aliquots of product mixture were withdrawn to analyze the con-
version and selectivity at regular time intervals. The product was
analyzed by GC (Schimadzu 17A, Japan) and GC–MS (Schimadzu
GCMS-QP2010, Japan). To ensure reproducibility, the experiments
were repeated under identical reaction conditions.
FT-IR spectra of Rh-TPPTS-HMS and RhCl(TPPTS)3 were given in
Fig. 4. The stretching vibrations of ꢁOSO and ꢁSO were observed at
1197 and 1039 cm−1, respectively for RhCl(TPPTS)3. Rh-TPPTS-HMS
showed broad vibration bands at 1078 cm−1 for Si–O–Si stretching.
The bands corresponding to ꢁOSO and ꢁSO of RhCl(TPPTS)3 were
overlapped in the Si–O–Si stretching vibrations and hence could
not be seen in the spectrum of Rh-TPPTS-HMS. Other main absorp-
tion bands of RhCl(TPPTS)3 were observed at 1465 and 1400 cm−1
for vibrational bands of phenyl ring and 788 cm−1 for C–H out of
plane bending vibration of phenyl ring. These bands are shifted
3. Results and discussion
3.1. Catalyst characterization
The catalyst was characterized for the formation of HMS by P-
XRD and is shown in Fig. 1. It showed an intense reflection near
2.0◦ of 2Â corresponding to the (1 0 0) plane [18]. It is similar to the
observation of Tanev et al. that the formation of HMS was confirmed

N. Sudheesh et al. / Applied Catalysis A: General 409–410 (2011) 99–105
101
Fig. 2. 31P NMR of (A) RhCl(TPPTS)3 and 31P CP-MAS NMR of (B) Rh-TPPTS-HMS.
in Rh-TPPTS-HMS at 1467 and 1383 cm−1 for vibrational bands of
phenyl ring and 797 cm−1 for C–H out of plane bending vibration
of phenyl ring showing the encapsulation of RhCl(TPPTS)3 into the
mesopores of HMS. The peak shift observed after encapsulation of
RhCl(TPPTS)3 complex into the HMS is due to the coordination of
RhCl(TPPTS)3 complex with –NH2 group of the dodecylamine and
also may be due to the possible formation of hydrogen bonding
with the surface –OH groups inside the pores. The appearance of
bands at 2924 and 2854 cm−1 in Rh-TPPTS-HMS correspond to the
CH2 stretching vibrations of the dodecylamine present in the pores
of Rh-TPPTS-HMS catalyst.
(22%) corresponded to the dodecyl amine present in the pores of
HMS. The second weight loss from 260 ◦C to 400 ◦C corresponded
to the RhCl(TPPTS)3 complex encapsulated in the HMS.
The TEM image and Rh elemental mapping of Rh-TPPTS-HMS
are given in Fig. 5. TEM image showed the mesoporous structure of
the catalyst. It is the typical wormhole structure of the HMS. The
elemental mapping of Rh in the Rh-TPPTS-HMS showed the finely
dispersed nature of the RhCl(TPPTS)3 in the HMS pores.
ICP analysis of the Rh-TPPTS-HMS was done to determine the
amount of rhodium present in the catalyst and found to be 1.5 wt%.
The synthesis of catalyst includes the water–ethanol medium in
which the RhCl(TPPTS)3 was soluble to form homogeneous solu-
tion leading to higher amount of encapsulation rather than partial
encapsulation and simple adsorption on the surface.
Thermogravimetric analysis (TGA) of the catalyst showed a
two stage weight loss corresponding to the organic template and
RhCl(TPPTS)3 complex. The first weight loss from 140 ◦C to 250 ◦C

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N. Sudheesh et al. / Applied Catalysis A: General 409–410 (2011) 99–105
90
80
70
60
50
40
30
20
10
0
HMS
Rh-TPPTS-HMS
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure
Fig. 3. N2 adsorption isotherm of HMS and Rh-TPPTS-HMS.
Fig. 4. FT-IR spectra of RhCl(TPPTS)3 and Rh-TPPTS-HMS.
3.2. Hydroformylation of vinyl esters
3.2.1. Effect of the amount of the catalyst on the
hydroformylation of vinyl acetate
Hydroformylation of vinyl esters were carried out by taking
23.3 mmol of substrate and 50 mg of the catalyst and 40 bar of syn
gas at 100 ◦C and the results were given in Table 1. The catalyst
was found to be active for the hydroformylation of functionalized
olefin, vinyl esters. Vinyl acetate, vinyl propionate, vinyl butyrate
and vinyl benzoate were evaluated for hydroformylation. All were
given 100% conversion with high selectivity to iso-aldehyde. There
were no formation of normal aldehyde but a small amount of corre-
sponding acid was formed in each case. The formation of acid during
the hydroformylation of vinyl esters was reported in literature [4].
The formation of acid was increased with increase in the substrate
chain length. The catalyst was investigated in detail for the param-
eters like amount of the catalyst, substrate, partial pressure of CO
and H2, and temperature.
The amount of the catalyst was studied from 10 to 150 mg of the
catalyst by keeping all other parameters constant for hydroformy-
lation of vinyl acetate and the corresponding results are shown in
Fig. 6. The conversion was increased with increase in the amount of
the catalyst. It was due to the increase in the active rhodium species
by increase in the amount of the catalyst. The conversion was 22%
for 10 mg catalyst which was increased to 48% for 50 mg and to 93%
at 150 mg. A linear trend in conversion was observed on increas-
ing the catalyst amount. Only one of the product i.e., 2-acetoxy
propanal was formed throughout the catalyst variation, confirm-
ing the regioselective nature of the catalyst. Small amount of acetic
acid was observed during the hydroformylation reaction due to the
breakdown of vinyl acetate. An amount of 50 mg of the catalyst was
taken for the detail investigations of the other parameters.
Fig. 5. TEM image and Rh mapping of Rh-TPPTS-HMS.

N. Sudheesh et al. / Applied Catalysis A: General 409–410 (2011) 99–105
103
Table 1
100
Hydroformylation of vinyl esters.
Entry Substrate
Time (h) % Conversion % Selectivity
iso-Aldehyde Othersa
90
80
70
60
50
40
30
20
10
1
2
3
4
Vinyl acetate
4
8
12
48
74
100
98
96
94
2
4
6
Vinyl propionate
Vinyl butyrate
Vinyl benzoate
4
8
12
42
71
100
98
93
93
2
7
7
4
8
12
33
65
100
97
93
91
3
7
9
% Conversion
% Selectivity
4
8
12
28
62
100
96
91
88
4
9
12
Reaction conditions: substrate = 23.3 mmol, catalyst = 50 mg, syn gas = 40 bar,
5
10
15
20
25
30
temp. = 100 ◦C, solvent = toluene (50 ml).
a
H2 pressure, bar
Corresponding acid and aldehyde: acetic acid, propionic acid, butyric acid, ben-
zoic acid and propanal.
Fig. 7. Effect of H2 pressure on conversion and selectivity at vinyl
acetate = 23.3 mmol, catalyst = 50 mg, CO = 20 bar, temp. = 100 ◦C, solvent = toluene
(50 ml), time = 4 h.
3.2.2. Effect of partial pressure of H2 on the hydroformylation of
vinyl acetate
The effect of partial pressure of H2 on the conversion and selec-
tivity was studied from 5 to 30 bar of pH2 and the results were
given in Fig. 7. The conversion was increased on increasing the par-
tial pressure of H2. The conversion increased from 13% for pH2 of
5 bar to 73% for 30 bar of hydrogen partial pressures. The selectiv-
ity was not much affected by the partial pressure of hydrogen but
there was a decrease in formation of acetic acid at lower hydrogen
pressures.
lower conversions. The selectivity as such was not much affected
with pCO, however, it was slightly more at lower pressure.
3.2.4. Effect of the amount of vinyl acetate on its
hydroformylation
Effect of the amount of vinyl acetate on hydroformylation was
studied in the range of 0.5–3 g and the results are given in Fig. 9.
The conversion was decreased on increasing the amount of vinyl
acetate from 0.5 g (70%) to 3 g (35%). The lower conversion at higher
amounts was due to higher substrate to catalyst ratio. The number
of active catalyst center with respect to the number of vinyl acetate
was very low in the higher substrate amount leading to lower con-
version levels. Also the higher amount of substrate leads to higher
formation of acetic acid.
3.2.3. Effect of partial pressure of CO on the hydroformylation of
vinyl acetate
The results of the dependence of partial pressure of CO on con-
version and selectivity are given in Fig. 8. The conversion was
increased on increasing the partial pressure of CO from 5 (5%) to 20
(48%) bar and further increase in pCO gave a decreasing trend (33%
at 30 bar pCO). This observation may be because of the CO inhibi-
tion which is common in the hydroformylation reactions [23]. At
higher CO concentrations, the di- and tri-carbonyl rhodium species
are formed which are the deactive forms of the catalyst and lead to
3.2.5. Effect of temperature on the hydroformylation of vinyl
acetate
The effect of temperature on hydroformylation of vinyl acetate
was studied between 80 and 120 ◦C and the results are given in
100
90
80
70
60
50
40
30
100
90
80
70
60
50
40
30
20
20
% Conversion
% Selectivity
% Conversion
% Selectivity
10
0
10
0
5
10
15
20
25
30
0
20
40
60
80
100
120
140
160
CO pressure, bar
Catalyst amount, mg
Fig. 8. Effect of CO pressure on conversion and selectivity at vinyl
acetate = 23.3 mmol, catalyst = 50 mg, H2 = 20 bar, temp. = 100 ◦C, solvent = toluene
(50 ml) and time = 4 h.
Fig. 6. Effect of catalyst amount on conversion and selectivity at vinyl
acetate = 23.3 mmol, syn gas = 40 bar, temp. = 100 ◦C, solvent = toluene (50 ml),
time = 4 h.

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N. Sudheesh et al. / Applied Catalysis A: General 409–410 (2011) 99–105
Table 2
Reusability of the catalyst.
100
90
80
70
60
50
40
30
20
10
0
Recycle Run
Time (h)
% conversion
% selectivity
2-Acetoxy propanal
Others
Fresh catalyst
4
8
12
48
74
100
98
96
94
2
4
6
1st recycle
2nd recycle
3rd recycle
4
8
12
35
73
98
97
97
94
3
3
6
4
8
12
33
61
75
96
92
90
4
8
10
% Conversion
% Selectivity
4
8
12
30
53
62
93
87
83
7
13
17
Reaction conditions: vinyl acetate = 23.3 mmol (2 g), catalyst = 50 mg, syn gas = 40 bar,
0.5
1.0
1.5
2.0
2.5
3.0
temp. = 100 ◦C, solvent = toluene (50 ml).
Amount of substrate, g
Fig. 9. Effect of amount of substrate on conversion and selectivity at catalyst = 50 mg,
syn gas = 40 bar, temp. = 100 ◦C, solvent = toluene (50 ml) and time = 4 h.
form of the catalyst [25]. The conversion was dropped from 48%
at 4 h for fresh catalyst to 30% at 4 h for 3rd recycle. The conver-
sion at 12 h was 100% for fresh catalyst where as it was dropped to
62% for 3rd recycle. Also the selectivity was decreased on increas-
ing the recycle runs. The Rh loss after first recycle was 1.8% of the
total Rh content in the employed amount of the catalyst. But in the
further cycles the percentage loss of Rh was found to be under not
detectable limit indicating that the Rh complex was stable inside
the pores of HMS without leaching.
From these observations it was important to confirm the recy-
clability of the catalyst in order to see that the catalyst was
effective for heterogeneous hydroformylation reactions. For this
the reusability of the catalyst was tested for another substrate 1-
hexene to avoid the concern of acetic acid. The recycled catalyst
separated from vinyl acetate hydroformylation was subjected for
hydroformylation of 1-hexene.
The result of activity of 1-hexene hydroformylation is given in
Table 3. The run I corresponds to catalyst taken directly after the 3rd
recycle of hydroformylation of vinyl acetate. The run II corresponds
to the recycled catalyst after the hydroformylation of 1-hexene by
the catalyst used in run I. It was observed that the catalyst was
effective for hydroformylation of 1-hexene. Conversion and selec-
tivity to aldehyde of 50% and 18%, respectively, were obtained at
2 h for the catalyst used directly after vinyl acetate recycle (run I).
This conversion and selectivity was increased with the time. Con-
version (99%) and selectivity to aldehyde (50%) was obtained at
8 h of reaction time for run I. The conversion and selectivity were
increased on increasing the recycle runs. When the recycle run
increases the coordinated acetic acid may get dissociated in the
high pressure conditions in the presence of 1-hexene, CO and H2.
This could make the catalyst retain its activity by forming hydridic
form of the catalyst and showed enhancement in its activity after
each recycle.
It is of interest if the catalyst retained its activity by hydroformy-
lation of 1-hexene, could catalyze vinyl acetate again. Therefore
the catalyst after III run was washed with toluene and used again
to conduct hydroformylation of vinyl acetate. The results obtained
were remarkable that it gave 88% conversion with 95% selectivity
to 2-acetoxy propanal with 5% of acetic acid and propanal. This
result showed that the catalyst can be recycled by treating the
spent catalyst with 1-hexene, CO and H2 at high pressures so that
the carboxylate rhodium complex can be again converted to active
catalyst.
Fig. 10. The conversion was increased on increasing the tempera-
ture. A conversion of 27% at 80 ◦C was increased to 72% at 120 ◦C.
The selectivity to 2-acetoxy propanal was affected by temperature.
The formation of acetic acid was minimal at lower temperatures.
The higher temperature increased the formation of acetic acid; even
6% of acetic acid was formed at 120 ◦C. Hence the selective hydro-
formylation of vinyl acetate can be done at lower temperatures to
get 2-acetoxy propanal without much decomposition into acetic
acid.
3.2.6. Reusability of the catalyst
The catalyst was tested for its recyclability under similar reac-
tion conditions and the results are given in Table 2. The catalyst after
each cycle was washed with toluene and used for next cycle. It was
observed that the catalyst activity got decreased during recycling.
This may be due to the formation of acetic acid during the hydro-
formylation which causes deactivation of the catalyst [24]. Acetic
acid formed will coordinate with the rhodium to form carboxylate
rhodium complex which reduces the concentration of the hydridic
100
90
80
70
60
50
40
30
20
% Conversion
% Selectivity
10
0
80
90
100
110
120
Temperature, oC
FT-IR spectra of deactivated catalyst after the 3rd recycle of
vinyl acetate hydroformylation and the obtained regenerated cat-
alyst after treating with 1-hexene, CO and H2 were recorded and
Fig. 10. Effect of temperature on conversion and selectivity at vinyl
acetate = 23.3 mmol, catalyst = 50 mg, syn gas = 40 bar, solvent = toluene (50 ml) and
time = 4 h.

N. Sudheesh et al. / Applied Catalysis A: General 409–410 (2011) 99–105
105
Table 3
Reusability of the catalyst obtained after the third recycled catalyst from Table 2 for hydroformylation of 1-hexene.
Run
Time (h)
% conversion
% selectivity
2/3-Hexene
n-Heptanal
iso-Heptanal
2-Ethyl 3-methyl butanal
I
2
4
8
50
78
99
99
82
58
50
40
9
14
18
20
7
21
24
30
2
7
8
12
10
II
2
4
8
52
80
99
99
79
57
44
30
9
20
22
29
9
19
26
31
3
4
8
12
10
III
2
4
8
55
97
99
99
62
53
39
20
18
20
26
33
17
22
27
35
3
5
8
12
12
Reaction conditions: catalyst = 50 mg, 1-hexene = 2 g, syn gas = 40 bar, temp. = 100 ◦C, solvent = toluene (50 ml).
partial pressure of CO and H2 and temperature were investigated
and found to be influential on conversion and selectivity. The cata-
lyst was tried to recycle for hydroformylation of vinyl acetate and
observed that the formation of acetic acid inhibits the catalytic
activity. To overcome the inhibition caused due to the acetic acid
formation, the recycling was done with 1-hexene as a substrate
which addressed that the deactivated catalyst can be regenerated
under hydroformylation conditions by treating with 1-hexene, CO
and H2 to retain the active catalyst species.
Acknowledgments
The authors acknowledge CSIR, New Delhi for the financial sup-
port through the Network Project for the Development of Specialty
Inorganic Materials for Diverse Applications. One of the authors,
NS acknowledges CSIR, New Delhi for the award of Senior Research
Fellowship.
References
Fig. 11. FT-IR spectra of (a) deactivated catalyst and (b) regenerated catalyst.
[1] M. Beller, B. Cornils, C.D. Frohning, C.W. Kohlpaintner, J. Mol. Catal. A: Chem.
104 (1995) 17–85.
[2] S.K. Sharma, V.K. Srivastava, R.S. Shukla, P.A. Parikh, R.V. Jasra, New J. Chem. 31
(2007) 277–286.
[3] D. Hoegaerts, P.A. Jacobs, Tetrahedron Asymm. 10 (1999) 3039–3043.
[4] Y.L. Borole, R.V. Chaudhari, Ind. Eng. Chem. Res. 44 (2005) 9601–9608.
[5] G. Fremy, E. Monflier, J. Carpentier, Y. Castanet, A. Mortreux, J. Mol. Catal. A:
Chem. 129 (1998) 35–40.
[6] P.J. Thomas, A.T. Axtell, J. Klosin, W. Peng, C.L. Rand, T.P. Clark, C.R. Landis, K.A.
Abboud, Org. Lett. 9 (2007), 2665–2658.
[7] H.B. Tinker, US Patent 4 072 709 (1978) to Monsanto Company.
[8] I. Chibata, Synthetic Production and Utilisation of Amino Acids, Wiley, New
York, 1974, p. 201.
[9] A.G. Abatjoglou, D.R. Bryant, L.C. D’espeosito, J. Mol. Catal. 18 (1983) 381–390.
[10] A.M. Trzeciak, J.J. Ziółkowski, J. Mol. Catal. 43 (1987) 15–20.
[11] T. Horiuchi, E. Shirakawa, K. Nozaki, H. Takaya, Organometallics 16 (1997)
2981–2986.
[12] N.R. Vautravers, D.J. Cole-Hamilton, Chem. Commun. 9 (2009) 2–94.
[13] X. Zhang, B. Han, M. Huang, Y. Jiang, Polym. Adv. Technol. 12 (2001) 693–696.
[14] P. Arya, G. Panda, N.V. Rao, H. Alper, S.C. Bourque, L.E. Manzer, J. Am. Chem. Soc.
123 (2001) 2889–2890.
are given in Fig. 11. All the characteristic bands of Rh-TPPTS-HMS
were observed in deactivated (Fig. 11a) and regenerated (Fig. 11 b)
catalysts. In deactivated catalyst the band corresponding to ꢁCO of
acetate group attached to the Rh center was observed at 1736 cm−1
(Fig. 11a). The other major IR bands are also seen in the deactivated
catalyst with a small shift in the position of bands. This may be due
to the coordination of acetate group with Rh and also the possible
presence of substrate, product and toluene in the recycled catalyst.
In the FT-IR spectrum of the regenerated catalyst by hydroformy-
lation of 1-hexene an appreciably reduced intensity corresponding
to ꢁCO of acetate group was observed (Fig. 11 b). This indicated
that the coordinated acetate got reduced in the catalyst during the
hydroformylation process of 1-hexene.
4. Conclusions
[15] J.P.K. Reynhardt, Y. Yang, A. Sayari, H. Alper, Chem. Mater. 16 (2004) 4095–4102.
[16] N. Sudheesh, S.K. Sharma, R.S. Shukla, R.V. Jasra, J. Mol. Catal. A: Chem. 296
(2008) 61–70.
RhCl(TPPTS)3 (TPPTS = m-trisulphonato triphenyl phosphine)
was encapsulated into the mesopores of hexagonal mesoporous
silica (HMS) by in situ method. The catalyst was thoroughly char-
acterized to confirm the encapsulation and heterogenization of
RhCl(TPPTS)3. The synthesized heterogeneous catalyst was eval-
uated for hydroformylation of vinyl esters. The conversion of 100%
was obtained with high selectivity to iso-aldehyde with small
amounts of corresponding acid and propanal. Vinyl acetate was
taken as a representative vinyl ester for detailed parametric inves-
tigations. The parameters like amount of the catalyst, substrate,
[17] N. Sudheesh, S.K. Sharma, R.S. Shukla, R.V. Jasra, J. Mol. Catal. A: Chem. 316
(2010) 23–29.
[18] S. Damyanova, L. Dimitrov, R. Mariscal, J.L.G. Fierro, L. Petrov, I. Sobrados, Appl.
Catal. A: Gen. 256 (2003) 183–197.
[19] P.T. Tanev, T.J. Pinnavia, Science 267 (1995) 865–867.
[20] P.T. Tanev, M. Chibwe, T.J. Pinnavia, Nature 368 (1994) 321–323.
[21] C. Bianchini, H.M. Lee, A. Meli, F. Vizza, Organometallics 19 (2000) 849–853.
[22] H. Zhu, Y. Ding, H. Yin, L. Yan, J. Xiong, Y. Lu, H. Luo, L. Lin, Appl. Catal. A: Gen.
245 (2003) 111–117.
[23] F. Monteil, R. Queau, P. Kalck, J. Organomet. Chem. 480 (1994) 177–184.
[24] A.A. Dabbawala, R.V. Jasra, H.C. Bajaj, Catal. Commun. 11 (2010) 616–619.
[25] A.G. Abatjoglou, D.R. Bryant, L.C. D’Esposito, J. Mol. Catal. 18 (1983) 381–390.