Superior performance of a nanostructured platinum catalyst in water: Hydrogenations of alkenes, aldehydes and nitroaromatics

Article abstract of DOI:10.1002/adsc.200700034

The hydrogenations of >C=C<, >C=O and nitro groups in ArNO ₂, with a water-soluble, polymer [poly(diallyldimethylammonium chloride)] supported, platinum carbonyl cluster {[Pt₃₀(CO) ₆₀]^2-} derived catalyst 1, have been studied. The performance of 1 has been compared with that of two other platinum catalysts: catalyst 2 prepared by the hydrogen reduction of [PtCl₆]^2- supported on the same water-soluble polymer, and 3, a commercial platinum catalyst (5 % Pt on alumina). Our catalyst 1 has been found to be more active than 2 and 3, and by TEM it has been shown that the nanoparticles in 1 are much smaller than those in 2. In the hydrogenation of o-chloronitrobenzene both 1 and 2 were found to be more selective (no hydrodehalogenation) than 3. To evaluate the advantages of water as a solvent, comparative studies have been carried out in three different solvent systems: water, methanol and a 1:1 mixture of water and toluene. Hydrogenations in methanol have been found to be accompanied by induction times while no such induction time is observed in water. Both liquid (methyl pyruvate, benzaldehyde, safflower oil and styrene) and waterinsoluble solid nitroaromatics (o- and m-chloronitrobenzene and p-aminonitrobenzene) have been tested as substrates, and for all the substrates the activity in water was found to be higher.

Full text of DOI:10.1002/adsc.200700034

FULL PAPERS
DOI: 10.1002/adsc.200700034
Superior Performance of a Nanostructured Platinum Catalyst
in Water: Hydrogenations of Alkenes, Aldehydes and
Nitroaromatics
a
a
b,
a,
Prasenjit Maity, Susmit Basu, Sumit Bhaduri, * and Goutam Kumar Lahiri *
a
Department of Chemistry, Indian Institute of Technology-Bombay, Powai, Mumbai 400076, India
Fax : (+91)-22-2572-3480; e-mail: lahiri@chem.iitb.ac.in
Reliance Industries Limited, Swastik Mills Compound, V. N. Purav Marg, Chembur, Mumbai-400071, India
b
Fax : (+91)-22-6767-7381; e-mail: sumit_bhaduri@ril.com
Received: January 19, 2007; Revised: May 13, 2007
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: The hydrogenations of >C=C<, >C=O a solvent, comparative studies have been carried out
and nitro groups in ArNO , with a water-soluble, po- in three different solvent systems: water, methanol
2
lymer [poly(diallyldimethylammonium chloride)] and a 1:1 mixture of water and toluene. Hydrogena-
2À
supported, platinum carbonyl cluster {[Pt (CO) ] } tions in methanolhave been found to be accompa-
30
60
derived catalyst 1, have been studied. The perfor- nied by induction times while no such induction time
mance of 1 has been compared with that of two is observed in water. Both liquid (methyl pyruvate,
other platinum catalysts: catalyst 2 prepared by the benzaldehyde, safflower oil and styrene) and water-
2À
hydrogen reduction of [PtCl6] supported on the insoluble solid nitroaromatics (o- and m-chloronitro-
same water-soluble polymer, and 3, a commercial benzene and p-aminonitrobenzene) have been tested
platinum catalyst (5% Pt on alumina). Our catalyst 1 as substrates, and for all the substrates the activity in
has been found to be more active than 2 and 3, and water was found to be higher.
by TEM it has been shown that the nanoparticles in
1
are much smaller than those in 2. In the hydroge-
nation of o-chloronitrobenzene both 1 and 2 were Keywords: hydrogenation catalysts; ionic polyelec-
found to be more selective (no hydrodehalogena- trolyte; nanocatalyst; on-water effect; platinum car-
tion) than 3. To evaluate the advantages of water as bonylc ul ster
2
À
Introduction
ylc ul ster [Pt (CO) ] , on a water-soluble polymer,
30 60
poly(diallyldimethylammonium
From the point of view of environmentally benign (Scheme 1). The freshly prepared polymer supported
chemicalprocesses, the use of water rather than or- material has CO-protected platinum nanoparticles
ganic solvents is an important theme of current re- within the size range of 2–8 nm with ca. 40% being
chloride),
4
[1–5]
search.
water-soluble, but the products are immiscible or in- hydrogenation of double bonds of >C=C< and
soluble, the separation of products from catalyst can >C=O functionalities in water. During catalysis the
In industrialprocesses if the cat ay lst is
within 4–6 nm. This material catalyzes the selective
[
6]
be easily achieved. Also many organic reactions CO ligands are lost but the basic nanometric features
when carried out in water have been reported to yield of the platinum particles are retained. The above-
[
7–12]
[1–15]
improvements in rates and selectivities.
Especially mentioned reports
on the remarkable influence of
noteworthy is the report where insoluble reactants water and other solvents on rate and selectivity,
stirred in aqueous suspensions, a condition designated prompted us to investigate the performance of the
[
13–14]
as “on-water”, show rate acceleration.
also a recent report where the selectivity of a gold
nanocatalyst has been found to be critically depen- following three primary objectives. First, scrutinizing
There is cluster-derived catalyst in greater detail.
The work presented here was undertaken with the
[
15]
dent on the solvents employed.
Very recently we have shown
the activity and structuraldifferences, if any, between
[
16]
that catalyst 1 the cluster-derived catalyst 1 and that of another liter-
could be prepared by supporting the platinum carbon- ature
[
17]
reported
platinum
nanocatalyst,
2
Adv. Synth. Catal. 2007, 349, 1955 – 1962
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1955

Prasenjit Maity et al.
FULL PAPERS
Scheme 1. Designations of the support and different catalysts used in this work.
(
Scheme 1). This comparison is important since the tion of clusters of clusters. Our compound 1 catalyzes
preparation of 2 involves hydrogen reduction of selective hydrogenations of double bonds of olefinic
2À
[
PtCl6] in the presence of 4, i.e., the polymer used (>C=C<) and carbonylic (>C=O) functionalities,
by us for the synthesis of 1. Second, it is important to but under hydrogen pressure, i.e., catalytic conditions,
compare the performance of these two nanocatalysts loses the CO groups and there is a general decrease
with that of a commercial platinum catalyst (5% plat- in the size of the nanoparticles. The time-monitored
inum on alumina) 3, so that the advantages of nano- spectrophotometric changes of 1 on reaction with di-
catalysts could be conclusively established. Third, we hydrogen have been shown to be consistent with the
[
16]
needed to see whether water is indeed the best known reactions (a) and (b) of Scheme 2. The over-
medium for the cluster-derived catalyst from the all reduction in the size of the nanoparticles under hy-
point of view of rates and/or turnover numbers drogenation conditions is most probably due to the
(
TON). Moreover, we wanted to find out if with our formation of aggregates of lower nuclearity, decar-
catalyst, the “on-water” effect, i.e., increased rates bonylated clusters (see later).
with sparingly water-soluble solid substrates, could
As the main objective of the work presented here
also be achieved. As described below, our results was to evaluate the advantages of using 1 as a catalyst
have revealed that 1 and water are indeed the best and water as a solvent, we first studied the hydroge-
catalyst and reaction medium, respectively.
nation of methylpyruvate and nitrobenzene. The rea-
sons for choosing methylpyruvate were to see if in
the presence of Cinchona alkaloids, 1 could catalyze
the enantioselective formation of methyl lactate.
Enantioselective hydrogenation of methyl pyruvate
using heterogeneous platinum catalysts and Cinchona
alkaloids as chiral modifiers is a much studied reac-
Results and Discussion
Performance of 1 for the Hydrogenation of Methyl
Pyruvate and Nitrobenzene in Water and Methanol
[
18–20]
tion.
Enantioselective hydrogenations of pyruvate
The synthesis and characterization of the poly(diallyl- esters have also been reported for colloidal platinum-
dimethylammonium chloride)-supported, high nucle- based[2,1,22C] inchona alkaloid-modified catalytic sys-
2À
arity Chini cluster [Pt (CO) ] by spectroscopy (IR, tems.
30
60
NIR, NMR) and TEM has recently been reported by
Surprisingly, either in water or in methanol, using 1
[16]
us. The freshly prepared, polymer-supported mate- as the catalyst and Cinchona alkaloids as chiral modi-
rial has CO-protected platinum nanoparticles within fiers, no enantioselectivity could be obtained in the
the size range of 2–8 nm with ca. 40% being within hydrogenation of methylpyruvate. This is in contrast
4–6 nm. The particles of different sizes result from to the behaviour of a cinchonidium-functionalized
loose aggregations of the parent cluster, i.e., forma- mesoporous silica (MCM-41)-supported, platinum
1956
asc.wiley-vch.de
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Adv. Synth. Catal. 2007, 349, 1955 – 1962

Superior Performance of a Nanostructured Platinum Catalyst in Water
FULL PAPERS
Scheme 2. Reduction of a platinum carbonyl cluster (Chini cluster) in the presence of dihydrogen.
[
20]
cluster-derived catalyst.
The obvious conclusions bonds. We also wanted to study the selectivity of hy-
from these results are that the catalytic properties of drogenation of o-chloronitrobenzene, and the “on-
are different from those of cinchonidium-functional- water” effect with solid nitroaromatics (see later). As
ized MCM-41 catalysts. More importantly, although shown in Figure 1 (inset), 1 catalyzes the hydrogena-
1
2À
both [PtCl ] -derived colloidal platinum and 1 can be tion of nitrobenzene to aniline, with ca. 1200 turn-
6
used as nanocatalysts in water, they show important overs in 60 and 80 min in water and methanol, respec-
difference in terms of selectivity. Most probably in tively. Here again in methanol there is an induction
the case of 1, the polymer matrix prevents the easy time and the initialTOF measured over 20 miniutes
À1
coordination of cinchonidine to the platinum particles, are 24 and 2.4 min respectively.
thereby ruling out the formation of enantioselective
sites.
In all our previous works where platinum carbonyls
had been used as the precursor of supported catalysts
With 1 as the catalyst, good turnovers (1200) of we have established that the platinum clusters lose
[
16,20]
methylpyruvate to methyl al ctate are obtained over a
the CO ligands before or during catalysis.
We had
period of ca. 12 h in water. In methanolmore time
also shown that the polystyrene-supported clusters
(
ca. 16 h) is required for the same extent of reaction become catalytically active only after thermal or pho-
and, as can be seen from Figure 1, there is a remark- tochemicaldecarbony al tion, i.e., when they are coor-
[
23]
able difference between the initial rates in these two dinatively unsaturated. The existence of an induc-
solvents. In methanol there is an induction time when tion time in methanoland its absence in water are
the catalyst shows less activity, but in water there is therefore due to the fact the carbonyl ligands are lost
no such induction time. Thus in methanoland water
the initialturnover frequencies (TOF) measured over
three hours are 28 and 160 h , respectively.
rapidly in water, but less rapidly in methanol.
À1
Similar differences in the initial rates are also ob- Comparative Performances of 1–3 for the
served in the hydrogenation of nitrobenzene in meth- Hydrogenation of Double Bonds in >C=C< and
anoland water. Nitrobenzene was chosen because we
wanted to explore the scope of the hydrogenation re-
>C=O Functionalities
action beyond that of >C=C< or >C=O double The comparative catalytic activities of 1, 2 and 3 in
water have been evaluated for the hydrogenation of a
few representative substrates that have >C=C< or
>
C=O double bonds (see Table 1). The hydrogena-
tion of safflower oil, the triglyceride of mainly
~80%) linoleic acid (cis,cis-9,12-octadecadienoic
(
acid, see Figure 2, inset), is a reaction of considerable
industrialimportance. On its hydrogenation in water
the oil layer turns into a waxy solid. The extent of hy-
drogenation can be conveniently measured by
1
3
C NMR by monitoring of the intensities of the sig-
nals due to the olefinic carbons. As can be seen from
Figure 2, when 1 is used as the catalyst, only a negligi-
ble amount of residual unsaturation remains in the
product.
As can be seen from Table 1, for the hydrogenation
of safflower oil, 2 and 3 give very similar but notably
fewer turnovers than 1. The change in the iodine
value, a traditional way of measuring relative unsatu-
ration in oils and fats, also indicates that 1 is more
active than 2 and 3 (see ExperimentalSection). Thus
Figure 1. Comparative time-monitored conversion plot in
water and methanolfor methylpyruvate and nitrobenzene
(
inset) hydrogenation catalyzed by 1. Reaction conditions:
3
00 K, 50 bar hydrogen pressure, 10 mL solvent (water or the initial iodine value of 115 of safflower oil drops to
22, 47 and 48, for 1, 2 and 3, respectively. It is also
methanol), substrate to catalyst molar ratio 1200:1.
Adv. Synth. Catal. 2007, 349, 1955 – 1962
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1957

Prasenjit Maity et al.
FULL PAPERS
[a]
Table 1. Comparative catalytic activities of 1, 2 and 3.
Entry No. Substrate
Product
Substrate amount/Time [h] Catalyst % Conversion (TON)
[b]
1
2
3
4
5
6
Safflower Oil Hydrogenated Safflower Oil
2 g/24 h
1
2
3
1
2
3
>98% (142)
81 (115)
80 (114)
100 (1180)
98 (1156)
97 (1144)
1
g (9.6 mmol)/12 h
7
8
9
1
2
3
100 (1202)
80 (961)
83 (997)
1
1
g (9.8 mmol)/12 h
g (10.6 mmol)/6 h
10
11
12
1
2
3
99 (1145)
50 (578)
45 (520)
13
14
15
1
2
3
100 (1558)
90 (1402)
55 (857)
2
g (15.7 mmol)/2 h
[
a]
Hydrogenation of typicalsubstrates cata yl zed by 1–3 in water. Reaction conditions: catalyst amount equivalent to 8.15”
À3
1
0
mmolof p al tinum, 50 bar H
p1ressure, solvent (water) 5 mL, temperature 300 K (except for safflower oil 353 K).
2
Products were analyzed by GC and H NMR.
[
b]
TON calculated on the basis of molecular weight of the triglyceride of linoloic acid.
13
1
Figure 2. (a) C NMR spectrum ( H decoupled) of safflower oil and (inset) the structure of the main constituent of safflower
1
3
1
oil: triglyceride of linoloic (cis,cis-9,12-octadecadienoic) acid. (b) C NMR spectrum ( H decoupled) of hydrogenated saf-
flower oil.
1958
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Superior Performance of a Nanostructured Platinum Catalyst in Water
FULL PAPERS
[a]
Table 2. Comparative catalytic activities of 1, 2 and 3 in the hydrogenation of aldehydes.
Entry no.
Substrate
Product
Substrate amount/Time [h]
Catalyst
% Conversion (TON)
1
2
3
4
5
6
7
8
9
1
2
3
1
2
3
1
2
3
1
2
3
99 (1686)
88 (1498)
52 (885)
98 (1381)
80 (1127)
35 (493)
73 (658)
32 (288)
39 (351)
99 (863)
52 (453)
75 (654)
1 g (13.88 mmol)/6 h
1 g (11.49 mmol)/6 h
1 g (7.35 mmol)/6 h
1 g (7.11 mmol)/6 h
10
11
12
[
a]
Hydrogenation of typical aldehydes apart from benzaldehyde catalyzed by 1–3 in water. Reaction conditions: catalyst
À3
amount equivalent to 8.15”10 mmolof p al tinum, 50 bar H pressure, solvent (water) 5 mL, temperature 300 K. Prod-
2
1
ucts were analyzed by GC and H NMR.
clear from the conversion data of styrene, methyl pyr-
Among these test substrates, for the hydrogenation
uvate, benzaldehyde and o-chloronitrobenzene that of benzaldehyde to benzyl alcohol, 1 is about twice as
for all of these substrates 1 is more active than 2 or 3. active as the other two. In view of these findings, the
In most of the cases significantly higher turnovers are relative activities of 1–3 have been evaluated for two
obtained with 1 and the activities of the three cata- aliphatic and two other aromatic aldehydes and the
lysts are approximately in the order of 1>2ꢀ3 results are given in Table 2. Catalyst 1 is found to be
except for o-chloronitrobenzene where the order is clearly more active than both 2 and 3 for all the alde-
1
>2>3.
hydic substrates.
In metal-catalyzed reactions, the correlation be-
tween smaller particle size and higher catalytic activi-
[
24]
ty is a well established observation.
TEM micro-
graphs of 1 and 2 have been recorded to see if the dif-
ference in their relative activities could be due to
such a difference in particle size. As shown in
Figure 3, the platinum particles in 2 are indeed much
larger (>20 times) than the ones in 1, and while in 1
the particle size ranges from 2 to 8 nm, in 2 it ranges
from 40 to 200 nm. Thus the TEM data clearly show
that for smaller nanoparticles, platinum carbonyls
rather than hexachloroplatinate must be used.
There are many reports on catalysis with cluster-de-
[
25,26]
rived materials
. It may be noted that the general
trend for the cluster-derived nanoparticles to grow
after a large numbers of catalytic turnovers is also ob-
served for 1. In nitrobenzene hydrogenation, after
turnovers ꢁ2500, platinum particles of ~10 nm sizes
are seen at the boundaries of the polymer support
(
see Supporting Information). The generalreduction
in the sizes of the nanoparticles reported by us earli-
[
16]
er refers to micrographs recorded after ~500–1000
turnovers. As mentioned earlier this is due to the for-
mation of aggregates of lower nuclearity, decarbony-
lated cluster ofclusters . This explanation is strongly
supported by controlexperiments (cata yl tic run with-
out substrates) where similar reductions in size are
consistently observed.
Figure 3. (a), (b) TEM images of freshly prepared and used
. (c), (d) TEM images of used 2 at two different magnifica-
tions.
1
It may also be noted that the reactions shown in
Table 1 are chemoselective, there is no hydrogenation
Adv. Synth. Catal. 2007, 349, 1955 – 1962
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
1959

Prasenjit Maity et al.
FULL PAPERS
[a]
of the aromatic rings or the ester group, neither is Table 3. Effect of solvent on TON for liquid substrates.
there any hydrogenolysis of benzyl alcohol. The selec-
Solvents
% Conversion (TON)
tivity aspect is of specialre el vance for the hydrogena-
tion o-chloronitrobenzene. The chemoselective reduc-
tion of o-chloronitrobenzene with the avoidance of
the hydrodehalogenation product aniline is of consid-
[
27–29]
erable industrial importance.
In so far as plati-
num catalysts are concerned, it has been shown that Water
100 (1180)
18.2 (215)
100 (1202)
79 (950)
99 (1145)
62 (717)
high selectivity could be achieved only in supercritical Water-toluene
[28]
carbon dioxide.
A recent report also shows that Methanol72.7 (858)
69 (834)
97.9 (1133)
nanoparticles of cobalt and Ni-Pd are very effective
for the hydrogenation of a variety of nitroaromat-
[a]
Hydrogenation of water immiscible liquid substrates cat-
alyzed by 1 in three different media. Reaction condi-
[29]
ics. Another recent report describes gold nanoparti-
cle-catalyzed, selective reductions of nitro groups in
À3
tions: metalcontent 8.15”10
mmol, substrate 1 g,
50 bar H pressure, reaction time 12 h (for benzaldehyde
2
[
30]
the presence of other functionalgroups.
In view of
6 h), solvent 5 mL, temperature 300 K.
these reports, the products from the hydrogenations
of o-chloronitrobenzene with 1–3 as catalysts have
been carefully analyzed.
[
a]
With 1 as the catalyst, the hydrogenation of o-chloro-
nitrobenzene in an aqueous suspension yields only o-
chloroaniline. No aniline or any other by-product is
detected by high-sensitivity gas chromatography (de-
tection limit ꢁ0.4%). However, under identicalcon-
ditions 3 gives ~2% aniline. Interestingly, the other
nanocatalyst 2 also does not give detectable levels of
aniline. Finally, it may be noted that although o-chlor-
onitrobenzene is a solid and practically insoluble in
water, its efficient hydrogenation can be carried out
in an aqueous suspension. This aspect has been fur-
ther studied and is discussed in the following section.
Table 4. Effect of solvent on TON for solid nitroaromatics.
Solvents
% Conversion (TON)
Water
Water-toluene (1:1)
100 (1558)
80 (1250)
75 (1168)
40 (623)
100 (1778)
66 (1173)
[a]
Hydrogenation of three substrates catalyzed by 2 in two
different media. Reaction conditions: metalcontent
À3
8
.15”10 mmol, Substrate 2 g, 50 bar H pressure, reac-
2
tion time 120 min, solvent 5 mL, temperature 300 K.
Products were analyzed by GC and H NMR. Solid sub-
Superiorityof Water as a Solvent
1
strates were first grinded to fine powdery form and then
added to the aqueous catalyst solution. In water-toluene
biphasic system, substrates were dissolved in toluene.
As mentioned in the Introduction, one of the central
themes of this work was to evaluate whether or not
with 1 as the catalyst, water as a reaction medium
offers any specialadvantage. This question has been
addressed by carrying out hydrogenations of both
liquid and solid substrates. The liquid substrates
chosen for this purpose are immiscible in water, while ics, which are practically insoluble in water, any spe-
the solids, all nitroaromatics, are sparingly soluble in cialadvantage in terms of TON might be observed.
water. For the liquid substrates comparative studies The catalytic hydrogenation reactions have been car-
have been carried out in water, methanoland a bipha-
ried out in two different media: water and a a bipha-
sic medium consisting of a 1:1 (by volume) mixture of sic medium consisting of water and toluene (1:1). As
water and toluene. The superiority of water over both can be seen from Table 4, in water significantly higher
mixed solvent and methanol is evident from the ratios turnover numbers (~25–50% more) are obtained for
of the TON obtained in different media (Table 3). the hydrogenation of all the substrates. One of the
Thus, for styrene, methylpyruvate and benza dl edyde,
factors for the enhanced rate may plausibly involve
the ratios of the TON in water, a mixture of water the equilibrium steps of Eq. (1) and Eq. (2) that sche-
and toluene, and in methanol are: 100:18:72; matically represent the reactions in the two media.
100:79:69; and 100:63:99.
If the equilibrium step of Eq. (1) is thermodynami-
As mentioned earlier, higher TON and rates for cally more favorable than that of Eq. (2), then the rel-
water-insoluble solids have recently been reported for ative concentrations of the nitroaromatics in the
a Diels–Alder reaction and this phenomenon has aqueous phase will also be more for Eq. (1). This
[
13,14]
been described as “on-water”effect.
In view of would result in a higher rate for the catalytic hydroge-
this we wanted to find out if for the solid nitroaromat- nation step that follows.
1960
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Adv. Synth. Catal. 2007, 349, 1955 – 1962

Superior Performance of a Nanostructured Platinum Catalyst in Water
FULL PAPERS
medium. Catalysts 1 and 2 were prepared and characterized
by the methods reported in our earlier work. Catalyst 3
Conclusions
[16]
was purchased from Aldrich Germany and used as received.
In conclusion, ion pairing of a platinum carbonyl clus-
ter with the quaternary ammonium groups of a water-
soluble polymer gives a platinum nanocatalyst that is
more active than a nanocatalyst prepared by hydro-
Experimental Catalytic Conditions
All hydrogenation reactions were carried out in an auto-
clave under hydrogen pressure at 300 K. In a typical experi-
ment 150 mg of catalyst were dissolved in either 5 mL dis-
tilled water or methanol in a 20-mL beaker and 1 g of sub-
strate was added to it. Then it was kept under the specified
hydrogen pressure in the autoclave at 300 K (otherwise
2À
gen reduction of [PtCl ] , or a commercialp al tinum
6
catalyst. Between the two nanocatalysts (1 and 2), the
cluster gives much smaller nanoparticles than
2À
[
PtCl ] . In the hydrogenation of o-chloronitroben-
6
zene both the nanocatalysts show higher chemoselec- mentioned in specialcases) for the respective time with vig-
tivity than the commercial platinum catalyst. For rep- orous stirring. After the reaction the product was separated
resentative substrates including safflower oil and in- by solvent extraction with ethyl acetate and subsequently
analyzed by GC or proton NMR spectroscopic techniques.
soluble organic solids, the activities in water are
Biphasic reactions were carried out in 1:1 (v/v) water and
found to be greater than those in methanolor a 1:1
toluene/ethyl acetate by following a similar method.
mixture of water and toluene.
The TON of safflower oil hydrogenation was determined
1
from the H NMR spectrum of hydrogenated safflower oil.
Due to hydrogenation the peak area for olefinic hydrogens
(
at 5.3 ppm) decreases considerably but that of the glycerol
Experimental Section
moiety (at 4.2 ppm) remains unaffected. By comparing the
peak areas of these two signals, remaining olefinic unsatura-
tion is calculated. Iodine values of safflower oil and its hy-
drogenated product were estimated using the Hüblmethod
which is a standard technique for the determination of
Preparation of the cluster-derived catalyst and subsequent
manipulation with it were performed using standard Schlenk
techniques under an atmosphere of nitrogen. Solvents were
dried by standard procedures (methanolover Mg-turnings/
iodine), distilled under nitrogen, and used immediately.
Starch solution was prepared according to conventional pro-
cedure prior to the titration for iodine value determination.
All hydrogenation reactions were performed in an autoclave
[31]
iodine value.
Supporting Information
TEM picture of used catalyst (after 2500 TON) with nitro-
benzene as a substrate (Figure S1).
1
13
at 300 K. H/ C NMR spectra were recorded on a 400 MHz
Varian spectrometer. TEM experiments were performed
using a Philips 1200 EX at 120 kV. UV-vis-NIR measure-
ments were performed on a Perkin Elmer lamda-950 spec-
trophotometer. FT-IR spectra were taken on a Nicolet spec-
trophotometer with samples prepared as KBr pellets. All
the samples were analyzed by gas chromatographic tech-
niques with an FID detector (Shimadzu GC-14 A gas chro-
matograph) using a capillary column (CBP20M-25–025).
The bulk platinum content of fresh catalyst 2 was deter-
mined on an 8440 Plasma Lab ICP-AES instrument.
Acknowledgements
Financial assistance from Reliance Industries Limited,
Mumbai and Council ofScienti ifc and Industrial Research,
New Delhi, India is gratefully acknowledged.
Poly(diallyldimethylammonium chloride) (polyDAD-
MAC, low molecular weight), 20 wt% solution in water, References
sodium hexachloroplatinate, methyl pyruvate, acrylic acid,
styrene, 5% platinum on alumina were purchased from Al-
drich, Germany and used as received. Carbon monoxide
was supplied by BOC, India. Resublimated iodine, mercu-
rous chloride, carbon tetrachloride, sodium acetate, benzal-
dehyde and all aromatic nitro compounds were puschased
from SD fine chemicals, India and used after proper distilla-
tion. Safflower oil was taken from a local market. All other
chemicals were of reagent grade and used after proper dis-
tillation prior to the catalytic experiments. Distilled water
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