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
was used for the catalytic studies in water or biphasic water
[1] Organic Synthesis in Water, (Ed.: P. A. Grieco), Black-
ie, London, 1998.
[2] C. J. Li, Chem. Rev. 1993, 93, 2023.
[3] U. M. Lindstrom, Chem. Rev. 2002, 102, 2751.
[4] R. Breslow, Acc. Chem. Res. 1991, 24, 159.
[5] R. Breslow, Structure and Reactivity in Aqueous Solu-
tion, ACS Symp. Ser., 1994, No. 568, 291.
[6] Aqueous-phase Organometallic Catalysis: Concepts and
Applications, (Eds.: B. Cornils, W. A. Herrmann),
Wiley-VCH, Weinheim, 1998.
Adv. Synth. Catal. 2007, 349, 1955 – 1962
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1961