-
Indian Journal of Chemical TechnologyVol. 3, November 1996, pp.
324· 328
Studies on some oxidation reactions using a Ru~III)supported
catalyst
Mukesh Upadhyay, Anjali Shivanekar & Uma Chudasama
Department of Chemistry, Faculty of Science, M S University of
Baroda, Baroda 390 002, India
Received 29 January 1996; accepted 27 June 1996
A metal catalyst has been prepared by supporting Ru(III) onto
zirconium molybdate to catalyzeoxidation reactions. The material
has been characterised and the catalytic activity has been
studiedvia hydrogen peroxide decomposition. Further, oxidation of a
few organic substrates such as norbor-nene, cis-cyclooctene,
styrene, cyclohexene and cyclohexane have been carried out.
The selective oxidation of organic compounds hasgained
importance in the chemical and petro-chemical industries in recent
years I. Among these,epoxidation of olefins, in particular, has
receivedmuch attention+". Epoxidation reaction' is an im-portant
reaction in organic synthesis because theformed epoxides are
intermediates that can beconverted into a variety of products.
Among the transition metals, ruthenium and itscomplexes are
extremely versatile oxidation cata-lysts, both homogenous and
heterogenous for awide range of organic substrates'. Ruthenium
andits complexes have been successfully employed ascatalysts in a
number of reactions=!", This ismainly because of the fact that
ruthenium exhibitsa wide range of oxidation states/? with a facile
in-terconversion of these, from one oxidation stateto another.
Ruthenium catalytic systems used sofar in the experimental work
seem to offer a lowenergy reaction pathway for the reactants
leadingto a fairly large turnover number of the product"and the
conditions for ruthenium catalysed sys-tems are very mild ".
Catalysis by supported metal ions is an area ofintense interest.
The metal ions have usually beenaffixed to polymer, silica or
alumina surfaces. Re-cently, ruthenium has been supported on to
dif-ferent supports like polyoxometallates" and zir-conia?", These
catalysts are found to be highly ac-tive for reactions such as
oxidation and hydrogen-ation23.24. The ion exchange method of
catalystimmobilization is simple when compared to theprocedures
required for the attachment of com-plexes to polymers-Y". The
synthesis and ion ex-change properties of crystalline and
amorphouszirconium molybdate have been studied earli-er2R•29•
Efforts have not been made to examine the
catalytic properties of zirconium molybdate. In-creasing
interest in supported metal catalysts, aswell as the commercial
importance of epoxidationof olefins, prompted the preparation of a
support-ed metal catalyst which could be used in oxida-tion
reactions. The present work consists of pre-paration of a catalyst
in which Ru(III) is support-ed onto zirconium molybdate (ZM). The
com-pound has been characterised for elemental analy-sis,
thermogravimetric analysis, surface area mea-surement (BET method)
and Fourier transforminfrared (FTIR). The catalytic activity has
beenstudied through hydrogen peroxide decomposi-tion. Further,
oxidation reactions of a few organicsubstrates such as norbornene,
cis-cyclooctene,styrene, cyclohexene and cyclohexane have
beeninvestigated.
Experimental ProcedureMaterials - Zirconium oxychloride and
ammo-
nium molybdate (BDH), ruthenium trichlorideand cyclohexane
(Fluka), styrene, cis-cyclooctene,cyclohexene and norbornene
(Aldrich) were usedas received. Water used was double
distilled,while dioxan was purified by a known method":The purities
of anisole (used as an internal stand-ard) and chlorobenzene was
ascertained by gas-chromatography. High purity nitrogen was
used.Sodium hypochlorite (NaOCI) was synthesized bya reported
method-",
Preparation of the support (ZM) - Zirconiummolybdate (ZM) was
prepared by the ammoniummolybdate method as reported earlier".
Preparation of the catalyst [Ru(//f) supported onZM;RuZM]
The acid treated ion exchanger (1 g) was placed
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UPADHYAY et al: Ru(III) SUPPORTED CATALYST 325
in a glass conical flask fitted with a stopper and25 mL of known
concentration of rutheniumtrichloride solution was added. The
exchangerwas kept in contact with the metal ion solutionfor 24 h
with intermittent shaking. It was finallyfiltered, washed with
conductivity water till thecomplete removal of the adhering metal
ion anddried at 100°C. All washings were collected withthe
filterate to determine the remaining quantityof Rutlll) ion. The
concentration of Ruilll) ionpresent on the exchanger was calculated
from thedifference between the initial and final concentra-tion of
the solution.
Catalytic test reactionHydrogen peroxide decomposition - A
weighed
quantity of the catalyst was shaken with 10 mL (4vol) of H202 at
25°C. The desired concentration ofH20Z was obtained by successive
dilution fromthe stock solution. The volume of O, evolved
wasmeasured at various time intervals and also aftercomplete
decomposition of the HzOz using a gasburette". Experiments were
carried out at differ-ent temperatures within a range of 25-40°C.
Theinfluence of various quantities of the catalyst used(0.025-0.075
g) and the effect of varying the con-centration of HzOz were
studied at 35°C.
Epoxidation of alkenes - All reactions werecarried out in a
schlenk tube, in nitrogen atmos-phere. The substrate and catalyst
were added in adioxan-water (7 : 3) mixture in which the
substrateis soluble and the solvent was deaerated bybubbling
nitrogen for 10 min. To this mixture, thesubstrate followed by the
internal standard wereadded. The total volume of the system was
10mL. Sodium hypochlorite (NaOCl) was added asan oxidant. The time
at which sodium hypochlor-ite was added was considered as the
initial time ofthe reaction. The mixture was stirred at
ambienttemperature for 2 h. Aliquots (1 mL) were with-drawn from
the reaction mixture with the help ofa Hamilton syringe and were
injected into the gaschromatograph. A Shimadzu GC 15 A,
equippedwith an integrator, detector (TCD) and flame ioni-zation
detector (FID) was used to monitor theprogress of the reaction.
Characterization methodsThe samples were analysed for zirconium
and
molybdenum. Zirconium was determined gravi-metrically as
zirconium oxide while molybdenumwas determined gravimetrically as
molybdenumoxide by the a-benzoin oxime method-". Ruflll)was
estimated spectrophotometrically by the Ru-thenium-Thiourea
method":
Thermogravimetric analysis of samples wereperformed on a
Shimadzu DT= 30 at a heatingrate of 1O°C/min under air. FTIR
spectra of thesamples were obtained using a KBr-wafer on aPerkin
Elmer FTIR, model 1720X, with Epson Hi80 printer/plotter. The
surface area of the materi-als was measured by the nitrogen
adsorption BETmethod and recorded on a Carlo-Erba sorptomat-ic
series-1800, at - 196°C.
Results and DiscussionChemical analysis indicates the
composition of
ZM, Zr: Mo to be 1: 1. The number of watermolecules have also
been calculated using Alber-ti's35 formula. From chemical analysis
and thermo-gravimetric analysis, the proposed formula forZM is
Zr02.Mo04.15H20.
TGA of ZM shows sharp change within thetemperature range of
100-180°C, correspondingto the loss of external water molecules.
After this,a slow change in weight loss is observed, whichmay be
due to the condensation of structural hy-droxyl groups. TGA of
Ru-ZM shows additionalweight loss within the temperature range of
360-424°C probably due to the removal of rutheniumfrom the
support.
The FI1R spectra of ZM shows broad bands inthe region - 3400 em
- 1 corresponding to asym-metric and symmetric hydroxo - OH and
aquo- OH stretches. A medium band at - 1620 cm-1and broad shoulder
at - 935 cm-1 indicates thepresence of aquo - [H - °-HJ bending and
zir-conium-oxygen stretching respectively. FI1R ofRu-ZM shows an
additional band at - 620 cm-1which may be attributed to Ru-O
stretching.
The surface area of Ru-ZM is 143 m2/g againstZM which is 25
m2/g.
In the present investigation, the kinetic analysisis based on
the initial rate data because the reac-tion rate approaches
equilibrium after a lapse oftime.
For Ru-ZM, it was found that the rate was in-dependent of
initial concentration of H202 (Table1a, Fig. 1), while an increase
in the amount of thecatalyst increased the rate of reaction (Table
Ib,Fig. 2). An increase in the reaction temperatureincreases the
rate of decomposition (Table lc,Fig. 3).
The colour of the surface adsorbed metal ionchanges from dark
brown to light brown when itcomes in contact with HzOz. The colour
persistedas long as any residual H202 remained in the sys-tem.
After complete decomposition of the hydro-gen peroxide, the
catalyst regained its original
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326 INDIAN J. CHEM. TECHNOL.. NOVEMBER 1996
Table I-Catalytic activity of Ru( III) sorbed on
zirconiummolybdate
a - Influence of concentration of hydrogen peroxide"
Concentration ofH202 (vol}.
Specific reaction rate104K, min-I
5.00
7.50
lO.OO
2.97
2.97
2.96
b - Influence of catalyst on decomposition of
hydrogenperoxide=
Quantity of Ru(III) Specific reaction rate104K,min-1
3.50 X 10-3
7.00 X 10-3
1.05 X 10-2
2.06
2.96
3.10
c - Influence of temperature on decomposition of
hydrogenperoxide!
Temperature'C
Specific reaction rate104K, min-I
Energy ofactivationkcal mol-I
25
30
35
40
1.28
2.06
2.96
4.20
13.00
0.05 g, reaction tempera--Quantity of catalystture = 35'C"Volume
of hydrogen peroxide - 10 mL (4 vol), reactiontemperature =
35'C
"Quantity of catalyst = 0.05 g, volume of hydrogenperoxide = 10
mL (4vol)
colour. This could be due to the formation of aperoxo
species36-38•
Based on the above observations the followingreaction mechanism
has been suggested, as pro-posed earlier'v". It is known36.37 that
H202 disso-ciates to
... (1)
The surface Ru(Ill} may interact with HOl ionsto form an
intermediate complex.
Surface - Ru3+ + HOl -+Surface" lRu{H02 )]2:" ... (2)
A second molecule of H202 may then interactwith the intermediate
complex to form the pro-ducts
1.7 r-----------,
JCIa01o
o 40Tim~,s
Fig. 1 - Plot of log( a - x) vs time for different
concentrationof hydrogen peroxide ITa) 5 vol ,(b) 75 vol and (cl
10
vol 1
••I
a 1.50sa
1·40
o 10 20 30Tim~ ,s
Fig. 2 - Plot of log(a- x) vs time for different amounts of
ca-talyst [(a) 75 mg, (b) 50 mg and (c) 25 mg)
Surface - [Ru(H02)J2 + + H202 -+Surface - Ru3+ + H20 + O2 + OH-
... (3)
During the course of decomposition of H202,pH increases, which
is in keeping with the abovemechanismlv". From the Arrhenius plot
(Fig. 4)the energy of activation calculated is 13 kcallmol.
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UPADHYAY et al.: Ru(m) SUPPORTED CATALYST
1·7
a
o 10 20 30 40Tim~, s
Fig. 3 - Plot of log (at-x) vs time at different temperatures
[(a)40°C, (b) 35°C, (c) 30°C and (d) 25°C
The above reactions, suggest the probable useof Ru-ZM as an
oxidation catalyst. In order toconfirm this, some oxidation
reactions of alkenesand alkanes such as norbornene, styrene,
cis-cyclooctene, cyclohexene and cyclohexane werecarried out using
Ru-ZM as a catalyst. It wasfound that alkenes or alkanes used did
not under-go oxidation in absence of either catalyst or anoxidant.
Thus catalyst and oxidant are both essen-tial for the epoxidation
reactions.
Generally, the above mentioned substrates yieldthe following
products on oxidation.
Norbornene -+ Norbornene oxideNorbornenol exoNorbomenol endo
cis-cyclooctene -+ Cyclooctene oxideStyrene -+ Styrene oxide
PhenylacetaldehydeAcetophenoneBenzaldehyde
Cyclohexene -+ Cyclohexene
oxide2-Cyclohexen~-1-one2-cyclohexene-l-ol
Cyclohexane -+ CyclohexanolCyclohexanone
327
-3·3r-------------,
-3'
¥ -3,6
'"o-3"
-3'&
- 3·9
3·1 3-2 3-3 3 4 3-5
11T X 103 K-1,Fig. 4 - Plot of log K vs liT X 10-3 (Arrhenius
plot)
Table 2 - Epoxidation of various olefins with sodiumhypochlorite
catalysed by Ru-ZM
Substrate Product % Yield basedon oxidant
Norbomene Norbomene oxide 12.00
cis-Cyclooctene cis-Cyclooctene oxide 1(;.00
Styrene Styrene oxide 5.00Benzaldehyde 8.00
Cyclohexene Cyclohexene oxide 6.002-Cyclohexene-ll..one
2.002-Cyclohexene-l-ol 13.00
Cyclohexane Cyclohexanone 6.00
The results of oxidation of alkenes and alkaneswith sodium
hypochlorite using Ru-ZM as cata-lyst are shown in Table 2. As seen
from Table 2norbomene and cis-cyclooctene give the respec-tive
oxides selectively. Oxidation of styrene alsoselectively gives
benzaldehyde as a major productwhile styrene oxide is found to be
less. This isdue to the oxidative cleavage of styrene. Oxida-tion
of cyclohexene is accompanied by a largeamount of allylic
hydroxylation and subsequentformation of ketone, 2-Cyclohexene-l-ol
is foundin large amount as compared to cyclohexene ox-ide and
2-cyclohexene-l-one. Oxidation of cyclo-hexane gives cyclohexanone
selectively.
A phase transfer catalyst could transfer ions,free radicals and
molecules from the aqueous tothe organic phase. Since the present
reactions
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328 INDIAN J. CHEM. TECHNOL., NOVEMBER 1996
were carried out in dioxan-water media., it wasthought of
interest to carry out the reactions usinga phase transfer catalyst,
in order to observe anychange in the yields of the products
obtained. Thereactions were carried out under same conditionsexcept
making use of..cetyl tetra ammonium bro-mide (CTAB) as a phase
transfer catalyst. Theyields observed are however, almost the
same.
This study shows that the use of a phase trans-fer catalyst does
not have much effect on theyields of the products obtained and
confirms theuse of Ru-ZM as an oxidation catalyst.
AcknowledgementThanks are due to the Head, Department of
Chemistry, for providing necessary laboratoryfacilities. One of
the authors (AS) is also thankfulto CSIR, New Delhi for the award
of a fellowship.
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