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

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

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.

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

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.

References1 Selective catalytic oxidation of Hydrocarbons - A critical

A nalysis, Catalytic Assoc, Inc. Santer Clara, CA (1979).2 Castellino A J & Bruice T C, J Am Chem Soc, 110

(1988) 158.3 Castellino A J & Bruice T C, J Am Chem Soc, 110

(1988) 191.4 Taquikhan M M & Prakash Rao A, J Mol Catal; 39

(1987) 331.5 Garrison M J & Bruice T C, JAm Chem Soc, 111 (1989)

191.6 Halpern J, James B R & Kemp A L W, JAm Chem Soc,

83 (1961) 4097.7 Read G & Urgellas M, J Chem Soc Dalton Trans, (1985)

1591.8 Taquikhan M M, Mirza S A & Bajaj H C, J Mol Catal,

37(1986)253.9 TaquikhanMM, Oxidn Commun, 9 (1986) 105.

10 Anna B & Florian D, Waid Chern, 46 (1992) 367.11 Kluson P & Cerneny L, Chem Listy, 88(9)(1994) 555.12 Shiji M, Naoto C & Fumitoshi K, Shokubi, 36(8) (1994)

5265.13 Strohmeier W & Buckow G J, Organomet Chern, 110

(1976) C17.14 Tsuji J & Suzuki H, Chem Leu, (1977) 1085.15 Lyons J E,J Chem Soc Chem Commun, (1975)412.

16 Knifton J F, Tetrahedron Lett, 26 (1975) 2163.17 Grey R A, Pez G P & Wallo A, J Am Chem Soc, 103

(1981) 7536.18 Halpern J, Harrod J F & James B R, JAm Chem Soc, 88

(1966)5150.19 Fink Suess G & Reiner J J, Organomet Chern, 221 (1981)

C36.20 Livingston S E, Comprehensive Inorganic Chemistry (Per-

gamon Press, New York), 3 (1973) 1190.21 Evans D, Osdborn J A & Wilkinson G, J Chem Soc, (A)

(1968) 3133.22 Gore E S, Plat Met Rev, 27 (1989) 111.23 Neumann R & Khenkin A, Inorg Chern, 34(23) (1995)

57530.24 Kumbhar P S, Coq B, Moreau C, Moreacu P, Planiex J M

& Warawdekar M G, in Catalysis modem trends, (NarosaPublishing House, New Delhi) edited by Gupta N M .&Chakraborty D K, (1995).

25 Amphlett C B, Inorganic Ion Exchangers, (Elsevier, Am-sterdam) 1964.

26 Clearfield A, Nancollas G H & Blessing R H, Ion Ex-change and Solvent Extraction, (Eds) Marinsky J H &Marcus Y (Marcel Dekker, New York) Vol 5, 1973.

27 Clearfield A, Ed, Inorganic Ion Exchange Materials,(CRC Press, Inc, Boca Raton) 1982.

28 Clearfield A & Blessing R H, J Inorg Nucl Chern, 34(1972) 2643.

29 Vesely V & Pekarek V, Talanta, 19 (1972) 219.30 Vogel A I, (Eds) Fruniss B S, Hannaford, Rogers V, Smith

P W C & Tatchell A R, Text book of practical organicchemistry, 4th Ed. (Longman, London) 1978.

31 Lee R W, Nakagaki P C, Balasubramanian P N & BruiceT C, Proc Natl A cad Sci; USA, 85 (1988) 641.

32 Gupta J R P, Sharma R N & Prasad B B, J Sci Res, BHU,23 (1972) 103.

33 Vogel A 1, Text book of quantitative inorganic analysis,4th ed, (Longman, London) 1978.

34 Gilbert H A & Frederick Y, Anal Chern, 22 (1956) 1277.35 Alberti G & Torracca E J, Inorg Nucl Chern, 30 (1968)

3075.36 Ram R N & Prasad B B, Z Phys Chern, (Leipzig), 259

(1978) 1169.37 Sigel H, Fischer B R, Wyss K & Prijs B, Inorg Chern, 18

(1979) 1354.38 Sharma V S, Schubert J, Brooks H B & Sicilo F, J Am

Chem Soc, 92 (1970) 822.39 Shivanekar A S & Chudasama U V, J Mol Catal; 55

(1989) 199.40 Shivanekar A S & Chudasarna U V. Trans Met Chern, 15

(1990) 226.