Ruthenium containing hydrotalcite as a solid base catalyst for >C{double bond, long}C< double bond isomerization in perfumery chemicals

Article abstract of DOI:10.1016/j.molcata.2009.10.017

Ruthenium containing hydrotalcite (Ru-Mg-Al) is used as a solid base catalyst for >C{double bond, long}C< double bond isomerization of methyl chavicol, eugenol, safrole, allylbenzene, dimethoxy allylbenzene and 3-carene. The catalyst showed excellent conversion and selectivity for isomerization reaction in shorter reaction time (2 h). Catalytic activity and reusability of Ru-Mg-Al was compared with ruthenium impregnated catalysts such as, Ru-HT, Ru-MgO, Ru-CaO, Ru-SiO₂ and Ru-alumina for isomerization of methyl chavicol to trans-anethole. Ru-Mg-Al catalyst was reused four times without loss in its activity, however, significant loss in the conversion of methyl chavicol and selectivity of trans-anethole was observed on reusability of other ruthenium impregnated catalysts. The conversion of methyl chavicol and selectivity of trans-anethole was found to increase on increasing the reaction temperature as well as amount of catalyst. At 0.005 g catalyst amount, 55% conversion of methyl chavicol with 68% selectivity of trans-anethole was observed that increased to 93% with 82% selectivity of trans-anethole at 0.05 g catalyst amount. On further increase in the amount of catalyst to 1 g, conversion increased to 98% with 88% selectivity of trans-anethole.

Full text of DOI:10.1016/j.molcata.2009.10.017

Journal of Molecular Catalysis A: Chemical 317 (2010) 27–33
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Ruthenium containing hydrotalcite as a solid base catalyst for >C C< double
bond isomerization in perfumery chemicals
Sumeet K. Sharmaa,b, Parimal A. Parikhb, Raksh V. Jasraa,∗
a Discipline of Inorganic Materials & Catalysis, Central Salt and Marine Chemicals Research Institute (CSIR), G.B. Marg, Bhavnagar 364002, Gujarat, India
b Department of Chemical Engineering, SV National Institute of Technology, Surat 395007, Gujarat, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 June 2009
Received in revised form 5 October 2009
Accepted 14 October 2009
Available online 22 October 2009
Ruthenium containing hydrotalcite (Ru–Mg–Al) is used as a solid base catalyst for >C C< double bond
isomerization of methyl chavicol, eugenol, safrole, allylbenzene, dimethoxy allylbenzene and 3-carene.
The catalyst showed excellent conversion and selectivity for isomerization reaction in shorter reaction
time (2 h). Catalytic activity and reusability of Ru–Mg–Al was compared with ruthenium impregnated
catalysts such as, Ru–HT, Ru–MgO, Ru–CaO, Ru–SiO2 and Ru–alumina for isomerization of methyl chav-
icol to trans-anethole. Ru–Mg–Al catalyst was reused four times without loss in its activity, however,
significant loss in the conversion of methyl chavicol and selectivity of trans-anethole was observed on
reusability of other ruthenium impregnated catalysts. The conversion of methyl chavicol and selectivity
of trans-anethole was found to increase on increasing the reaction temperature as well as amount of cata-
lyst. At 0.005 g catalyst amount, 55% conversion of methyl chavicol with 68% selectivity of trans-anethole
was observed that increased to 93% with 82% selectivity of trans-anethole at 0.05 g catalyst amount. On
further increase in the amount of catalyst to 1 g, conversion increased to 98% with 88% selectivity of
trans-anethole.
Keywords:
Methyl chavicol
Anethole
Eugenol
Hydrotalcite
Solid base catalyst
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
and eugenol to trans-isoeugenol in homogeneous reaction condi-
tions [5,6]. In another study, hydrotalcite, ion exchanged zeolites
>C C< double bond isomerization reaction is of great interest
because of its potential commercial applications for the synthesis
of fine and perfumery chemicals [1]. For example, trans-anethole is
a valuable perfumery chemical [2,3] and intermediate for the syn-
thesis of other chemicals. Synthetically, trans-anethole is produced
via double bond isomerization of methyl chavicol [4] using strong
liquid base like potassium hydroxide and sodium hydroxide used
in stoichiometric amounts. Highest conversion of methyl chavicol
(56%) with 82:18 trans- to cis-anethole ratio has been reported in
12 h at 200 ◦C [4]. However, this method suffers from drawbacks
like, post-synthesis work-up to separate spent KOH or NaOH from
reactant/product mixture, use of solvent, longer reaction time and
lower conversion. Therefore, it is desirable to develop an environ-
mentally benign catalytic process for the solvent free synthesis of
trans-anethole via double bond isomerization of methyl chavicol in
a shorter reaction time.
were used as catalysts for isomerization of methyl chavicol in 10 h
reaction time [7]. Kishore and Kannan studied the catalytic activ-
ity of as-synthesized hydrotalcite having divalent and trivalent
metals in varied ratios for isomerization of eugenol [8], safrole
[9,10] and estragole [11] in various polar and non-polar organic
solvents. In another study, hydrotalcite of different compositions
and varied divalent to trivalent cations ratio were used as cata-
lysts for the isomerization of methyl chavicol and eugenol in the
presence of dimethyl formamide (DMF) as a solvent [8,11]. Con-
version of eugenol was achieved up to 75% with 85% selectivity of
trans-isoeugenol in 6 h at substrate to catalyst ratio 2:1. The main
drawbacks of these studies are the use of DMF as a solvent, very
low substrate to catalyst ratio, non-reusability of catalyst and lower
conversion using impregnated catalyst.
Hydrotalcite
or
layered
double
hydroxides
(HT;
[M(II)1−xM(III)x(OH2)]x+(CO3
)x/n·mH2O; where M(II) = Mg or
2−
In our earlier reports, transition metal complexes of rhodium,
ruthenium and palladium were demonstrated as potential catalysts
for double bond isomerization of methyl chavicol to trans-anethole
divalent cation and M(III) = Al or trivalent cation) is an attractive
catalyst due to the availability of wide variety of basicity which can
be achieved by proper tuning of the M(II) and M(III) molar ratio,
intercalation of suitable anion in the interlayer space or activation
of hydrotalcite at 450 ◦C. Various metals can be introduced into
the brucite layer via isomorphic substitution of M(II) or M(III)
cations at the octahedral sites, which are expected to be the active
sites for organic transformations [12,13]. Ruthenium incorporated
∗
Corresponding author at: R&D Centre, VMD, Reliance Industries Limited, Vado-
dara 391346, Gujarat, India. Tel.: +91 265 6696313; fax: +91 265 6693934.
E-mail addresses: rakshvir.jasra@ril.com, rvjasra@gmail.com (R.V. Jasra).
1381-1169/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2009.10.017

28
S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 317 (2010) 27–33
hydrotalcite samples are reported to be highly active catalyst
for oxidation of alcohols and aromatic compounds [14], direct
alkylation of nitriles with primary alcohols [15] and for the one-
pot synthesis of quinolines [16]. Apart from these applications,
the literature is silent on the potential of ruthenium containing
hydrotalcite as a catalyst for various organic transformations.
The present manuscript describes the use of ruthenium con-
taining hydrotalcite (Ru–Mg–Al) as a reusable eco-friendly catalyst
for solvent free double bond isomerization in perfumery chemicals
such as methyl chavicol, eugenol, safrole, allylbenzene, dimethoxy
allylbenzene and 3-carene (Scheme 1).
2.2.2. Synthesis of ruthenium impregnated catalysts
Impregnation of ruthenium (Ru) metal on solid base supports
namely HT(3.5), MgO, CaO, alumina, SiO2 was carried out to
compare the catalytic activity of Ru-impregnated catalysts with
Ru–Mg–Al by the following procedure. An aqueous solution of
RuCl3·xH2O (0.5 mmol) in 40 mL deionized double distilled water
was added drop wise to the suspension of 5.1 g of respective solid
support in 40 mL water under N2 atmosphere. The mixture was vig-
orously stirred for 16 h at 30 ◦C. The slurry was filtered and washed
with hot distilled water until the filtrate was free from Cl− ions
(silver nitrate test). Then the filter cake was dried at 80 ◦C for 14 h.
2.3. Characterization of catalysts
2. Experimental
Powder X-ray diffraction (P-XRD) patterns of synthesized cat-
alysts were recorded on a Philips X’Pert MPD system equipped
with XRK 900 reaction chamber, using Ni-filtered Cu K␣ radiation
(ꢀ = 1.54056 Å) over a 2ꢁ range of 5–70◦. Operating voltage and cur-
rent were kept at 40 kV and 40 mA, respectively. The percentage
crystallinity of HT(3.5) and Ru–Mg–Al were calculated by the sum-
mation of integral intensities of diffraction peaks corresponding
to (0 0 3) and (0 0 6) planes. The values of unit cell parameters (a
and c) of HT(3.5) and Ru–Mg–Al samples were calculated by the
formula: a = 2(d1 1 0) and c = 3(d0 0 3); where d1 1 0 and d0 0 3 are the
basal spacing values of (1 1 0) and (0 0 3) planes respectively [17].
Fourier transform infra-red (FT-IR) spectra of synthesized cat-
alysts were recorded with a PerkinElmer Spectrum GX FT-IR
spectrometer in the region of 400–4000 cm−1 using KBr pellets.
Thermogravimetric analysis (TGA) of HT(3.5) and Ru–Mg–Al sam-
ples were carried out using a Mettler Toledo TGA/SDTA 851e
equipment in nitrogen flow (flow rate = 50 mL/min) at a heating
rate of 10 ◦C/min and the data were processed using stare software.
Surface area of synthesized catalysts was measured using ASAP
2010 Micromeritics, USA. The samples were activated at 120 ◦C for
4 h under vacuum (5 × 10−2 mmHg) prior to N2 adsorption mea-
surements. The specific surface area of the samples was calculated
from N2 adsorption isotherms measured at 77.4 K as per Brunauer,
Emmett, Teller (BET) method. Chemical analyses of the catalysts
were carried out using Inductive Coupled Plasma (ICP) Spectrome-
ter, PerkinElmer, Optima 2000 instrument.
2.1. Materials
Magnesium chloride [MgCl2·6H2O; 98%], aluminum chloride
[AlCl3·9H2O; 98%], sodium carbonate [Na2CO3; 99.9%], sodium
hydroxide [NaOH; 99.9%], silica [SiO2; surface area = 200 m2/g], CaO
[surface area = 92 m2/g], MgO [surface area = 130 m2/g] and alu-
mina [Al2O3; surface area = 192 m2/g] were purchased from S.D.
Fine Chemicals Ltd., Mumbai, India and used as received. Ruthe-
nium trichloride [RuCl3·xH2O], methyl chavicol, eugenol, safrole,
allylbenzene, 3-carene, dimethoxy allylbenzene and tetradecane
(98%) were procured from Sigma–Aldrich, USA and used without
further purification. The double distilled milli-pore deionized water
was used for the synthesis of catalysts.
2.2. Catalyst preparation
2.2.1. Synthesis of ruthenium hydrotalcite [Ru–Mg–Al]
Ruthenium grafted hydrotalcite was prepared by co-
precipitation method at a constant pH [12]. In a typical synthesis
procedure, an aqueous solution (A) containing MgCl2·6H2O
(0.0522 mol), AlCl3·H2O (0.0144 mol) and RuCl3·xH2O (0.5 mmol)
in 50 mL double distilled deionized water was prepared. The solu-
tion A was added drop wise into a second solution (B) containing
Na2CO3 (0.079 mol) in 50 mL double distilled deionized water,
in around 45 min under vigorous stirring at 30 ◦C. Constant pH
of the mixture was maintained by adding 1 M NaOH solution.
Content was then transferred into the teflon coated stainless steel
autoclave and aged at 80 ◦C for 16 h under autogenous water
vapor pressure. After 16 h, the precipitate formed was filtered
and washed thoroughly with hot distilled water until the filtrate
was free from Cl− ions as tested by silver nitrate solution. The
obtained filter cake was dried in an oven at 80 ◦C for 14 h. The
solid material (yield = 5.1 g) named as Ru–Mg–Al, was ground and
stored under vacuum. The activation of Ru–Mg–Al was carried out
in a muffle furnace at 450 ◦C for 4 h. Synthesis of Mg–Al hydrotal-
cite sample with Mg/Al molar ratio of 3.5 [HT(3.5)] was done as
per the above-mentioned procedure without use of RuCl3·xH2O
solution.
2.4. Isomerization reaction and products analysis
For the double bond isomerization reactions, calculated amount
of reactant and catalyst were taken with 0.01 g tetradecane (used
as an internal GC standard) in a 25 mL double necked round bottom
flask. One neck of the flask was fitted with refluxing condenser and
another neck of the flask was blocked with silicon rubber septa.
The flask was kept in an oil bath equipped with temperature and
agitation speed controllers and the reaction was carried out under
nitrogen atmosphere. The analysis of product mixture was carried
out by gas chromatography (GC; Shimadzu 17A, Japan), having 5%
diphenyl and 95% dimethyl siloxane universal capillary column
(60 m length and 0.25 mm diameter) and flame ionization detec-
tor (FID). The initial column temperature was increased from 100
to 220 ◦C at the rate of 10 ◦C/min using nitrogen as a carrier gas.
The temperature of injection port and FID were kept at 250 and
300 ◦C, respectively, during the analysis of product mixture. The
retention times for each compound were determined by injecting
pure compound under identical GC conditions.
Experiments were repeated under identical reaction conditions
to ensure the reproducibility of the reaction. Conversion and selec-
tivity data were found to be reproducible within 2% variation.
For kinetic studies, samples (0.1 mL) were taken out during the
course of experiment using glass syringe at different time inter-
vals. For reusability of the catalysts, spent catalyst was washed with
Scheme 1. Double bond isomerization of methyl chavicol.

S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 317 (2010) 27–33
29
Fig. 1. P-XRD patterns of HT(3.5) and Ru–Mg–Al samples.
Fig. 2. FT-IR spectra of HT(3.5) and Ru–Mg–Al samples.
methanol to remove adsorbed reactant/products from the surface
of catalysts. After that the catalyst was dried for 10 h at 100 ◦C and
reused for isomerization reaction.
Ru–alumina and Ru–SiO2 were observed similar to their pristine
counterparts (Fig. 1; Supporting Information).
3. Results and discussion
FT-IR spectra of HT(3.5) and Ru–Mg–Al samples (Fig. 2) showed
all the characteristic peaks of hydrotalcite structure [18,19]. The
peak at around 3450–3480 cm−1 is due to the ꢂOH mode of H-
bonded hydroxyl groups in the layers and broadening of this peak
is dependent on the strength of hydroxyl bonds. Shoulder present
at 3000 cm−1 is attributed to the hydrogen bonding of hydroxyl
groups of layered lattice and/or water molecules with interlayer
carbonate anions [18]. Band that appeared at around 1640 cm−1 is
due to the deformation mode of interlayer water molecules. Inten-
sity of this band suggests the content of water molecules in the
material. The sharp, intense vibrational band at around 1370 cm−1
is assigned to the asymmetric ꢂ3 mode of interlayer carbonate
anions and absence of the band at around 1050 cm−1 suggests
the retention of D3h symmetry of carbonate anions in the inter-
3.1. Characterization of catalyst
The sharp and symmetric reflections of (0 0 3) and (0 0 6)
planes at low values of 2ꢁ angles (11–23◦) and broad, asym-
metric reflections at higher 2ꢁ angles (34–66◦) were observed in
the P-XRD patterns of HT(3.5) and Ru–Mg–Al samples (Fig. 1).
These reflections at respective 2ꢁ angles are typical characteristics
of the hydrotalcite and revealed a good dispersion of aluminum
and ruthenium in the brucite layers [18]. The P-XRD pattern of
Ru–Mg–Al sample shows that the characteristic original planes
of HT(3.5) are retained after incorporation of ruthenium in the
brucite sheet. Presence of CO3
2−
anions in the interlayer space
of HT(3.5) and Ru–Mg–Al samples was confirmed by the charac-
teristic basal spacing of (0 0 3) plane; d0 0 3 = 7.65 Å. Any additional
peaks corresponding to other crystalline phases were not observed
in the P-XRD pattern of Ru–Mg–Al. The intensities of (0 0 3) and
(0 0 6) planes, which are directly related to the crystallinity were
observed to decrease to 88% for Ru–Mg–Al sample as compared
to pristine HT(3.5) (Table 1). Decrease in the crystallinity on intro-
ducing the ruthenium cations in hydrotalcite structure (Ru–Mg–Al)
could be attributed to the increase in the number of cations of
higher ionic radii in brucite sheet. Increase in the value of a was
also observed for Ru–Mg–Al sample (3.069 Å) as compared to pris-
tine hydrotalcite (3.064 Å) due to larger ionic radii of ruthenium
(0.68 Å) as compared to aluminum (0.53 Å). Decrease in the value of
unit cell parameter c was observed for Ru–Mg–Al sample (23.38 Å)
as compared to the value for HT(3.5) (23.41 Å). This results into
decrease in charge density on layers due to weaker interaction
(or decrease in Coulombic attractive force) between the negatively
charged interlayer anions and positively charged brucite like lay-
ers [12,16,18]. P-XRD patterns of Ru–HT(3.5), Ru–MgO, Ru–CaO,
layer space. The bands in low frequency region (below 1000 cm−1
)
are related with Mg–OH, Al–OH and Ru–OH vibrational modes in
brucite-type layers. The bands at 950 cm−1 for the deformation of
Al–OH and at 780 cm−1 for Al–OH translation were also observed.
The peak at around 660 cm−1 (ꢂ4) is attributed to the in-plane car-
bonate bending. The band at 560 cm−1 is assigned to the translation
modes of hydroxyl groups, influenced by Al3+ cations (Mg/Al–OH
translation) [20]. The presence of band at 418 cm−1 is attributed to
the Mg–OH vibrational mode.
Thermogravimetric analysis (TGA) curves of HT(3.5) and
Ru–Mg–Al shown in Fig. 3 reveal two stage weight loss accompa-
Table 1
Physical characterization of the catalysts.
HT(3.5)
Ru–Mg–Al
Crystallinity, %
100
88
Unit cell parameter (a), Å
Unit cell parameter (c), Å
W1, %; (T1, ◦C)
3.064
23.41
8; (80–160)
36; (300–550)
76
3.069
23.38
13; (180–220)
26; (320–450)
80
W2, %; (T2, ◦C)
Surface area, m2/g
Fig. 3. TGA of HT(3.5) and Ru–Mg–Al samples.

30
S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 317 (2010) 27–33
nied by endothermal transformations. TGA curves of HT(3.5) and
Ru–Mg–Al samples showed similar weight loss patterns. The 13%
weight loss was observed in the Ru–Mg–Al sample at first stage
(180–200 ◦C) which is attributed to the loss of physically adsorbed
water molecules with relatively smaller amounts of condensed
water molecules and CO2. The 26% weight loss in second stage
(300–450 ◦C) was observed due to removal of condensed water
molecules and carbon dioxide from the carbonate anion present in
the interlayer space of Ru–Mg–Al. During this temperature range,
interlayer carbonate anions were thermally oxidized by a nearby
interlayer water molecule to produce volatile CO2 and interlayer
hydroxyl anions. Observed lower weight loss in the Ru–Mg–Al sam-
ple as compared to HT(3.5) is due to the presence of ruthenium
cations in the matrix of brucite sheet which led to higher ther-
mal stability of the catalyst. Ruthenium content in the Ru–Mg–Al
hydrotalcite sample was calculated by ICP and EDX analysis. The
percentage ruthenium content in the Ru–Mg–Al hydrotalcite sam-
ple was found to be 1.0% (by wt).
BET surface area of HT(3.5) and Ru–Mg–Al samples was found
to be 76 and 80 m2/g, respectively (Table 1). Increase in the surface
area for ruthenium containing hydrotalcite sample is attributed to
the observed decrease in the crystallinity as compared to [HT(3.5)]
sample which is also seen from P-XRD patterns. Surface area
of other ruthenium impregnated samples, Ru–HT, Ru–alumina,
Ru–MgO, Ru–SiO2, Ru–CaO was found to be 82, 161, 92, 172,
80 m2/g, respectively. The catalytic activity of Ru–Mg–Al was
investigated for double bond isomerization of methyl chavicol to
anethole, a base catalyzed reaction, by varying the amount of cata-
lyst and reaction temperature.
Fig. 5. Effect of reaction temperature on conversion of methyl chavicol and selec-
tivity of trans-anethole using Ru–Mg–Al as a catalyst.
lyst. No conversion of methyl chavicol was observed in the absence
of the catalyst.
The conversion of methyl chavicol was found to increase on
increasing the reaction temperature (Fig. 5). At 100 ◦C, only 41%
conversion of methyl chavicol was observed, which increased to
98% on increasing the reaction temperature to 210 ◦C. At lower tem-
perature (100 ◦C), 74% selectivity of trans isomer was observed that
increased to 88% at 210 ◦C.
3.3. Catalytic activity and reusability of various ruthenium
impregnated catalysts
3.2. Catalytic activity of Ru–Mg–Al for double bond isomerization
of methyl chavicol
The catalytic activity and reusability of Ru–Mg–Al was
compared with ruthenium impregnated catalysts namely, hydro-
talcite [Ru–HT(3.5)], magnesium oxide (Ru–MgO), calcium oxide
(Ru–CaO), silica (Ru–SiO2) and alumina (Ru–Al2O3) (Table 2) by
keeping similar ruthenium content at optimum reaction condi-
tions. Pristine hydrotalcite, magnesium oxide, calcium oxide, silica
and alumina were also used as catalysts to observe the role of ruthe-
nium on their catalytic activity. Ruthenium incorporated in the
brucite layer (Ru–Mg–Al) catalyst gave 98% conversion of methyl
chavicol with 88% selectivity of trans-anethole within 2 h reaction
time. Conversion and selectivity data for isomerization of methyl
chavicol were observed to remain unchanged even after fourth run,
confirming that the catalyst is reusable for the isomerization reac-
tion without loss in its activity. The ruthenium metal complexes
in homogeneous condition are well documented in the literature
for isomerization of olefinic double bond [6]. The higher activity
of Ru–Mg–Al catalyst as compared to HT(3.5) is due to presence
of ruthenium in the brucite layer via isomorphic substitution of
Mg or Al cations in the octahedral sheet is expected to be respon-
sible for double bond isomerization reaction. Most of the active
sites (hydroxyl groups coordinated to the ruthenium cations) are
located at the outer surface of Ru–Mg–Al catalyst that makes it as
an active and reusable catalyst. Another reason for higher activity
of Ru–Mg–Al catalyst is the increased surface area of Ru–Mg–Al
sample which favors the enhanced catalytic activity of the material
as compared to the pristine hydrotalcite. No significant leaching of
the ruthenium metal from the Ru–Mg–Al catalyst was observed in
the ICP analysis of filtrate, due to the strong coordination of ruthe-
nium cations in the hydrotalcite matrix as well as to the hydroxyl
groups.
Catalytic activity of Ru–Mg–Al was evaluated for the isomeriza-
tion of methyl chavicol to trans-anethole and the corresponding
data on methyl chavicol conversion and trans-anethole selectivity
are shown in Fig. 4. Conversion of methyl chavicol and selectiv-
ity of trans-anethole was observed to increase with increase in the
amount of catalyst up to 0.1 g. On further increase in the amount
of catalyst, no significant effect on conversion and selectivity of
trans-anethole was observed. Therefore, 0.1 g catalyst amount was
chosen as an optimum catalyst amount for further study. Lower
catalytic activity at low catalyst amount is due to the unavailability
of sufficient active sites for isomerization reaction. As the amount
of catalyst increased, availability of the active sites for double bond
isomerization increases significantly. Therefore, higher conversion
of methyl chavicol was observed on increasing the amount of cata-
Ru–HT(3.5) showed comparable results, i.e. 97% conversion
of methyl chavicol and 87% selectivity of trans-anethole, to the
Ru–Mg–Al catalyst. However, conversion and selectivity were
Fig. 4. Catalytic activity of Ru–Mg–Al sample for isomerization of methyl chavicol
to trans-anethole at varied amount of catalyst.

S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 317 (2010) 27–33
31
Table 2
tine CaO as a catalyst (15%). Rapid decrease in the conversion and
selectivity data is due to the faster leaching of ruthenium metal. ICP
analysis of Ru–CaO shows that the 86% of ruthenium was leached
out from the catalyst after third cycle. Ruthenium impregnated sil-
ica and alumina also gave similar conversion of methyl chavicol
(98%). However, higher selectivity of trans-anethole was observed
with Ru–alumina (84%) as compared to Ru–SiO2 (79%). On reusabil-
ity of catalyst, rapid decrease in the conversion and selectivity
was observed for Ru–SiO2 as compared to Ru–alumina. The lower
conversions of methyl chavicol, i.e. 5 and 10% were found when
pristine SiO2 and alumina, respectively, were used as catalysts.
From the above data, Ru–Mg–Al was observed as a reusable catalyst
for the double bond isomerization of methyl chavicol to trans-
anethole. Except Ru–CaO, no significant effect of solid supports
was observed on the conversion of methyl chavicol and selectiv-
ity of trans-anethole for isomerization of methyl chavicol. However,
leaching of ruthenium from the solid supports has significant effect
on the catalytic activity and reusability of ruthenium impregnated
catalysts. Lower activity of Ru–CaO may be due to the lower surface
area of catalyst.
Conversion and selectivity data of various ruthenium containing catalysts for iso-
merization of methyl chavicol to anethole.
Catalyst
Cycle
% Conversion
% Selectivitya
trans-Anethole
cis-Anethole
First
Second
Third
98
98
98
97
88
88
88
87
12
12
12
13
Ru–Mg–Al
Fourth
First
Second
Third
97
95
92
88
87
85
81
76
13
15
19
24
Ru–HT(3.5)
Fourth
First
Second
20
4
80
81
20
19
HT(3.5)
Ru–MgO
First
Second
Third
97
97
89
84
85
82
78
71
15
18
22
29
Fourth
MgO
First
Second
24
6
72
70
28
30
Ru–CaO
First
Second
Third
62
15
7
90
87
85
84
10
13
15
16
3.4. Kinetic study for isomerization of methyl chavicol at
optimum reaction conditions
Fourth
3
For the kinetic study, reaction was carried out by taking 10 g
methyl chavicol with 1 g Ru–Mg–Al as a catalyst at 210 ◦C reaction
temperature. The kinetic profile for conversion of methyl chavicol
and formation of cis- and trans-anethole with respect to time is
shown in Fig. 6. 60% conversion of methyl chavicol was achieved
within 2 min of reaction time that was observed to increase to
95% in 10 min. Most of the methyl chavicol was consumed for the
formation of thermodynamically stable trans-anethole, however,
small amount of cis-anethole was also observed at beginning of
the reaction. As the reaction proceeded, formation of cis-anethole
was also observed to increase. Initial rate of reaction for consump-
tion of methyl chavicol was found to be 0.0026 mol g−ca1t min−1 in
the conversion range up to 25%. The initial rate of reaction for the
formation of cis- and trans-anethole was calculated as 0.0003 and
0.0023 mol g−ca1t min−1, respectively. The higher initial rate of reac-
tion shows that the formation of trans isomer is more favorable in
the present reaction conditions as compared to cis isomer.
CaO
First
Second
15
2
75
65
25
35
First
Second
Third
98
85
77
70
79
73
62
59
21
27
38
41
Ru–SiO2
Fourth
First
Second
5
–
45
–
55
–
SiO2
First
Second
Third
98
94
90
87
84
80
77
73
16
20
23
27
Ru–Alumina
Fourth
First
Second
10
2
72
–
28
–
Alumina
a
Reaction conditions: methyl chavicol = 5.0 g, catalyst = 0.5 g, tempera-
ture = 210 ◦C and reaction time = 2 h.
observed to decrease on reusability of the catalyst for the isomer-
ization of methyl chavicol. For example, the conversion of methyl
chavicol decreased from 97 to 88% with 76% selectivity for trans-
anethole at the end of fourth cycle. Decrease in the conversion
and selectivity is attributed to the leaching of ruthenium cations
as 6% leaching was confirmed by ICP analysis from the surface of
impregnated catalyst [Ru–HT(3.5)] during the catalytic reaction.
20% conversion of methyl chavicol was achieved with 80% selec-
tivity of trans-anethole in 2 h using pristine hydrotalcite of Mg/Al
molar ratio (3.5) [HT(3.5)] as a catalyst. On reuse of the catalyst,
only 4% conversion of methyl chavicol was observed, which shows
that the [HT(3.5)] is not a reusable catalyst in the present study
for double bond isomerization reaction. On impregnation of ruthe-
nium on MgO, the conversion of methyl chavicol increased from
24% (using pristine MgO as a catalyst) to 97% with 85% selectivity
of trans isomer. The activity of Ru–MgO was observed to decrease
on reusability experiments. At the end of fourth cycle, conversion
of methyl chavicol decreased to 84% with 71% selectivity of trans-
anethole. Among all ruthenium impregnated catalysts, Ru–CaO
showed lower conversion of methyl chavicol (62%) with higher
selectivity of trans-anethole (90%). The conversion was found to
decrease very rapidly on the reusability experiments. Only 3% con-
version of methyl chavicol was achieved at the end of fourth cycle,
which is lower than the conversion observed by the use of pris-
3.5. Isomerization of other perfumery chemicals using Ru–Mg–Al
as a catalyst
In view of observed higher catalytic activity and reusability
of Ru–Mg–Al sample for isomerization of methyl chavicol, dou-
Fig. 6. Progress of double bond isomerization of methyl chavicol to anethole with
respect to time using Ru–Mg–Al as a catalyst.

32
S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 317 (2010) 27–33
Table 3
Table 5
Conversion and selectivity data for double bond isomerization of various chemicals
with Ru–Mg–Al as a catalyst.
Effect of ruthenium content on catalytic activity of Ru–Mg–Al for double bond iso-
merization of methyl chavicol.
Run
Reactant
% Conversiona
% Selectivity
Run
wt% Ruthenium content
in Ru–Mg–Al
% Conversiona
% Selectivity
trans isomer
cis isomer
trans isomer
cis isomer
1
2
3
4
5
7
0.3
0.5
1.0
1.5
5
61
79
98
100
100
100
89
89
88
88
80
73
11
11
12
12
14
17
1
2
3
4
5
6
Methyl chavicol
Eugenol
Allylbenzene
Dimethoxy allylbenzene
Safrole
98
94
96
92
97
88
88
89
88
88
89
72
12
11
12
12
11
–
10
3-Carene
a
Reaction conditions: reactant = 5.0 g, Ru–Mg–Al = 0.5 g, temperature = 210 ◦
C
a
Reaction conditions: reactant = 5.0 g, catalyst = 0.5 g, temperature = 210 ◦C and
and reaction time = 2 h.
reaction time = 2 h.
ble bond isomerization in other perfumery compounds such as,
eugenol, allylbenzene, dimethoxy allylbenzene, safrole, 3-carene
was studied using Ru–Mg–Al as a catalyst. 98% conversion of methyl
chavicol with 88% selectivity of trans-anethole was observed within
2 h reaction time (Table 3). Double bond isomerization of eugenol
showed 94% conversion of eugenol with 89% selectivity of trans-
isoeugenol. Lower conversion of eugenol as compared to methyl
chavicol could be attributed to the higher boiling point and vis-
cosity of the reactant. The allylbenzene isomerization showed 96%
conversion with 88% selectivity for trans isomer. In case of isomer-
ization of dimethoxy allylbenzene, 92% conversion was observed.
For isomerization of safrole, 97% conversion with 89% selectivity
of trans-isosafrole was achieved. The data presented in this study
for solvent free catalytic isomerization of safrole and eugenol is
comparable with the results reported by Kishore et al., using hydro-
talcite as a catalyst (substrate to catalyst ratio 2:1) in the presence
of solvent, DMSO [9]. 88% conversion of 3-carene with 72% selec-
tivity of 2-carene was observed using Ru–Mg–Al as a catalyst for
isomerization of 3-carene. These data indicates that the Ru–Mg–Al
is a highly active and reusable catalyst for double bond isomer-
ization of variety of substrates related to the fine and perfumery
chemicals.
was observed with 70% selectivity of trans-anethole in 10 h reac-
tion time. The conversion increased to 20% with 80% selectivity of
trans-anethole using activated hydrotalcite of Mg/Al molar ratio
3.5 as a catalyst. The conversion of methyl chavicol is achieved
even in longer reaction time (10 h) when pristine hydrotalcite was
used as a catalyst as compared to the Ru–Mg–Al (2 h) for double
bond isomerization of methyl chavicol. As-synthesized hydrotal-
cite of varied Mg/Al molar ratio showed higher conversion and
selectivity of trans isomer as compared to activated hydrotalcite
as a catalyst. These results confirmed that the hydroxyl groups
present in the hydrotalcite play an important role for the reloca-
tion of double bond. When the catalyst was calcined at 450 ◦C, the
material converted into mixed oxides phase of higher surface area
and strong basic in nature (rich in Lewis basic sites) as compared to
the as-synthesized hydrotalcite (Brønsted basic sites) [21]. In case
of hydrotalcite-based catalysts, the observed results in the present
study clearly showed that the catalyst having strong (Lewis) basic
sites is less active as compared to the catalyst rich in Brønsted basic
sites (as-synthesized hydrotalcite).
The effect of ruthenium content on catalytic activity of
Ru–Mg–Al for double bond isomerization of methyl chavicol was
evaluated by varying the ruthenium content from 0.3 to 10% (by
wt). At lower ruthenium loading (0.3%), 61% conversion of methyl
chavicol was obtained which increased to 98% on increasing the
amount of ruthenium to 1.0% in Ru–Mg–Al catalyst (Table 5). The
conversion of methyl chavicol increased to 100% on increase in the
ruthenium loading to 1.5%. The selectivity of trans-anethole was
not observed to change significantly up to 1.5% ruthenium con-
tent in Ru–Mg–Al catalyst, however, selectivity of trans-anethole
decreased significantly to 80% on increasing the ruthenium content
to 5% which further decreased to 73% at 10% ruthenium content in
Ru–Mg–Al catalyst. The decrease in the selectivity of trans-anethole
at higher ruthenium content in catalyst is due to the formation of
other side products.
3.6. Effect of activation of catalysts on their activity for
isomerization of methyl chavicol
The catalytic activity of Ru–Mg–Al and pristine hydrotalcite of
varied Mg/Al molar ratio was observed to decrease on activation at
450 ◦C for 4 h (Table 4). For example, conversion of methyl chavicol
and selectivity of trans-anethole were observed to decrease from
98 to 48% and 88 to 80%, respectively, on activation of Ru–Mg–Al
catalyst. With pristine hydrotalcite, the conversion of methyl chav-
icol was observed to increase on increasing the Mg/Al molar ratio
of activated hydrotalcite from 2.0 to 3.5. For activated hydrotal-
cite of Mg/Al molar ratio 2.0, 8% conversion of methyl chavicol
Table 4
Isomerization of methyl chavicol to anethole using thermally activated catalystsa.
Run
Reactant
Catalyst
% Conversionb
% Selectivity
T, h
trans isomer
cis isomer
1
2
3
4
5
6
7
8
9
Methyl chavicol
Eugenol
Safrole
Allylbenzene
3-Carene
Methyl chavicol
Methyl chavicol
Methyl chavicol
Methyl chavicol
Ru–Mg–Al
Ru–Mg–Al
Ru–Mg–Al
Ru–Mg–Al
Ru–Mg–Al
HT(3.5)
HT(3.0)
HT(2.5)
HT(2.0)
48
41
43
40
38
20
16
14
8
80
81
77
79
70
80
78
74
70
20
19
23
21
30
20
22
26
30
2
2
2
2
2
10
10
10
10
a
Activated at 450 ◦C for 4 h.
b
Reaction conditions: reactant = 5.0 g, catalyst = 0.5 g, temperature = 210 ◦C and reaction time = 2 h.

S.K. Sharma et al. / Journal of Molecular Catalysis A: Chemical 317 (2010) 27–33
33
4. Conclusions
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Acknowledgement
SKS thanks Council of Scientific and Industrial Research (CSIR),
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molcata.2009.10.017.