Title


Science and Technology Indonesia
e-ISSN:2580-4391 p-ISSN:2580-4405
Vol. 6, No. 3, July 2021

Research Paper

Heterogeneous Catalytic Conversion of Citronellal into Isopulegol and Menthol:
Literature Review
Amri Yahya1, Dwiarso Rubiyanto1, Is Fatimah1*
1Chemistry Department, Universitas Islam Indonesia, Kampus Terpadu UII, Jl. Kaliurang Km 14, Sleman, Yogyakarta, Indonesia, 55584
*Corresponding author: isfatimah@uii.ac.id

AbstractThe conversion of citronellal into isopulegol is a key route in the production of a number of important chemicals. In the perspectiveof green conversion, the use of a heterogeneous catalyst is superior due to its ease in separation and reusability, so it facilitatesa highly economical conversion. In this review, we examine the use of some transition metals in cyclization reactions, which aresuitable for citronellal conversion into isopulegol, and consider the potential progress in clay-based catalysts. The structure of claywhich potentially provides the porosity by modification and supporting active metal is proposed to be the low-cost catalyst for theconversion. As other mechanism by porous materials-supported metal, the porosity of clay support contributes to conduct thesurface adsorption mechanism and the Broensted acid supply, meanwhile the metal acts as active site for cyclization, and in theone-pot conversion into menthol, as both cyclization and hydrogenation.
KeywordsCitronellal, Isopulegol, Menthol, Catalysis Process

Received: 7 February 2021, Accepted: 14 June 2021
https://doi.org/10.26554/sti.2021.6.3.166-180

1. INTRODUCTION

Along with the increasing demand for valuable chemicals in
drug, food, and therapeutics applications, new strategies are
developing for exploring raw materials derived from natural
products, including essential oil derivative products (Sharma
et al., 2019). In the pharmaceutical industry, the search contin-
ues for new bioactive compounds derivatives from essential oil
products. One of the secondary metabolites that plays a role
is citronellal. Citronellal has the potential to be used as a raw
material for natural medicine and anticancer drugs (de Sousa,
2015; Lenardão et al., 2007). Citronellal is known to be cheap,
readily available, and a very versatile starting material for some
organic syntheses, including the asymmetric synthesis of chi-
ral compounds used for producing aroma products such as
pheromones, perfumes, and essences (da Silva et al., 2004;
Jung et al., 2012; Yadav and Lande, 2006). Some processes
for citronellal conversion play important roles for such plat-
forms, including the strategic steps of extraction, characteriza-
tion, racemic separation, and catalytic conversion. In addition
to its direct use in therapeutics, citronellal is used in conversion
reactions to obtain its important derivatives (Jung et al., 2012).

The isomerization of citronellal into isopulegol. the reduc-
tion into citronellol, and the direct and indirect conversion into
menthol are valuable reactions in industry. For example, con-

sidering the world’s large consumption of menthol in avors
for food and scents for toiletries, it would seem that menthol
will remain in high demand. In the perspective of sustainability
and increasing process eciency, the optimization of citronellal
extraction and conversion, including catalytic conversion, with
intensied procedures is considered a crucial point (Knirsch
et al., 2010). This review discusses the facts about, potential
developments in, and optimization of citronellal extraction and
conversion. As the main route in menthol production, catalytic
conversion of citronellal into isopulegol and menthol is high-
lighted. Numerous papers have reported using heterogeneous
catalysts for the single conversion of citronellal to isopulegol
and the one-pot conversion into menthol (Adilina et al., 2015).
The combined transition metal and solid supports were func-
tionalized within the conversion mechanism.

2. CITRONELLA OIL: SOURCE AND EXTRACTION
METHOD
Citronellal is a tradename of 3,7-dimethyl-6-octenal (struc-
ture is presented in Figure 1). Citronellal is a monoterpene,
predominantly formed by the secondary metabolism of plants,
which is usually derived as an essential oil through distillation
and extraction. Citronellal, along with other terpenes such as
citral, geranial, linalool, and citronellol, is typically isolated
from more than 30 plants that produce essential oils (Lenardão

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Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

Figure 1. Conversion of Citronellal

et al., 2007). Table 1 presents some methods for citronella oil
extraction.

The predicted annual production of citronella oil is around
2300 metric tons, and derived from many sources such as
Cymbopogon nardus, Cymbopogon citronella, and Cymbopogon win-
terianus (Hamzah et al., 2013; Salea et al., 2018). These plants
are easily cultivated with no specic requirements, increasing
the ease with which citronella oil can be produced. Gener-
ally, the citronellal is present together with other components
such as citral, neral, and terpenes. Two types of citronella oil
are known commercially: Ceylon citronella oil, obtained from
Cymbopogon nardus (inferior type), and Java type citronella oil
obtained from Cymbopogon winterianus (superior type). The
Ceylon chemotype consists of geraniol (18–20%), limonene
(9–11%), methyl isoeugenol (7–11%), citronellol (6–8%), and
citronellal (5–15%). The Java chemotype consists of citronel-
lal (32–45%), geraniol (11–13%), geranyl acetate (3–8%), and
limonene (1–4%) (Salea et al., 2018).

Dierent methods of distillation have been reported, such
as extractive distillation, hydrodistillation (HD), steam distilla-
tion, and Soxhlet extraction, along with their process intensi-
cation strategies. Hydrodistillation, considered to be the most
traditional method, has manyintensication procedures, forex-
ample, ohmic-assisted hydrodistillation (OAHD), which is the
combination of ohmic heating and hydrodistillation (Gavahian
et al., 2018). OAHD has been reported as an eective method
to enhance extraction performance by faster heating compared
to other methods. Heat inside the materials is generated and
the temperature is raised faster in OAHD than in conventional
heating methods (Gavahian et al., 2018). This experiment
reported by Gavahian et al., 2018 revealed an increase in yield
of valuable compounds from Cymbopogon leaves, including a
3.6% higher yield of citronella oil compared to conventional
distillation. Another similar enhancement of hydrodistillation
is microwave-assisted hydrodistillation (MAHD). The eective
molecular heating within the essential oil extraction by MAHD
reduced the extraction time by 67% when compared to conven-
tional distillation (Milone et al., 2000). The use of MAHD for

Figure 2. Synthesis of Menthol from Citronellal (Plößer et al.,
2016)

citronellal extraction from Cymbopogon citratus produced higher
yields and faster extraction times compared to conventional
distillation: MAHD gave a yield of 0.35% v/w for a 90-minute
extraction time, while conventional distillation gave a yield of
0.15% v/wfora360-minute extraction time (Tran et al., 2019).

The intensication process of extraction can be performed
with supercritical carbon dioxide, microwave irradiation, and
sono-hydrodistillation (Hamzah et al., 2013; Solanki et al.,
2018). Various optimum conditions involve parameters such as
temperature, pressureandrawmaterial loading. Thesignicant
increase in yield is due to the increase in density and solvency
power, and it depends on operating parameters and the solvent.
For example, the supercritical carbon dioxide extraction of
citronella grass by compressed propane exhibited an increased
kinetic constant and equilibrium yield (Guedes et al., 2018).

Compressed propane showed a higher equilibrium yield
and kinetic constant than supercritical CO2 under similar con-
ditions (40◦C and 6-9 MPa). However, supercritical CO2 is
a non-toxic and lipophilic alternative solvent with applicable
critical temperature and pressure in industrial practice. The
addition of ethanol to the solvents increased both equilibrium
and kinetic properties even more, because the co-solvent in-
teracts with the polar fraction, playing a complementary role
along with the non-polar propane or CO2. It is important to
mention that the best results were obtained for the runs us-
ing a compressed propane solvent at 60◦C and 2 MPa and
supercritical CO2 (solvent) with ethanol (co-solvent), with an
ethanol-to-raw-material mass ratio of 1:1.

3. CITRONELLAL CONVERSION INTO ISOPULE-
GOL AND MENTHOL
As shown in Figure 2, citronellal can be converted into isopule-
gol, neoiso-isopulegol, citronellol, iso-isopulegol, neo- isopule-
gol, and menthol.

The conversion of citronellal into isopulegol is a pathway in
the production of menthol, which is widely utilized in the phar-
maceutical, soap, and toothpaste industries Raut and Karup-
payil (2014). Isopulegol has been reported as a good antioxi-
dant and anti-inammatory (Ramos et al., 2020), antihyper-
lipidemic (Kalaivani and Sankaranarayanan, 2019), analgesic
(Kalaivani and Sankaranarayanan, 2019), and antitumor agent

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Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

Table 1. Some Methods for Citronella Oil Extraction

Source Extraction method Remark Reference

Cymbopogon Ohmic-heated hydro- The maximum amount of

(Hamzah et al., 2013)

nardus distillation, hydro-distillation, extracted oil yield by ohmic
and steam distillation heated hydro-distillation

was 7.64 mL/kWh,
by hydro-distillation

was 3.87 mL/kWh, and
by steam distillation methods was

1.69 mL/kWh, respectivel
Cymbopogon Supercritical CO2 The highest essential oil yield

(Wu et al., 2019)

citronella L extraction (SFE) was predicted at extraction time
120 min, extraction pressure 25 MPa,

extraction temperature 35◦C,
and CO2 ow 18 L/h for
the SFE processing

Cymbopogon Manual extraction and Average percent yield in

(Wany et al., 2013)

winterianus hydro-distillation the manual extraction and
Jowitt hydro-distillation procedure

was 0.8 and 1% respectively,
which was better as compared
to steam distilled oil (0.7%)

Cymbopogon Sono The optimum yield of oil was

(Solanki et al., 2018)
winterianus hydrodistillation obtained as 4.118% (w/w) at 21
Jowitt min extraction time, and

5 g solid loading
Taiwanese Hydrodistrillation (HD) HD and OAHD gave similar yield,

(Gavahian et al., 2018)
citronella and ohmic-assisted but OAHD saved 46% and 79%
grass hydrodistillation (OAHD) of the process time and energy,

respectively.
Cymbopogon Microwave-assisted MAHD produced higher yield and

(Moradi et al., 2018)
citratus hydrodistillation (MAHD) faster time (0.35% v/w, 90 min)

compared to conventional distillation
(0.15% v/w, 360 min)

Citronella Supercritical CO2 The supercritical carbon dioxide

(Guedes et al., 2018)
grass extraction extraction of citronella grass by

compressed propane exhibited
the increased kinetic constant

and equilibrium yield
Cymbopogon Supercritical CO2 High selectivity was obtained at

(Silva et al., 2011)nardus extraction 353.15 K and 18.0 MPa, with a more
pure essential oil

Cymbopogon Supercritical CO2 The highest citronella oil yield (3.206%)
(Salea et al., 2018)winterianus extraction was achieved at a factor combination of

15 MPa, 50 °C and 180 min

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Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

Table 2. Mechanism of Intramolecular Cyclization Reactions in Various Catalysts

Catalyst Compound Mechanism Target Compound Conversion (%) Reference

PBu3 N-allylic
Intramolecular

𝛼-amino nitril - (Zheng et al., 2016)Cyclization

Cu(II)
(1,4 phenylene)- Intramolecular benzodiimidazole-

99 (Mesias-Salazar et al., 2020)
bisguanidines Cyclization diylidenes

Cu(I)
(1,4 phenylene)- Intramolecular

1-Aryl-1H-benzotriazole 97
(Liu et al., 2010)

bisguanidines Cyclization

Au(III) 𝛼-Pyrroles
Intramolecular Pyrrolopyridinones and

68 (Li and Lin, 2015)
Cyclization Pyrroloazepinones

Fe(II)
Alkynes and Intramolecular

1,3-oxathiane derivative 98
(Sonehara et al., 2017)

Thiosalicylic Acid Cyclization

Rh(III)
Isoquinolone Intramolecular

Indolizidine 65-77 (Xu et al., 2012)
Anulation

Pt(II)
o-Isopropyl-substi Intramolecular

Indenes -
(Wang et al., 2014)

tuted Aryl Alkynes Cyclization

Cs(III) 2-Bromoindoles
Intramolecular 2-(gem-bromovinyl)-N-

-
(Li et al., 2013)

Cyclization methylsulfonyl-anilines

Rh(III) Arylnitrones
Intramolecular

Indolines - (Liu et al., 2016)
Cyclization

Ti(IV)
Isatins and 5-

Cyclization spiro[3,3’-oxindoleoxazoline] >99
(Badillo et al., 2011)

methoxy oxazole

Zr(II) Citronellal
Intramolecular

Isopulegol - (Tobisch, 2006)
Cyclization

Zn(II) Citronellal
Intramolecular

Isopulegol 94 (Imachi et al., 2007)
Cyclization

Ru(III) Citronellal
Cyclization and

Menthol 80 (Azkaar et al., 2019)
Hydrogenation

Pt(II) Citronelal
Cyclization and

Menthol 85 (Azkaar et al., 2019)
Hydrogenation

NiS Citronelal
Cyclization and

Menthol 100
(Cortés et al., 2011)

Hydrogenation

(Jaafari et al., 2012). Isopulegol is also the intermediate for
the synthesis of the anti-inuenza compound octahydro-2H-
chromenes Ilyina et al., 2021 and bioactive 2H-chromene
alcohols as an antiviral agent (Laluc et al., 2020). Exclusively,
isopulegol, especially (–)-isopulegol, is the starting compound
in the production of menthol, which is a compound in high
demand throughout the world (Coman et al., 2009; Plößer
et al., 2014). Menthol is of prime importance in avoring
and pharmaceutical applications, as it elicits cooling and “fresh”
sensations. Menthol is a chiral compound that can occur as
eight possible stereoisomers: (±)-menthol, (±)-neomenthol,
(±)-isomenthol and (±)-neoisomenthol. Of these, (–)-menthol
is the product of interest.

At the industrial level, menthol production is performed by
the Takasago process, which involves citronellal isomerization
on an aqueous ZnBr2 catalyst (Brunner, 2020; Nicolaou et al.,
2000). The conversion of citronellal into isopulegol consists
of acid-catalyzed cyclization, and the conversion of isopulegol
into menthol includes hydrogenation (Figure 2).

Instead of enzymatic conversion (Bastian et al., 2017), iso-
merization by a chemical catalyzed process, which takes on
the role of acid catalysis, is chosen due to the eectiveness of

the isomerization mechanism (Shah et al., 2018). In terms of
energy eciency, selectivity, and repeatability in the industrial
scale, these conversions require eective catalytic processes and
catalysts. In previous research and industry alike, citronellal
isomerization and cyclization took place with a variety of ho-
mogeneous catalysts, but the catalysts often created disposal
problems and were dicult to separate and recover (Guidotti
et al., 2000; Vetere et al., 2002). Using the green chemistry
perspective, the replacement of homogeneous catalysts with
heterogeneous catalysts, in which the phase of the catalyst and
reactants dier in form, is a viable alternative.

The mechanism of heterogeneous catalysis consists of the
surface reaction, which reduces the activation energy of the
reaction, as schematically represented in Figure 3.

The capability of heterogeneous catalysis to conduct ad-
sorption of the reactants is the main point for the mechanism,
and as it happens, the surface interaction among the adsorbed
reactants is the crucial step for nally producing and releasing
the products. The transition metals and their combination with
solid supports are widely used, adapted with the characteristics
of the reaction. As the citronellal conversion into isopulegol in-
volves the acid catalysis mechanism, the transition metals such

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Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

Figure 3. General Mechanism of Surface Reaction in
Heterogeneous Catalysis

as ruthenium (Ru), Pt, Zr, and Ir were reported to be eective
due to the availability of the Lewis acid sites. The availability of
the d-orbital of the transition metal acts as a Lewis acid, which
is capable of forming a bond with a 𝜋-electron of the double
bonds of the reactant (citronellal). In separating this way, the
conversion of isopulegol into menthol is through a hydrogena-
tion mechanism, which in particular involves the capability
of the catalyst to adsorb hydrogen (H2). Some metals such
as Ni, Pt and Au were reported to have excellent activity for
this mechanism (Azkaar et al., 2019; Plößer et al., 2014). The
combination of Lewis acidity from transition metals and the
solid support consisting of Broensted acidity and a high surface
area gave an excellent improvement in yield and eectivity of
the reaction. The solid supports provide not only stability in
sites for reactant adsorption, but also, especially for the porous
materials, an advantage in the catalyst stability and reusabil-
ity. In addition, heterogeneous catalysts allow for regeneration
and reusability, and some specic heterogeneous catalysts can
provide direction for increasing the selectivity of the structure
of certain products and the properties of the catalyst (Coman
et al., 2009). To our knowledge, the review on heterogeneous
catalytic conversion of citronellal into isopulegol and menthol
is not yet presented. Considering the importance of isopulegol
as intermediate for many compounds, and menthol in vari-
ous applications, the aim of this review is to discuss potential
heterogeneous catalysts in green conversion of citronellal to
isopulegol and menthol.

4. CITRONELLAL CONVERSION INTO ISOPULE-
GOL
Citronellal conversion into isopulegol possesses a strategic path-
way, one route of which leads to the production of menthol,
consisting of two processes: citronellal cyclization and hydro-
genation. In addition to preventing unwanted hydrogenation
of citronellal, dimerization and defunctionalization (forming
p-menthenes and p-menthanes), the challenge of using het-
erogeneous catalysts lies in the formation of diastereoisomers,
namely isopulegol, iso-isopulegol, neo-isopulegol, and neoiso-
isopulegol, as shown in Figure 4 (Plößer et al., 2016).

Although in industrial applications the mechanism of the
citronellal cyclization reaction is still under debate, one pro-
posed mechanism of the cyclization reaction occurs through
protonation of the citronellal carbonyl group, which takes place
after a stable carbocation is formed by intramolecular rear-

Figure 4. Citronellal Cyclization Gives Four Diastereoisomers
(Vandichel et al., 2013)

rangement, and ends with the deprotonation that produces
isopulegol (Makiarvela, 2004).

The Takasago process, in which (–)-menthol is produced by
the hydrogenation of (–)-isopulegol obtained from (+)-citronell
al through acid catalyzed cyclization, is an important reac-
tion in pharmaceutical industries (Cortés et al., 2011). The
mechanism includes the ene-cyclization of (+)- citronellal to
(–)-isopulegol over aqueous ZnBr2 as a homogeneous cata-
lyst, which causes a large amount of waste due to its non-
regenerability. In order to make the process commercially
attractive, synthesis of isopulegol with high stereoselectivity
for the isomer (–)-isopulegol is important. Many studies high-
lighted that the selectivity is closely related to Lewis acidity
(Shah et al., 2018; Milone et al., 2000; Shieh et al., 2003).
With this background, most methods of the synthesis of het-
erogeneous catalysts were focused on activity, selectivity and
stability, mainly by anchoring or immobilizing acid sites on
stable inorganic materials. Such porous mediaas silica-alumina
and silica-based materials were reported to be good supports
(Shieh et al., 2003).

Combined experimental and theoretical studies reveal that
the catalytic mechanisms and characteristics play a role in eval-
uating the catalyst performance and the selectivity of Lewis
acids toward the desired stereoisomers (Sekerová et al., 2019).
Some of the Lewis acid catalysts used are Zn, Zr, Ti and a
Ni-based catalyst in supported form (Chuah et al., 2001; Fa-
timah et al., 2008; Guidotti et al., 2000; Jimeno et al., 2013).
The result is that a Lewis acid catalyst becomes the main factor
that contributes to the selectivity and catalytic activity of the
cyclization reaction (Vandichel et al., 2013). A Lewis acid can
act as an electron pair acceptor, as ZnBr2, ZnCl2, and ZnI2 can
act as catalysts for citronellal cyclization (Nisyak et al., 2017).
The mechanism of citronellal cyclization is shown in Figure 4.

One type of Lewis acid catalyst is the zirconium-based
catalyst. The results of research by Chuah et al., 2001 showed
that zirconium hydroxide and zirconium phosphate catalysts
also have activity and selectivity in the cyclization reaction of
citronellal to isopulegol. The presence of Lewis and Bronsted
acid catalyst sites is very important in the citronellal cyclization
reaction, as depicted in the reaction mechanism proposed in
Figure 5 (Álvarez-Rodríguez et al., 2012; Fatimah et al., 2014;
Ravasio et al., 2000; Sudiyarmanto et al., 2017).

The mechanism begins with the formation of a citronellal
coordination bond to a Lewis acid through free electrons of
carbonyl O atoms and 𝜋 electrons of citronellal alkenes to Zr

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Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

Figure 5. Mechanism of Citronellal Cyclization (Tursiloadi
et al., 2015)

atoms, followed by protonation of the Bronsted acid (–Zr-OH)
sites against citronellal carbonyl O atoms (Chuah et al., 2001).

In line with the previous results, the conversion of citronel-
lal to isopulegol was successfully conducted through a cycliza-
tion mechanism with a ZnBr2/𝛽-Zeolite catalyst (Balu et al.,
2010). The result is that the ZnBr2/𝛽-Zeolite catalyst pro-
vides better activity than the 𝛽-Zeolite catalyst alone, where
forZnBr2/𝛽-Zeolite the conversion value of citronellal to isop-
ulegol is 100%, with a selectivity to isopulegol compounds of
75.28% at 120◦C and a reaction time of 60 minutes. By a simi-
larmechanism,ZnBr2/SiO2 catalyzedcitronellaloil conversion
gave a selectivity to isopulegol of 94.35%, and a conversion of
96.44% (Nuryanti et al., 2019). The mechanism of the cycliza-
tion reaction involves the formation of a ring compound from
the chain by the formation of new bonds. The cyclization reac-
tion is an intramolecular reaction where the reaction occurs in
the molecule itself. The factors that inuence the relationship
between structure and reactivity intramolecularly include: in-
duction, resonance, steric eects and hydrogen bonding. The
intramolecular cyclization mechanisms in various metal cat-
alysts are presented in Table 2. It is seen that the presented
reaction conversions are quite high (68–100%), which further
conrms that the conversion is related to the eective interac-
tion between the metal catalyst and the 𝜋-bonds of the organic
molecule (Li and Lin, 2015).

Based on the study of density functional theory (DFT), the
transition state is coming from the linking between the active
sites of the metal catalyst and the 𝜋-bonds. The bonding re-
sults in the potential energy surface near the stationary point
and involves the activation of C=C bonds (double or triple
bonds). The possible charge distribution among the resonance
structures of molecules will lead to electron-rich properties of
the internal alkyne carbon, which is thus more nucleophilic
than the carbonyl carbon. The increasing energy facilitates the

1,2-migration of the internal alkyne carbon from the pyrrole’s
𝛼- to 𝛽-carbon. The shifting energy also accelerates the inter-
action with hydrogen in the subsequent hydrogenation step (Li
and Lin, 2015).

Table 2 shows some transition metals in the cyclization
mechanism, especially in the regiospecic organic synthesis.
The presence of the active site provides transformation and
indicates a highly convergent route to a wide variety of car-
bocyclic and heterocyclic structures. The PBu3 catalyst acts
as a Lewis base to strengthen the nucleophilicity of the active
reaction site (Zheng et al., 2016).

In addition, the cyclization reaction can be carried out with
Lewis and Bronsted acid catalysts. Lewis acidity plays a role
in providing coordination bonds for unsaturated metal ions,
whereas Bronsted acidity plays an important role not only as an
activating agent, but also in controlling the diastereoselectivity
of reactions through hydrogen bonding interactions (Vetere
et al., 2002).

From the perspective of time eciency and minimizing
waste, the one-pot conversion of citronellal into menthol is a
better approach (Cortés et al., 2011; Makiarvela et al., 2005).
Bifunctional catalysts and the superacid solid catalysts act prop-
erly for both mechanisms. One-pot reactions catalyzed by
Pt−, Ru−, and Ni−based catalysts were reported (Cortés et al.,
2011).

Similar to other organic reaction mechanisms with transi-
tion metal catalysts, the supporting materials inuence either
the dispersion and stabilityof the active metal or the mass trans-
fer of the reactant feed for conducting surface reactions. Table
3 lists the activity of some porous material-supported metal
catalysts in the citronellal conversion. The interaction between
the active metal and the support plays a role in controlling the
surface reactivity, and furthermore, the conversion and selec-
tivity. For example, when producing menthol on an MCM-41
support, the reactivity and selectivity of the active metals rank
in the following order: Ni > Pd > Ru > Ir (Makiarvela et al.,
2005). The ratio of Bronsted to Lewis surface acidity governs
the possible side reactions. This is also identied by the use of
Ni-supported material on clay minerals (Fatimah et al., 2015;
Fatimah et al., 2016).

From Table 3, it can be seen that although in general the
higher the specic surface area of the catalyst, the higher the
conversion, the catalytic conversion and selectivity in cycliza-
tion and hydrogenation is not only inuenced by the specic
surface area of the supports, but also by their interaction with
the supported metal. Acidity of the supports provides the sur-
face acidityforsucientlypromoting the cyclization step, while
the presence of supported metal enhances the catalyst-reactant
adsorption surface interaction upon formation of isopulegol, as
well as the hydrogen transfer in hydrogenation (Imachi et al.,
2007; Balu et al., 2010). The dominant silica content in the
solid supports tends to promote Bronsted acid, while the pres-
ence of Al gives a combination of Bronsted and Lewis acidity.
In addition, for the hydrogenation step, the study from Nie
et al., 2006 showed an increasing Ni loading from the Ni/BEA

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Table 3. Comparison on Activities of Some Metal-Supported Porous Materials in Citronellal Conversion

Catalyst

Metal Surface

Surface acidity

Conversion Selectivity Selectivity

Referencecontent area (%) to isopulegol to menthol
(%) (m2/g) (%) (%)

ZnBr2/C8-HMS 2.6 1200 94 86 - (Imachi et al., 2007)
Ni/MCM-41 15 659 96 8 74 (Nie et al., 2006)

Ni/Natural Zeolite 5 29 - 50 50 0 (Adilina et al., 2015)
Ru/H-MCM-41 10 522 - 96.4 2.2 46.6 (Vajglová et al., 2020)
Pd/Ga-SBA-15 1.92 799 65 mmol pyridine/g >90 15 75 (Balu et al., 2010)
Pt/Al-MCM-41 2.02 905 199 mmol pyridine/g 95 15 60 (Balu et al., 2010)
Cu/Al-MCM-41 1.85 752 210 mmol pyridine/g 90 8 87 (Balu et al., 2010)

Zr/Pillared montmorillonite 5 97.5 1.05 mmol butylamine/g 89.8 98.5 - (Fatimah et al., 2016)
Ru(Bpy)/Saponite 1.89 229.35 - 98.12 95.02 2.58 (Fatimah et al., 2015)

catalysts that leads to faster hydrogenation and selectivity to
produce menthol in a one-pot conversion. Particularly, the
hydrogenationratewas insignicantly inuencedbythe increas-
ing particle size, for example, in the Ru-deposited material on
MCM-41 (Vajglová et al., 2020), and Pt–Ga-MCM-41 (Balu
et al., 2010). The nanoparticles formed from active metals
demonstrated a highly stable catalytic activity, as represented
by better reusability (Balu et al., 2010; Fatimah et al., 2019).

Heterogeneous catalysts suitable for the cyclization reac-
tion of citronellal-enes must have strong Lewis acids and weak
Bronsted acids (Chuah et al., 2001). The fast reaction rate of
ene reactions in (+)-citronellal cyclization with a sulfate zirco-
nium catalyst aects stereoselectivity. The result is a maximum
stereoselectivity of 61%. However, high stereoselectivity (72%)
was obtained from a zirconium hydrate catalyst. A ZrO2 acid
catalyst, which has a low surface area, is also active in cycliza-
tion. In addition, a high ene reaction rate can also be obtained
when using a SiO2-Al2O3 mixed catalyst with a maximum
stereoselectivity of 72%. One of the factors determining the
activity of the ZrO2 and Al2O3 catalysts is the dierence in
their surface acidity type. ZrO2 exhibits both Bronsted and
Lewis acid sites, while the acidity of Al2O3 comes from the
Lewis acid only (Makiarvela, 2004).

Figure 6. The Reaction Mechanism of Citronellal Cyclization
to Isopulegol with Zirconium Hydroxide Catalyst (Chuah
et al., 2001)

Other factors of the reaction system, such as the ow and
batch systems, showed dierent results. The use of the extrac-
tivesynthesismethodhasamajor inuenceonphysicochemical
properties, especially on the level of Bronsted acidity, metal
dispersion, and metal distribution in the material. In a batch
reactor, Ru and Pt catalysts each support the acidity indepen-
dently. This catalyst owsystem does not depend on the acidity
of the catalyst or the size of the metal particles, but it does de-

pends on the reaction kinetics, especially the mass transfer.
This is evidenced by the stereoselectivity of menthol of 73%
(Azkaar et al., 2019).

5. CLAY-BASED HETEROGENEOUS CATALYSTS

Clay minerals contain silica-alumina frameworks characterized
as a layered structure with exchangeable cations that potentially
can be replaced with metal or metal oxide. The modication
of clay can be conducted based on the exchange of alkali or
earth alkali (Na+, K+, Mg2+, Ca2+) cations with other metal
cations, giving increasing porosity caused by an expansion of
the interlayer distance (Banković et al., 2012; Barakan and Ag-
hazadeh, 2019). Cations located in the interlayer space can be
exchanged with organic and organometallic cations in solution
or in solid conditions (Belver et al., 2012; Wang et al., 2016).
Natively, clay minerals containing Bronsted acid and Lewis
acid sites refer to the interlayer charges and the silica content
within the structures. As the cation exchange is conducted with
polyoxometal cations of transition metals, the formation of
Lewis acid sites can be achieved instead of the enhancement
of chemical interactions, such as hydrogen bonds, ion-dipole
interactions, coordination bonds, and transfer forces or van der
Waals forces. Previous studies have reported that tetraalkylam-
monium compounds can be easily introduced into the inter-
layer space, causing changes in pore structure and shifting of
the interlayer distance (Mao et al., 2009; Nagendrappa, 2011).
However, this thermal material is not stable at temperatures
above 250°C. Incorporation of metal oxides as pillars increases
Bronsted and Lewis acidity. In addition, this material can be
used in redox or cycloaddition reactions as well as catalytic ac-
tivity due to its high specic surface area (Cecilia et al., 2018).

According to Baloyi et al., 2018, the development of cat-
alysts, with a focus on low cost, stability, reusability and an
environmentally friendly aspect, and catalysts such as pillared
clays, will lead to the discovery of eective solids as heteroge-
neous catalysts. In silica-aluminamaterials, clay-based catalysts
exhibit ahighsurfacearea, andtheycanbemodiedandreused
(Chmielarz et al., 2018; Kooli et al., 2016).

In previous studies, González et al., 2017 reported that
montmorillonite had been pillared by Al137+ polycations, us-
ing concentrated solutions and clay mineral dispersions. The
reaction is assisted by microwave radiation, producing a new

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Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

intercalation solid, and leading to an Al pillared solid after
calcination at 500◦C. The solids obtained show structural char-
acteristics comparable to those of Al-PILC prepared from the
classical method (Manos et al., 2001; Pinto et al., 2012).

Several modication schemes can be applied to identify
a more active catalyst for the homogeneous distribution of
metal or metal oxide catalysts in the clay structure. As an eort
to preserve the specic surface area along with surface acidity,
modiedclaywithaporousstructurewasalsoattempted, oneof
these being in the form of a porous clay heterostructure (PCH)
(Kalmakhanova et al., 2019; Liu et al., 2007). Modication
showed that the formation of metal oxides in the interlayer
space of the smectite clay structure provides stability, and more
importantly, maintains surface acidity in certain acid catalytic
mechanisms (Cecilia et al., 2018; Panda, 2018; Radwan et al.,
2009).

The results of the research by Chmielarz et al., 2018 re-
ported that the BET surface area (SBET) was determined for
calcined Ti-PILC and Ti-PCH. Ti-PILC calcination at 550°C
produced samples with the highest surface area of 212 m2/g.
At higher temperatures, partial collapse of the Ti-PILC pillar
structure is possible. The Ti-PCH calcination at 600°C pro-
duced a material with a surface area of 573 m2/g, which is
much higher than Ti-PILC.

In the study of Kooli et al., 2017, smectite polarized with
various numbers of Al species was reported and character-
ized, and the further use of this precursor was successful in the
synthesis of Al-PCH materials. As a result, a greater specic
surface area value was achieved and varied from 740 to 850
m2/g with the acid site. The Al content in the pillared clay
and the PCH derivatives inuence the catalytic data due to the
dierent strengths of the acid sites and textures.

High surface acidity and surface area are the main factors
aecting the increase in catalytic activity. In addition, the ad-
vantagesofusingPCH,especially inmaintainingsurfaceacidity
in many catalytic mechanisms, are mainly attributed to PCH
(Zhouetal.,2013). ThecombinationofmetaloxidesandPCH
is also expected to provide mutually benecial relationships for
several desirable properties in the reaction, including catalyst
activity and selectivity, referring to the presence of metals as
the specicity of the active site (Cecilia et al., 2018; Chmielarz
et al., 2018; Kooli et al., 2017).

Surfactants are another determining factor in PCH syn-
thesis. The preparation of the H+-titanosilicate/dodecylamine
(DDA)/tetraethylortho-silicate (TEOS) intercalation compo
und is rapidly hydrolyzed in water to form H+-titanosilicate
pillared siloxane and calcined for 5 hours at 500◦C to produce
a mesoporous H+-titanosilicate. The results obtained show a
basal distance of 4.16–4.32 nm, a uniform pore size of 2.8–3.4
nm, and a large surface area of 535–618 m2/g. These results
suggest that the DDA molecule plays a decisive role in pore
formation, as it acts as a base catalyst and as a micelle-like tem-
plate during the hydrolysis of TEOS and contributes to the
formation of solid silica pillars (Park et al., 2009). Therefore,
the schematic of PCH formation is shown in Figure 7.

Figure 7. Schematic Representation of PCH Formation
(Rubiyanto et al., 2019)

Figure 8. Schematic Representation of Citronellal Conversion
by Clay-Supported Metal

The pillared clay can also act as a solid support for other
metals or metal oxides, for example, TiO2 dispersed in silica-
pillaredmontmorillonite (TiO2/SiO2-montmorillonite). Previ-
ousworkreportedthat theuseofaTiO2/SiO2-montmorillonite
catalyst played a signicant role in increasing the total reaction
conversion from 87.80% in the use of SiO2-montmorillonite
and from 85.38% using natural montmorillonite to 95.53%
(Fatimah et al., 2008). The increase in total conversion and
selectivity to isopulegol was related to the Lewis acidity of
TiO2/SiO2-montmorillonite and the increase in the specic
surface area of the material. However, it is possible that the
specic surface acidity plays a greater role than the physico-
chemical character of the materials in this range. This means
that the TiO2 dispersion on the SiO2-montmorillonite cata-
lyst does not have a signicant role in increasing the reaction
rate. Changes in physicochemical properties of catalysts by
the presence of titanium dispersion play a role in directing the
mechanism so that it plays a signicant role in the selectivity
and catalytic activity. Figure 8 represents the mechanism of
citronellal conversion using clay-supported metal/metal oxide.

Theverysimple inorganicmaterial,montmorillonite,which
is a natural acid clay, can eectively promote the synthesis of
nitrogen-containing octahydroacridine, with 92% yield in one
hour and at room temperature, ranging from aniline and cit-

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Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

ronellal, as well as the main components of several essential oils.
The use of a solid acid catalyst gives a high selectivity to isop-
ulegol compounds. Therefore, the use of solid acid catalysts
can minimize waste and shows high potential for sustainability
(Zaccheria et al., 2018).

The synthesis of Zr-montmorillonite in acetonitrile is used
inthecitronellalcyclizationreaction. Thepresenceandstrength
of Lewis acid catalyst Zr-montmorillonite plays a role in pro-
ducing isopulegol 98% with stereoselectivity to (–)-isopulegol
90%. As some Lewis acids are used that are stronger than
Ti4+/Zr4+, such as Al2O3, SiO2-TiO2 and SiO2-ZrO2, the
stereoselectivity with respect to the (–)-isopulegol are 70, 62,
and 62%, respectively. The type of Lewis acid carried on meso-
porous materials, ZnBr2/SiO2, can produce (–)-isopulegol with
a maximum stereoselectivity of 86% (Makiarvela, 2004).

Guidotti et al., 2000 suggested that the conversion of cit-
ronellal to isopulegol epoxide using a mesoporous titanium
silicate catalyst (Ti-MCM-41) in one step at the same time
resulted in 68% yield. The cyclization process of citronellal to
isopulegol takes place in a toluene solvent for 6 hours, and then
tertbutylhydroxyperoxide (TBHP) and acetonitrile are added
to convert isopulegol to isopulegol epoxide for 18 hours at 76%
and selectivity 90%. A catalyst consisting of nickel dispersed
in zeolite (Ni/ZAB) was also reported to be eective for the
conversion of citronellal oil to isopulegol from lemon grass oil,
which reached a total conversion of 100% and a selectivity of
57% (Tursiloadi et al., 2015).

The signicant role of specic surface area was summarized
from the signicant increasing citronellal conversion and se-
lectivity toward isopulegol over Zn-dispersed-in-clay, via the
formation of a porous clay heterostructure (Zn/PCH), accord-
ingto(Rubiyantoetal.,2019). Thephysicochemicalproperties
increase in line with the increase in catalytic activity and selec-
tivity in the conversion of citronellal to isopulegol, compared
to Zn/pillared clay (Zn/PCH). Zn/PCH showed a 98.9% con-
version rate for the 3-hour reaction and 100% selectivity for
isopulegol production, and showed good reusability.

Surface acidity enhancement was also reported for a com-
bination of bimetals: nickel and zirconium in the form of
nickel immobilized zirconia pillared saponite (Ni-Zr/SAP).
Zr-pillared saponite (Zr/SAP) was prepared by microwave-
assisted pillarization, and it was employed as the solid support
of nickel by the impregnation method. The physicochemical
characterization identication showed that zirconia was suc-
cessfully distributed as pillars, and nickel was dispersed in the
pillared material. Both modications increased the specic
surface area, pore volume and surface acidity as a result of the
formation of pillars and homogeneous particle distribution.
Compared to saponite and Zr/SAP, the Ni-Zr/SAP composite
demonstrated a signicant improvement in citronellal conver-
sion and selectivity towards isopulegol. The presence of nickel
plays a role in the one-pot conversion of isopulegol into men-
thol over a catalytic hydrogen transfer reaction. As nickel has
specialization for hydrogenation mechanisms, Ni-Zr/SAP pro-
duced menthol in a signicant selectivity (13%) (Fatimah et al.,

2016; Fatimah et al., 2015). It was reported that the selectivity
in producing menthol was inuenced by the reaction method,
forwhich themicrowave-assistedhydrogenationshowedhigher
conversion and selectivity compared to the conventional re-
ux method, but for both methods, isomenthone as another
hydrogenation product was identied.

The increasing quantity and distribution of surface acidity
can be achieved by dispersion in a clay support via pillariza-
tion. Zirconium-pillared montmorillonite (Zr/MMT) demon-
strated the increased surface acidity that was in line with the in-
creased citronellal conversion into isopulegol, according to Fa-
timah et al., 2014. Moreover, the surface acidity enhancement
was achieved by sulfation into the form of sulfated-Zr/MMT
(S-Zr/MMT). The contribution of pillarization through in-
creasing specic surface area by the higher basal spacing d001
of the structure, together with the formation of ZrO2 pillars,
were the factors identied for the catalytic activity. In addition,
by the anchored sulphate functional groups on the surfaces,
the super-acidity of the surface was created, reected as the
highest activity of 98.52% citronellal conversion obtained by
S-Zr/MMT.

In a dierent form, the dispersed active metal catalyst of
tris(bipyridine) ruthenium (II) into a saponite clay support
(Ru(Bpy)3/Sap) for the bifunctional conversion was also re-
ported. The (Ru(Bpy)3/Sap) exhibited activity in citronellal
and citral conversions in catalytic hydrogen transfer under the
microwave irradiation method. The hydrophobicity of the
complex provides the possibility of acidity transfer as demon-
strated by the activity in a non-solvent reaction system. The
anchored metal complex in the support is remarkably main-
tained for 5 uses in its recycling activity (Fatimah et al., 2019).

Considering the role of surface acidity on the catalyst, hy-
drophobicity, and maintenance of catalyst performance in
terms of reusability, the chosen heteropoly acid (HPA) cat-
alysts in clay supports is hypothesized to give more eective
catalytic mechanisms. The majority of catalytic applications of
HPA are related to the stable and stronger acidity coming from
the available Keggin HPAs heteropoly anions of the formula
[XM12O40]n, where X is the heteroatom (such as P

5+ and Si4+)
and M is the addendum atom (such as Mo6+ and W6+).

Tungsten (W) is a transition metal and has various cat-
alytic applications in the form of tungsten sulde, tungstic acid,
polyoxotungstates (HPW) and polyoxometallics (POM). The
advantages of tungsten, especially in its heterogeneous form,
are itshighBronstedacidity, redoxability, thermalstability, and
hydrophobicity (Nagendrappa, 2011; Telalović et al., 2010;
Zhou et al., 2013).

HPWs possess stronger acidity than conventional solid acid
catalysts such as zeolites, acidic metal oxides, and mineral acids.
Theacidityofconcentratedaqueousandnon-aqueoussolutions
of HPWis higher than that of H2SO4 and HClO4 by about 1.5
or0.3 units of the Hammett acidity function. The acid strength
ofKegginHPWsdecreases in thefollowingorder: H3PW12O40
> H4SiW12O40 > H3PMo12O40 > H4SiMo12O40 (Alsalme
et al., 2010). The superacidity characteristics of HPWs al-

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low them to catalyze esterication activity of oleic acid with
methanolat roomtemperatureandtodisplayahigheresterica-
tion activity compared to Amberlyst 35W resin (Alsalme et al.,
2010; Nogueira et al., 2020). Similarly, the HPW exhibited a
high activity of 1-propanol and 1,1-diacetates from a variety
of aldehydes at room temperature (Heravi et al., 2006). The
conclusions from many studies on HPW catalysis have demon-
strated the usefulness of HPW, being more eective than ordi-
nary protonic acids. Emphasis is placed on the optimization of
HPW as a reusable catalyst with high performance to achieve
the economic and technical advantages in applications, and one
of various alternative methods is the immobilization of HPA
onto porous material.

The studyon immobilization of 12-tungstophosphoric acid
(HPW) on the catalytic activity of H3PW12O40/mesoporous
acid activated bentonite (AAB) was carried out. The results
showed that the 2-propanol transformation increased substan-
tially with the conversion, and the reaction selectivity also
increased with increasing HPW concentration. In addition,
the proposed catalyst increases the oxidation of 2-propanol to
acetone and suppresses the dehydration of propanol to acid-
catalyzed propylene. The catalytic activity increases the forma-
tion of acetone and decreases the activityof propene formation,
which indicates that a catalyst with a high HPW concentra-
tion can function as an ecient catalyst for oxidation reactions
(Rožić et al., 2011).

Immobilization of HPW and POT into supports such as
polymers, silica, alumina, zeolites, and carbon materials not
only increases the stability of the POT supported through co-
valent bonding, but also increases the spread of the POT active
site into the support. At present, although tungsten based het-
erogeneous catalysts are used in industry with high eciency
for some reactions, regeneration of POM-based catalysts is
generally dicult. Therefore, to encourage the use of W-based
heteropoly acid catalysts, it is very important to develop cat-
alytic systems that can be regenerated eciently through cata-
lyst heterogenization (Enferadi-Kerenkan et al., 2018). Silica
supported H3PW12O40 (PW), which has high hydrophobicity,
and which is the strongest heteropoly acid in the Keggin series,
is an ecient, environmentally friendly heterogeneous catalyst
for the liquid-phase isomerization of a-pinene and longifolene
into their more valuable isomers–camphene and isolongifolene
(da Silva Rocha et al., 2009). The environment friendly ben-
ets of the catalyst can be derived from its ease of separation
from the reaction system without neutralization, and it may be
easily reused (Robles-Dutenhefner et al., 2001).

According to Cortés et al., 2011, an H3PW12O40/SiO2
catalyst was used to convert (+)-citronellal to (–)-isopulegol
and (+)-neo-isopulegol as the main products with almost 100%
conversion, with a total selectivity between 95 and 100%, and
80% are selective against (–)-isopulegol. The catalyst can be
used repeatedly without decreasing activity. While the Pd-
H3PW12O40/SiO2 catalyst is an ecient heterogeneous bifunc-
tional catalyst forconversion in one process from (+)-citronellal
to menthol with aconversion result of up to 92%, and 85% stere-

oselectivity for the desired product (menthol) (da Silva Rocha
et al., 2007).

Meso/macroporous H3PW12O40/ SiO2 nanocomposites
with high specic surface area were prepared using cationic sur-
factants and monodispersed polystyrene (PS) as dual templates.
The results of X-ray photoemission spectroscopic (XPS) mea-
surements showed a high dispersity of Keggin-type heteropoly
acids (HPA) on the silica matrix. There is an optimum value
for the use of cationic surfactants and the right calcination tem-
perature of the H3PW12O40/SiO2 meso/macroporous catalyst
which leads to a very high specic surface area of 1,457.7 m2/g
at a calcination temperature of 450°C (Yue et al., 2020).

In addition, several materials containing tungsten oxide
(WO3) were prepared and deposited on SiO2 by the sol-gel
method and the wet impregnation method. The tungsten oxide
weight varies (1, 10, 25 and 40 wt%), namely W10, W25, and
W40. The WO3-SiO2 catalytic activity of these materials was
tested in the intramolecular citronellal Prins cyclization reac-
tion. The reaction conditions (temperature 70–90°C, amount
of catalyst 1–10% catalyst density) had an eect on citronellal
conversion and selectivity in producing isopulegol. The best
results (90% isopulegol, 97% selectivity of isopulegol forma-
tion, 24 hours) were obtained using the IMP W25 catalyst
(10 wt%, 50°C). It is possible to reuse the W25 catalyst twice
without losing signicant activity. The available materials indi-
cate a suitable catalyst for citronellal cyclization (Vrbková et al.,
2020).

In a study by Braga et al., 2012, it was reported that a cata-
lyst based on 12-tungstophosphoric acid supported on meso-
porous MCM-41 (2–40 wt%) was prepared and tested in cit-
ronellal cyclization. The characterization of the ingredients
conrmed the Keggin anion treatment. These materials give
rise to acidity that is related to the presence of Bronsted and
hydrogen bond sites. The increase in HPW load is directly
proportional to the number of Bronsted sites in the material.
All the catalysts that were actively prepared in the citronellal
cyclization formed the main stereoisomer (–)-isopulegol, but
kinetic studies showed that 20% HPW/MCM-41 had the best
performance with a conversion of about 96% and a selectivity
of 65% foran hourreaction. This catalyst was reused four times
with a low deactivation rate, keeping the selectivity almost the
same. Thus, the successful application of HPW supported on
MCM-41 for this acid-catalyzed cyclization is demonstrated,
and detailed information on the stability of the catalyst as well
as the kinetics of the reaction is provided.

6. FUTURE PERSPECTIVE

Thecombinationofsurfaceacidityandporosityofsupportwith
a metal catalyst plays a role in preserving heterogeneous acid
catalysts in the citronellal conversion. From the perspective of
green chemistry, some considerations are concluded. The one-
potcitronellal conversion intomenthol ispreferrablecompared
to two-step reactions, therefore the capability of catalysts for
both cyclization and hydrogenation mechanisms is an impor-
tant issue. The reusability of the catalyst that accommodates

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Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

its use in several cycles will contribute to minimizing waste
and achieving a more economical process. The high-selective
product, especially for a specied isomer is determined by the
use of specic transition metal. The chemical and thermal
stability of the catalyst is the signicant feature, and in addition,
the design of a stable catalyst based on low-cost material has a
good chance of being developed. The modied clay with good
porosity, such as in the porous clay heterostructure form, is
hypothesized to be a good candidate for a low-cost catalyst sup-
port. From our literature review, we have determined that the
combinations of clay-based materials with superacidity, such
as a heteropoly acid, need to be explored and optimized.

7. ACKNOWLEDGEMENT

Authors gratefullyacknowledge the Hibah Penelitian Unggulan
Perguruan Tinggi 2021, Contract No. 1805.1/LL5/PG/2021
for research funding.

REFERENCES

Adilina, P. R., A. Sulaswatty, I. B. Adilina, R. Pertiwi, and
A. Sulaswatty (2015). Conversion of ( ± ) -Citronellal and Its
Derivatives To ( - ) -Menthol Using Bifunctional. Biopropal
Industri, 6; 1–6

Alsalme, A. M., P. V. Wiper, Y. Z. Khimyak, E. F.
Kozhevnikova, and I. V. Kozhevnikov (2010). Solid Acid
Catalysts based on H3PW12O40 Heteropoly Acid: Acid
and Catalytic Properties at a Gas–solid Interface. Journal of
Catalysis, 276(1); 181–189

Álvarez-Rodríguez, J., I. Rodríguez-Ramos, A. Guerrero-Ruiz,
E. Gallegos-Suarez, and A. Arcoya (2012). Inuence of the
Nature of Support on Ru-supported Catalysts for Selec-
tive Hydrogenation of Citral. Chemical Engineering Journal,
204(206); 169–178

Azkaar, M., P. Mäki-Arvela, Z. Vajglová, V. Fedorov, N. Ku-
mar, L. Hupa, J. Hemming, M. Peurla, A. Aho, and D. Y.
Murzin (2019). Synthesis of Menthol from Citronellal Over
Supported Ru- and Pt-catalysts in Continuous Flow. Reac-
tion Chemistry & Engineering, 4(12); 2156–2169

Badillo, J. J., G. E. Arevalo, J. C. Fettinger, and A. K. Franz
(2011). Titanium-Catalyzed Stereoselective Synthesis of
Spirooxindole Oxazolines. Organic Letters, 13(3); 418–421

Baloyi, J., T.Ntho, andJ.Moma(2018). SynthesisandApplica-
tionofPillaredClayHeterogeneousCatalysts forWastewater
Treatment: a Review. RSC Advances, 8(10); 5197–5211

Balu, A. M., J. M. Campelo, R. Luque, and A. A. Romero
(2010). One-step Microwave-assisted Asymmetric Cyclisa-
tion/hydrogenation of Citronellal to Menthols using Sup-
ported Nanoparticles on Mesoporous Materials. Organic &
Biomolecular Chemistry, 8(12); 2845

Banković, P., A. Milutinović-Nikolić, Z. Mojović, N. Jović-
Jovičić, M. Žunić, V. Dondur, and D. Jovanović (2012).
Al,Fe-pillared Clays in Catalytic Decolorization of Aque-
ous Tartrazine Solutions. Applied Clay Science, 58; 73–78

Barakan, S. and V. Aghazadeh (2019). Synthesis and charac-

terization of Hierarchical Porous Clay Heterostructure from
Al, Fe -pillared Nano-bentonite using Microwave and Ul-
trasonic Techniques. Microporous and Mesoporous Materials,
278; 138–148

Bastian, S. A., S. C. Hammer, N. Kreß, B. M. Nestl, and
B. Hauer (2017). Selectivity in the Cyclization of Citronellal
Introduced by Squalene Hopene Cyclase Variants. Chem-
CatChem, 9(23); 4364–4368

Belver, C., P. Aranda, M. Martín-Luengo, and E. Ruiz-Hitzky
(2012). New Silica/alumina–clay Heterostructures: Proper-
ties as Acid Catalysts. Microporous and Mesoporous Materials,
147(1); 157–166

Braga, P. R., A. A. Costa, E. F. de Freitas, R. O. Rocha, J. L.
de Macedo, A. S. Araujo, J. A. Dias, and S. C. Dias (2012).
IntramolecularCyclizationof (+)-citronellalusingSupported
12-tungstophosphoric Acid on MCM-41. Journal of Molecu-
lar Catalysis A: Chemical, 358; 99–105

Brunner, H. (2020). Takasago Process to (-)-menthol. Wiley
Cecilia, J. A., C. García-Sancho, E. Vilarrasa-García,
J. Jiménez-Jiménez, and E. Rodriguez-Castellón (2018).
Synthesis, Characterization, UsesandApplicationsofPorous
Clays Heterostructures: A Review. The Chemical Record,
18(7-8); 1085–1104

Chmielarz, L., A. Kowalczyk, M. Skoczek, M. Rutkowska,
B. Gil, P. Natkański, M. Radko, M. Motak, R. Dębek, and
J. Ryczkowski (2018). Porous Clay Heterostructures Inter-
calated with Multicomponent Pillars as Catalysts for Dehy-
dration of Alcohols. Applied Clay Science, 160; 116–125

Chuah, G., S. Liu, S. Jaenicke, and L. Harrison (2001). Cy-
clisation of Citronellal to Isopulegol Catalysed by Hydrous
Zirconia and Other Solid Acids. Journal of Catalysis, 200(2);
352–359

Coman, S. M., P. Patil, S. Wuttke, and E. Kemnitz (2009).
Cyclisation of Citronellal Over Heterogeneous Inorganic
Fluorides-highly Chemo and Diastereoselective Catalysts
for (±)-isopulegol. Chem. Commun., (4); 460–462

Cortés, C. B., V. T. Galván, S. S. Pedro, and T. V. García
(2011). One Pot Synthesis of Menthol from (±)-citronellal
on Nickel Sulfated Zirconia Catalysts. Catalysis Today,
172(1); 21–26

da Silva, K. A., P. A. Robles-Dutenhefner, E. M. Sousa, E. F.
Kozhevnikova, I. V. Kozhevnikov, and E. V. Gusevskaya
(2004). Cyclization of (+)-citronellal to (-)-isopulegol Cat-
alyzed by H3PW12O40/SiO2. Catalysis Communications,
5(8); 425–429

da Silva Rocha, K. A., P. A. Robles-Dutenhefner, I. V.
Kozhevnikov, and E. V. Gusevskaya (2009). Phospho-
tungsticHeteropolyAcidasEcientHeterogeneousCatalyst
for Solvent-free Isomerization of alpa-pinene and Longifo-
lene. Applied Catalysis A: General, 352(2); 188–192

da Silva Rocha, K. A., P. A. Robles-Dutenhefner, E. M. Sousa,
E.F.Kozhevnikova, I.V.Kozhevnikov,andE.V.Gusevskaya
(2007). Pd-heteropolyAcid as aBifunctional Heterogeneous
Catalyst for One-pot Conversion of Citronellal to Menthol.
Applied Catalysis A: General, 317(2); 171–174

© 2021 The Authors. Page 176 of 180



Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

deSousa, D.P., editor (2015). BioactiveEssentialOilsandCancer.
Springer International Publishing

Enferadi-Kerenkan, A., T.-O. Do, and S. Kaliaguine (2018).
Heterogeneous Catalysis by Tungsten-based Heteropoly
Compounds. Catalysis Science & Technology, 8(9); 2257–
2284

Fatimah, I., D. Rubiyanto, and T. Huda (2008). Peranan
Katalis Tio2/Sio2-Montmorillonit Pada Reaksi Konversi
Sitronelal Menjadi Isopulegol. Reaktor, 12(2); 83

Fatimah, I., D. Rubiyanto, and T. Huda (2014). Eect of
Sulfation on Zirconia-Pillared Montmorillonite to the Cat-
alytic Activity in Microwave-Assisted Citronellal Conversion.
International Journal of Chemical Engineering, 2014; 1–7

Fatimah, I., D. Rubiyanto, and T. Huda (2015). Preparation
and Characterization of Ni/Zr-Saponite as Catalyst in Cat-
alytic Hydrogen Transfer Reaction of Isopulegol. Materials
Science Forum, 827; 311–316

Fatimah, I., D. Rubiyanto, T. Huda, Z. Zuhrufa, S. P. Yudha,
and N. C. Kartika (2016). Novel Sulphated Zirconia Pillared
Clay Nanoparticles as Catalyst in Microwave Assisted Con-
version of Citronellal. Materials Technology, 31(4); 222–228

Fatimah, I., D. Rubiyanto, N. I. Prakoso, A. Yahya, and Y.-L.
Sim (2019). Green Conversion of Citral and Citronellal us-
ing Tris(bipyridine)ruthenium(II)-supported Saponite Cata-
lyst under Microwave Irradiation. Sustainable Chemistry and
Pharmacy, 11; 61–70

Gavahian, M., Y.-T. Lee, and Y.-H. Chu (2018). Ohmic-
assisted Hydrodistillation of Citronella Oil from Taiwanese
CitronellaGrass: ImpactsontheEssentialOilandExtraction
Medium. Innovative Food Science & Emerging Technologies,
48; 33–41

González, B., A. Pérez, R. Trujillano, A. Gil, and M. Vicente
(2017). Microwave-Assisted Pillaring of a Montmorillonite
withAl-Polycations inConcentratedMedia. Materials, 10(8);
886

Guedes, A. R., A. R. C. de Souza, E. F. Zanoelo, and M. L.
Corazza (2018). Extraction of Citronella Grass Solutes with
Supercritical CO2, Compressed Propane and Ethanol as Co-
solvent: Kinetics Modeling and Total Phenolic Assessment.
The Journal of Supercritical Fluids, 137; 16–22

Guidotti, M., R. Psaro, N. Ravasio, and G. Moretti (2000).
One-pot Conversion of Citronellal into Isopulegol Epoxide
on Mesoporous Titanium Silicate. Chemical Communications,
(18); 1789–1790

Hamzah, M. H., H. C. Man, Z. Z. Abidin, and H. Jamaludin
(2013). Comparison of Citronella Oil Extraction Meth-
ods from Cymbopogon nardus Grass by Ohmic-heated
Hydro-distillation, Hydro-Distillation, and Steam Distilla-
tion. BioResources, 9(1); 256–272

Heravi, M. M., F. Derikvand, and F. F. Bamoharram (2006).
Dodecatungstophosphoric Acid (H3PW12O40): A Novel
and Ecient Recyclable Catalyst for Synthesis of 1,1-
Diacetates from Aromatic Aldehydes in Solvent-Free Sys-
tem and Their Deprotection. Synthetic Communications,
36(21); 3109–3115

Ilyina, I. V., O. S. Patrusheva, V. V. Zarubaev, M. A. Misiurina,
A. V. Slita, I. L. Esaulkova, D. V. Korchagina, Y. V. Gatilov,
S. S. Borisevich, K. P. Volcho, and N. F. Salakhutdinov
(2021). InuenzaAntiviralActivityofF-andOH-containing
Isopulegol-derived Octahydro-2H-chromenes. Bioorganic
& Medicinal Chemistry Letters, 31; 127677

Imachi, S., K. Owada, and M. Onaka (2007). Intramolecu-
lar Carbonyl-ene Reaction of Citronellal to Isopulegol Over
ZnBr2-loadingMesoporousSilicaCatalysts. JournalofMolec-
ular Catalysis A: Chemical, 272(2); 174–181

Jaafari, A., M. Tilaoui, H. A. Mouse, L. A. M'bark, R. Aboufa-
tima, A. Chait, M. Lepoivre, and A. Zyad (2012). Compara-
tive Study of the Antitumor Eect of Natural Monoterpenes:
Relationship to Cell Cycle Analysis. Revista Brasileira de
Farmacognosia, 22(3); 534–540

Jimeno, C., J. Miras, and J. Esquena (2013). TiO2(SiO2)x
and ZrO2(SiO2)x Cryogels as Catalysts for the Citronellal
Cyclization to Isopulegol. Catalysis Letters, 143(6); 616–623

Jung, E., S. Byun, S. Kim, M. Kim, D. Park, and J. Lee
(2012). Isomenthone Protects Human Dermal Fibroblasts
from TNF-alpha-induced Death Possibly by Preventing Ac-
tivationof JNKandp38MAPK. FoodandChemicalToxicology,
50(10); 3514–3520

Kalaivani, K. and C. Sankaranarayanan (2019). Isopulegol
Ameliorates Dyslipidemia by Modulating Adipokine Secre-
tion in High Fat Diet/Streptozotocin Induced Diabetic Rats.
Journal of Drug Delivery and Therapeutics, 9(4); 126–136

Kalmakhanova, M. S., J. L. D. de Tuesta, B. K. Massalimova,
and H. T. Gomes (2019). Pillared Clays from Natural Re-
sources as Catalysts for Catalytic Wet Peroxide Oxidation:
Characterization and Kinetic Insights. Environmental Engi-
neering Research, 25(2); 186–196

Knirsch, M. C., C. A. dos Santos, A. A. M. de Oliveira
Soares Vicent, and T. C. V. Penna (2010). Ohmic Heating-A
Review. Trends in FoodScience & Technology, 21(9); 436–441

Kooli, F., Y. Liu, K. Hbaieb, and R. Al-Faze (2016). Char-
acterization and Catalytic Properties of Porous Clay Het-
erostructures from Zirconium Intercalated Clay and its Pil-
lared Derivatives. Microporous and Mesoporous Materials, 226;
482–492

Kooli, F., Y. Liu, K. Hbaieb, and R. Al-Faze (2017). Prepara-
tion and Catalytic Activities of Porous Clay Heterostructures
from Aluminium-intercalated Clays: Eect of Al Content.
Clay Minerals, 52(4); 521–535

Laluc, M., P. Mäki-Arvela, A. F. Peixoto, N. Li-Zhulanov,
T. Sandberg, N. F. Salakhutdinov, K. Volcho, C. Freire, A. Y.
Sidorenko, and D. Y. Murzin (2020). Catalytic Synthesis of
Bioactive 2H-chromene Alcohols from (-)-isopulegol and
Acetone on Sulfonated Clays. Reaction Kinetics, Mechanisms
and Catalysis, 129(2); 627–644

Lenardão, E. J., G. V. Botteselle, F. de Azambuja, G. Perin,
and R. G. Jacob (2007). Citronellal as Key Compound in
Organic Synthesis. Tetrahedron, 63(29); 6671–6712

Li, P., Y. Ji, W. Chen, X. Zhang, and L. Wang (2013). The
Facile Synthesis of 2-bromoindoles via Cs2CO3-promoted

© 2021 The Authors. Page 177 of 180



Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

IntramolecularCyclizationof2-(gem-dibromovinyl)anilines
under Transition-metal-free Conditions. RSC Adv., 3(1);
73–78

Li, Y. and Z. Lin (2015). Gold(III)-Catalyzed Intramolecular
Cyclization of alpha-Pyrroles to Pyrrolopyridinones and
Pyrroloazepinones: A DFT Study. Organometallics, 34(14);
3538–3545

Liu, J., X. Li, S. Zuo, and Y. Yu (2007). Preparation
and Photocatalytic Activity of Silver and TiO2 Nanopar-
ticles/montmorillonite Composites. Applied Clay Science,
37(4); 275–280

Liu, Q. L., D. D. Wen, C. C. Hang, Q. L. Li, and Y. M. Zhu
(2010). A Novel and Regiospecic Synthesis of 1-Aryl-
1H-benzotriazoles via Copper(I)-Catalyzed Intramolecular
Cyclization Reaction. Helvetica Chimica Acta, 93(7); 1350–
1354

Liu, T., X. W. Zheng, L. L. Han, Y. P. Li, S. M. Han, and
Z. Y. Yu (2016). Mechanistic Insight into the Selective
Cyclization of Arylnitrones to Indolines Via Rh(III) Catalyst:
a Theoretical Study. RSC Advances, 6(28); 23265–23271

Makiarvela, P. (2004). Cyclization of Citronellal Over Zeo-
lites and Mesoporous Materials for Production of Isopulegol.
Journal of Catalysis, 225(1); 155–169

Makiarvela, P., N. Kumar, D. Kubicka, A. Nasir, T. Heikkila,
V. Lehto, R. Sjoholm, T. Salmi, and D. Murzin (2005). One-
pot Citral Transformation to Menthol Over Bifunctional
Micro and Mesoporous Metal Modied Catalysts: Eect of
Catalyst Support and Metal. Journal of Molecular Catalysis A:
Chemical, 240(2); 72–81

Manos, G., I. Y. Yusof, N. Papayannakos, and N. H. Gangas
(2001). Catalytic Cracking of Polyethylene Over Clay Cata-
lysts. Comparison with an Ultrastable Y Zeolite. Industrial
& Engineering Chemistry Research, 40(10); 2220–2225

Mao, H., B. Li, X. Li, Z. Liu, and W. Ma (2009). Mesoporous
Nickel (or cobolt)-doped silica-pillared Clay: Synthesis and
Characterization Studies. Materials Research Bulletin, 44(7);
1569–1575

Mesias-Salazar, A., O. S. Trofymchuk, C. G. Daniliuc, A. An-
tiñolo, F. Carrillo-Hermosilla, F. M. Nachtigall, L. S.
Santos, and R. S. Rojas (2020). Copper (II) as Cata-
lyst for Intramolecular Cyclization and Oxidation of (1,4-
phenylene)bisguanidines to Benzodiimidazole-diylidenes.
Journal of Catalysis, 382; 150–154

Milone, C., C. Gangemi, G. Neri, A. Pistone, and S. Galvagno
(2000). Selective One Step Synthesis of (-) Menthol from
(+) Citronellal on Ru Supported on Modied SiO2. Applied
Catalysis A: General, 199(2); 239–244

Moradi, S., A. Fazlali, and H. Hamedi (2018). Microwave-
assisted Hydro-distillation of Essential Oil from Rosemary:
Comparison with Traditional Distillation. Avicenna journal
of medical biotechnology, 10(1); 22

Nagendrappa, G. (2011). Organic Synthesis using Clay and
Clay-supported Catalysts. Applied Clay Science, 53(2); 106–
138

Nicolaou, D., Vourloumis, N. Winssinger, and P. S. Baran

(2000). The Art and Science of Total Synthesis. Angewandte
Chemie - International Edition Chem. Int. Ed, 39; 44–122

Nie, Y., G.-K. Chuah, and S. Jaenicke (2006). Domino-
cyclisation and Hydrogenation of Citronellal to Menthol
Over Bifunctional Ni/Zr-Beta and Zr-beta/Ni-MCM-41
Catalysts. Chemical Communications, 9(7); 790–792

Nisyak, K., E. D. Iftitah, and R. T. Tjahjanto (2017). Kon-
versi Sitronelal Menjadi Senyawa Isopulegol dengan Katalis
ZnBr2/beta-Zeolit. JurnalKimiadanKemasan, 39(2); 47–54

Nogueira, J. S. M., J. P. A. Silva, S. I. Mussatto, and
L. M. Carneiro (2020). Synthesis and Application of
Heterogeneous Catalysts Based on Heteropolyacids for 5-
Hydroxymethylfurfural Production from Glucose. Energies,
13(3); 655

Nuryanti, N., R. Wijayanti, and M. Masdikoh (2019). Produksi
IsopulegoldenganCyclisasiCitronellalMenggunakanKatalis
Heterogen ZnBr2/SiO2 untuk Aplikasi Green Medicine.
Jurnal Sains Farmasi & Klinis, 6(2); 85–94

Panda, A. K. (2018). Thermo-catalytic Degradation of Dier-
ent Plastics to Drop in Liquid Fuel using Calcium Bentonite
Catalyst. International Journal of Industrial Chemistry, 9(2);
167–176

Park, K.-W., J. H. Jung, J. D. Kim, S.-K. Kim, and O.-Y.
Kwon(2009). PreparationofMesoporousSilica-pillaredH+-
titanosilicates. Microporous and Mesoporous Materials, 118(3);
100–105

Pinto, M. L., J. Marques, and J. Pires (2012). Porous Clay
Heterostructures with Zirconium for the Separation of Hy-
drocarbon Mixtures. Separation and Purication Technology,
98; 337–343

Plößer, J., M. Lucas, and P. Claus (2014). Highly Selective
Menthol Synthesis by One-pot Transformation of Citronel-
lal using Ru/H-BEA Catalysts. Journal of Catalysis, 320;
189–197

Plößer, J., M. Lucas, J. Wärnå, T. Salmi, D. Y. Murzin, and
P. Claus (2016). Kinetics of the One-Pot Transformation of
Citronellal to Menthols on Ru/H-BEA Catalysts. Organic
Process Research & Development, 20(9); 1647–1653

Radwan, D., L.Saad, S.Mikhail, andS.Selim(2009). Catalytic
Evolution of Sulfated Zirconia Pillared Clay in n-hexane
Transformation. J. Appl. Sci. Res, 5(12); 2332–42

Ramos, A. G. B., I. R. A. de Menezes, M. S. A. daSilva, R. Tor-
res Pessoa, L. J. de Lacerda Neto, F. Rocha Santos Passos,
H. D. Melo Coutinho, M. Iriti, and L. J. Quintans-Júnior
(2020). Antiedematogenic and Anti-inammatory Activ-
ity of the Monoterpene Isopulegol and its beta-cyclodextrin
(beta-CD) InclusionComplexinAnimalInammationMod-
els. Foods, 9(5); 630

Raut, J. S. and S. M. Karuppayil (2014). A Status Review on
the Medicinal Properties of Essential Oils. Industrial Crops
and Products, 62; 250–264

Ravasio, N., N. Poli, R. Psaro, M. Saba, and F. Zaccheria
(2000). Bifunctional Copper Catalysts. Part II. Stereoselec-
tive Synthesis of (-)-menthol Starting from (+)-citronellal.
Topics in Catalysis, 13(3); 195–199

© 2021 The Authors. Page 178 of 180



Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

Robles-Dutenhefner, P. A., K. A. da Silva, M. R. H. Sid-
diqui, I. V. Kozhevnikov, and E. V. Gusevskaya (2001). Hy-
dration and Acetoxylation of Monoterpenes Catalyzed by
Heteropoly Acid. Journal of Molecular Catalysis A: Chemical,
175(1-2); 33–42

Rožić, L., B. Grbić, N. Radić, S. Petrović, T. Novaković,
Z. Vuković, and Z. Nedić (2011). Mesoporous 12-
tungstophosphoric Acid/activated Bentonite Catalysts for
Oxidation of 2-propanol. Applied Clay Science, 53(2); 151–
156

Rubiyanto, D., N. I. Prakoso, I. Sahroni, R. Nurillahi, and
I. Fatimah (2019). ZnO-Porous Clay Heterostructure from
Saponite as Green Catalyst for Citronellal Cyclization. Bul-
letin of Chemical Reaction Engineering & Catalysis, 15(1); 137–
145

Salea, R., S. Hiendrawan, E. Subroto, B. Veriansyah, and R. R.
Tjandrawinata (2018). Supercritical Carbon Dioxide Extrac-
tion of Citronella Oil from Cymbopogon Winterianus using
Taguchi Orthogonal Array Design. International Journal of
Applied Pharmaceutics, 10(6); 147

Sekerová, L., P. Březinová, T. T. Do, E. Vyskočilová, J. Krupka,
L. Červený, L. Havelková, B. Bashta, and J. Sedláček (2019).
Sulfonated Hyper-cross-linked Porous Polyacetylene Net-
works as Versatile Heterogeneous Acid Catalysts. Chem-
CatChem, 12(4); 1075–1084

Shah, A.K., S.Park, H.A.Khan, U.H.Bhatti, P.Kumar, A.W.
Bhutto, and Y. H. Park (2018). Citronellal Cyclisation Over
Heteropoly Acid Supported on Modied Montmorillonite
Catalyst: Eects of Acidity and Pore Structure on Catalytic
Activity. Research on Chemical Intermediates, 44(4); 2405–
2423

Sharma, R., R. Rao, S. Kumar, S. Mahant, and S. Khatkar
(2019). Therapeutic Potential of Citronella Essential Oil: A
Review. Current Drug Discovery Technologies, 16(4); 330–339

Shieh, D. L., C. C. Tsai, and A. N. Ko (2003). Liquid-phase
Synthesis of Isopulegol from Citronellal using Mesoporous
Molecular Sieves MCM-41 and Zeolites. Reaction Kinetics
and Catalysis Letters, 79(2); 381–389

Silva, C. F., F. C. Moura, M. F. Mendes, and F. L. P. Pes-
soa (2011). Extraction of Citronella (Cymbopogon nardus)
Essential Oil using Supercritical co2: Experimental Data
and Mathematical Modeling. Brazilian Journal of Chemical
Engineering, 28(2); 343–350

Solanki, K. P., M. A. Desai, and J. K. Parikh (2018). Sono
Hydrodistillation for Isolation of Citronella Oil: A Sym-
biotic Eect of Sonication and Hydrodistillation Towards
Energy Eciency and Environment Friendliness. Ultrasonics
Sonochemistry, 49; 145–153

Sonehara, T., S. Murakami, S. Yamazaki, and M. Kawatsura
(2017). Iron-Catalyzed Intermolecular Hydrothiolation of
Internal Alkynes with Thiosalicylic Acids, and Sequential
IntramolecularCyclizationReaction. OrganicLetters,19(16);
4299–4302

Sudiyarmanto, L.N.Hidayati, A.Kristiani, andF.Aulia (2017).
Hydrogenation of citral into its derivatives using heteroge-

neous catalyst. In AIP Conference Proceedings
Telalović, S., A. Ramanathan, G. Mul, and U. Hanefeld (2010).
TUD-1: Synthesis and Application of a Versatile Catalyst,
Carrier, Material. J. Mater. Chem., 20(4); 642–658

Tobisch, S. (2006). Intramolecular Hydroamina-
tion/cyclisation of Aminoallenes Mediated by a Cationic
Zirconocene Catalyst: a Computational Mechanistic Study.
Dalton Transactions, (35); 4277

Tran, T. H., D. C. Nguyen, T. N. N. Phu, V. T. T. Ho, D. V. N.
Vo, L. G. Bach, and T. D. Nguyen (2019). Research on
Lemongrass Oil Extraction Technology (Hydrodistillation,
Microwave-Assisted Hydrodistillation). Indonesian Journal of
Chemistry, 19(4); 1000

Tursiloadi, S., A. Litiaz, R. Pertiwi, I. Adilina, and K. Sembir-
ing (2015). Development of Green Nickel-Based Zeolite
Catalysts for Citronella Oil Conversion to Isopulegol. Proce-
dia Chemistry, 16; 563–569

Vajglová, Z., N. Kumar, M. Peurla, K. Eränen, P. Mäki-Arvela,
and D. Y. Murzin (2020). Cascade Transformations of (±)-
citronellal to Menthol Over Extruded Ru-MCM-41 Cata-
lysts in a Continuous Reactor. Catalysis Science & Technology,
10(23); 8108–8119

Vandichel, M., F. Vermoortele, S. Cottenie, D. E. D. Vos,
M. Waroquier, and V. V. Speybroeck (2013). Insight in
the Activity and Diastereoselectivity of Various Lewis Acid
Catalysts for the Citronellal Cyclization. Journal of Catalysis,
305; 118–129

Vetere, V., G. F. Santori, A. Moglioni, G. Y. M. Iglesias, M. L.
Casella, and O. A. Ferretti (2002). Hydrogenation of (-)-
menthone, (+)-isomenthone, and (+)-pulegone with Plat-
inum/tin Catalyst. Catalysis Letters, 84(4); 251–257

Vrbková, E., B. Šteová, M. Zapletal, E. Vyskočilová, and
L. Červený (2020). Tungsten Oxide-based Materials as Ef-
fective Catalysts in Isopulegol Formation by Intramolecular
Prins Reaction of Citronellal. Research on Chemical Intermedi-
ates, 46(9); 4047–4059

Wang, Y., W. Liao, G. Huang, Y. Xia, and Z.-X. Yu (2014).
Mechanisms of the PtCl2-Catalyzed Intramolecular Cycliza-
tion of o-Isopropyl-Substituted Aryl Alkynes for the Syn-
thesis of Indenes and Comparison of Three sp3 C–H Bond
Activation Modes. The Journal of Organic Chemistry, 79(12);
5684–5696

Wang, Y., X. Su, Z. Xu, K. Wen, P. Zhang, J. Zhu, and H. He
(2016). Preparation of Surface-functionalized Porous Clay
Heterostructures Via Carbonization of Soft-template and
their Adsorption Performance for Toluene. Applied Surface
Science, 363; 113–121

Wany, A., A. Kumar, S. Nallapeta, S. Jha, V. K. Nigam, and
D. M. Pandey (2013). Extraction and Characterization of
Essential Oil Components based on Geraniol and Citronellol
fromJavaCitronella (CymbopogonwinterianusJowitt). Plant
Growth Regulation, 73(2); 133–145

Wu, H., J. Li, Y. Jia, Z. Xiao, P. Li, Y. Xie, A. Zhang, R. Liu,
Z. Ren, M. Zhao, C. Zeng, and C. Li (2019). Essential
Oil Extracted from Cymbopogon citronella Leaves by Su-

© 2021 The Authors. Page 179 of 180



Yahya et. al. Science and Technology Indonesia, 6 (2021) 166-180

percritical Carbon Dioxide: Antioxidant and Antimicrobial
Activities. Journal of Analytical Methods in Chemistry, 2019;
1–10

Xu, X., Y. Liu, and C.-M. Park (2012). Rhodium(III)-
Catalyzed Intramolecular Annulation through C-H Acti-
vation: Total Synthesis of (±)-Antone, (±)-Septicine, (±)-
Tylophorine, and Rosettacin. Angewandte Chemie Interna-
tional Edition, 51(37); 9372–9376

Yadav, G. D. and S. V. Lande (2006). Novelties of Kinetics of
Chemoselective Reduction of Citronellal to Citronellol by
Sodium Borohydride under Liquid-liquid Phase Transfer
Catalysis. JournalofMolecularCatalysisA:Chemical, 247(1-2);
253–259

Yue, D., J. Lei, L. Zhou, X. Du, Z. Guo, and J. Li (2020). Ox-
idative Desulfurization of Fuels at Room Temperature using
Ordered Meso/macroporous H3PW12O40/SiO2 Catalyst

with High Specic Surface Areas. Arabian Journal of Chem-
istry, 13(1); 2649–2658

Zaccheria, F., F. Santoro, E. Iftitah, and N. Ravasio (2018).
Brønsted and Lewis Solid Acid Catalysts in the Valorization
of Citronellal. Catalysts, 8(10); 410

Zheng, L., M. Tang, Y. Wang, X. Guo, D. Wei, and Y. Qiao
(2016). A DFT Study on PBu3-catalyzed Intramolecular
Cyclizations of N-allylic substituted alpha-amino Nitriles
for the Formation of Functionalized Pyrrolidines: Mecha-
nisms, Selectivities, and the Role of Catalysts. Organic &
Biomolecular Chemistry, 14(11); 3130–3141

Zhou, C. H., H. Zhao, D. S. Tong, L. M. Wu, and W. H.
Yu (2013). Recent Advances in Catalytic Conversion of
Glycerol. Catalysis Reviews, 55(4); 369–453

© 2021 The Authors. Page 180 of 180


	INTRODUCTION
	CITRONELLA OIL: SOURCE AND EXTRACTION METHOD
	CITRONELLAL CONVERSION INTO ISOPULEGOL AND MENTHOL
	CITRONELLAL CONVERSION INTO ISOPULEGOL
	CLAY-BASED HETEROGENEOUS CATALYSTS
	FUTURE PERSPECTIVE
	ACKNOWLEDGEMENT