Conversion of (±)-Citronellal and Its Derivatives …… (Indri Badria Adilina)

CONVERSION OF (±)-CITRONELLAL AND ITS DERIVATIVES TO (-)- USING BIFUNCTIONAL NICKEL ZEOLITE CATALYSTS

(Konversi (±)-Citronellal dan Turunannya Menjadi (-)-Mentol Menggunakan Katalis Nikel Zeolit Dwi-Fungsi)

Indri Badria Adilina, Ralentri Pertiwi and Anny Sulaswatty Research Centre for Chemistry-Indonesian Institute of Sciences Puspiptek Area Serpong, Tangerang 15314, Indonesia e-mail: [email protected] Naskah diterima 19 September 2014, revisi akhir 6 April 2015 dan disetujui untuk diterbitkan 16 April 2015

ABSTRAK. (±)-Citronellal and its derivatives were converted to (-)-menthol by a one-pot reaction system using zeolite based nickel catalysts. The catalysts were prepared by immobilization of nickel on natural zeolite (NZ) or synthetic zeolite (ZSM- 5) by a simple cation exchange method. Calcination and treatment procedures were able to significantly increase the surface area and pore volume of NZ based catalysts whereas negligible changes in the properties were observed for that of ZSM-5. Catalytic reactions were carried out at 70ºC by stirring the mixture in the air for cyclization of (±)-citronellal to (±)-isopulegol followed by hydrogenation towards the desired (-)-menthol at 2 Mpa of H2 pressure. The Ni/NZ catalyst was able to convert a (±)-citronellal derivative yielding 9% (-)-menthol (36% selectivity) with conversion up to 24%, whereas Ni/ZSM5 catalyst directly converted 65% (±)-citronellal to give 4% menthol (6% selectivity). These zeolite based catalysts are therefore potential materials for the conversion of biomass feed stock to value-added chemicals. Keywords: citronellal, citronella oil, menthol, nickel catalyst, zeolite

ABSTRACT. (±)-Sitronelal dan turunannya telah dikonversi menjadi (-)-mentol dalam sistem reaksi one-pot menggunakan katalis nikel berbasis zeolit. Katalis dipreparasi melalui imobilisasi nikel pada zeolit alam (NZ) atau zeolit sintetik (ZSM-5) dengan metode pertukaran ion. Prosedur kalsinasi dan perlakuan hidrogen dapat meningkatkan secara signifikan luas permukaan dan volume pori dari katalis berbasis NZ sedangkan perubahan yang tidak besar terlihat untuk ZSM-5. Reaksi katalitik dilakukan pada suhu 70ºC dengan mengaduk campuran di dalam udara untuk siklisasi (±)-sitronelal menjadi (±)-isopulegol dilanjutkan dengan hidrogenasi menjadi (-)- mentol pada 2 Mpa tekanan H2. Katalis Ni/NZ dapat mengkonversi turunan (±)- sitronelal menghasilkan 9% mentol (selektifitas 36%) dengan konversi sampai 24%, sedangkan katalis Ni/ZSM5 mengkonversi 65% (±)-sitronelal dan menghasilkan (-)- mentol 4% (selektifitas 6%). Katalis berbasis zeolit ini adalah material yang berpotensi untuk konversi bahan biomasa menjadi bahan kimia bernilai tambah. Kata kunci: katalis nikel, mentol, minyak sereh wangi, sitronelal, zeolit

1. INTRODUCTION Meanwhile synthetic (-)-menthol is Menthol is a flavor chemical, which industrially produced by Takasago is used extensively in food, cosmetic and International Corp. and Symrise using pharmaceutical industries (Nie, et.al., or m-cresol as the protocol in a 2007). Natural menthol can be supplied catalytic process, however, the process through extraction of Mentha arvensis involves consecutive steps and require an plant followed by a separation process. amount of homogeneous catalysts to aid the reaction. The developments of

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alternative methods are strongly desired, metal is more favourable than precious especially those using a more effective metals such as Pt, Pd and Ru. We have protocol which can minimize synthetic previously reported the conversion of steps together with a more environmentally citronellal to isopulegol using acidified friendly heterogeneous catalyst. natural zeolite H-NZ, natural bentonite H- Synthesis of (-)-menthol from NB, and synthetic zeolite H-ZSM5 citronellal, may be performed in a one-pot catalysts (Adilina, et.al., 2014). A higher reaction system by an efective two step selectivity of 86% isopulegol was obtained process, i.e. cyclisation of (+)-citronellal to using H-NZ compared to that of H-NB and (-)-isopulegol followed by hydrogenation H-ZSM5 in mild reaction conditions. of the isopulegol to (-)-menthol (Mertens, Further application of H-NZ was evaluated et.al., 2003). Acid catalysts such as SiO2, for the one-pot synthesis of menthol from Al-MCM-41 and ZnBr2, have been citronellal using dual-catalyst system of reported to serve as an efficient cyclization the acidified natural zeolite and Raney-Ni catalyst of citronellal. The Bronsted acid catalyst, conversion of (±)-citronellal up to site was able to increase the rate of 80% was achieved giving 68% (v/v) citronellal isomerization although formation of racemic (±)-methol (Adilina, formation of (-)-isopulegol were still low. et.al., 2008). Besides the fact that NZ Industrially, ZnBr2 is used and may give based catalysts are considered more 94% selectivity to isopulegol, however, the economical than other syntesized silica- process implies the use of some alumina compounds since these materials compounds harmful to the environment. are abundant and readily available, For the second process, the modification through immobilization of hydrogenation reaction of isopulegol to metals of the zeolite creates extra Lewis menthol requires a metal catalyst which acidity on the catalyst and results in a can adsorb hydrogen molecules and higher selectivity for the desired menthol. accelerate the reaction. Ni is a low cost In this paper, we present the preparation of base metal which exhibits high activity in bifunctional nickel zeolite catalysts from the processes of cracking, isomerization, natural zeolite (NZ) and synthetic zeolite hydrogenation, as well as ring opening of (ZSM-5) and their application in the one- hydrocarbons. Various studies have pot synthesis of (-)-menthol from (±)- reported the use of Ni metal as an active citronellal and its derivatives. metal on catalyst for the hydrogenation reaction of isopulegol to menthol, 2. RESEARCH METHODS including Ni/ZnBr2/-zeolite catalyst (Nisyak, et.al., 2013), NiZrS catalyst Preparation and Characterization of Zeolite Based Catalysts (Cortes, et.al., 2011) and Ni/-Al2O3 catalyst (Iftitah, et.al., 2011). A Ni/Al- Nickel supported on zeolite (NZ, MCM-41 catalyst was reported to ZSM5) was prepared via typical cation transform citronellal to menthol in good exchange procedure (Kimball, et.al., 1981) selectivity (Nie, et.al., 2007). The weak by adding 5 g zeolite to an amount of acid sites of Al-MCM-41 facilitated the distilled water containing 10 wt% Ni from cyclisation of citronellal to isopulegol and Ni(NO3)2.6H2O (Merck). The solution was upon hydrogenation, 70–75% racemic (±)- stirred at room temperature for 24 h. The o menthol was formed. catalyst was then dried at 100 C for 2 h o Zeolite is an aluminosilicate mineral and then calcined at 350 C for 2 h. Before and may exhibit both Bronsted and Lewis the catalytic testing, some catalysts were o acid sites which are essential for the reduced under H2 flow for 2 h at 300 C and o conversion of citronellal to menthol. Pt/H- 500 C for NZ and ZSM5 catalysts, beta zeolite was reported to assist the one- respectively. Characterizations of the step formation giving 76% yield of (–)- catalysts were conducted by a surface area menthol (Mertens, et.al., 2006). analyser, X-ray fluorescence and X-ray Nevertheless, the use of non-expensive Ni diffraction.

2 Conversion of (±)-Citronellal and Its Derivatives …… (Indri Badria Adilina)

Catalytic Testing and Product Analysis blockage of porous structure in the ZSM-5 The catalytic test was carried out in framework occurred after the Ni loading. o 20 mL autoclave at 70 C as previously 2) X-ray fluorescence analysis repoted by Adilina, et.al. (2008). (±)- Table 2 summarizes the elemental Citronellal and its derivatives (5 mmol) composition of SiO and Al O in the was added into the autoclave and 0.1 g 2 2 3 Ni/NZ and Ni/NZ-HT catalysts. Results bifunctional catalyst was added with 5 mL show that both catalysts have SiO content cyclohexane (Merck). After 3 h, H was 2 2 higher than that of Al O . The Si/Al ratio is flowed with a constant pressure of 2 MPa 2 3 the ratio of the number Si atoms to the for another 3 h. Reaction products were number of Al atoms in the zeolite analyzed by gas chromatography using framework and a higher Si/Al ratio is biphenyl as an internal standard (Shimadzu known to give a higher acid behavior. The 14A, column DB5-MS 30 m x 0.25 m x Ni content was measured as 1% for both 0.25 m, FID detector). Ni/NZ and Ni/NZ-HT catalysts.

3. RESULTS AND DISCUSSION Table 2. Elemental Analysis of NZ Based Characterization of Bifunctional Zeolite Catalysts Based Catalysts 1) Surface area analyzer measurement The surface area, pore size, volume, and pore size of various bifunctional zeolite based catalyst were measured by a surface area analyzer according to the BET 3) X-ray diffraction analysis method. As can be observed in Table 1, the The crystalline structures of Ni/NZ surface area of Ni/NZ (entry 2) and Ni/NZ- catalysts were determined by XRD HT (entry 3) increased slightly after analysis. The XRD patterns of the parent immobilization and subsequent hydrogen NZ and that after immobilization of Ni are treatment, respectively. shown in Fig. 1. According to the results, clinoptilolite (2 = 13.68°, 26.78°, 30.12°) Table 1. Surface area, pore volume, and pore and mordenite (2 = 19.74°, 22.42°, size of Ni/NZ and Ni/ZSM5 catalysts 25.82°, 27.92°) phases were dominant in the NZ structure and no peaks indicating phases of SiO2 and Al2O3 were detected. The structure of zeolites consists of silicon, aluminum and that form a framework with cavities and channels inside where cations, water or small molecules may reside. A high peak intensity at 2=26.78° indicated that the Meanwhile natural zeolite as the parent NZ compose of moderite as its main catalyst pre cursor tends to show a smaller constituent mineral with some existence of surface area and pore volume (entry 1). clinoptilolite. This is presumably due to a number of When compared with the pattern of impurities in their framework such as Ni/NZ and Ni/NZ-HT catalysts, no change oxides of Na, K, Ca, Mg and Fe, which in the value of 2 were observed for the may cover the active surface. In the case of modified NZ, however, the peak intensity Ni/ZSM5 and Ni/ZSM5-HT, the surface increased after the immobilization of Ni. area was detected lower than that of the This is suggested due to the calcination parent ZSM-5, although the change of their and hydrogen treatment processes which pore volume and pore size was may remove impurities in the NZ neglectable. It is predicted that a partial framework. These results show that the

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Fig 1. XRD patterns of Ni/NZ catalysts. (a) NZ, (b) Ni/NZ, (c) Ni/NZ-HT

Table 3. Conversion of citronellal and its derivatives to menthol using various catalysts Entry Catalyst Conversion Yield (±)- Yield (-)- Yield Selectivity (-)- (%) isopulegol (%) menthol (%) others(%) menthol (%) 1a Ni/NZ 100 7 0 93 0 2b Ni/NZ 90 4 0 86 0 3 Ni/NZ-HT 97 12 0 85 0 4c Ni/NZ-HT 24 - 9 16 36 5a Ni/ZSM5 65 22 4 39 6 6 Ni/ZSM5-HT 48 8 0 40 0 7d Ni/ZSM5-HT 77 14 2 61 3 8 Blank 0 0 0 0 0 o Reaction conditions: (±)-citronellal (5 mmol), catalyst (0.1 g), cyclohexane (5 mL), 70 C, 6h, 2 MPa H2. areaction time: 24 h, btoluene as solvent, cisopulegol as reactant, dcatalyst: 0.2 g. structure of the modified zeolites remains obtained. The catalyst was able to yield 7% intacteven after the loading of Ni metals. of isopulegol, the intermediate of menthol, Meanwhile no peaks related to the Ni and however, no formation of menthol was NiO phase were found in the observed (entry 1). Other by products are diffractograms, indicating that the Ni predicted to be mainly and 3,7- metals were highly dispersed onthe Ni/NZ dimethyl octanol (Fig 2). When toluene and Ni/NZ-HT catalysts. was used as the solvent, no significant Conversion of (±)-Citronellal and Its increase in the isopulegol and menthol Derivatives to (-)-Menthol yield was seen (entry 2). It has been reported that catalysts with weak Bronsted Conversion of (±)-citronellal and its acid and high Lewis acid sites will give a derivatives to (-)-menthol over various high selectivity in the cyclization reaction bifunctional Ni zeolite based catalysts was of citronellal to isopulegol (Chuah, et.al., | carried out in an autoclave at 70 C such as 2008). summarized in Table 3. The catalytic activity was first tested for Ni/ZN catalyst To determine whether the Ni metal for 24 h using cyclohexane as a solvent active site in the catalyst was effective for and 100% conversion of citronellal was the hydrogenation reaction, catalytic

4 Conversion of (±)-Citronellal and Its Derivatives …… (Indri Badria Adilina)

citronellal (entry 8) which shows that the presence of catalysts is highly essential for the conversion of citronella oil and its derivatives to (-)-menthol. The plausible mechanism for the conversion of (±)-citronellal to (-)-menthol using zeolite catalyst is assumed to occur through several steps. At first is the protonation of the carbonyl group of citronellal on the catalylitic zeolite acid site, followed by intramolecular re- arrangement of citronellal to form a more stable carbocation, which there by generates isopulegol. Secondly, adsorption of hydrogen molecules and subsequent hydrogenation of the alkene group of isopulegol on the catalytic Ni metal site. And finally desorption of the desired menthol product from the bifunctional Ni Fig 2. Products derived from citronellal zeolite catalyst. reactions using (±)-citronellal and its 4. CONCLUSIONS derivative (±)-isopulegol as the starting Conversion of (±)-citronellal and its material were conducted using Ni/NZ-HT derivatives to (-)-menthol proceeded using catalyst. bifunctional Ni zeolite catalysts. These The amount of (-)-menthol obtained catalysts were prepared from natural as a reaction product were analyzed using zeolite (NZ) and synthetic zeolite ZSM-5 a gas chromatography equiped with a DB- (ZSM-5) by immobilization of Ni using a 5MS column by which the detection simple cation-exchange procedure. method gave an adequate difference of Calcination and hydrogen treatment peak retention time between (+)-menthol procedures were able to significantly and (-)-menthol. Results reveal that no increase the surface area and pore volume yield of (-)-menthol was obtained when of NZ based catalysts whereas negligible citronellal was used as the reactant (entry changes in the properties were observed 3). On the other hand, 9% yield of (-)- for that of ZSM-5. Ni/NZ-HT catalyst menthol could be obtained from isopulegol showed good activity of 24% conversion with 24% conversion giving 36% of a (±)-citronellal derivative yielding 9% selectivity (entry 4). From these results, it of (-)-menthol and 36% selectivity whereas can be observed that the Ni/NZ catalyst a 4% yield of (-)-menthol and 6% was indeed able to act as a bifunctional selectivity was seen in the direct catalyst for the conversion, although the Ni conversion of 65% (±)-citronellal using the metal active site cannot play its role more Ni/ZSM5 catalyst. Optimization of the efficiently in the hydrogenation reaction reaction parameters are essential to since the number of isopulegol formed enhance the yield of (-)-menthol is under from citronellal was still low. In the cases further investigation. Therefore, low cost of Ni/ZSM5 and Ni/ZSM5-HT catalysts, Ni zeolite catalysts were able to lower conversions of citronellal were seen demonstrate promising competitive and only 4% (-)-menthol was formed. catalytic activity with other supported Nevertheless, higher yields of 21% metal catalysts which generally yields the isopulegol were obtained (entry 5-7). racemic (±)-menthol from (±)-citronellal Finally, control reaction without the use of and are potential materials for the synthesis any catalysts revealed no conversion of of flavor chemicals from citronella oil.

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