CHAPTER I
INTRODUCTION
1.1 General Background
One
of the major current challenges for the chemists and scientists is to design clean
or *,
-, reen chemical transformations in which less polllltlng. The chemical processes
should not lead to permanent damage towards environment thus consequently disturb the ecological balance. Subsequently, environmentally and not dan( Yerous products have received massive attentions recently. The eagerness to make chemical
manufacturing environmentally friendly is not a new issue. Such awareness was there because of our better understanding on the causes of environmental degradation
towards human and earth in particular. Consequently, lots of scientific organizations
and industries have put clean technology as a vital concern for their research and de\elopnlent's aim.
In order to minimize hazardous waste exposed to the environment, chemists hays designed and produced a bulky of improved methodologies, including the use of
clays as chemical catalysts. As been reviewed by Kaur and Kishore (2012). natural aluminosilicates such as clays and zeolites, are solids acids that are notably considered
as Sauahle competitors to replace liquid acids in catalysis reactions. Among We two good catalysts. natural and modified clays have serious attention due to their tremendous versatile properties. Particularly fir the most common and potential modified clays in organic synthesis application are the montmorillonite-K10 (MMT
-K l0) and montmorillonite KSF. Both of them are synthetic clays produced from natural MMT and easily available in large quantities from various suppliers.
Furthermore. MMT-K 10 has higher surface area (about 250 111 2(1-1) in contrast to that of KSF (10 n]'ý,, - making it more eficctive and excellent catalyst (Kaur and Kishore.
2'012).
Clays have considerable potential as hetero,.; eneous catalytic materials due to their large surface area and cation exchange capacity (Kureshy et al., 2004). The major clay mineral of bentonite is MMT. It is widely and commercially available clay that alwavs beine treated to enhance its catalytic properties (Wallis et al., ? 007). For instance acid-treated MMT has been utilized as catalyst for plentiful reactions by the last fcvy decades e. g. the epoxidation of short-chain alkenes (Kureshv et al., 2004, Jiang et al., 2009: Boudjema et al., ? 014): the vegetable oils epoxidation reactions
such as castor oils and soybean oil (Farias et al., 2011 ): various reactions of- organic synthesis (Kaur & Kishore, 20I2): transesteriiication of castor oil with methanol (f acula ct al., 2014): biodegradation ofcrude oil aromatic compounds (L'gochukwu et al., 2014).
A -reat study has been concentrated in the catalytic epoxidalion of alkenes by various oxidants in consideration of epoxides as flexible intermediates and
indicators to variety of beneficial chemical outcomes and commodities (Behera N, Panda, 2013) such as drll"s, perfum materials. agroche'nlicals, f od additives and
sweetelicrs. L-poxldal1o11 process usually involves the homogeneous systelll which utilizes peracids as oxidizing agents and strong mineral acids as catalysts.
Periodically the process also involves metal complexes that are used as catalyst. For example. various molybdenum complexes such as Nloo, (acac),. A100, (ox), and
MoO, (PDTC), were tested in catalytic epoxidation of cyclohexene (Gnecco et al., 2004). All complexes perform high selectivity to the corresponding epoxide underneath investigated conditions. Besides, five different molybdenum complexes were also tested for cvclohexene and cvclohcxane oxidation. comparing tert- butylhydroproxide (TBHP) and H, O, (30%) as oxidants and exhibit high yield of products (Spada. 2015). However there are some disadvantages of using these types of homogeneous catalysts: i. e. generate corrosion of the equipments and produce extensive residue (Campanella et al., 2004, Campanella et al.. _'005: Muný, roo et al..
? 00S).
In contrast, the use of' heterogeneous catalysts has many advantages in
comparison with homogeneous catalysts. The most common benefits are facile separation and easily recovery of recyclable solid catalyst from the reaction mixture (Campanella & Baltanas. 2007. Jiang et al., 2009). There are a lot of reactions done by the use of' heterogeneous catalysts. Molybdenum hexacarbonvl (Mo(CO)6) immobilized on functionalized polystyrene has been occupied as an active and
greatly recyclable catalyst fir alkene epoxidation with TBHP (Griv ani et al.. 2006:
Taneestaninejad et. at.. 2006). Besides. Farias et al., (2011 ) investigated on the
catalytic activity of vanadyl acetylacetonate anchored onto MMT K 10 for the epoxidation ofgeramol with TBI-IP. The immobilized molybdenum-SchiffbaSe
complex on the surface of multi-wall carbon nanotubes also found to he a competent heterogeneous catalyst in epoxidation of' olefins (Mastcri-Farahani & Abednatanzi.
'013). AISO. the molybdenum complex tethered to the surf; ice of activated carbon being a staple heterogeneous catalyst fi)r the epoxidation of olefins (Masteri-
Farahani S: Abednatanzi, 2014). Recently. acetvlacetonatc complexes of vanadium
and molybdenum supported on lUnctlonallzed boehmlte nano-particles for the catalytic epoxidation of alkenes have given high turn-over frequency (TOF) values (Mirzaee et al., 2017). Heterogeneous catalytic system shows high catalytic activity
and also gives a minimization of residue thus eüects in low impact ftr CIl\ Irolllllclltal ISSUC.
Porous material catalyst has been in widely attention by researchers due to high suriice area and active site that contributed to the high activity. selectivity and
conversion of products. The use oi' MMT in this catalytic study as a porous material catalyst is due to its massive reasons. One of the special properties of MI\MT clays is they are formed by layered silicates. MMT clays that are usually used in organic
synthesis, are also among the various inorganic supports for reagents. Besides, they are commercially Utilized as an efficient, economical and versatile catalyst for ºllany organic reactions (Kaur & Kishore, 2012). Furthermore, both Bronsted and Lewis acidic catalytic sites are available in MMT structure. The interlamellar region mainly
incorporate by the Bronsted sites while the edge sites mainly incorporated by the Lewis sites. The quantity of water located between the sheets affects the acidity of the
clays (Yahiaoui et al.. 2003). Therelire, its natural occurrence along with the properties of, ion exchange allows it to work as an efficient catalyst. The interlayer cations are exchangeable, hence allowing modilication of* the acidic nature of the material (Kaur S: Kishore. 2012). Thus. MMT particularly MIM]' K10 becomes known as an efficient acidic catalyst in organic chemistry, including in the epoxidatioll reactions (Farins et al., 201 I ).
MMT elavs have been used as eatalýsts iior numeruus rnýzanic reactions particularly chcºxiclaticul rracticºns, because they offer \ari0us achanta-rs. For
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instance. the epoxidation reactions catalyzed by MMT are usually carried out under mild conditions with high yields, conversion and selectivity (. 1iang et al., 2009:
Khedher ct al., 2009: Farms ct al., 2011 ). Moreover, the workup of the epoxidation reaction with MMT catalyst is very simple, in which requires only filtration to remove the catalyst since the MMT clay does not dissolve in the soly ent as reaction medium.
It must simply be filtered away once the reaction is finish. In consequence. MMT catalysts are easily recovered and reused.
This Nvork is carried out as a result of the advantages of' modified
montmorillonite as an cpoxidation catalyst. its low cost in production as well as its high conversion and selectivity of products in catalytic ruction. Herein. this research focused on the immobilization of early transition metal complexes (molybdenum and
vanadium) on MMT-K 10. The immobilized metal complexes were characterized extensively by various techniques and the catalytic potentials were investigated in the cpoxidation of short chain alkene i. e. cyclohexene under suitable conditions using TBI-IP as oxidant.
ý
1.2 Problem Statement
Catalytic cpoxidation reaction is one of' the most ambiguous processes in chemical industry, and it is also considered as one ofthe most crucial reaction to produce useful
chemical compounds. In epoxldatlon reaction, utilization of peracids as oxidizing agents together with strong mineral acids as catalysts giving various drawbacks: not selective, naive effect of corrosion to the equipment and bring about large residue.
Epoxidation reaction usually uses heavy metal-based as catalysts which are
costly and oencratc hazardous toxic waste that can oive harm to the env ironment.
Whlle, transition metal complexes aregaillillg more attention as alternative catalysts
In organic compound oxidation (Spada, 2015) due to its more environmentally
friendly properties. Early transition metal elements such as molybdenum (Grivani et
al., 2006: Tangestanincjad et. al., 2008: Farias ct al.. 2010. Von. 2012) and vanadium (Farias ct al.. 2011. Vandichel ct at., 2012) have been reported to be the most active
catalyst and have very good catalytic activity. However, these homogeneous catalysts are still haying various drawbacks compared to heterogeneous catalyst that used other materials as a support.
Nowadays, researchers are giving Hulse relevance to another Owl key ! actor
that given huge possibility of' supporting catalyst with teolites (}lu et al.. 2010).
carbon materials (Masteri-Farahani & Abcdnatanzi.
22014). silica and clay materials (Khedhcr ct al.. 2009: Tian et al.. 214: Corner ct al.. 2014) or polymeric membrane (ýý'an ct al.. 2004). The immobilisation of the catalyst on a support is one of' the tcchlliLILICs that can improve the catalytic perfollllance and consequently it Can Make it easy to separate.
O
MMT clays hold the properties of Bronsted and Lewis acidity (Kau- K.
Kishorc, 2012), swellability (Klopro gge ct al.. 2006) and exchangeability (Tian et al., 2014). However, this unmodified MMT possesses only its natural occurrence as well
as ion exchange capacities. With these special properties. MMT-K10. a conlnlercially
available type of MMT is possible to he modified with transition metal elements to get more advantages and being more efficient as a catalyst. Hence, this current work studied on the role of immobilized transition metal complexes on MM I -K1 0 as heteroI'eneous catalyst for epoxidation reaction of cv'clohexene "VOLJId be a worth investigation.
1.3 Research Objectives
The purpose of this study is to lind the most promising immobilized metal complexes on MMT-K 10 that , I\ c the highest yield and the most selective epoxide in cvclohexene epoxidation reaction. Three objectives have been accomplished in order to achieve the purpose oC the study:
I. Fo immobilize different concentration of metal complexes (molybdellum
acetylacetonate or yanadyl acetylacetonate) on NIMT-K 10.
2. To characterise the physical and chemical properties of the modified catalysts using these techniques and instruments; X-ray diffragtogranls (XR[)). Fourier transform infrared spectroscopy (F'IIK). thermocrayimeuic analysis (TGA).
surface area analysis. scanning electron microscopy (SEM) and Atomic Absorption Spectroscopy (AAS).
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3. To measure the conversion and selectivity of the products Irom cyclohexene epoxidation reaction using the immobilized metal complexes on MMT-K10 as catalvsts.
1.4 Scope of the Research
The metal complexes used in this study are molybdenyl acetylacetonate and yanadyl
acetylacetonate. These liquid complexes are chosen because of their good performances and being efficient catalysts among another catalyst (Gnecco et al..
2004). The concentration of the metal complexes for both molybdenum and vanadium
complexes used were 0.05 M, 0.1 M, 0.15 M and 0.2 M. Various concentrations of' complexes were studied to observe the effect of catalyst concentration on the cpoxidation products. Previously, 0.1 M complexes concentration have been used by
Farias (201 1) to test for the epoxidation of both soybean and castor oils, using tert- butyl hydroperoxide (TBill) as oxidizing agent. The immobilized catalyst showed an
enhanced activity and also catalytic stability in recycling experiments. The best results for epoxidation reactions respecting castor oil were obtained under conditions of S0 'C
for 24 hours (I00 °'o conversion and 75 (jo selectivity) and catalytic reuse (Farms et al..
2011).
All Catalysts were tested for epoxidation of' cyclohexcnc at different reaction
tines rangcs from 30 - 300 nllnuies, in order to obtain the optimum catalytic activity thus the best Catalyst later is identified. Cyclohexene was chosen as a good starting,
material or as a substrate due to its simple structure of short-chain alkene and high tendency to lium an epoxide (Carey, 2000).
