The highly strained ring in epoxides makes these compounds very versatile intermediates. Epoxidized vegetable oils are gaining a lot of attention as renewable and environmentally friendly feedstock with various industrial applications such as plasticizers, lubricant base oils, surfactants, etc. Numerous papers have been published on the development of the epoxidation methods and the number is still growing. This review reports the synthetic approaches and applications of epoxidized vegetable oils.
The chemicals derived from oils and fats of vegetable and animal origin, or so-called oleochemicals, represent one of the cheapest and highly available sources of potential feedstock for replacing petroleum-derived products. This renewable raw material has also become an important feedstock for the chemical industry (Biermann
Basic oleochemical transformations to obtain fatty alcohol from oil.
The global production of vegetable oils includes soybean, canola, palm, linseed, rapeseed, corn, cottonseed, peanut, sesame, and sunflower oil. Between 2002 and 2013, the total worldwide production of oils and fats increased by 57%. In 2013, a total of 75.7 million tonnes of oils and fats were traded in the global market in which palm oil contributed to 58.1% of the total global edible oil exports followed by soybean oil (12.7%), sunflower oil (8.7%) and rapeseed oil (5.4%) (Choo,
Basic oleochemicals are divided into four groups: fatty acids, the respective methyl esters, amines and alcohols. Glycerol is later added to the list (Richtler and Knaut,
Most of the classical, well-established chemical transformations of fatty acids and their derivatives involve reactions at the terminal carboxyl group, for instance esterification, amidation and amination to generate esters, amides and amines, respectively, as building blocks in the production of high value added products. Surfactant is one of the main oleochemical products that can be derived from the hydrogenation of fatty acid methyl ester derivatives to give fatty alcohols, an example of chemical modification on the carboxyl group (
Fatty acid composition in palm oil (“About Palm Oil,”
Numerous synthetic methods to access epoxide have been explored, such as epoxidation with aldehydes and molecular oxygen, dioxiranes, H2O2/tungsten heteropolyacids, and H2O2/methyl trioxorhenium as well as the Halcon process. However, none of these methods can be scaled up for industrial applications.
The oxygen transfer to the double bond can be achieved
Reaction temperature, molar ratio (concentration of oxygen donor, oxygen carrier and ethylenic unsaturation), catalysts type (homogeneous or heterogeneous) and catalyst loading are some of the variables taken into account in the studies of epoxidation of the unsaturated fatty acids (Ni and Salimon,
Hypochlorination of the olefinic acid followed by dehydrohalogention, is one of the earliest preparations of the epoxy acids
Hypochlorination of olefin (Swern,
In industrial processes, the Prilezhaev reaction,
Mechanism for epoxide formation mediated by peracids.
When epoxidation is carried out using hydrogen peroxide and the unsaturated fatty acid without the presence of organic peracid, no reaction is observed, as the peracid is essential for transfering the active oxygen from the aqueous to the oil phase (Nowak
Products of side reactions from epoxide
Conversion as high as 98% was reported for the methyl ester of palm fatty acid distillate (PFAD-ME) producing a respective epoxide compound using a molar ratio of 1:1:4 (PFAD-ME:formic acid:H2O2) at 50 oC (Lee
Thus, over the last ten years, many studies have been reported on homogeneous and heterogeneous catalytic epoxidation, from the enzyme-to metal-catalyzed reaction of vegetable oils with different oxidants considering the advantages offered by the modified fatty acids derived from vegetable oils.
Acidic ionic exchange resin was then introduced as a heterogeneous catalyst replacing the inorganic acid catalyst with improved yield and/or selectivity. Mungroo
In 2011, Cai and co-worker (Cai
Molecular oxygen (O2) can act as oxygen donor
The metal complex catalyst can be recycled up to ten times as reported in the Ru-catalyzed epoxidation of methyl oleate in a perfluorinated solvent (Klement
The industrial production of propylene oxide mediated by TBHP and ethylbenzene hydroperoxide was first developed by The Halcon Corp. and Atlantic Richfield Oil Corp. (later ARCO) in 1970s using isobutane and ethylbenzene, respectively. Interestingly, this method produced
Halcon process mediated by ethylbenzene hydroperoxide.
Titanium-derived catalysts are used both as homogeneous and heterogeneous catalysts. The latter are found to be more efficient for the epoxidation reaction. The use of a titanium tartrate complex as a homogeneous catalyst in the Sharpless-Katsuki epoxidation is one of the well-known examples of asymmetric epoxidation (Li and Wang,
Guidotti
However, simple amorphous Ti-SiO2 is shown to be a good alternative to titanosilicates (especially for much more expensive Ti-MCM-41 material) as a comparable yield of up to 60% epoxidised methyl oleate can be obtained with good selectivities (>90%). Rios
The use of organic hydroperoxides is not limited to metal catalysts. In 2001, Piazza
The biocatalyzed reaction is more environmental friendly and it is more selective. This method is considerably favored as it suppresses undesirable ring opening of the epoxide (Biermann
The earliest report of enzymatic epoxidation was made in the early 1930s using
The first chemo-enzymatic epoxidation was carried out in 1990 (Björkling
Orellana-Coca
The use of oat seed (
The effect of different epoxidation methods has been investigated by Saithai
A recent publication of enzymatic-mediated epoxidation was reported by Grausem
In general, low stability of the enzyme under certain reaction conditions limits the potential of this method compared to chemical treatment due to the sensitivity of the enzyme to the concentration of hydrogen peroxide. The enzyme has been reported to be stable at a temperature of up to 50 oC. Nevertheless, this reaction condition is not favorable due to the decomposition of H2O2 and possible reduced catalytic activity of the enzyme.
Metalloporphyrins are a combination of a porphyrin and a metal such as heme. These compounds have been shown to selectively catalyze various reactions, i.e. oxygenation, oxidation, oxidative chlorination and dismutation.
A recent work concerning the catalytic epoxidation of fatty acid methyl esters (FAMEs) was reported by Zhang
Structures of metallophyrin developed by Zhang for catalytic epoxidation (Zhang
Dioxiranes have been shown to be one of the most versatile reagents for epoxidation as they transfer an oxygen atom efficiently to a variety of organic substrates (Curci
Catalytic cycle of DMDO as oxidant (Frohn
Dimethyldioxirane (DMDO) is the simplest form of dioxirane. This reagent is not commercially available due to instability during transport and storage but it can be prepared by reacting acetone and the triple salt Oxone® (2KHSO5·KHSO4·K2SO4) in the laboratory, both on small and large scales (Adam
Adam
There have been previous studies on the epoxidation of vegetable oil mediated by ethylmethyldioxirane (EMDO), an analogue of the dioxiranes. In 2007, Akintayo reported complete conversion of the double bond in the epoxidation of
Generally, further application of the oils as oleochemicals are determined by the fatty acid composition (Hill,
C14 – C24 fatty acid composition of some major vegetable oils (Saurabh
Vegetable Oil | Fatty acid composition, wt% |
|||||||||
---|---|---|---|---|---|---|---|---|---|---|
14:0 | 16:0 | 18:0 | 20:0 | 22:0 | 24:0 | 18:1 | 22:1 | 18:2 | 18:3 | |
Corn | - | 12 | 2 | Tr | - | - | 25 | - | 6 | Tr |
Cottonseed | - | 28 | 1 | - | - | - | 13 | - | 58 | 0 |
Linseed | - | 5 | 2 | - | - | - | 20 | - | 18 | 55 |
Palm (Rupilius and Ahmad, |
2 | 42 | 5 | - | - | - | 41 | - | 10 | - |
Peanut | - | 11 | 2 | 1 | 2 | 1 | 48 | - | 32 | 1 |
Rapseed | - | 3 | 1 | - | - | - | 64 | - | 22 | 8 |
Sesame | - | 13 | 4 | - | - | - | 53 | - | 30 | - |
Soybean | - | 12 | 3 | - | - | - | 23 | - | 55 | 6 |
Sunflower | - | 6 | 3 | - | - | - | 17 | - | 74 | - |
Tr = traces.
A wide range of chemicals can be derived from epoxidized fatty acids, for example, polyols, glycol, carbonyl compounds, lubricants, plasticizers for polymer, etc. (Saurabh
One of the primary markets for epoxidized vegetable oils (mainly soybean) is as plasticizers and hydrogen chloride acceptors for use in plastic materials, especially polyvinyl chloride (PVC). As PVC exposed to heat and/or light, the HCl evolved which may cause the development of undesirable color and rapid deterioration of the polymer (Greenspan and Gall,
A recent study by Kandula
Corrosion is a common problem faced in our daily lives. The idea of using renewable resources in coating technology is crucial as an effort to reduce our reliance on non-renewable petroleum-based products (Alam
Dihydroxystearic acid which is derived from the hydroxylation of epoxidized palm fatty acid has shown to exhibit rust inhibition properties evaluated using stainless steel rod in bis (2-ethylhexyl) sebacate and tris (2-ethylhexyl) phosphate (Rahman and Sadi,
Lubricant is a substance employed to reduce wear or tear of one or both surfaces in mutual contact and moving in relation to each other. In general, vegetable oils possess most of the necessary lubricity properties such as good contact lubrication, high viscosity index (lowest changes in viscosity with temperature), high flash point and low volatility. Above all, the presence of a high degree of unsaturation in vegetable oils led to low thermal and oxidative stability, which can be improved by epoxidation (Akintayo,
The evaluation of palm kernel oil’s (PKO) properties as lubricant has been reported previously. The properties of PKO were compared with heavy duty oil (SAE 40) and light duty oil (SAE 30) and it was shown that PKO is a promising base oil for the production of value-added lubricating products with comparable properties that meet SAE specifications (Musa,
The study of the production of polyols with branched ether and ester compounds, with epoxidized vegetable oils as the intermediates has been carried out for the improvement of their properties. The epoxides will then be subjected to ring-opening reaction under acidic conditions to produce alcohols which will then be subjected to esterification reactions (Adhvaryu
Moser
The reaction of the epoxygenated fatty acids with low-molecular-weight mono- or polyfunctional alcohols or acids
Preparation of low viscosity and light-colored fatty acid-based polyols can be carried out in a three-step reaction, depending on several parameters at each step such as temperature, pressure, amount of catalyst used, molar ratio of reactant, and reaction time. Catalyst loading was reported as crucial factor to be controlled to produce light-colored polyol in the first step (Hoong
A patent was filed for the conversion of used frying oils into polyol
Self-levelling polyurethane or epoxy/polyurethane multilayer systems are widely used in the flooring industry because of good chemical and mechanical properties such as minimal shrinkage, high mechanical strength and durability, and the reasonable cost of installation offered by these materials. Apart from that, they can also be used to bind porous filler materials and rubber particles to produce composites for sport tracks and playing fields (Höfer,
The epoxygenated palm olein acrylate derived from the respective epoxide was studied for use in the synthesis of radiation curable resins (Mohd Nor
Most of commercial ionic and non-ionic surfactants are derived from C12 and C14 fatty acids which are abundant in PKO. Fatty acids with longer carbon chains are barely used due to their hydrophobic property and less suitable for micelle formation. As for palm oil that contains longer chain fatty acids, the modification of the fatty acids has been carried out to increase the polarity of the fatty acids. Epoxide can serve as an intermediate to attach the polar groups to internal positions of the fatty acids (Dierker and Schäfer,
Ring opening of epoxidized methyl oleate (Dierker and Schäfer,
The surfactants with tensidic properties synthesized by the modification of long chain fatty acids were shown to be comparable or with better properties than those of commercial surfactants of C12 and C14 fatty acids (Dierker and Schäfer,
Ring-opening of epoxidized methyl oleate occurred when reacted with bifunctional levulinic acid to form cyclic ketals, by controlling the temperature and acid concentration, led to potential new surfactants derived from oleochemicals (Doll and Erhan,
In a pharmacological study, the epoxidation of arachidonic acid catalyzed by cytochrome P450 (CYP) epoxygenase generated the corresponding epoxygenated fatty acid, the epoxyeicosatrienoic acid – an important mediator involved in regulating various biological processes including inflammation, pain and angiogenesis (Zhang
Due to the vast applications, and environmentally friendly properties of the epoxidized vegetable oils, the development of synthetic methods is highly anticipated in addition to the increasing awareness for caring for the environment. Several conditions must be taken into account in the continuous research on epoxide synthesis: i) presence of acid (as co-reagent or generated during the reaction) lower epoxide yield and; ii) cost of by-product removal (Piazza,
Mild conditions in the epoxidation of fatty acids mediated by dioxiranes have made this method one of the most attractive approaches to be developed especially for larger scale reactions. To our knowledge, the effect of the stereochemistry of epoxidized vegetable oils on their properties has never been studied previously.
The studies for developing synthetic methods for the epoxidation of unsaturated fatty acids are important to afford high oxirane content and selectivity. As for industrial scale, the reaction conditions are significant in order to minimize operation costs, and avoid side reactions. The
Various applications of epoxidized vegetable oils have made this product a valuable intermediate or end-product due to the versatility of the three-membered ring epoxy in chemical reactions, and the green properties of the materials such as no toxicity and biodegradability.
The authors would like to thank the Malaysian Palm Oil Board (MPOB) for their support in producing this review paper. Our gratitude is also extended to Puan Rosnah Ismail and Prof. Kamaruzaman Jusoff, Senior Research Fellows of MPOB.