Technological Aspects of Chemoenzymatic Epoxidation of Fatty Acids, Fatty Acid Esters and Vegetable Oils: A Review

Magnetic whole-cell biocatalyst based on intracellular lipases of Candida catenulata as promising technology for green synthesis of epoxy fatty acids

This study focuses on the development a green synthesis of epoxy fatty acids (EFAs) which are commonly used as the plasticizer in polymer industries. The intracellular lipases of Candida catenulata cells as a whole-cell biocatalyst (WCB) were examined in the bio-epoxidation of free fatty acids (FFAs) with hydrogen peroxide. The FFAs in soybean soap stock, an industrial by-product of vegetable oil factories, was used as the feedstock of the process. To remove phosphates from soap stock a degumming process was tested before the bio-epoxidation reaction and results revealed that the EFAs yield was improved using the degummed fatty acids (DFAs). The attachments of magnetic Fe3O4 nanoparticles to the surface of WCBs facilitated the recovery of the biocatalyst, and were improved stabilities. The activation energy for the magnetic whole-cell biocatalysts (MWCB) was 48.54 kJ mol-1, which was lower than the WCB system (51.28 kJ mol-1). The EFA yield was about 47.1 % and 33.8 % after 3 h for the MWCBs and 2 h for the WCBs, respectively. The MWCBs displayed acceptable reusability in the repetitious bio-epoxidation reaction with maintaining 59 % of the original activity after 5 cycles whereas the performance of the WCBs was 5.9 % at the same conditions. The effects of influential factors such as reaction time, molar ratio of H2O2 to CC, and batch and semi-batch operations were investigated for both biocatalyst systems. The quality of EFAs was characterized by FTIR and GC-MS analyses.

Fluorescence Lifetime of Chlorophyll α in Oxidized Edible Vegetable Oil

To promote the application of time-resolved fluorescence in oxidation determination of edible vegetable oil, fluorescence lifetime of chlorophyll α in oxidized edible vegetable oils was recorded and analyzed by simulated microenvironment experiments and spectral methods. It was showed that fluorescence lifetime of chlorophyll α decreased with the increase of polarity in the early stage of oxidation, and increased with the increase of viscosity in the later stage of oxidation. Conjugation effect and hydrogen bonding existed in the microenvironment of oxidized edible vegetable oil were considered to be the factors leading to the increase of fluorescence lifetime. The change mechanism of fluorescence lifetime in oxidized edible vegetable oil was supplied, which was considered to be strong support for the application of time-resolved fluorescence.

Enzymatic and Synthetic Routes of Castor Oil Epoxidation

Epoxidation of castor oil in synthetic and enzymatic routes was carried out in order to promote a system with less environmental impact. The epoxidation reactions of castor oil compounds upon addition of lipase enzyme with and without acrylic immobilization and with reaction times of 24 and 6 h, as well as the synthetic compounds upon addition of Amberlite resin and formic acid, were investigated using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance in hydrogen molecules (¹H-NMR). The analysis indicated that the enzymatic reactions (6 h) and synthetic reactions provided a conversion from 50 to 96% and epoxidation from 25 to 48%, resulting from peak stretching and signal disintegration in the hydroxyl region due to the appearance of H₂O in the interaction of peracid with catalyst. In systems without toluene, a dehydration event with a peak absorbance of 0.02 AU, indicating a possible vinyl group at 2355 cm^-1 in enzymatic reactions without acrylic immobilization, was observed and resulted in a selectivity of 2%. In the absence of a solid catalyst, an unsaturation conversion of castor oil above 90% was achieved; however, this catalyst is necessary for the epoxidation to take place, whereas the lipase enzyme becomes able of epoxidizing and dehydrating the castor oil upon changing the time or reaction system. The conversation from 28 to 48% of solid catalysts (Amberlite and lipase enzyme) displays their importance to the instauration conversion of castor oil into oxirane rings.

Synthesis of Bio-Based Thermoset Mixture Composed of Methacrylated Rapeseed Oil and Methacrylated Methyl Lactate: One-Pot Synthesis Using Formed Methacrylic Acid as a Continual Reactant

Methacrylated vegetable oils are promising bio-based polymerizable precursors for potential material application in several fields, such as coating technologies or 3D printing. The reactants' availability for their production is an enormous advantage, but the modified oils also exhibit high apparent viscosity values and poor mechanical properties. This work focuses on a way to produce oil-based polymerizable material precursors in a mixture with a viscosity modifier in a one-batch process. The required methacrylic acid for the modification of epoxidized vegetable oils can be obtained as a secondary product of the methacrylation of methyl lactate forming a polymerizable monomer along with the acid. This reaction results in a yield of over 98% of methacrylic acid. Epoxidized vegetable oil can be added into the same batch using acid for oil modification which results in the one-pot mixture of both methacrylated oil and methyl lactate. The structural verifications of products were provided via FT-IR, ¹H NMR, and volumetric methods. This two-step reaction process produces a thermoset mixture with a lower apparent viscosity of 142.6 mPa·s in comparison with methacrylated oil exhibiting a value of 1790.2 mPa·s. Other physical-chemical properties of the resin mixture such as storage modulus (E' = 1260 MPa), glass transition temperature (T_g = 50.0 °C), or polymerization activation energy (17.3 kJ/mol) are enhanced in comparison with the methacrylated vegetable oil. The synthesized one-pot mixture does not require additional methacrylic acid due to the use of the one formed in the first step of the reaction, while the eventual thermoset mixture exhibits enhanced material properties compared to the methacrylated vegetable oil itself. Precursors synthesized in this work may find their purpose in the field of coating technologies, since these applications require detailed viscosity modifications.

Aquivion perfluorosulfonic superacid as an effective catalyst for selective epoxidation of vegetable oils

The acid-promoted epoxidation of vegetable oils was studied using a variety of acidic ion exchange resins as heterogeneous acid catalysts. Quantitative and selective epoxidation of a series of vegetable oils with different composition of saturated, mono-, di- and tri-unsaturated fatty acids was obtained upon identification of the more efficient catalyst and experimental conditions. Furthermore, optimized reaction conditions were successfully applied to the epoxidation of a waste cooking oil, thus extending our procedure to the valorization of a biowaste, an area of increasing importance within a more sustainable society. The use of quantitative ¹HNMR besides making accurate evaluation of the amounts of reagents to be employed and of the selectivity, allowed facile and rapid quantification of mono-, di- and tri-epoxides, thus providing an indirect indication on the fatty acid composition of the vegetable oils, even in the presence of very low quantities of linolenic acid.

Fatty Acids and their Derivatives as Renewable Platform Molecules for the Chemical Industry

Oils and fats of vegetable and animal origin remain an important renewable feedstock for the chemical industry. Their industrial use has increased during the last 10 years from 31 to 51 million tonnes annually. Remarkable achievements made in the field of oleochemistry in this timeframe are summarized herein, including the reduction of fatty esters to ethers, the selective oxidation and oxidative cleavage of C-C double bonds, the synthesis of alkyl-branched fatty compounds, the isomerizing hydroformylation and alkoxycarbonylation, and olefin metathesis. The use of oleochemicals for the synthesis of a great variety of polymeric materials has increased tremendously, too. In addition to lipases and phospholipases, other enzymes have found their way into biocatalytic oleochemistry. Important achievements have also generated new oil qualities in existing crop plants or by using microorganisms optimized by metabolic engineering.

Oxidative Stability of Vegetal Oil-Based Lubricants

Lipids are widely distributed in nature and are one of the most important components of natural foods, synthetic compounds, and emulsions. To date, there is a strong social demand in the industrial sector for the use of sustainable products with a minimal environmental impact. Depending on their origin and composition, lipids can be employed as a plausible alternative as biodegradable lubricants in order to reduce the use of conventional mineral oil lubricants and mitigate their environmental impact. This perspective provides an overview of the advantages and constrains of vegetal oils under different lubrication regimes and the tribochemical reactions that can take place. Also, the different factors and pathways that influence their oxidation, the key role of moisture, and the changes of physical properties under pressure and temperature are reviewed. Special emphasis is devoted to the oxidation instability of fatty acids and vegetal oils and the physical and chemical approaches to improve oxidative and thermal stability are described in detail.

Sustainable access to fully biobased epoxidized vegetable oil thermoset materials prepared by thermal or UV-cationic processes

Beyond the need to find a non-toxic alternative to DiGlycidyl Ether of Bisphenol-A (DGEBA), the serious subject of non-epichlorohydrin epoxy resins production remains a crucial challenge that must be solved for the next epoxy resin generations. In this context, this study focuses on the valorization of vegetable oils (VOs) into thermoset materials by using (i) epoxidation of the VOs through the “double bonds to epoxy” synthetic route and (ii) synthesis of crosslinked homopolymers by UV or hardener-free thermal curing processes. A thorough identification, selection and physico-chemical characterization of non-edible or non-valuated natural vegetable oils were performed. Selected VOs, characterized by a large range of double bond contents, were then chemically modified into epoxides thanks to an optimized, robust and sustainable method based on the use of acetic acid, hydrogen peroxide and Amberlite® IR-120 at 55 °C in toluene or cyclopentyl methyl ether (CMPE) as a non-hazardous and green alternative solvent. The developed environmentally friendly epoxidation process allows reaching almost complete double bond conversion with an epoxy selectivity above 94% for the 12 studied VOs. Finally, obtained epoxidized vegetable oils (EVOs), characterized by an epoxy index from 2.77 to 6.77 m_eq. g⁻¹ were cured using either UV or hardener-free thermal curing. Both methods enable the synthesis of 100% biobased EVO thermoset materials whose thermomechanical performances were proved to linearly increase with the EVOs' epoxy content. This paper highlights that tunable thermomechanical performances (T_α from −19 to 50 °C and T_g from −34 to 36 °C) of EVO based thermoset materials can be reached by well selecting the starting VO raw materials.

Beyond the need to find a non-toxic alternative to DiGlycidyl Ether of Bisphenol-A (DGEBA), the serious subject of non-epichlorohydrin epoxy resins production remains a crucial challenge that must be solved for the next epoxy resin generations.

Conversion of Oleic Acid into Azelaic and Pelargonic Acid by a Chemo-Enzymatic Route

A chemo-enzymatic approach for the conversion of oleic acid into azelaic and pelargonic acid is herein described. It represents a sustainable alternative to ozonolysis, currently employed at the industrial scale to perform the reaction. Azelaic acid is produced in high chemical purity in 44% isolation yield after three steps, avoiding column chromatography purifications. In the first step, the lipase-mediated generation of peroleic acid in the presence of 35% H₂O₂ is employed for the self-epoxidation of the unsaturated acid to the corresponding oxirane derivative. This intermediate is submitted to in situ acid-catalyzed opening, to afford 9,10-dihydroxystearic acid, which readily crystallizes from the reaction medium. The chemical oxidation of the diol derivative, using atmospheric oxygen as a stoichiometric oxidant with catalytic quantities of Fe(NO₃)₃∙9∙H₂O, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), and NaCl, affords 9,10-dioxostearic acid which is cleaved by the action of 35% H₂O₂ in mild conditions, without requiring any catalyst, to give pelargonic and azelaic acid.

Catalytic developments in the epoxidation of vegetable oils and the analysis methods of epoxidized products

Functionalization of vegetable oils (VOs) including edible, non-edible, and waste cooking oil (WCOs) to epoxides (EVOs) is receiving great attention by many researchers from academia and industry because they are renewable, versatile, sustainable, non-toxic, and eco-friendly, and they can partially or totally replace harmful phthalate plasticizers. The epoxidation of VOs on an industrial scale has already been developed by the homogeneous catalytic system using peracids. Due to the drawbacks of this method, other systems including acidic ion exchange resins, polyoxometalates, and enzymes are becoming alternative catalysts for the epoxidation reaction. We have reviewed all these catalytic systems including their benefits and drawbacks, reaction mechanisms, intensification of each system in different ways as well as the physicochemical properties of VOs and EVOs and new findings in recent years. Finally, the current methods including titrimetric methods as well as ATR-FTIR and 1H NMR for determination of conversion, epoxidation, and selectivity of epoxidized vegetable oils (EVOs) are also briefly described.

Tailoring chemoenzymatic oxidation via in situ peracids

Epoxidation chemistry often suffers from the challenging handling of peracids and thus requires in situ preparation. Here, we describe a two-phase enzymatic system that allows the effective generation of peracids and directly translate their activity to the epoxidation of olefins. We demonstrate the approach by application to lipid and olefin epoxidation as well as sulfide oxidation. These methods offer useful applications to synthetic modifications and scalable green processes.

Epoxidación enzimática de metil ésteres de ácidos grasos de origen vegetal y sus aplicaciones como alternativa para sustituir a los derivados del petróleo

Recientemente, la modificación de aceites vegetales para obtener ésteres metílicos de ácidos grasos (FAMEs) o biodiesel ha emergido como una alternativa para la sustitución de los derivados del petróleo, esto debido a los problemas ambientales y de salud que genera su uso. Debido a su estructura química es posible epoxidar estas moléculas y usarlas directamente para producir plastificantes o lubricantes. Sin embargo, éstas también pueden ser sujetas a modificaciones para mejorar sus propiedades y el de servir como intermediarias para la síntesis de poliuretanos. Puesto que los métodos convencionales para la producción de epóxidos también son una fuente potencial de contaminación, se ha sugerido el uso de catalizadores enzimáticos como una alternativa sostenible o “Verde” para su preparación, ya que permiten obtener productos con alta pureza y mejores rendimientos. Este artículo presenta una revisión de la literatura disponible centrándose en la epoxidación enzimática de los FAMEs, así como sus principales aplicaciones.

Effect of an Anhydride Excess on the Curing Kinetics and Dynamic Mechanical Properties of Synthetic and Biogenic Epoxy Resins

This work analyzes the effect of the anhydride excess on the nonisothermal curing kinetics and on the final properties of synthetic and biobased epoxy resins. Diglycidyl ether of bisphenol A (DGEBA) and epoxidized soybean oil (ESO) were crosslinked using methyltetrahydrophthalic anhydride (MTHPA) as a curing agent and 1-methylimidazole (1MI) as an initiator. It was shown that the ESO/MTHPA/1MI system reacts slower than the DGEBA/MTHPA/1MI system, giving place to a more significant evaporation of the curing agent during the reaction. As a result, an excess of anhydride improves the final thermal properties of the ESO/MTHPA/1MI network, contrary to the behavior observed for DGEBA/MTHPA/1MI. The knowledge of the kinetics of the curing process and the optimal amount of the curing agent for each system is of critical importance for a more efficient processing of these materials.

Optimization of the Loading of an Environmentally Friendly Compatibilizer Derived from Linseed Oil in Poly(Lactic Acid)/Diatomaceous Earth Composites

Maleinized linseed oil (MLO) has been successfully used as biobased compatibilizer in polyester blends. Its efficiency as compatibilizer in polymer composites with organic and inorganic fillers, compared to other traditional fillers, has also been proved. The goal of this work is to optimize the amount of MLO on poly(lactic acid)/diatomaceous earth (PLA/DE) composites to open new potential to these materials in the active packaging industry without compromising the environmental efficiency of these composites. The amount of DE remains constant at 10 wt% and MLO varies from 1 to 15 phr (weight parts of MLO per 100 g of PLA/DE composite). The effect of MLO on mechanical, thermal, thermomechanical and morphological properties is described in this work. The obtained results show a clear embrittlement of the uncompatibilized PLA/DE composites, which is progressively reduced by the addition of MLO. MLO shows good miscibility at low concentrations (lower than 5 phr) while above 5 phr, a clear phase separation phenomenon can be detected, with the formation of rounded microvoids and shapes which have a positive effect on impact strength.

Room-temperature production of bio-based aldehydes from vegetable oil-derived epoxide via H2WO4@Al-MCM-41 as recyclable catalyst

The oxidative cleavage of vegetable oils and their derivatives to produce bio-based aldehydes is a potentially useful process, although the aldehyde products are readily oxidized to carboxylic acids and thus seldom obtained in high yields. The present study developed a room-temperature method for the synthesis of bio-aldehydes via the oxidative cleavage of vegetable oil-derived epoxides, using H₂WO₄ as the catalyst, H₂O₂ as the oxidant, and t-BuOH as the solvent. Reactions were carried out at temperatures ranging from 25 to 35 °C for 3.5–10.5 h, and provided >99% conversion and >90% aldehyde yield. In particular, an approximately 97% yield was obtained at 25 °C after 10.5 h. As the reaction proceeded, the H₂WO₄ dissolved to form a W-containing anion. Several mesoporous Al-MCM-41 materials having different Si/Al ratios were hydrothermally synthesized and used as adsorbents to recover the catalyst by adsorbing these anions. The adsorption capacity of the Al-MCM-41 was found to increase with decreases in the Si/Al ratio. The Al-MCM-41 had little effect on the oxidative cleavage reaction at 25 °C, and thus could be directly added to the reaction system. The excellent anion adsorption performance of the Al-MCM-41 greatly improved the reusability of the H₂WO₄ catalyst. When using the Al-MCM-41 with the best adsorption performance, there was no significant decrease in the activity of the catalyst following five reuses.

>90% bio-aldehydes yield was obtained from H₂WO₄-catalyzed epoxy vegetable oil at room-temperature; Al-MCM-41 was added to recover catalyst via adsorption.

Technological Parameters of Epoxidation of Sesame Oil with Performic Acid

The course of epoxidation of sesame oil (SO) with performic acid formed „in situ” by the reaction of 30 wt% hydrogen peroxide and formic acid in the presence of sulfuric acid(VI) as a catalyst was studied. The most advantageous of the technological independent parameters of epoxidation are as follows: temperature 80°C, H2O2/ C=C 3.5:1, HCOOH/C=C 0.8:1, amount of catalyst as H2SO4/(H2O2+HCOOH) 1 wt%, stirring speed at least 700 rpm, reaction time 6 h. The iodine number (IN), epoxy number (EN), a relative conversion to oxirane (RCO) and oxirane oxygen content (EOe) were determined every hour during the reaction. Under optimal conditions the sesame oil conversion amounted to 90.7%, the selectivity of transformation to epoxidized sesame oil was equal to 93.2%, EN = 0.34 mol/100 g, IN = 0.04 mol/100 g oil (10.2 g/100 g oil), a relative conversion to oxirane RCO = 84.6%, and oxirane oxygen content of EOe = 5.5%.

Biocatalytic Oxidation Reactions: A Chemist's Perspective

Oxidation chemistry using enzymes is approaching maturity and practical applicability in organic synthesis. Oxidoreductases (enzymes catalysing redox reactions) enable chemists to perform highly selective and efficient transformations ranging from simple alcohol oxidations to stereoselective halogenations of non-activated C-H bonds. For many of these reactions, no "classical" chemical counterpart is known. Hence oxidoreductases open up shorter synthesis routes based on a more direct access to the target products. The generally very mild reaction conditions may also reduce the environmental impact of biocatalytic reactions compared to classical counterparts. In this Review, we critically summarise the most important recent developments in the field of biocatalytic oxidation chemistry and identify the most pressing bottlenecks as well as promising solutions.

Chemoenzymatic epoxidation of alkenes with Candida antarctica lipase B and hydrogen peroxide in deep eutectic solvents

Epoxides are important synthetic intermediates for the synthesis of a broad range of industrial products.

Recent advances in the field of selective epoxidation of vegetable oils and their derivatives: a review and perspective

The present critical review reports the recent progress of the last 15 years in the selective epoxidation of vegetable oils and their derivatives, in particular unsaturated fatty acids (UFAs) and fatty acid methyl esters (FAMEs).

Technological aspects of vegetable oils epoxidation in the presence of ion exchange resins: a review

A review paper of the technology basics of vegetable oils epoxidation by means of peracetic or performic acid in the presence of acidic ion exchange resins has been presented. The influence of the following parameters: temperature, molar ratio of acetic acid and hydrogen peroxide to ethylenic unsaturation, catalyst loading, stirring intensity and the reaction time on a conversion of ethylenic unsaturation, the relative percentage conversion to oxirane and the iodine number was discussed. Optimal technological parameters, mechanism of epoxidation by carboxylic peracids and the possibilities of catalyst recycling have been also discussed. This review paper shows the application of epoxidized oils.