Synthesis of Long Chain Unsaturated-α,ω-Dicarboxylic Acids from Renewable Materials via Olefin Metathesis

The self-metathesis reaction of soy, rapeseed, tall, and linseed oil fatty acids was investigated for the synthesis of symmetrical long-chain unsaturated-α,ω-dicarboxylic acids. The metathesis reactions were carried out in the presence of a Grubbs catalyst under solvent-free condition at a catalyst loading of 0.01 mol% to fatty acid substrate at 50 °C. Under these conditions, the conversions of starting unsaturated acids to metathesis products were >80% and the isolated yields of unsaturated dicarboxylic acid products were >70% of theoretical. This approach represents an effective and efficient route for the synthesis of these potentially useful dicarboxylic acids since they can serve as important intermediates in the production of several materials such as biodegradable polymers. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the US Department of Agriculture.     

Cross‐metathesis of methyl 10‐undecenoate with diethyl maleate: Formation of an α,ω‐diester via a metathesis reaction network

The cross‐metathesis of methyl 10‐undecenoate 1 derived from castor oil as a renewable raw material with diethyl maleate 2 was investigated. These reactions were carried out with several phosphine and N‐heterocyclic carbene ruthenium catalysts. The reaction conditions were optimised for high conversions in combination with high cross‐metathesis selectivity. This single‐step and atom‐economic synthetic method illustrates an efficient and selective preparation procedure of linear α,ω‐dicarboxylic acid esters starting from renewable resources and comparatively inexpensive base chemicals. Further by‐products are hardly obtained due to their consumption in secondary metathesis reactions. Hence, a sustainable alternative for polyamide and polyester monomers is presented.     

Renewable Aliphatic Polyesters from Fatty Dienes by Acyclic Diene Metathesis Polycondensation

Three renewable, linear, aliphatic polyesters were prepared by Acyclic diene metathesis (ADMET) polymerization of α,ω-dienes derived from fatty acids. Condensation of 9-decenoic acid with allyl 9-decenoate, ethylene glycol, and 9-decen-1-ol proceeded in high conversion (≥94%) and purity (>99%) to give α,ω-dienes suitable for subsequent polycondensation. Polymerization was achieved using 1.0 mol% Hoveyda-Grubbs second-generation metathesis catalyst in combination with 2.0 mol% 2,6-dichloro-1,4-benzoquinone as an isomerization inhibitor under vacuum to drive equilibria toward polymer formation via ethene removal. Polymerization in the presence of solvent promoted ring-closing metathesis (RCM) at the expense of polymer, with cyclization increasing as the concentration of monomer decreased. Thus, ADMET polymerizations were performed in bulk to mitigate RCM. The resulting polymers with M _n and Ð that ranged from 6.6 to 8.9 kDa and 1.75–2.14, respectively, contained 76% or more of renewable carbon content and exhibited atom and carbon economies of greater than 84%. Melt (T _m) and crystallization (T _c) temperatures were 20.8–48.4 °C and 3.8–37.6 °C, respectively, and increased as ester density decreased within polymer structures. Sub-ambient glass transitions ranged from −10.3 to −50.0 °C. Lastly, the polymers were thermally stable below 320 °C, as 10% mass loss (T₁₀) occurred above 340 °C, which indicated that they existed as liquids for at least 319 °C (T₁₀ − T _m) before decomposing.     

Ring-Opening Metathesis Polymerization and Related Olefin Metathesis Reactions in Benzotrifluoride as an Environmentally Advantageous Medium

A tremendous number of solvents, either as liquids or vapors, contaminate the environment on a daily basis worldwide. Olefin metathesis, which has been widely used as high-yielding protocols for ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), and isomerization reactions, is typically performed in toxic and volatile solvents such as dichloromethane. In this study, the results of our systematic experiments with the Grubbs G1, G2, and Hoveyda-Grubbs HG2 catalysts proved that benzotrifluoride (BTF) can replace dichloromethane (DCM) in these reactions, providing high yields and similar or even higher reaction rates in certain cases. The ROMP of norbornene resulted not only in high yields but also in polynorbornenes with a high molecular weight at low catalyst loadings. Ring-closing metathesis (RCM) experiments proved that, with the exception of the G1 catalyst, RCM occurs with similar high efficiencies in BTF as in DCM. It was found that isomerization of (Z)-but-2-ene-1,4-diyl diacetate with the G2 and HG2 catalysts proceeds at significantly higher initial rates in BTF than in DCM, leading to rapid isomerization with high yields in a short time. Overall, BTF is a suitable solvent for olefin metathesis, such as polymer syntheses by ROMP and the ring-closing and isomerization reactions.     

Unexpected Results of a Turnover Number (TON) Study Utilising Ruthenium‐Based Olefin Metathesis Catalysts

A turnover number (TON) study of ruthenium‐based metathesis catalysts has been conducted for ring‐closing metathesis (RCM) in dilute solution. Unexpectedly the results indicate that 1^st generation metathesis catalysts can give higher TON in RCM of simple unsubstituted terminal olefins than their second generation counterparts. In particular, the 1^st generation Hoveyda–Grubbs catalyst showed unexpectedly high activity, particularly when compared to the 2^nd generation catalysts.     

Hybrid‐Bridged Silsesquioxane as Recyclable Metathesis Catalyst Derived from a Bis‐Silylated Hoveyda‐Type Ligand

The synthesis of a bis‐silylated Hoveyda‐type monomer is described as well as the preparation of several organic‐inorganic hybrid materials derived from it by a sol‐gel process (with and without tetraethyl orthosilicate) and by anchoring to MCM‐41. The resulting materials were treated with second generation Grubbs' catalyst to generate second generation Hoveyda–Grubbs‐type alkylideneruthenium complexes covalently bonded to the silica matrix. These materials are recyclable catalysts for the ring‐closing metathesis reaction of dienes and enynes.     

Comparison of Reactivity in the Cross Metathesis of Allyl Acetate‐Derivatives with Oleochemical Compounds

The metathesis of unsaturated oleochemicals is an excellent tool for generating α,ω‐difunctional substrates, which are useful intermediates for polymer synthesis. This article describes the cross metathesis of allyl acetate and cis‐1,4‐diacetoxy‐2‐butene with methyl 10‐undecenoate and methyl oleate, which are oleochemical key substrates. Detailed optimizations led to high conversion rates and yields of the desired products under mild reaction conditions by using a low concentration of commercially available homogeneous ruthenium catalysts.     

Hybrid Organic‐Inorganic Materials Derived from a Monosilylated Hoveyda‐type Ligand as Recyclable Diene and Enyne Metathesis Catalysts

The synthesis of a monosilylated Hoveyda‐type monomer is described as well as the preparation of several organic‐inorganic hybrid materials derived from it by sol‐gel processes and by anchoring to commercial silica gel and MCM‐41. The resulting materials were treated with first and/or second generation Grubbs’ catalyst to generate Hoveyda–Grubbs’ type alkylidene ruthenium complexes covalently bonded to the silica matrix. These materials are efficient recyclable catalysts for the ring‐closing metathesis reaction of dienes and enynes, even for the formation of tri‐ and tetrasubstituted olefins.     

Lipoxygenase as a versatile biocatalyst

This review of lipoxygenase and lipoxygenase pathway enzymes focuses on the potential for the efficient production of useful compounds. Although the existence of lipoxygenase has been inown for many years, only recently has there been progress toward understanding the conditions required to improve yields and immobilize its activity. Maintaining a high O₂ tension is necessary to obtain good yeilds of hydroperoxides; whereas, partial anaerobic conditions can lead to hydroperoxide decomposition. Fatty hydroperoxides, obtained from lipoxygenase action, can serve as precursors for further transformation by either enzymes or chemical reactions. Well over one-hundred products from lipoxygenase-generated hydroperoxides of linoleic acid alone have been described. Examples will be given of the formation of fatty acids with epoxide, hydroxy, ketone, cyclic, and multiple functional groups. The cleavage of fatty hydroperoxides into short-chain aldehydes and alcohols also will be described. Many of the products have biological activity, suggesting a significant physiological function for lipoxygenase.     

Ruthenium‐Indenylidene Complexes: Scope in Cross‐Metathesis Transformations

A comparative study examining the catalytic activity of a series of five indenylidene‐containing ruthenium complexes in olefin cross‐metathesis reactions is presented. Results reveal the greater efficiency of precatalyst 5 , highlighting the key role of the N,N′‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr) ligand for this transformation. The scope of this precatalyst was investigated and several microwave experiments were carried out allowing for catalyst loadings as low as 0.1 mol%. Overall, cross‐metathesis products were isolated in moderate to excellent yields with high stereoselectivity.     

Ring-Opening Olefin Metathesis Polymerisation (ROMP) as a Potential Cross-Linking Mechanism for Siloxane Polymers

Reported here are some results of rapid Ring Opening Metathesis Polymerization (ROMP) of norbornene-functional oligomeric siloxanes using a Ru-based catalytic system. The in situ formation of the active metal carbene catalyst by addition of a diazo compound to norbornene-functional siloxane containing the catalytic system, [(p-cymene)RuCl₂]₂/PCy₃ allowed fast but controlled polymerization of the norbornene functionalities. Thus, in a solventless system, polymerization of a norbornene-functional siloxane, e.g., 1,1,1,2,3,3,3-heptamethyl-2-norbornen-5-yltrisiloxane, at 60°C with low catalyst levels (2 to 200 ppm) led to a colourless monolithic gel in less than 30 seconds. Besides being an efficient cross-linking technology, ROMP of suitable precursors may also be a source of novel silicone-organic materials.     

Unique adhesive properties of pressure sensitive adhesives from plant oils

We report novel insights into the adhesive performance of bio-based pressure sensitive adhesives (PSAs). Three different homopolymers based on renewable fatty acid methyl esters were characterized in terms of their mechanical and adhesive properties. The polymers display the typical dependence of adhesive properties on molecular weight and degree of crosslinking, as quantified by shear modulus, tack and peel measurements. The absolute values of characteristic adhesion parameters are in the range of commercially available petrochemical PSAs. Curing of applied PSA films at elevated temperature results in a pronounced maximum in tack and peel strength at a critical curing time, which corresponds to a change from cohesive to adhesive failure. Thus, demand-oriented tailoring of adhesive properties can be achieved via an appropriate choice of curing time. Moreover, these bio-based adhesives offer improved adhesion on hydrophobic substrates and high water-resistance without any whitening, thus rendering them an attractive alternative to conventional petroleum-based products. These peculiar features are attributed to the high hydrophobicity of the used monomers.     

Bio‐Based Rubbers by Concurrent Cationic and Ring‐Opening Metathesis Polymerization of a Modified Linseed Oil

Bio‐based rubbers prepared by tandem cationic polymerization and ROMP using a norbornenyl‐modified linseed oil, Dilulin?, and a norbornene diester, NBDC, have been prepared and characterized. Increasing the concentration of the NBDC in the mixture results in a decrease in the glass transition temperature. The new bio‐based rubbers exhibit tensile test behavior ranging from relatively brittle (18% elongation) to moderately flexible (52% elongation) and with decreasing values of tensile stress with increasing NBDC content. Thermogravimetric analysis reveals that the bio‐based rubbers have maximum decomposition temperatures of over 450 °C with their thermal stability decreasing with increasing loadings of NBDC.

     

Renewable resources in coatings technology: a review

In recent years an increasing interest is observed in the development of more environment friendly paints and coatings. This paper discusses advances in the use of renewable resources in formulations for various types of coatings. In particular, current research on the application of plant proteins and vegetable oils in coatings systems is addressed. In ongoing plant protein research at ATO-DLO corn, but particularly wheat gluten, was modified chemically to obtain aqueous protein dispersions that have excellent film-forming characteristics and strong adhesion to various surfaces. In particular, wheat gluten films have very interesting mechanical properties, such as an extensibility over 600%. Gas and moisture permeabilities were found to be easily adjustable by changing the exact formulation of the protein dispersion. Durability and water resistance of the coatings can be tailored by, for example, varying the degree of crosslinking of the protein binder. Based on the observed characteristics of the modified protein binders the development of novel, organic solvent-free paints and coatings appears to be well within reach. Regarding vegetable oil-based binders, research at ATO-DLO and elsewhere includes the application of oils from conventional as well as new oilseed crops. A very interesting new vegetable oil originates from such crops as Euphorbia lagascae and Vernonia galamensis, which have high contents ( > 60%) of an epoxy fatty acid (9c,12,13 epoxy-octadecenoic acid or vernolic acid) that can be used as a reactive diluent. Another interesting new oil is derived from Calendula officinalis, or ‘marigold’. This oil contains>63% of a C18 conjugated triene fatty acid (8t, l0t,12c-octadecatrienoic acid or calendic acid) like that in lung oil. Current research is focused on the film-forming abilities of these oils and of chemical derivatives of these oils, in particular in emulsion systems.     

Olefin Metathesis on a TLC Plate as a Tool for a High‐Throughput Screening of Catalyst‐Substrate Sets

A methodology for screening either various catalysts for a given metathesis reaction, i.e., ring opening‐ring closing alkene metathesis (RO‐RCM) and cross‐metathesis (CM), or various substrates for a given pre‐catalyst on a thin layer chromatography (TLC) plate has been developed. As the substrates elute with the solvent, this TLC‐based system acts as a heterogeneous catalyst bed (“TLC reactor”). Selected promising catalyst candidates were screened on a TLC plate and their initial catalytic potential as observed in the TLC test was later fully confirmed in a classical heterogeneous reaction set‐up using standard commercially available silica (D11‐10). Reacting polyfunctional, natural product‐like substrates in our TLC reactor allows the simultaneous screening of various substrates and the convenient micro‐scale preparation and isolation of potentially biologically active products.     

Rubbery Thermosets by Ring‐Opening Metathesis Polymerization of a Functionalized Castor Oil and Cyclooctene

Rubbery thermosets prepared by ROMP of a modified castor oil containing norbornene moieties and cyclooctene have been synthesized and characterized. The thermosets range from 55 to 85 wt.‐% oil and are flexible, slightly transparent and have a sand‐like hue. Increasing concentration of the modified castor oil in the feed ratio results in an increase in the extracted (unreacted or oligomeric) components in the final thermoset. Thermogravimetric analysis reveals that all of the specimens have temperatures of maximum degradation around 500 °C. DMA and TGA analysis on solvent‐extracted specimens show that the presence of the soluble fractions helps to plasticize the materials and give added thermal stability.

     

Ferrocene Redox Controlled Reversible Immobilization of Ruthenium Carbene in Ionic Liquid: A Versatile Catalyst for Ring‐Closing Metathesis

A ferrocene‐tagged ruthenium carbene 15 that can be reversibly immobilized in an ionic liquid (IL) via the controlled oxidation and reduction of a ferrocene tag was prepared. This offers a new strategy which uses redox chemistry to control immobilization and to recycle both the catalyst and the IL. In this experiment, 11 recycles were performed for the ring‐closing metathesis (RCM) of a substrate using 16 as the catalyst in an ionic liquid (IL). More importantly, after the reaction was completed, the ruthenium catalyst was easily separated from the supporting IL by just adding decamethylferrocene (DMFc) to reduce the cationic ferrocene and then extracting it with benzene. Thus, this recycle system offers an easy way to recycle both the ruthenium catalyst and the IL.