Fatty acids olefin metathesis

Fig. 4 Renewable platform chemicals used in olefin metathesis (a) plant oils and fatty acids, (b) terpenes and terpenoids, (c) phenylpropanoids, (d) natural rubber (cw-1,4-poly isoprene), (e) carbohydrates, (f) amino acids and peptides, and (g) furans...

The application of olefin metathesis to fatty acids and related compounds has its starting point in 1972 with the selective transformation of methyl oleate into equimolar amounts of 9-octadecene and dimethyl 9-octadecene-l,18-dioate by Van Dam, Mittelmeijer, and Boelhouwer (Scheme 1) [29]. In this early work, 1-2 mol% of a... 

The olefin metathesis of biodiesel (mixture of fatty acid methyl esters) in the presence of 1 -hexene was used by Meier et al. as a way to improve the distillation... 

Olefin metathesis is also a highly versatile technique for the synthesis of polymers from renewable resources. In this respect, especially ADMET polymerization and ROMP have been used to prepare macromolecules starting from fatty acid precursors due to their inherent double-bond functionality. Nevertheless, also other feedstock and methods have been applied, as will be reviewed within this section. 

The 10-undecenoic acid motif has also been attached to isosorbide in the preparation of a fatty acid-/carbohydrate-based monomer [131]. ADMET polymerization in the presence of C3 and C4 produced fully renewable unsaturated polyesters (Scheme 18). Most importantly, the transesterification of these polyesters with MeOH, and subsequent analysis by GC-MS of the products, allowed for the quantification of double-bond isomerization during ADMET in a very simple manner. This strategy was then extended to fatty acid-based ADMET polyesters synthesized in the presence of indenylidene metathesis catalysts [132]. With these studies, the knowledge on the olefin isomerization in ADMET reactions was widened, and it is now possible to almost completely suppress this undesired side reaction. 

Ferulic acid, a phenolic acid that can be found in rapeseed cake, has been used in the synthesis of monomers for ADMET homo- and copolymerization with fatty acid-based a,co-dienes [139]. Homopolymerizations were performed in the presence of several ruthenium-based olefin metathesis catalysts (1 mol% and 80°C), although only C5, the Zhan catalyst, and catalyst M5i of the company Umicore were able to produce oligomers with Tgs around 7°C. The comonomers were prepared by epoxidation of methyl oleate and erucate followed by simultaneous ring opening and transesterification with allyl alcohol. Best results for the copolymerizations were obtained with the erucic acid-derived monomer, reaching a crystalline polymer (Tm — 24.9°C) with molecular weight over 13 kDa. 

A new procedure for GSL synthesis via olefin cross metathesis (164) is highly versatile in terms of the hydrophobic agly-cone. A protected 5 carbon amino alkene diol is the central building block to which the protected carbohydrate donor, long chain fatty acid, or, by olefin cross metathesis, the long alkenyl chain of the base can be coupled, in a variety of sequences. This atypical synthetic flexibility should allow a stmctural approach to dissecting the role of the lipid moiety in GSL receptor function and intracellular trafficking. 

Olefin metathesis is the catalytic exchange of groups attached to a double bond. It presents a number of interesting possibilities for modifying the alkyl chain of fatty acids (Figure 17). 

Metathesis of olefins, through the use of transition metal catalysis, is an important application in the petrochemical as well as in the polymer chemical industry for the production of special olefins and polymers (cf. Section 2.3.3). This chemistry is also applicable to unsaturated fatty acid esters, such as acetic acid methyl ester. However, the high price and unsustainability of the catalysts, compared with the fatty acids as substrates, have made commercial utilization not yet possible nevertheless they are of great interest for researchers in this field. 

To prepare 9-decenoic and 13-tetradecenoic acid methylester, we used the transition-metal catalysed olefin metathesis [6, 7], actually applied in petro- and polymerchemistry in seven industrial processes [8], As stated first by C. Boelhouwer et al. [9, 10], this reaction is valid not only for olefins, but for unsaturated fatty acid esters, too. 

Berezin, M. Y., Ignatov, V. M., Belov, P. S., Elev, I. V., Shelimov, B.N., Kazansky, V. B. (1991) Mechanism of Olefin Metathesis and Active Site Formation on Photoreduced Molybdenum Catalysts. 5. Metathesis of Unsaturated Fatty Acid Esters, Kinet. Ratal. 32, 379-389. 

The double bonds that are present in some fatty acids may im-dergo olefin metathesis reactions. For example, the ethenolysis of fatty acid methyl esters in the presence of a Grubbs first generation catalyst was used to synthesize cD-unsaturated fatty acid methyl esters (68,69). 

Epoxidation, hydroformylation, dimerisation, thiol-ene coupling, oxidative cleavage, and olefin metathesis attack the double bonds of unsaturated oils, fatty acids, or fatty acid esters. These reactions have been exploited for the synthesis of interesting monomers from renewable resources [1-3,13,14]. 

Fatty acid esters are generally obtained from the transesterification of fats and oils with a lower alcohol, e.g. methanol, along with glycerol. More than 90% of all oleochemical reactions (conversion into fatty alcohols and fatty amines) of fatty acid esters (or acids) are carried out at the carboxy functionality. However, transformation of unsaturated fatty acid esters by reactions of the carbon-carbon double bond, such as hydrogenation, epoxidation, ozonolysis, and dimerization, are becoming increasingly of industrial importance. Here we will discuss another catalytic reaction of the carbon-carbon double bond, viz. the olefin metathesis reaction, in which olefins are converted into new products via the rupture and reformation of carbon-carbon double bonds [2]. Metathesis of unsaturated fatty acid esters provides a convenient route to various chemical products in only a few reaction steps. 

Olefin metathesis is a catalytic reaction. A wide range of transition metal compounds will catalyse the reaction, the most important being based on W, Mo, Re and Ru. A problem in the case of functionalized olefins such as unsaturated fatty acid esters is the deactivation of catalytic sites, caused by the complexation of the polar functional group to the active site. This results in turnover numbers that are much lower than those obtained for the metathesis of analogous simple olefins. Relevant catalyst systems will be discussed in Section 4. 

Cross-metathesis of an olefinic compound with ethene is called ethenolysis. Ethenolysis of unsaturated fatty acid esters results in the synthesis of shorter-chain co-unsaturated esters, compounds with a broad range of application. Excess ethene can easily be applied (e.g. by use of ethene pressures of 30 bar) to suppress self-metathesis of the ester and to force the conversion to completion. Ethenolysis of methyl oleate produces methyl 9-decenoate and 1-decene [20,21] equation (9). 

The metathesis of olefins bearing functional groups provides potential routes to many valuable compounds. Metathesis catalysts, most of which contain a Lewis acid, are unfortunately poisoned by polar and basic compounds. As yet, only a few catalytic systems have proved to be active in metathesizing functionalized alkenes. In the homogeneous disproportionation of these substrates, the catalytic combination WCl —Sn(CH3)4 is still the best known [63]. In addition to its well known application in the conversion of unsaturated oxygen containing olefins, such as fatty acid esters and unsaturated ethers, its effectiveness for the homogeneous metathesis of unsaturated amines has also been described [64]. 

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