Hydroformylations of unsaturated fatty acids

The application of hydroformylation is not limited to unfunctionalized petrochemicals. Also, renewables are of interest for industrial applications. One good available resource is oleocompounds which possess C=C-double bonds [16]. Ucciani and Lai first investigated the hydroformylation of unsaturated fatty acid esters using cobalt catalysts such as cobalt laurate or dicobalt octacarbonyl (Scheme 6) [17, 18]. 

Also, bulky phosphite-modified rhodium catalysts are highly reactive for the hydroformylation of unsaturated fatty acid esters [23]. The catalyst was able to yield turnover numbers (TON) of 400-500 when moderate conditions with 20 bar synthesis gas pressure and 100°C were applied. These phosphites, like tris (2-ferf-butyl-methyl) phosphite, have higher activity than phosphines like triphenylphosphine. 

Muilwijk KF, Kamer PCJ, van Leeuwen PWNM (1997) A bulky phosphite-modified rhodium catalyst for the hydroformylation of unsaturated fatty acid esters. J Am Oil Chem Soc 74 223-228... 

Hydroformylation of unsaturated fatty acids was first investigated in the late 1960s and early 1970s [1]. Thereafter, both university and industrial research became... 

In addition, polymeric phosphine-Pd(II) complexes are shown to be useful in the hydrogenation, hydrosilylation and hydroformylation of methyl ester of unsaturated fatty acid (118). 

Recently, we reported that the rhodium/BIPHEPHOS-catalyzed hydroformylation of trans-4-octene (Scheme 6) provides an interesting approach for the synthesis of n-nonanal [23]. In this context trans-4-octene can also be seen as a model substance for hydroformylation of internally unsaturated fatty acid esters. This could open up access to the use of renewable resources for the synthesis of valuable n-aldehydes. 

Modern biobased lubricants are mainly based on rapeseed oil, sunflower oil, soybean oil, and animal fats. These oils easily undergo oxidation due to their content of polyunsaturated fatty acids such as linoleic acid and linolenic acid. Efforts have been made to modify the oils to provide a more stable material and a product more competitive in performance to mineral oil-based lubricants. This modification can involve partial hydrogenation of oil and a shifting of its fatty acids to high oleic acid content [21]. Other reported changes that address the problem of unsaturation include alkylation, acylation, hydroformylation, hydrogenation, oligomerization (polymerization), and epoxidation [20, 22]. 

Linear o)-hydroxy fatty acids may be obtained by hydroformylation of o)-unsaturated fatty acids in the presence of a rhodium catalyst, followed by hydrogenation of the resultant products. As an example, methyl 10-undecenoate produces methyl 12-hydroxydodecanoate with high regioselectivity and yield through the above stated reactions. 

Up until now, mostly pure substrates such as methyl oleate and its -isomer, methyl elaidate, have been tested as model substrates for hydroformylation, but in a few cases, linoleates, linolenates, and esters of ricinoleic acid have also been investigated (Figure 6.10). Oleic acid can be derived from new sunflower, linoleic acid from soybean, linolenic acid from linseed, and ricinoleic acid from castor oil. The long-chain mono-unsaturated fatty acid erucic acid (C22) can be extracted from old rapeseed oil. 

Anyway, it is well known that micellar effects are common in hydroformylation conducted in all varieties of aqueous systems. The addition of surfactants often helps the reactions in biphasic media, possibly due to solubilization of hydrophobic reagents in micelles, which thus function like cooperative phase-transfer agents. For example, the hydroformylation of unsaturated fats or methyl esters of unsaturated long-chain natural fatty acids (oleic, linolenic acids) can be successfully done using biphasic tech-... 

The hydrogenation step following hydroformylation serves two important purposes. It reduces the aldehyde intermediate product to the desired primary alcohol functional group, which is the primary site of reactivity of the polyol with isocyanates. It also reduces the residual olefins in the FAMEs to saturated hydrocarbons, thus eliminating the pathway to Hock degradation and odor development, which is inherent to other processes that leave fatty acid unsaturation in the polyols. This step eliminates the typical vegetable oil odor from the final namral oil polyols of this process. 

Epoxidation of oleic and linoleic acid was readily achieved by treatment with the acetonitrile complex of hypofluorous acid (55). Phase-transfer-catalyzed biphasic epoxidation of unsaturated triglycerides was accomplished with ethylmethyldioxirane in 2-butanone (56). The enantioselective formation of an a,P-epoxy alcohol by reaction of methyl 13()S)-hydroperoxy-18 2(9Z,llfi) with titanium isopropoxide has been reported (57). An immobilized form of Candida antartica on acrylic resin (Novozyme 435) was used to catalyze the perhydrolysis and the interesterification of esters. Unsaturated alcohols were converted with an ester in the presence of hydrogen peroxide to esters of epoxidized alcohols (e.g., epoxystearylbutyrate) directly (58). Homoallyl ethers were obtained from olefinic fatty esters by the ethylaluminium-in-duced reactions with dimethyl acetals of formaldehyde, acetaldehyde, isobutyralde-hyde, and pivaldehyde (59). Reaction of 18 2(9Z, 12Z) with 50% BF3-methanol gave monomethoxy and dimethoxy derivatives (60). A bulky phosphite-modified rhodium catalyst was developed for the hydroformylation of methyl 18 1 (9Z)and 18 1(9 ), which furnished mixtures of formylstearate and diformylstearate (61). 

Best known is the hydroformylation (oxo) reaction between unsaturated fatty adds and synthesis gas (hydrogen and carbon monoxide) under pressure (500-2000 psi) in the presence of cobalt carbonyl at about 100 C. The product is mainly a mixture of isomeric formylstearic acids and hydroxymethyl-stearic acids. The reaction is accompanied by some reduction of double bonds. With homogeneous... 

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]. 

By the effect of a Rh/C catalyst modified with PPhg at 140 bar syngas pressure and 110 °C on a complex substrate mixture of fatty acid methyl esters with one or more double bonds, besides the formation of monoformyl stearate, some diformy-lated products were found [34]. Moreover, unsaturated monoformyl esters were detected together with triformyl esters derived from methyl linolenate. The formation of 1,4-diformyl esters in the hydroformylation of methyl linoleate over the 1,3-diformyl isomers was explained by the thermodynamic stability of the transient Rh-acyl complex A over the chelate B with a smaller ring size. 

Besides isomerization of the olefinic substrates, some other side reactions may complicate the hydroformylation of fatty acids. Such reactions are decarboxylation and decarbonylation (see also Chapter 8) under formation of saturated or unsaturated compounds reduced by one carbon atom (Scheme 6.88) [37]. For example, at high temperatures and long reaction times, the formed aldehydes can undergo dehydrocarbonylation (a). Subsequent hydrogenation produces saturated fatty acids [25, 38]. This reaction sequence may lead to the false conclusion that hydrogenation of the starting olefin has taken place. The same products can suffer decarbonylation (b). On the other hand, decarboxylation of formyl carboxyl acids produces aldehydes (c). 

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