Carboxylic acids hydroformylation catalysts

If cobalt carbonylpyridine catalyst systems are used, the formation of unbranched carboxylic acids is strongly favored not only by reaction of a-olefins but also by reaction of olefins with internal double bonds ( contrathermo-dynamic double-bond isomerization) [59]. The cobalt carbonylpyridine catalyst of the hydrocarboxylation reaction resembles the cobalt carbonyl-terf-phos-phine catalysts of the hydroformylation reaction. The reactivity of the cobalt-pyridine system in the hydrocarboxylation reaction is remarkable higher than the cobalt-phosphine system in the hydroformylation reaction, especially in the case of olefins with internal double bonds. This reaction had not found an industrial application until now. 

DSM jointly with Du Pont de Nemours308 have patented platinum catalysts generated from the water soluble sulfonated ligand 30 (Table 2 m=0, n=0, m=l, n=2 m=l, n=l, Ar=nBu-S03Li) and used in the aqueous phase hydroformylation of internally unsaturated carboxylic acids, esters or nitriles to their corresponding formyl derivatives which are useful intermediates for the preparation of di-carboxylic acids (e.g. adipic acid). For example, TOFs up to 105 h-1 were achieved in the hydroformylation of 3-pentenoic acid catalysed by Pt/30 (m=0, n=0) at 100°C and 80 bar CO/H2 to give aldehydes with a selectivity of 83% (n/i=3.4), valeric acid (4.6%) and adipic acid (8.1%).308 The products were separated from the aqueous catalyst solution by extraction with ether. Five recycles of the aqueous catalyst solution showed that the Pt/30 (m=0, n=0) catalyst retains its activity. 

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

Precipitation of the catalyst from the reaction medium, followed by filtration, as in the cobalt-based hydroformylation process (see Section 5.4). Here cobalt is removed from the reaction products in the form of one of its salts or as the sodium salt of the active carbonyl catalyst. The aqueous salts can be recycled directly, but sometimes they are first converted into an oil-soluble long-chain carboxylic acid salt, such as the corresponding naphthenate, oleate, or 2-ethylhexanoate. 

In a continuation of this work, Breit and Smejkal (43) showed that when a-p unsaturated carboxylic acids are exposed to hydroformylation conditions in the presence of supramolecular catalyst 5, the reaction takes a completely unexpected path, yielding a product corresponding to a decarboxylative hydroformylation (Scheme 1, bottom). Under standard hydroformylation conditions, moderate activity for the hydrogenation of the double bond was observed, but no aldehyde product was detected (Scheme 1, top). 

In addition to catalyzing hydroformylation, the platinum SPO complexes are excellent hydrogenation catalysts for aldehydes (as already demonstrated by the side products of hydroformylation), in particular, in the absence of carbon monoxide. Further, in ibis process, the facile heterolytic splitting of dihydrogen may play a role. The hydrogenation of aldehydes requires the presence of carboxylic acids, and perhaps the release of alkoxides from platinum requires a more reactive proton donor than that available on the nearby SPO. For example, 4 hydrogenates 2-methylpropanal at 95 °C and 40 bar of H2 to give the alcohol, with a TOF of 9000 mol moN h (71). 

Cobalt catalysts completely dominated industrial hydroformylation rmtil the early 1970s, when rhodium catalysts were commercialized. Most aldehydes produced are hydrogenated to alcohols or oxidized to carboxylic acids. Esterification of the alcohols with phthalic anhydride produces dialkyl phtha-late plasticizers that are primarily used for polyvinyl chloride plastics - the largest single end-use. Detergents and surfactants make up the next largest category, followed by solvents, lubricants, and chemical intermediates. 

The production of carboxylic acids via carbonylation catalysis is the second most important industrial homogeneous group of processes. Reppe developed most of the basic carbonylation chemistry in the 1930s and 1940s. The first commercial carbonylation process was the stoichiometric Ni(CO)4-based hydroxycarbonylation of acetylene to give acrylic acid (see Section 3.5 for details). This discovery has since evolved into a trae Ni-catalyzed process, used mainly by BASF. The introduction of rhodium catalysts in the 1970s revolutionized carboxylic acid production, particularly for acetic acid, much in the same way that Rh/PPhs catalysts changed the importance of hydroformylation catalysis. 

Hydrocarboxylation of the Ce-Cs a-olefins with cobaltcarbonyl/pyridine catalysts at 200 °C and 20 MPa gives predominantly the linear carboxylic acids. The acids and their esters are used as additives for lubricants. The Ce-Cio a-olefins are hydroformylated to odd-numbered linear primary alcohols, which are converted to polyvinylchloride (PVC) plasticizers with phthalic anhydride. Oligomerization of (preferably) 1 -decene, applying BF3 catalysts, gives oligomers used as synthetic lubricants known as poly-a-olefins (PAO) or synthetic hydrocarbons (SHC) [11, 12]. The C10-C12 a-olefins can be epoxidized by peracids this opens up a route to bifunctional derivatives or ethoxylates as nonionic surfactants [13]. 

Hydroformylation of various heterofunctionalized olefins can be carried out with a number of chirally modified catalysts. Asymmetric induction is usually higher than with unfunctionalized hydrocarbons, presumably, due to additional binding of the substrate to the catalysts65,75. Thus, this method is applicable to the synthesis of hydroxy and amino carboxylic acids and other conversion products of primary functionalized aldehydes. These results are compiled in Table 7. 

Hydroformylation (Equation (14)) is one of the very largest homogeneous catalytic reactions carried out by industry making over 15 billion pounds of aldehyde products each year. These are subsequently hydrogenated to alcohols or oxidized to carboxylic acids. There are several recent excellent reviews on hydroformylation catalysis (cf. Refs 7,7a-7c). Industry is generally more interested in the linear aldehyde product, and much of hydroformylation catalyst development work has been directed at increasing the linear to branched regioselectivity (L B, also referred to as normal to iso), reaction rates, and catalyst stability (lifetime). There are three main hydroformylation catalysis... 

For Rh-catalyzed hydroformylation of higher alkenes, preferably phosphine-based catalysts are used for the conversion of 1 -alkenes, enabling linearities of 80-90%. The low-volatile nature of the higher aldehydes and their heavy ends clearly disadvantage any process with distillative catalyst/product separation (type 11). Mitsubishi Chemical has reported the start-up of such a unit in 1970 (23 kt/a), using the unmodified Rh catalyst and Cs-Ci4 1-alkenes [36], but that unit is probably obsolete. A better type 11 process is run by Celanese since 1980 they convert C -Cg 1-alkenes to hear aldehydes on 18 kl/a scale (for production of carboxylic acids), using Rh/TPP and distillative separation under vacuum [78, 79]. Probably, Cg is the maximum alkene carbon number to be used in a type n process. 

Breit and coworkers have reported the Rh-catalyzed hydroformylation of carboxylic acids using ligand 74 (Scheme 1). The catalyst displays high activity relative to PPh3, and selectively reacts at the terminal position of... 

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