Cobalt-catalyzed production

In contrast to triphenylphosphine-modified rhodium catalysis, a high aldehyde product isomer ratio via cobalt-catalyzed hydroformylation requires high CO partial pressures, eg, 9 MPa (1305 psi) and 110°C. Under such conditions alkyl isomerization is almost completely suppressed, and the 4.4 1 isomer ratio reflects the precursor mixture which contains principally the kinetically favored -butyryl to isobutyryl cobalt tetracarbonyl. At lower CO partial pressures, eg, 0.25 MPa (36.25 psi) and 110°C, the rate of isomerization of the -butyryl cobalt intermediate is competitive with butyryl reductive elimination to aldehyde. The product n/iso ratio of 1.6 1 obtained under these conditions reflects the equihbrium isomer ratio of the precursor butyryl cobalt tetracarbonyls (11). 

The principal product of the hydroformylation which is most desired in industrial applications is a linear aldehyde. The unmodified, cobalt-catalyzed processes produce a mixture of linear and branched aldehydes, the latter being mostly an a-methyl isomer. For the largest single application—propylene to butyraldehydes—the product composition has an isomer ratio (ratio of percent linear to percent branched) of (2.5 t.0)/l. The isobutyraldehyde cannot be used to make 2-ethylhexanol, and iso-... 

Conflicting results have been reported for the effects of catalyst concentration in the cobalt-catalyzed reaction. In early work, Hughes and Kirshenbaum (31) reported that these parameters were very influential in determining product composition high temperatures and high catalyst concentrations resulted in products containing decreased amounts of the... 

In addition to the increased proportion of linear product, other differences from the unmodified cobalt-catalyzed reaction may be noted. The... 

The cobalt-catalyzed hydroformylation of acrolein diacetate in ethanol proceeded in a complicated fashion. The products obtained are listed in Table XXVI. These products are rationalized by the following sequence The initial products formed were m-aldehyde (l,l-diacetoxy-3-formylpro-pane, ca. 60%), isoaldehyde (1,1 -diacetoxy-2-formylpropane, 5-10%) and propionaldehyde diacetate, ca. 5%. In the alcohol solvent, the aldehydes were converted to the corresponding acetals. A portion of the n-aldehyde was converted to 2,5-diethoxytetrahydrofuran by acid catalysis, and the isoaldehyde was thermally decomposed to 2-methyl-3-acetoxyacrolein. 

With respect to quantitative results, Rathke and Feder have shown (13) that when account is taken of the secondary reactions in the cobalt-catalyzed system the fractions of primary products MeOH(fi), Me02CH(f2), and (CH20H)2(f3) can be rationalized as follows ... 

Malacria and co-workers76 were the first to report the transition metal-catalyzed intramolecular cycloisomerization of allenynes in 1996. The cobalt-mediated process was presumed to proceed via a 7r-allyl intermediate (111, Scheme 22) following C-H activation. Alkyne insertion and reductive elimination give cross-conjugated triene 112 cobalt-catalyzed olefin isomerization of the Alder-ene product is presumed to be the mechanism by which 113 is formed. While exploring the cobalt(i)-catalyzed synthesis of steroidal skeletons, Malacria and co-workers77 observed the formation of Alder-ene product 115 from cis-114 (Equation (74)) in contrast, trans-114 underwent [2 + 2 + 2]-cyclization under identical conditions to form 116 (Equation (75)). 

Figure 2 shows the generally accepted dissociative mechanism for rhodium hydroformylation as proposed by Wilkinson [2], a modification of Heck and Breslow s reaction mechanism for the cobalt-catalyzed reaction [3]. With this mechanism, the selectivity for the linear or branched product is determined in the alkene-insertion step, provided that this is irreversible. Therefore, the alkene complex can lead either to linear or to branched Rh-alkyl complexes, which, in the subsequent catalytic steps, generate linear and branched aldehydes, respectively. 

The amidocarbonylation of aldehydes provides highly efficient access to N-acyl a-amino acid derivatives by the reaction of the ubiquitous and cheap starting materials aldehyde, amide, and carbon monoxide under transition metal-catalysis [1,2]. Wakamatsu serendipitously discovered this reaction when observing the formation of amino acid derivatives as by-products in the cobalt-catalyzed oxo reaction of acrylonitrile [3-5]. The reaction was further elaborated to an efficient cobalt- or palladium-catalyzed one-step synthesis of racemic N-acyl a-amino acids [6-8] (Scheme 1). Besides the range of direct applications, such as pharmaceuticals and detergents, racemic N-acetyl a-amino acids are important intermediates in the synthesis of enantiomeri-cally pure a-amino acids via enzymatic hydrolysis [9]. 

Aminocarbonylation can also be carried out by use of CO and a silyl amide. Watanabe et al. reported the cobalt-catalyzed aminocarbonylation of epoxides [55]. Some silyl amides such as PhCH2NHSiMe3 and Et2NSiMe3 were applicable to the reaction to give the /i-siloxy amide in good yields, whereas high reaction temperature was required. The use of 4-(trimethylsilyl) morpholine was found to be crucial for a milder and more efficient carboami-nation here, the reaction proceeded at ambient temperature under 0.1 MPa of CO. However, N-(2-hydroxyalkyl)morpholines, a product without carbonyla-tion, were yielded as by-products (Scheme 18) [56]. 

Raffinate-II typically consists of40 % 1-butene, 40 % 2-butene and 20 % butane isomers. [RhH(CO)(TPPTS)3] does not catalyze the hydroformylation of internal olefins, neither their isomerization to terminal alkenes. It follows, that in addition to the 20 % butane in the feed, the 2-butene content will not react either. Following separation of the aqueous catalyts phase and the organic phase of aldehydes, the latter is freed from dissolved 2-butene and butane with a counter flow of synthesis gas. The crude aldehyde mixture is fractionated to yield n-valeraldehyde (95 %) and isovaleraldehyde (5 %) which are then oxidized to valeric add. Esters of n-valeric acid are used as lubricants. Unreacted butenes (mostly 2-butene) are hydroformylated and hydrogenated in a high pressure cobalt-catalyzed process to a mixture of isomeric amyl alcohols, while the remaining unreactive components (mostly butane) are used for power generation. Production of valeraldehydes was 12.000 t in 1995 [8] and was expected to increase later. 

The product is formed in up to a 94% yield and can, moreover, be easily separated from the reaction mixture. Conventional alkylation reactions (56GEP952807, 56MI1) have yields that lie between 22 and 54%, suggesting that the cobalt-catalyzed procedure might be an attractive pathway for large scale production. 

The cobalt-catalyzed synthesis enables 2,2 -dipyridyl to be prepared directly from 2-cyanopyridine and acetylene in a 72% yield with a cyanopy-ridine conversion of 21%. The pyridine benzene ratio in the product is 2.7 1 [Eq.(18)]. 

Morken and co-workers have reported the highly enantioselective version of this reaction, albeit with low efficacy in the aldol-type coupling [8d, e]. Unfortunately, we obtain low enantioselectivity ee 2-4%) using chiral rhodium complexes under our reaction conditions. An intramolecular adaptation has led to new opportunities in cobalt-catalyzed carbocyclizations, wherein the use of PhSiHs was essential for smooth ring formation (Eq. 4) [9]. The identical products were also formed by a combination of [Rh(COD)2]OTf/(p-CE3Ph)3P and molecular hydrogen [10]. 

Hydrogenation of acetic anhydride to acetaldehyde (equation 23) has been demonstrated utilizing cobalt carbonyl under one atmosphere of hydrogen. However, the cobalt complex is short lived. A more efficient cobalt catalyzed reaction with substantial catalyst longevity was realized at a temperature of 190 and 3000 psi pressure CO and hydrogen. The main products were equal amounts of EDA and acetic acid. Upon investigation, this reaction was found exceptionally efficient at a more reasonable 1500 psi pressure provided that the temperature was maintained... 

Neither the thermal nor the cobalt-catalyzed decomposition of 3-butene-2-hydroperoxide in benzene at 100 °C. produced any acetaldehyde or propionaldehyde. In the presence of a trace of sulfuric acid, a small amount of acetaldehyde along with a large number of other products were produced on mixing. Furthermore, on heating at 100°C., polymerization is apparently the major reaction no volatile products were detected, and only a slight increase in acetaldehyde was observed. Pyrolysis of a benzene or carbon tetrachloride solution at 200°C. in the injection block of the gas chromatograph gave no acetaldehyde or propionaldehyde, and none was detected in any experiments conducted in methanol. 

Derivatives of the steroids androstene and pregnene have been transformed directly into A-acyl amino acids by an orthogonal catalysis procedure, utilizing [RhCl(nbd)]2 and Co2(CO)8 (Scheme 11). The rhodium phosphine catalyst (generated in situ in the presence of syn-gas and phosphine) affects hydroformylation of the internal olefin to generate aldehyde. In the presence of Co2(CO)8, A-acyl amino acids are obtained as the major products. An unstable amido alcohol intermediate, formed by reaction of the amide with aldehyde, is proposed to undergo cobalt-catalyzed GO insertion to yield the desired A-acyl amino acid. 

During this same time period, ethylene glycol was reported as a product in cobalt-catalyzed methanol homologation reactions methanol, ethanol, and glycol ethers were also found in similar reactions carried out to homologate w-propanol and w-butanol (34). Reaction conditions were 800-1000 atm of H2/CO at 225°C. 

Formate esters of the various alcohols formed are observed as major products in these cobalt-catalyzed reactions, and the mole ratio of formates to alcohols remains constant throughout a reaction. This observation would be consistent with the occurrence of a rapid carbonylation equilibrium process,... 

Fig. 3. Product distribution in cobalt-catalyzed CO hydrogenation with added tri-w-butylphosphine. (Reprinted from Ref. 38, by courtesy of Marcel Dekker, Inc.) Reaction conditions 149 atm H2, 149 atm CO, 182 C, 1,4-dioxane solvent, 3(n-C4H9)3P/Co, average HCo(CO)4 concentration is 0.03 M.

Rales to Primary Products in Cobalt-Catalyzed CO Hydrogenation at I82°C ... 

Product Selectivity and Rate as a Function of Pressure for Cobalt-Catalyzed CO Hydrogenation° b... 

Product Distribution in Cobalt-Catalyzed CO Hydrogenation in Various Solvents b... 

Fahey presents the products of (17) as uncomplexed formaldehyde and HCo(CO)3 rather than a bound-formaldehyde species (43). Free formaldehyde is a thermodynamically unfavorable product from H2 and CO (8), and significant stabilization may be expected as the result of coordination in a metal complex. However, thermodynamic calculations are presented which indicate that small equilibrium concentrations of formaldehyde could be present under the conditions of these cobalt-catalyzed reactions (43). Although small amounts of uncoordinated formaldehyde are indeed expected as a result of the following endothermic (36, 37) equilibrium ... 

The cobalt-catalyzed oxidation of cyclohexane takes place through cyclohexyl hydroperoxide with the cobalt catalyst acting primarily in the decomposition of the hydroperoxide to yield the products 870 877... 

Oxidation of Cyclododecane. 1,12-Cyclododecanedioic acid used in the production of polymers is synthesized in a two-step process864,866 similar to the manufacture of adipic acid. Cyclododecane is first oxidized to a mixture of cyclododecanol and cyclododecanone. Both the cobalt-catalyzed and the borate processes (Huels) are used. Further oxidation of the product mixture leads to 1,12-cyclododecanedioic acid. 

Benzoic acid is almost exclusively manufactured by the cobalt catalyzed liquid-phase air oxidation of toluene [108-88-3]. Large-scale plants have been built for benzoic acid to be used as an intermediate in the production of phenol (by Dow Chemical) and in the production of caprolactam (by Snia Viscosa)... 

Y. Kamiya illustrates the influence on catalytic activity of the form of the catalyst. Thus, in the cobalt-catalyzed oxidation of hydrocarbons in acetic acid solution, introduction of bromide ions increases the activity of the catalyst, especially when the metal ion concentration is fairly high. The presence of bromides also results in a marked increase in the proportion of carbonyl compounds among the products and it is believed that these are formed as a result of a propagation step in which bromine-containing cobaltous ions react with alkylperoxy radicals. 

Metal-catalyzed reactions of CO with organic molecules have been under investigation since the late 1930s and early 1940s, when Roelen (/) discovered the hydroformylation reaction and Reppe (2) the acrylic acid synthesis and other related carbonylation reactions. These early studies of the carbonyla-tions of unsaturated hydrocarbons led to extremely useful syntheses of a variety of oxygenated products. Some of the reactions, however, suffered from the serious problem that they produced isomeric mixtures of products. For example, the cobalt-catalyzed hydroformylation of propylene gave mixtures of n-butyraldehyde and isobutyraldehyde. 

Homolytic liquid-phase processes are generally well suited to the synthesis of carboxylic acids, viz. acetic, benzoic or terephthalic acids which are resistant to further oxidation. These processes operate at high temperature (150-250°C) and generally use soluble cobalt or manganese salts as the main catalyst components. High conversions and selectivities are usually obtained with methyl-substituted aromatic hydrocarbons such as toluene and xylenes.95,96 The cobalt-catalyzed oxidation of cyclohexane by air to a cyclohexanol-cyclohexanone mixture is a very important industrial process since these products are intermediates in the manufacture of adipic acid (for nylon 6,6) and caprolactam (nylon 6). However, the conversion is limited to ca. 10% in order to prevent consecutive oxidations, with roughly 70% selectivity.97... 

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