Cobalt as catalyst

Polyether Polyols. Polyether polyols are addition products derived from cyclic ethers (Table 4). The alkylene oxide polymerisation is usually initiated by alkah hydroxides, especially potassium hydroxide. In the base-catalysed polymerisation of propylene oxide, some rearrangement occurs to give aHyl alcohol. Further reaction of aHyl alcohol with propylene oxide produces a monofunctional alcohol. Therefore, polyether polyols derived from propylene oxide are not truly diftmctional. By using sine hexacyano cobaltate as catalyst, a more diftmctional polyol is obtained (20). Olin has introduced the diftmctional polyether polyols under the trade name POLY-L. Trichlorobutylene oxide-derived polyether polyols are useful as reactive fire retardants. Poly(tetramethylene glycol) (PTMG) is produced in the acid-catalysed homopolymerisation of tetrahydrofuran. Copolymers derived from tetrahydrofuran and ethylene oxide are also produced. 

As a general phenomenon, observed already by Fischer and coworkers, activity and FT synthesis selectivity develop in the initial time of a run in a process of Formierung (formation)16—in modem terms self-organization and catalyst restructuring. In order to achieve high performance of synthesis with cobalt as catalyst, the temperature had to be raised slowly up to the temperature of steady-state conversion. A distinct thermodynamically controlled state of the Co surface, populated with reactants and intermediates, can be assumed. This state depends on temperature and particularly on CO partial pressure, and its catalytic nature changes with changing conditions. 

For cobalt as catalyst, variations in reaction parameters have been studied as a means of controlling the product composition (or isomer ratio). Thus, variations in isomer ratio from 1 1 to about 4 1 were observed under widely differing conditions of temperature, catalyst concentration, partial pressure of hydrogen, and partial pressure of carbon monoxide. 

Aryl- or heteroarylzinc species have been successfully synthesized from the corresponding aryl or heteroaryl bromides or chlorides in high yields, on the laboratory scale (10 mmoles of substrate). The use of cobalt as catalyst allowed the synthesis of organozinc reagents using the sacrificial anode process with a wide variety of solvents. 

With cobalt as catalyst the plot of log [peracetic acid] vs. time was linear for each cobalt acetate concentration. The first-order rate constants obtained at different cobalt concentrations (k2 ) were plotted as a function of total cobalt (Cot) concentration, and the plot indicates a first-order dependence on total cobalt as shown in Figure 3. The experimental rate law for the cobalt-catalyzed decomposition is thus ... 

It appears more likely, however, that with metallic cobalt as catalyst the dicobalt octacarbonyl forms first, and in the presence of hydrogen, equili-... 

The first generation of hydroformylation processes (e.g., by BASF, ICI, Kuhlmann, Ruhrchemie) was exclusively based on cobalt as catalyst metal. As a consequence of the well-known stability diagram for cobalt carbonyl hydrides, the reaction conditions had to be rather harsh the pressure ranged between 20 and 35 MPa to avoid decomposition of the catalyst and deposition of metallic cobalt, and the temperature was adjusted according to the pressure and the concentration of the catalyst between 150 and 180 °C to ensure an acceptable rate of reaction. As the reaction conditions were quite similar, the processes differed only in the solution of the problem of how to separate product and catalyst, in order to recover and to recycle the catalyst [4]. Various modes were developed they largely yielded comparable results, and enabled hydroformylation processes to grow rapidly in capacity and importance (see Section 2.1.1.4.3). 

Since its discovery by Roelen in 1938 [l],the hydroformylation process was exclusively based on cobalt as catalyst metal, until the development of rhodium-phosphine complexes in the late 1960s [2]. Industrial efforts have been focused on the preparation of norraaZ-aldehydes (linear aldehydes) from 1-alkenes. In contrast, asymmetric hydroformylation, which requires iso-aldehydes (branched aldehydes) to be formed from 1 -alkenes, was first examined in the early 1970s by four groups independently, using Rh(I) complexes of chiral phosphines as catalysts [3,4,5,6]. Since then, a number of chiral ligands have been developed for... 

An indirect method of producing aldehydes and alcohols from carbon monoxide and hydrogen is the oxo-synthesis (originated by Roelen, Ruhrchemie, A.G.), in which aldehydes are produced by addition of carbon monoxide and hydrogen to olefins at relatively low temperatures and high pressures (cobalt as catalyst), according to the equations ... 

Contents of a-olefins among the straight chain olefins as a function of carbon number and time (t xp) with iron and cobalt as catalyst... 

With both - iron and cobalt as catalysts - the Fischer-Tropsch product consists mainly of aliphatic chains with a few methyl side groups. The branching reaction can be assumed more demanding in space than linear growth of chains and thereby constrained. 

Kabanov, V A., and Smetanyuk, V. I., The mechanism of the ethylene dimerization in the presence of bis[(ethylene)tris(tripenylphosphine)cobalt] as catalyst, Chem. Phys. Suppl, 5, 121, 1981. 

Very interesting are the results of recent investigations on the mechanisms of Co(II) mediated reductions of nitriles, alkenes and alkyl halides by LiAlH4 and NaBH4. Those studies have unambiguously identified borides and aluminides of cobalt as catalysts in all three reductions, a finding clearly at odds with commonly held notions about the mechanisms of such processes and which could also be relevant to other transition-metal—hydride systems [12]. 

Cobalt has an odd number of electrons, and does not form a simple carbonyl in oxidation state 0. However, carbonyls of formulae Co2(CO)g, Co4(CO)i2 and CoJCO),6 are known reduction of these by an alkali metal dissolved in liquid ammonia (p. 126) gives the ion [Co(CO)4] ". Both Co2(CO)g and [Co(CO)4]" are important as catalysts for organic syntheses. In the so-called oxo reaction, where an alkene reacts with carbon monoxide and hydrogen, under pressure, to give an aldehyde, dicobalt octacarbonyl is used as catalyst ... 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

The mixture of carbon monoxide and hydrogen is enriched with hydrogen from the water gas catalytic (Bosch) process, ie, water gas shift reaction, and passed over a cobalt—thoria catalyst to form straight-chain, ie, linear, paraffins, olefins, and alcohols in what is known as the Fisher-Tropsch synthesis. 

The conversion of CO to CO2 can be conducted in two different ways. In the first, gases leaving the gas scmbber are heated to 260°C and passed over a cobalt—molybdenum catalyst. These catalysts typically contain 3—4% cobalt(II) oxide [1307-96-6] CoO 13—15% molybdenum oxide [1313-27-5] MoO and 76—80% alumina, JSifDy and are offered as 3-mm extmsions, SV about 1000 h . On these catalysts any COS and CS2 are converted to H2S. Operating temperatures are 260—450°C. The gases leaving this shift converter are then scmbbed with a solvent as in the desulfurization step. After the first removal of the acid gases, a second shift step reduces the CO content in the gas to 0.25—0.4%, on a dry gas basis. The catalyst for this step is usually Cu—Zn, which may be protected by a layer of ZnO. 

Others. Oxahc acid is used for the production of cobalt, as a raw material of various agrochemicals and pharmaceuticals, for the manufacture of electronic materials (76—83), for the extraction of tungsten from ore (84), for the production of metal catalysts (85,86), as a polymerization initiator (87—89), and for the manufacture of zirconium (90) and beryhium oxide (91). 

Technical-Grade Terephthalic Acid. All technical-grade terephthahc acid is produced by catalytic, hquid-phase air oxidation of xylene. Several processes have been developed, but they all use acetic acid as a solvent and a multivalent heavy metal or metals as catalysts. Cobalt is always used. In the most popular process, cobalt and manganese are the multivalent heavy-metal catalysts and bromine is the renewable source for free radicals (51,52). 

Acetaldehyde can be used as an oxidation-promoter in place of bromine. The absence of bromine means that titanium metallurgy is not required. Eastman Chemical Co. has used such a process, with cobalt as the only catalyst metal. In that process, acetaldehyde is converted to acetic acid at the rate of 0.55—1.1 kg/kg of terephthahc acid produced. The acetic acid is recycled as the solvent and can be isolated as a by-product. Reaction temperatures can be low, 120—140°C, and residence times tend to be high, with values of two hours or more (55). Recovery of dry terephthahc acid follows steps similar to those in the Amoco process. Eastman has abandoned this process in favor of a bromine promoter (56). Another oxidation promoter which has been used is paraldehyde (57), employed by Toray Industries. This leads to the coproduction of acetic acid. 2-Butanone has been used by Mobil Chemical Co. (58). 

Zirconium tetrafluoride [7783-64-4] is used in some fluoride-based glasses. These glasses are the first chemically and mechanically stable bulk glasses to have continuous high transparency from the near uv to the mid-k (0.3—6 -lm) (117—118). Zirconium oxide and tetrachloride have use as catalysts (119), and zirconium sulfate is used in preparing a nickel catalyst for the hydrogenation of vegetable oil. Zirconium 2-ethyIhexanoate [22464-99-9] is used with cobalt driers to replace lead compounds as driers in oil-based and alkyd paints (see Driers and metallic soaps). 

Catalysts other than the above cobalt salts have been considered. Several patents suggest that cobalt bromide gives improved yields and faster reaction rates (12—16). The bromide salts are, however, very corrosive and require that expensive materials of constmction, such as HastaHoy C or titanium, be used in the reaction system. Only one faciHty, located in the UK, is beHeved to uti1i2e cobalt bromide catalyst in the production of ben2oic acid. 

The first CO route to make adipic acid is a BASF process employing CO and methanol in a two-step process producing dimethyl adipate [627-93-0] which is then hydroly2ed to the acid (43—46). Cobalt carbonyl catalysts such as Co2(CO)g are used. Palladium catalysts can be used to effect the same reactions at lower pressures (47—49). 

The earhest modification of the Oxo process (qv) employed cobalt hydrocarbonyl, HCo(CO)4, as catalyst. The reaction was carried out in the Hquid phase at 130—160°C and 10—20 MPa (1450—2900 psi) to give a ratio of n- to isobutyraldehyde of between 2 1 to 4 1. / -Butyraldehyde, the straight-chain isomer and the precursor of 2-ethylhexanol, was the more valuable product so that a high isomer ratio of n- to isobutyraldehyde was obviously advantageous. 

Metal salts of neodecanoic acid have also been used as catalysts in the preparation of polymers. For example, bismuth, calcium, barium, and 2kconium neodecanoates have been used as catalysts in the formation of polyurethane elastomers (91,92). Magnesium neodecanoate [57453-97-1] is one component of a catalyst system for the preparation of polyolefins (93) vanadium, cobalt, copper, or kon neodecanoates have been used as curing catalysts for conjugated-diene butyl elastomers (94). 

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. 

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