Metal-activated carbon catalysts carbonylation

Rh > Ir > Ni > Pd > Co > Ru > Fe A plot of the relation between the catalytic activity and the affinity of the metals for halide ion resulted in a volcano shape. The rate determining step of the reaction was discussed on the basis of this affinity and the reaction order with respect to methyl iodide. Methanol was first carbonylated to methyl acetate directly or via dimethyl ether, then carbonylated again to acetic anhydride and finally quickly hydrolyzed to acetic acid. Overall kinetics were explored to simulate variable product profiles based on the reaction network mentioned above. Carbon monoxide was adsorbed weakly and associatively on nickel-activated-carbon catalysts. Carbon monoxide was adsorbed on nickel-y-alumina or nickel-silica gel catalysts more strongly and, in part, dissociatively,... 

Liquid phase carbonylation of methanol to acetic acid with a rhodium complex catalyst is a well known process (ref. 1). The authors have found that group 8 metals supported on carbonaceous materials exhibit excellent activity for the vapor phase carbonylation of methanol in the presence of iodide promoter(ref. 5). Especially, a nickel on active carbon catalyst gave acetic acid and methyl acetate with the selectivity of 95% or higher at 100% methanol conversion under 10 atm and 250 °C. In the present study it has been found that a small amount of hydrogen which is always contained in the commercially available CO and requires much cost for being removed completely, accelerates greatly the carbonylation reaction. 

Band d (vco = 1800-1806 cm" ) corresponds to three-fold bridged CO on metallic rhodium particles. The intensity of band d increases systematically, its increase suggests a slow reduction of Rh(III) and Rh(I) to Rh(0). The metallic Rh may play an important role in increasing the mobility of CO on the catalyst surface and in the activation of reagents during the carbonylation reaction as observed at the hydrocarboxylation of ethylene in the presence of hydrogen (favors the appearance of metallic Rh) on RhCls/active carbon and on H[Rh(CO)2l2]/active carbon catalyst. ... 

Manufacture. Trichloromethanesulfenyl chloride is made commercially by chlorination of carbon disulfide with the careful exclusion of iron or other metals, which cataly2e the chlorinolysis of the C—S bond to produce carbon tetrachloride. Various catalysts, notably iodine and activated carbon, are effective. The product is purified by fractional distillation to a minimum purity of 95%. Continuous processes have been described wherein carbon disulfide chlorination takes place on a granular charcoal column (59,60). A series of patents describes means for yield improvement by chlorination in the presence of dihinctional carbonyl compounds, phosphonates, phosphonites, phosphites, phosphates, or lead acetate (61). 

Since 1985, several thousands of publications have appeared on complexes that are active as catalysts in the addition of carbon monoxide in reactions such as carbonylation of alcohols, hydroformylation, isocyanate formation, polyketone formation, etc. It will therefore be impossible within the scope of this chapter to review all these reports. In many instances we will refer to recent review articles and discuss only the results of the last few years. Second, we will focus on those reports that have made use explicitly of coordination complexes, rather than in situ prepared catalysts. Work not containing identified complexes but related to publications discussing well-defined complexes is often mentioned by their reference only. Metal salts used as precursors on inorganic supports are often less well defined and most reports on these will not be mentioned. 

Carbonylation of Methyl Acetate on Ni/A.C. Catalysts. Table II shows the catalytic activities of nickel and platinum group metals supported on activated carbon for the carbonylation of methyl acetate. Ruthenium, palladium, or iridium catalysts showed much lower activity for the synthesis of acetic anhydride than the nickel catalyst. In contrast, the rhodium catalyst, which has been known to exhibit an excellent carbonylation activity in the homogeneous system (1-13), showed nearly the same activity as the nickel catalyst but gave a large amount of acetic acid. 

Carbonylation of methanol to form acetic acid has been performed industrially using carbonyl complexes of cobalt ( ) or rhodium (2 ) and iodide promoter in the liquid phase. Recently, it has been claimed that nickel carbonyl or other nickel compounds are effective catalysts for the reaction at pressure as low as 30 atm (2/4), For the rhodium catalyst, the conditions are fairly mild (175 C and 28 atm) and the product selectivity is excellent (99% based on methanol). However, the process has the disadvantages that the proven reserves of rhodium are quite limited in both location and quantity and that the reaction medium is highly corrosive. It is highly desirable, therefore, to develop a vapor phase process, which is free from the corrosion problem, utilizing a base metal catalyst. The authors have already reported that nickel on activated carbon exhibits excellent catalytic activity for the carbonylation of... 

Mo and W hexacarbonyls, Mo(CO)6 and W(CO)6, alone do not induce polymerization of acetylenic compounds. However, UV irradiation toward these catalysts in the presence of halogenated compounds can form active species for polymerization of various substituted acetylenes. Carbon tetrachloride, CCI4, when used as the solvent for the polymerization, plays a very important role for the formation of active species, and thus cannot be replaced by toluene that is often used for metal chloride-based catalysts. Although these metal carbonyl-type catalysts are less active compared to the metal halide-based counterparts, they can provide high MW polymers. It is a great advantage that the metal carbonyl catalysts are very stable under air and thus handling is much easier. 

The discovery that additions of catalytic amounts of CoCl2, activated carbon, or metals on metal oxide or carbon supports are extremely effective in labilizing carbonyl groups in Fe(CO)5 is thus particularly noteworthy. Stepwise substitution products Fe(CO)5 x(CNR)x (x = 1-5) have been obtained in high yield with short reaction times using these catalysts (see Table III) (759). 

The substituent R may be alkyl, cydoalkyt. or benzyl. Catalysts are selected from transition metals which can form carbonyl complexes. Ruthenium and especially cobalt form active catalysts, although other metals like Rh. Pd. Ft. Os, Ir, Cr, Mn, Fe, and Nt have also been examined. If metals like ruthenium or iron catalysis are used, carbon dioxide is formed instead of water as the by-product. 

The carbonylation of allylic compounds by transition metal complexes is a versatile method for synthesizing unsaturated carboxylic acid derivatives (Eq. 11.22) [64]. Usually, palladium complexes are used for the carbonylation of allylic compounds [65], whereas ruthenium complexes show characteristic catalytic activity in allylic carbonylation reactions. Cinnamyl methyl carbonate reacts with CO in the presence of a Ru3(CO)i2/l,10-phenanthroline catalyst in dimethylformamide (DMF) to give methyl 4-phenyl-3-butenoate in excellent yield (Eq. 11.23) [66]. The regioselectivity is the same as in the palladium complex-catalyzed reaction. However, when ( )-2-butenyl methyl carbonate is used as a substrate, methyl ( )-2-methyl-2-butenoate is the major product, with the more sterically hindered carbon atom of the allylic group being carbo-nylated (Eq. 11.24). This regioselectivity is characteristic of the ruthenium catalyst [66]. 

The method of applying carbon monoxide which was first thought of, was in the form of the metal carbonyls—iron-pentacarbonyl and nickel tetracarbonyl—which in the presence of catalysts such as the activated carbon used in anti-gas filters evolve carbon monoxide. 

In the first reported direct A -carbonylation of nitroaromatics to isocyanates, simple Pd- or Rh-based systems were used to catalyze the reaction of aromatic mononitro compounds with carbon monoxide [11, 12]. Later, it became possible to work without the drastic reaction conditions that had been required initially, by using Lewis acid co-catalysts [13], Various catalysts and catalyst mixtures, normally based on Ru, Rh, or Pd complexes with co-catalysts, were described in numerous patents and publications [1, 3, 14—16], The careful choice of the composition of the triad consisting of metal salt, co-catalysts and ligand (preferably aromatic amines) led to efficient catalyst systems [14a-e] for the direct reductive carbonylation process. A quite active Pd-phenanthroline-H system with noncoordinating carboxylic acids such as 2,4,6-trimethlybenzoic acid as proton source is worth mentioning [14 d]. 

This preconditioning of the catalyst is necessary to separate the chemical reactions from the catalytic ones (7). In the first few minutes, the iron surface transforms to catalytically active pyrrhotite, as shown (7) by the gradual increase in carbon monoxide consumption and corresponding increase in carbon dioxide production. The initial gaseous sulfide by-products react with the iron in the catalyst to form iron sulfides. In a previous publication (8), it was shown that lattice sulfur is a more versatile and useful carbon monoxide-sufurizing agent than molecular sulfur. The hypothesis tested was that metal sulfides with relatively weak metal-to-sulfur bonds are more effective in forming the active intermediate (9) carbonyl sulfide. 

Several other methods have been employed for the preparation of carbon-supported catalysts, although to a lesser extent that impregnation methods. Nakamura et al. [38] prepared molybdenum catalysts for ethene homologation by physical deposition of gaseous [Mo(CO)6]. Their supports were commercial activated carbons that were subjected to different treatments to modify then-surface. The authors compared these supports with oxidic supports and concluded that the interaction between the metal carbonyl and the carbon supports were weaker. Furthermore, they observed that oxidation of the carbon surface was effective in enhancing the catalytic activity of Mo/C, and they ascribed this effect to the contribution of the surface oxygen groups to the partial oxidation of decomposed [Mo(CO)6]. 

It has been proven that the chiral Pd(II) complexes as transition metal catalysts vs Lewis acid catalysts bring a breakthrough in the frontier of catalytic asymmetric organic synthesis. Here we discussed the key issues based on asymmetric carbon-carbon bond formations anomalous six-membered ring formation, ene-type cyclization leading to five-membered rings, spiro cycliza-tion, alkaloid and quinoline synthesis, Suzuki-Miyaura coupling, and C-H bond activation/C-C bond formation by transition metallic Pd(II) catalysts. On the other hand, the carbonyl-ene reaction, hetero Diels-Alder reaction, and... 

With plahnum and palladium catalysts, supported on siUca, alumina and active carbon, both H2, O2 and CO probe molecules are available for dispersion measurements. For rhodium, the various values are taken from the work of Ferretti et al. [102]. For ruthenium and iridium, O2 cannot be used as a probe molecule for dispersion measurements, because there is formahon of bulk oxides. With nickel, only H2 gives reUable results, O2 and CO cannot be used as probe molecules for dispersion measurements, because there is formation of bulk oxides with O2 and metal-carbonyls with CO, but the dispersion of the sample can be additionally measured by magnetic measurements. 

High reaction temperatures in catalytic processes can lead to loss of active components by evaporation. This does not only occur with compounds that are known to be volatile (e. g., P2O5 in H3PO4, silica gel, HgCl2/activated carbon), but also by reaction of metals to give volatile oxides, chlorides, or carbonyls. In the oxidation of ammonia on Pt/Rh net catalysts (Ostwald nitric acid process), the catalyst reacts with the gas phase to form volatile Pt02- Furthermore, porous platinum growths are observed on the surface. This can be prevented by addition of rare earth oxides. 

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