Carbonylation, of dimethyl ether

Similar activation takes place in the carbonylation of dimethyl ether to methyl acetate in superacidic solution. Whereas acetic acid and acetates are made nearly exclusively using Wilkinson s rhodium catalyst, a sensitive system necessitating carefully controlled conditions and use of large amounts of the expensive rhodium triphenylphosphine complex, ready superacidic carbonylation of dimethyl ether has significant advantages. 

The reaction mechanism and rates of methyl acetate carbonylation are not fully understood. In the nickel-cataly2ed reaction, rate constants for formation of methyl acetate from methanol, formation of dimethyl ether, and carbonylation of dimethyl ether have been reported, as well as their sensitivity to partial pressure of the reactants (32). For the rhodium chloride [10049-07-7] cataly2ed reaction, methyl acetate carbonylation is considered to go through formation of ethyUdene diacetate (33) ... 

Vapor-Phase Carbonylation of Dimethyl Ether and Methyl Acetate with Supported Transition Metal Catalysts... 

It was found that a nickel-activated carbon catalyst was effective for vapor phase carbonylation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250 C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250 C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of acetic acid was formed in the carbonylation of methyl acetate. The route of acetic acid formation is discussed. A molybdenum-activated carbon catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. 

The synthesis of acetic acid (AcOH) from methanol (MeOH) and carbon monoxide has been performed industrially in the liquid phase using a rhodium complex catalyst and an iodide promoter ( 4). The selectivity to acetic acid is more than 99% under mild conditions (175 C, 28 atm). The homogeneous rhodium catalyst is also effective for the synthesis of acetic anhydride (Ac O) by the carbonylation of dimethyl ether (DME) or methyl acetate (AcOMe) (5-13). However, rhodium is one of the most expensive metals, and its proved reserves are quite limited. It is highly desirable, therefore, to develop a new catalyst as a substitute for rhodium. 

Carbonylation of Dimethyl Ether on Ni/A.C. Catalysts. The main product of this reaction was methyl acetate. Small amounts of... 

Figure 3 shows the effect of partial pressure of water on the rate of dimethyl ether carbonylation. It is apparent from Figure 3 that the reaction is markedly accelerated by added water. One possible explanation for this is the hydrolysis of dimethyl ether to methanol and its subsequent carbonylation. However, the contribution of the hydrolysis is quite small as shown in Figure 3. Therefore, the carbonylation of dimethyl ether via methanol should be negligible. The role of water for the reaction is not clarified yet.

Table I. Effects of Mel/DME and CO/DME Ratios on Carbonylation of Dimethyl Ether ...

Carbonylation of Dimethyl Ether and Methyl Acetate on Mo/A.C. Catalyst. In this section, the carbonylation of dimethyl ether and methyl acetate on Mo/A.C. catalyst was investigated. To our knowledge, molybdenum has never been reported to catalyze carbonylation reactions. 

Table V shows the results obtained for the carbonylation of dimethyl ether and methyl acetate with molybdenum catalysts supported on various carrier materials. In the case of dimethyl ether carbonylation, molybdenum-activated carbon catalyst gave methyl acetate with an yield of 5.2% which was about one-third of the activity of nickel-activated carbon catalyst. Silica gel- or y-alumina-supported catalyst gave little carbonylated product. Similar results were obtained in the carbonylation of methyl acetate. The carbonylation activity occured only when molybdenum was supported on activated carbon, and it was about half the activity of nickel-activated carbon catalyst.

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

The carbonylation of dimethyl ether to methyl acetate (equation 68) is catalyzed by [Ni(H20)6]Cl2 in the presence of PPh3 and [Cr(CO)6].424 This reaction was much faster than the subsequent carbonylation of the ester to acetic anhydride. The nature of the complexes formed under reaction conditions is unknown. The reaction requires both high temperature and CO pressure. 

A new CD process for the production of vinyl acetate from acetic acid, ethylene, and oxygen using a Pd-type catalyst at 338 20 K, 2-5 bar was disclosed. This illustrates the wide-ranging possibilities for the application of CD in a variety of processes for the chemical, petrochemical, and petroleum industry. The production of acetic acid from the carbonylation of dimethyl ether or methanol using RD and homogeneous catalyst was also patented. ... 

Fig. 6. Proposed elementary steps for carbonylation of dimethyl ether on acidic zeolites.

In subsequent developments, Eastman has reported two new alternative manufacturing routes to vinyl acetate (38). The first uses the carbonylation of dimethyl ether to acetic anhydride, followed by the reaction between acetic anhydride and acetaldehyde in a reactive distillation column to 3ueld vinyl acetate, whereas the second involves the intermediacy of ketene. Here ketene is hydrogenated to acetaldehyde, and the acetaldehyde is reacted with a second equivalent of ketene to produce vinyl acetate. Both of these routes are claimed to avoid the problematic and expensive acetic acid recycle. 

Cheung P, Bhan A, Sunley GJ, Iglesia E. Selective carbonylation of dimethyl ether to methyl acetate catalyzed by acidic zeolites. Angew Chem Int Ed 2006 45 1617—20. 

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