Acetic rhodium carbonyl catalyst

The problem of phosphine ligand dissociation and degradation is a common in attempts to modify the rhodium carbonylation catalyst. This arises from the relatively harsh conditions employed (i.e. aqueous acetic acid, HI,... 

Structure 4 is an intermediate for manufaeturing vitamin A (Scheme 2). The annual demand for vitamin A is about 3000 tons. Major producers are BASF, Hoffmann-La Roche and Rhone-Poulenc Animal Nutrition [55]. At an early stage in the synthesis BASF and Hoffmann-La Roche are using a hydroformylation step to synthesize 4 starting from l,2-diacetoxy-3-butene (5) and 1,4-di-aeetoxy-2-butene (6), respectively [56, 57]. The selectivity toward the branched product in the BASF process is achieved by using an unmodified rhodium carbonyl catalyst at a high reaction temperature. The symmetry of 6 in La Roche s process does not lead to regioselectivity problems. Elimination of acetic acid and isomerization of the exo double bond (La Roche) yields the final product 4 in both processes. 

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 carbonylation of methanol was developed by Monsanto in the late 1960s. It is a large-scale operation employing a rhodium/iodide catalyst converting methanol and carbon monoxide into acetic acid. An older method involves the same carbonylation reaction carried out with a cobalt catalyst (see Section 9.3.2.4). For many years the Monsanto process has been the most attractive route for the preparation of acetic acid, but in recent years the iridium-based CATIVA process, developed by BP, has come on stream (see Section 9.3.2) ... 

As a case study an acetic acid process has been given. Acetic acid is produced by a liquid-phase methanol carbonylation. Acetic acid is formed by the reaction between methanol and carbon monoxide which is catalysed by rhodium iodocarbonyl catalyst. The process diagram is shown in Figure 7. 

Monsanto developed the rhodium-catalysed process for the carbonylation of methanol to produce acetic acid in the late sixties. It is a large-scale operation employing a rhodium/iodide catalyst converting methanol and carbon monoxide into acetic acid. At standard conditions the reaction is thermodynamically allowed,... 

Reductive Carbonylation of Methanol. As discussed earlier, rhodium based catalysts are capable of catalyzing the reductive carbonylation of methyl acetate to ethylidene diacetate ( 1), as well as the carbonylation of methyl acetate to acetic anhydride (16). These reaction proceed only, wjjen, tjie reaction environment... 

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. 

The behaviour of the ruthenium catalysts is quite different from that previously reported for cobalt carbonyl catalysts, which give a mixture of aldehydes and their acetals by formylation of the alkyl group of the orthoformate (19). The activity of rhodium catalysts, with and without iodide promoters,is limited to the first step of the hydrogenation to diethoxymethane and to a simple carbonylation or formylation of the ethyl groups to propionates and propionaldehyde derivatives (20). 

Acetic Acid. Carbonylation of methanol is the most important reaction in the production of acetic acid.189-192 BASF developed a process applying C0I2 in the liquid phase under extreme reaction conditions (250°C, 650 atm).122 193 The Monsanto low-pressure process, in contrast, uses a more active catalyst combining a rhodium compound, a phosphine, and an iodine compound (in the form of HI, Mel, or T2).122 194—196 Methanol diluted with water to suppress the formation of methyl acetate is reacted under mild conditions (150-200°C, 33-65 atm) to produce acetic acid with 99% selectivity at 100% conversion. 

Two homogeneous metal complex water-gas shift catalyst systems have recently appeared 98, 99). The more active of these comes from our Rochester laboratory (99, 99a). It is composed of rhodium carbonyl iodide under CO in an acetic acid solution of hydriodic acid and water. The catalyst system is active at less than 95°C and less than 1 atm CO pressure. Catalysis of the water-gas shift reaction has been unequivocally established by monitoring the CO reactant and the H2 and C02 products by gas chromatography The amount of CO consumed matches closely with the amounts of H2 and C02 product evolved throughout the reaction (99). Mass spectrometry confirms the identity of the C02 and H2 products. The reaction conditions have not yet been optimized, but efficiencies of 9 cycles/day have been recorded at 90°C under 0.5 atm of CO. Appropriate control experiments have been carried out, and have established the necessity of both strong acid and iodide. In addition, a reaction carried out with labeled 13CO yielded the same amount of label in the C02 product, ruling out any possible contribution of acetic acid decomposition to C02 production (99). 

Finally, it should be mentioned that there is one important commercial application of the organic halide carbonylation. This is in the rhodium and methyl iodide-catalyzed conversion of methanol and carbon monoxide into acetic acid (25). The mechanism of the reaction appears to involve the oxidative addition of methyl iodide to the rhodium(I) catalyst followed by CO insertion and hydrolysis ... 

Acetic acid (CH3COOH) is a bulk commodity chemical with a world production of about 3.1 x 106 Mg/year, a demand increasing at a rate of +2.6% per year and a market price of US 0.44-0.47 per kg (Anon., 2001a). It is obtained primarily by the Monsanto or methanol carbonylation process, in which carbon monoxide reacts with methanol under the influence of a rhodium complex catalyst at 180°C and pressures of 30-40 bar, and secondarily by the oxidation of ethanol (Backus et al., 2003). The acetic fermentation route is limited to the food market and leads to vinegar production from several raw materials (e.g., apples, malt, grapes, grain, wines, and so on). 

Carbonylation of methanol has in recent years become a commercially important route for the production of acetic acid and methyl acetate. Industrial catalysts are at present homogeneous, based on cobalt and more recently rhodium compounds. The cobalt catalysts are less active 195) and require more severe operating conditions (i.e., 250°C, 650-750 atm) than the rhodium-based catalysts 196) (170-250°C, 7-14 atm). 

Acetica A process for making acetic acid by the heterogeneous carbonylation of methanol in a bubble column reactor. The catalyst is a rhodium carbonyl iodide, anchored by ion-pairing to a polyvinyl pyridine resin. Developed by Chiyoda Corporation and UOP and first described in 1998. Licensed to Guizhou Crystal Organic Chemical Group, China, in 2002 one plant was under construction in 2005. 

Chiyoda and UOP jointly developed an improved methanol carbonyl-ation process on the basis of this supported rhodium complex catalyst the process is called the Acetica process. This process for the production of acetic acid has found several industrial applications in Asia. The process description emphasizes the use of a three-phase reactor, a bubble column, or gas-lift reactor. The reactor column contains a liquid, a solid catalyst, and a bubbling gas stream containing CO efficient dissolution of the gas in the liquid is ensured by the design, which minimizes gas-liquid mass transfer resistance. 

It may be considered ironic that as early as 1969 a nearly complete description of the characteristic features of the subsequently presented LPO technology had been published by Monsanto researchers [5]. The company decided at that stage not to deal with hydroformylation any longer, but instead they concentrated on the development of the nowadays well-known acetic acid process (using modified rhodium carbonyl as catalyst) (cf. Section 2.1.2.1) [6]. 

The concept of co-carbonylation of methanol/methyl acetate mixtures was first introduced by BASF in the early 1950s, but the reaction chemistry was not fully developed to commercial realization [75]. Not until the mid-1980s, after the development of carbonylation processes to produce acetic acid and acetic anhydride, were co-carbonylation processes patented using homogeneous rhodium/iodine catalyst systems (Table 2) [2, 56]. The basic process concept is to manufacture acetic acid and acetic anhydride from methanol and carbon monoxide as the only raw materials and to generate methyl acetate within the process. Similiarly, the suitability of dimethyl ether as a raw material for the generation of the anhydride equivalent in addition to or as a substitute for methyl acetate was revealed by Hoechst [76]. To produce a small fraction of acetic acid besides acetic anhydride as the main product, the carbonylation of methyl acetate could be conducted with small amounts of water or methanol. This variant, first demonstrated by Hoechst [56], is practiced by Eastman Kodak [2]. 

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. 

Acetic anhydride is used in the manufacture of cellulose acetate-based film, cigarette filters, and plastics. Eastman Chemical developed a process that is based on gasification of coal in a Texaco gasifier to make synthesis gas which then is converted to methanol. The methanol is converted to methyl acetate by esterification with acetic acid and then carbonylated. The carbonylation process uses rhodium salt catalysts with ligands and an iodine promoter [30]. 

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