Carbonylation, of ethylene

Sometimes, keto esters are formed by successi e carbonylation. Carbonylation of ethylene in an alcohol affords propionate as the main product, accompanied by a small amount of 4-oxohexanoate (18)[3]. The homo-... 

Oxidative Carbonylation of Ethylene—Elimination of Alcohol from p-Alkoxypropionates. Spectacular progress in the 1970s led to the rapid development of organotransition-metal chemistry, particularly to catalyze olefin reactions (93,94). A number of patents have been issued (28,95—97) for the oxidative carbonylation of ethylene to provide acryUc acid and esters. The procedure is based on the palladium catalyzed carbonylation of ethylene in the Hquid phase at temperatures of 50—200°C. Esters are formed when alcohols are included. Anhydrous conditions are desirable to minimize the formation of by-products including acetaldehyde and carbon dioxide (see Acetaldehyde). 

The elimination of alcohol from P-alkoxypropionates can also be carried out by passing the alkyl P-alkoxypropionate at 200—400°C over metal phosphates, sihcates, metal oxide catalysts (99), or base-treated zeoHtes (98). In addition to the route via oxidative carbonylation of ethylene, alkyl P-alkoxypropionates can be prepared by reaction of dialkoxy methane and ketene (100). 

Propionic acid is accessible through the Hquid-phase carbonylation of ethylene over a nickel carbonyl catalyst (104), or via ethylene and formic acid over an iridium catalyst (105). Condensation of propionic acid with formaldehyde over a supported cesium catalyst gives MAA directiy with conversions of 30—40% and selectivities of 80—90% (106,107). Catalyst lifetime can be extended by adding low levels (several ppm) of cesium to the feed stream (108). 

Succinic acid diesters are also obtained by one-step hydrogenation (over Pd on charcoal) and esterification of maleic anhydride dissolved in alcohols (40) carbonylation of acrylates in the presence of alcohols and Co complex catalysts (41—43) carbonylation of ethylene in alcohol in the presence of Pd or Pd—Cu catalysts (44—50) hydroformylation of acetylene with Mo and W complexes in the presence of butanol (51) and a biochemical process from dextrose/com steep Hquor, using Jinaerobiumspirillum succiniciproducens as a bacterium (52). 

Rhodium catalyzed carbonylations of olefins and methanol can be operated in the absence of an alkyl iodide or hydrogen iodide if the carbonylation is operated in the presence of iodide-based ionic liquids. In this chapter, we will describe the historical development of these non-alkyl halide containing processes beginning with the carbonylation of ethylene to propionic acid in which the omission of alkyl hahde led to an improvement in the selectivity. We will further describe extension of the nonalkyl halide based carbonylation to the carbonylation of MeOH (producing acetic acid) in both a batch and continuous mode of operation. In the continuous mode, the best ionic liquids for carbonylation of MeOH were based on pyridinium and polyalkylated pyridinium iodide derivatives. Removing the highly toxic alkyl halide represents safer, potentially lower cost, process with less complex product purification. 

Recently, Eastman Chemical Company reported that ionic liquids can be successfully employed in a vapor take-off process for the carbonylation of methanol to acetic acid in the presence of rhodium and methyl iodide (3). While attempting to extend this earlier work to the carbonylation of ethylene to propionic acid, we discovered that, when using ionic liquids as a solvent, acceptable carbonylation rates could be attained in the absence of any added alkyl iodide or hydrogen iodide (4). We subsequently demonstrated that the carbonylation of methanol to acetic acid could also be operated in the absence of methyl iodide when using ionic liquids (5). 

In this manuscript, we will chronicle the discoveiy and development of these non-alkyl halide containing processes for the rhodium catalyzed carbonylation of ethylene to propionic acid and methanol to acetic acid when using ionic liquids as solvent. 

Ethylene Carbonylation. The classical rhodium catalyzed carbonylation of ethylene to propionic acid (Eqn. 1) used ethyl iodide or HI as a co-catalyst (6). In the presence of excess ethylene and CO the process could proceed further to propionic anhydride (Eqn. 2). While additional products, such as ethyl propionate (EtC02Et), diethyl ketone (DEK), and ethanol were possible (See Eqns. 3-5), the only byproduct obtained when using a rhodium-alkyl iodide catalyst was small amounts (ca. 1-1.5%) of ethyl propionate. (See Eqns. 3-5.)... 

Unfortunately, when the carbonylation of ethylene with a rhodium-ethyl iodide catalyst was operated in ionic liquid media generated the product mixture now contained a significant amoimt of EtC02Et (15-35%). (See Table 37.1.) Unless this selectivity issue was resolved, the carbonylation of ethylene in ionic liquids would have been imtenable. 

Closer examination of the mechanism for the Rh catalyzed carbonylation of ethylene provides a rationale for the poor selectivity. The mechanism for the carbonylation of ethylene (Scheme 37.1) is well known (6) and proceeds via two simultaneously operating mechanisms which generate a common EtRh(CO)2l2 intermediate which rapidly reacts with iodide (Eqn. 10) to generate EtRh(CO)2l3 . The first, and predominant, mechanism is a hydride mechanism (Eqns. 6-8 below) in which the proton required for the formation of HRh(CO)2l2 and initiation of the... 

It appeared that, we needed to limit or omit the ethyl iodide if we were going to operate the ethylene carbonylation in ionic liquids. Unfortunately, the previous literature indicated that EtI or HI (which are interconvertible) represented a critical catalyst component. Therefore, it was surprising when we found that, in iodide based ionic liquids, the Rh catalyzed carbonylation of ethylene to propionic acid was still operable at acceptable rates in the absence of ethyl iodide, as shown in Table 37.2. Further, we not only achieved acceptable rates when omitting the ethyl iodide, we also achieved the desired reduction in the levels of ethyl propionate. More importantly, when the reaction products were analyzed, there was no detectable ethyl iodide formed in situ. However, we should note that we now observed traces of ethanol which were normally undetectable in the earlier Ed containing experiments. 

The rhodium catalyzed carbonylation of ethylene and methanol can be conducted in the absence of added alkyl halide if the reactions are conducted in iodide based ionic liquids or molten salts. In the case of ethylene carbonylation, the imidazolium iodides appeared to perform best and operating in the absence of ethyl iodide gave improved selectivities relative to processes using ethyl iodide and ionic hquids. In the case of... 

C2 route Ethylene, CO, H2, H2CO Carbonylation of ethylene to BASF... 

Alpha process C2H4, CO, CH3OH, H2CO Catalytic carbonylation of ethylene to Lucite (to become... 

Acrylic acid can be prepared by the catalytic oxidative carbonylation of ethylene or by heating formaldehyde and acetic acid in the presence of KOH. 

Propanediol is produced either from the reductive hydration of acrolein (Degussa-DuPont process), or through reductive carbonylation of ethylene oxide (Shell process), or through fermentation of glucose via glycerol (DuPont-Genencor process). 

Sometimes, keto esters are formed. Carbonylation of ethylene in alcohol affords propionate (14) as a main product, accompanied by a small amount of 4-oxohexanoate (15) [3]. Keto esters are obtained by the carbonylation of some dienes via insertion of alkene to an acylpalladium intermediate [11]. Carbonylation of 1,5-COD (16) in alcohols affords the mono- and diesters 17 and 18 [12], On the other hand, bicyclo[3,3,l]-2-nonen-9-one (20) is formed in 40% yield in THF by the intramolecular insertion of the alkene to the acylpalladium bond in 19 [13],... 

While the direct carbonylation of ethylene to acrolein H2C=CHCHO is mildly endothermic, it becomes exothermic on addition of triethylorthoformate ... 

Discussion Point DP4 The palladium-catalyzed carbonylation of ethylene both to methyl propionate and to polyketones use weakly coordinating anions to achieve high activity. Discuss the features of the catalytic mechanism which give rise to this effect. 

The alkene carbonylation reaction is not always quite so straightforward thus the carbonylation of ethylene in the presence of an alcohol ROH can give, with a palladium or nickel catalyst, the 7-ketocaproic ester, in addition to the expected propionic ester. The formation of the 7-ketocaproic ester can be rationalized on the basis of the following ligand migration sequence, which... 

Zoeller and coworkers at Eastman Chemical Company Research Laboratories have reported an efficient system for the carbonylation of ethylene based on a iodide-promoted... 

BASF is the only producer of propionic acid by the carbonylation of ethylene, which is reacted exothermically AH - -64.5 kJ/mol) with carbon monoxide and water. Nickel chloride was patented as early as 1943 as a catalyst for the carbonylation of ethylene [8], For the industrial-scale process, however, a halogen-free system is used [9, 10]. Propionic acid is formed according to eq. (2). 

For the purpose of completeness, the synthesis of propionic acid from its anhydride by hydrolysis should be mentioned here. In principle, when the carbonylation of ethylene is conducted in propionic acid instead of water as a solvent, the reaction product is the anhydride (eq. (14)). 

The production of carboxylic acids other than propionic acid by carbonylation is of little industrial relevance today. In principle the same catalytic systems that can be used for the carbonylation of ethylene (or any other adequate equivalent) to propionic acid are applicable for the synthesis of the higher carboxylic acids from olefins [32]. 

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