Iodide catalyst

Acetic acid from methanol by the Monsanto process, CH3OH -1-CO CH3COOH, rhodium iodide catalyst, 3 atm (44 psi), 150°C (302°F), 99 percent selectivity of methanol. 

In 1988, Linstrumelle and Huynh used an all-palladium route to construct PAM 4 [21]. Reaction of 1,2-dibromobenzene with 2-methyl-3-butyn-2-ol in triethylamine at 60 °C afforded the monosubstituted product in 63 % yield along with 3% of the disubstituted material (Scheme 6). Alcohol 15 was then treated with aqueous sodium hydroxide and tetrakis(triphenylphosphine)palladium-copper(I) iodide catalysts under phase-transfer conditions, generating the terminal phenylacetylene in situ, which cyclotrimerized in 36% yield. Although there was no mention of the formation of higher cyclooligomers, it is likely that this reaction did produce these larger species, as is typically seen in Stephens-Castro coupling reactions [22]. 

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. 

Zinc iodide catalysts are also known. Desulfonylative iodination of naphthalenesulfonyl chlorides has been carried out by treatment with zinc iodide in the presence of a palladium(II) catalyst.642... 

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) ... 

It was discovered by Monsanto that methanol carbonylation could be promoted by an iridium/iodide catalyst [1]. However, Monsanto chose to commercialise the rhodium-based process due to its higher activity under the conditions used. Nevertheless, considerable mechanistic studies were conducted into the iridium-catalysed process, revealing a catalytic mechanism with similar key features but some important differences to the rhodium system [60]. 

In 1996, BP Chemicals announced a new methanol carbonylation process, Cativa , based upon a promoted iridium/iodide catalyst which now operates on a number of plants worldwide [61-69]. Promoters, which enhance the catalytic activity, are key to the success of the iridium-based process. The mechanistic aspects of iridium-catalysed carbonylation and the role of promoters are discussed in the following sections. 

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,... 

The robust nature of the rhodium-iodide catalyst is also revealed in reactions with ortho-halo phenols that proved to be problematic with the first-generation catalyst system (Section 9.3.1). By employing the [Rh(PPF-P Bu2)I] catalyst, complete conversion is obtained with 2-bromophenol to give 6 in 94% yield, and with 95% enantiomeric excess after only 1.5 h of reaction time at 1 mol% catalyst loading (Scheme 9.3) [11]. The ready availability of these ring-opened compounds has been utilized to prepare enan-tiomerically enriched benzofurans 7. 

Employing protic and halide additives can effectively reverse the deleterious effect with aliphatic amines [8, 11]. The optimum results are obtained when ammonium iodide is employed as the addihve in combination with the second-generation rhodium-iodide catalyst. Under these conditions, a variety of aliphatic amines can be used to generate the aminotetrahn products in high yields and with excellent enantiomeric excess (Scheme 9.4). From a technical perspective, ammonium iodide benefits from being a combined proton and iodide source that is air-stable and nonhygroscopic. 

Adipic acid can also be made from THF, obtained from furfural. It is carbonylated in the presence of nickel carbonyl-nickel iodide catalyst. Furfural is a chemurgic product obtained by the steam-acid digestion of corn cobs, oat hulls, bagasse, or rice hulls. 

Carbonylation of acetic acid to higher carboxylic acids can occur in presence of ruthenium/iodide catalysts. The reaction involves reduction and several carbonylation steps. The overall reaction may be written as follows ... 

Acetic acid has been generated directly from synthesis gas (CO/H2) in up to 95 wt % selectivity and 97% carbon efficiency using a Ru-Co-I/Bu4PBr "melt" catalyst combination. The critical roles of each of the ruthenium, cobalt and iodide catalyst components in achieving maximum selectivity to HOAc have been identified. Ci Oxygenate formation is observed only in the presence of ruthenium carbonyls [Ru(C0)3l3] is here the dominant species. Controlled quantities of iodide ensure that initially formed MeOH is rapidly converted to the more reactive methyl iodide. Subsequent cobalt-catalyzed carbonylation to acetic acid may be preparatively attractive (>80% selectivity) relative to competing syntheses where the [00(00)4] concentration is optimized that is, where the Co/Ru ratio is >1, the syngas feedstock is rich in 00 and the initial iodide/cobalt ratios are close to unity. 

It is clear that ruthenium-cobalt-iodide catalyst dispersed in low-melting tetrabutylphosphonium bromide provides a unique means of selectively converting synthesis gas in one step to acetic acid. Modest changes in catalyst formulation can, however, have profound effects upon liquid product composition. 

The reaction of dimethyl carbonate with synthesis gas requires a cobalt-iodide catalyst and operating conditions of 180 C and 4000 psig. The acetaldehyde rate approaches 30 M/hr with selectivities greater than 85%. The productivities are much better than with methanol however, recycle of the CO and methanol back to dimethyl carbonate is very difficult ... 

Thus the selected iodide catalyst, TOP18, has good catalytic activity, selectivity, and stability, it is readily soluble in 2,5-DHF and in warm alkane solvents. As a... 

In the decomposition of hydrogen peroxide, the iodide catalyst reacts in the first elementary step, and it is regenerated in the second step. 

The method has been applied by the submitters2 to the preparation of cyclohexylmethylpropiolaldehyde diethyl acetal (54% yield) from cyclohexylmethylacetylene and triethyl orthoformate of phenylethynyl n-butyl dimethyl ketal (40% yield) from phenylacetylene and trimethyl -orthovalerate and of phenylethynyl methyl diethyl ketal (34% yield) from phenylacetylene and triethyl orthoacetate. w-B utylpropiolaldehyde diethyl acetal was isolated in 32% yield by heating an equimolar mixture of 1-hexyne and triethyl orthoformate containing catalytic amounts of a zinc chloride-zinc iodide catalyst under autogenous pressure at 190° for 3 hours. 

Dialkyl sulfates and trialkyl phosphates will also undergo reaction with lead metal at elevated temperatures, preferably in the presence of an iodide catalyst, to form R4Pb i">. 

Recently, a new process for the conversion of ethylene to ethylene glycol has been developed.2243 Oxidation of ethylene by molecular oxygen in acetic acid, in the presence of a manganese acetate-potassium iodide catalyst, gives ethylene glycol diacetate in 98% selectivity ... 

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