Ethylene hydroesterification

Iridium with tributylphosphine like Co and Ru, is inferior to Rh as an ethylene hydroesterification catalyst. Palladium acetate gives no reaction. Propylene and other higher olefins react extremely slowly, even under optimum Rh tributylphosphine catalytic conditions. 

Strictly related to catalytic reactions involving CO and H20 are reactions in which CO and alcohols, ROH, or CO and amines, R2NH, are used as building blocks. The catalytic addition of carbon monoxide and an alcohol to an olefin yields carboxylic esters (hydroesterification). Thus, the synthesis of methyl propionate from ethylene, CO, and methanol using a catalytic system composed of Ru3(CO)u and [PPh4]I (190°C, 20 bar C2H4, 45 bar CO, 2.5 hr, yield 74%, CT 1000) has been reported (323) ... 

Alkyl formates react with olefins to give the corresponding esters. The hydroesterification reaction is catalyzed by ruthenium clusters. Thus, methyl propionate is accessible from methyl formate and ethylene... 

Diols and polyols have also been used effectively as proton sources in hydroesterification. For example, ethylene glycol, 1-octene, Co2(CO)g, and in the molar ratio... 

Several other types of hydrocarboxylations and hydroesterifications have been conducted with rates and selectivity that are appropriate for the synthesis of fine chemicals and commodity chemicals. One target for hydroesterification has been methyl methacrylate, the monomer of polyfmethyl methacrylate), which is the polymer often called "acrylic". It is estimated that 2.1 million metric tons of methyl methacrylate was produced in 2005. Much of this material is produced from acetone cyanohydrin, but two alternative routes could involve catalytic carbonylation. The first route would involve the hydroesterification of methylacetylene, and this chemistry relates to the original route to methyl methacrylate by carbonylation of methylacetylene using nickel carbonyl as catalyst. The second route involves the sequence of ethylene hydoesterification, aldol addition of the resulting ester to formaldehyde, and dehydration. This sequence comprises Lucite s new "Alpha" process and is shown in Equation 17.33. The route to methyl methacrylate by hydrocarboxylation of ethylene produces water as the only byproduct. 

Table 17.3. Effect of catalyst structure on the activity and seiectivity for hydroesterification of ethylene.

Two mechanisms for the hydroesterification of alkenes have been considered. One pathway—the "alkoxide cycle"— begins with the insertion of CO into a metal alkoxide (Scheme 17.18) and the other—"the hydride cycle"— begins with the insertion of an alkene into a metal hydride (Scheme 17.19). The relative importance of the different pathways depends on the identity of the dative ligand. However, hydroesterification of ethylene with the bis(di-ferf-butylphosphinomethyl)benzene ligand is now generally accepted to occur through a palladium hydride. The mechanism of the hydroesterification of alkynes is less established, but is likely to occur by a sequence that shares some steps with the mechanism for the hydroesterifcation of alkenes. 

Interestingly, methyl formate was successfully used in the absence of carbon monoxide for the catalytic hydroesterification of ethylene by the complex [PdH(Cl)(PBu3)2], generated in situ by addition of 1 equiv of NaBHj to PdCl2(PBu3)2 (Eq. 

Hydroesterification of ethylene to methyl propionate using methanol (instead of water, above) with a Pd catalyst is an industrially valuable method developed by INEOS to produce methyl methacrylate (MMA), an important intermediate in industry (2 million tons/year) for polymer synthesis (mainly Plexiglass or Perpex , a crystal-clear artificial glass with high hardness, resistance to fracture, and chemical stability). ... 

It is important to note that the hydrocarboxylation and carbonylation catalytic cycles involve common intermediates, but there are clear differences. In the hydrocarboxylation reaction, there is no oxidative addition or reductive elimination step, and all the intermediates have Rh. Other Fe-, Ru-, Co-, Rh-, Ir-, Pd-, and Pt-based hydrocarboxylation and/or hydroesterification catalysts are also known. Eastman Chemical has reported a Mo(CO)g-catalyzed ethylene hydrocarboxylation process that involves a radical mechanism. 

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