Reductive carbonylation methanol

This process comprises passing synthesis gas over 5% rhodium on Si02 at 300°C and 2.0 MPa (20 atm). Principal coproducts are acetaldehyde, 24% acetic acid, 20% and ethanol, 16%. Although interest in new routes to acetaldehyde has fallen as a result of the reduced demand for this chemical, one possible new route to both acetaldehyde and ethanol is the reductive carbonylation of methanol (85). 

Rh(CO)2(acac)(dppp)] as a catalyst (where acac = acetylacetonate) gives high rates (100-200 turnovers h 1) and selectivities in the reductive carbonylation of methanol to acetaldehyde comparable to the best Co catalysts, but at a much lower temperature (140 °Q and pressure... 

Diphosphine ligands (e.g. dppe, dppp) were originally found, by Wegman and coworkers [43], to be effective ligands in the rhodium-catalysed reductive carbonylation of methanol to give acetaldehyde (Eq. 9) or ethanol (Eq. 10) ... 

For the synthesis of fine chemicals, carbonylation, reductive carbonylation, and oxidative carbonylation of methanol can be applied as outlined in Table II. 

Although ethanol can be derived directly from synthesis gas alone - see above - reductive carbonylation (homologation) starting with methanol as a feed has received considerable attention, due to rates of conversion and better selectivity (see special chapters in ref. 3, A,... 

Acetaldehyde Production by Reductive Carbonylation of Methanol, Methyl Ketals, and Methyl Esters... 

Acetaldehyde is obtained from the reaction of synthesis gas with methanol, methyl ketals or methyl esters. The reactions are carried out with an iodide-promoted Co catalyst at 180-200 °C and 2000-5000 psig. In comparing the various feedstocks, the best overall process to make acetaldehyde involves the reductive carbonylation of methyl esters. In this case, acetaldehyde selec-tivities are > 95% ut acceptable rates and conversion. 

The reductive carbonylation (Equation 1) and homologation (Equation 2) of methanol are reactions of considerable interest to the chemical industry (1). These reactions provide a route to... 

Me have studied the Co-I-PPh catalyzed reductive carbonylation of methanol, dimethyl ketalsf dimethyl carbonate and methyl esters ( 10 JL5 >2 ) 0 goal was to achieve high acetaldehyde... 

Reductive Carbonylation of Methanol. The reductive carbonylation of methanol (solvent free) was studied at variable I/Co, PPh,/I, temperature, pressure, synthesis gas ratio and methanol conversion (gas uptake) in the batch reactor, A summary of the results is given in Table I. In general, the acetaldehyde rate and selectivity increase with increasing I/Co. The PPh /I ratio has little effect except in run //7 where the rate is drastically reduced at I/Co =3.5 and PPh /I r 2. A good set of conditions is I/Co =3 5 and PPh /I = 1,T where the acetaldehyde rate and selectivity is 7.6 M/nr and 765 at 170 °C and 5000 psig. The effect of methanol conversion at these conditions is obtained by compearing runs 13, 1, 14, and 15. The gas uptake was varied from 14000 to 4000 psi, which corresponds to observed methanol conversions of 68% to 38 te. 

Methyl acetate is the principal by-product in the reductive carbonylation of methanol. As indicated in Table I, decreasing the Hp/CO increases the methyl acetate selectivity. In the limit of pure CO, methyl acetate is obtained in 90-95% selectivity. 

The overall response to the reaction variables is very similar in the carbonylation and reductive carbonylation reactions. This may indicate similar catalysts and reaction mechanisms. In the carbonylation reaction Co(CO) " was identified by its characteristic CO stretching frequency ( v(CO) r 1890 cm" as the dominant species present in high pressure infrared experiments carried out at 170 °C and 5000 psig. Similar results were obtained in the reductive carbonylation of methanol. It is known that Co(CO) " rapidly reacts with CH I to yield CH C(0)Co(C0) (J9) however, in the carbonylation and reductive carbonylation reactions acyl-cobalt complexes are not observed by infrared under catalytic conditions. This indicates that once formed, the acyl complex rapidly reacts as outlined by Equations 7 and 8. 

Methyl acetate probably originates from the reaction of methanol with the intermediate cobalt-acyl complex. The reaction leading to the formation of acetaldehyde is not well understood. In Equation 8, is shown as the reducing agent however, metal carbonyl hydrides are known to react with metal acyl complexes (20-22). For example, Marko et al. has recently reported on the reaction of ri-butyryl- and isobutyrylcobalt tetracarbonyl complexes with HCo(CO) and ( ). They found that at 25 °C rate constants for the reactions with HCo(CO) are about 30 times larger than those with however, they observed that under hydroformylation conditions, reaction with H is the predominant pathway because of the greater concentration of H and the stronger temperature dependence of its rate constant. The same considerations apply in the case of reductive carbonylation. Additionally, we have found that CH C(0)Co(C0) L (L r PBu, ... 

Table I. The Effect of Reaction Variables in the Reductive Carbonylation of Methanol ...

Relative to the reductive carbonylation of methanol, the added recycle step is a disadvantage with dimethyl ketals. This disadvantage is offset by the lower pressure of operation and the noncorrosive halide-free catalyst, which permits cheaper materials of construction. 

The single step conversion of methyl acetate to ethylidene diacetate is catalyzed by either a palladium or rhodium compound, a source of iodide, and a promoter. The mechanism is described as involving the concurrent generation of acetaldehyde and acetic anhydride which subsequently react to form ethylidene diacetate. An alternative to this scheme involves independent generation of acetaldehyde by reductive carbonylation of methanol or methyl acetate, or by acetic anhydride reduction. The acetaldehyde is then reacted with anhydride in a separate step. 

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 reductive carbonylation of methanol to acetaldehyde has been possible when catalyzed by cobalt carbonyl species. This represents a "non-ethylene" route to acetaldehyde. Though rhodium may be expected to be substantially more active than cobalt, it is undesirable since hydrogen incorporation is obviously not seen (see equation 20). 

Halcon has developed a new non-noble metal catalyst for methanol reductive carbonylation (32). It is formed under more moderate conditions (1200 psi, 120 C) and permits a selective reaction at only 1200-1800 psi of reaction pressure. Under these conditions, the catalyst s activity is comparable with noble metal catalyzed carbonylations. The conversion rate is 1.5-3.0 mol/l.hr. and acetaldehyde selectivity is 85%. In concentrated solutions, a considerable portion of product acetaldehyde (20-40%) is converted to its acetal. The acetal can be readily hydrolyzed back to acetaldehyde at 100-150 without catalyst (33). Acetal formation is actually beneficial through prevention of undesirable acetaldehyde condensation reactions. 

Reductive carbonylation in alkaline methanol solution of Na2[PtCl6] 6H20 gives the series of dianions [Pt3(CO)6]2 (n = 3-10) the value of n depends on the alkaline reagent and the experimental conditions.1 The lowest term of this series of inorganic oligomers, which has been isolated in the solid state, is the [Pt6(CO)12]2- dianion. Its reported synthesis is based on the reduction with lithium metal in tetrahydrofuran (THF) of Pt(CO)2Cl2, or of preformed [Pt3(CO)6]2 (n > 3).1,2... 

Izumi et al. (369) found that Keggin-type heteropolyanions containing Mo or V show a promoting effect in the reductive carbonylation of nitrobenzene by PdCl2 to form methyl N-phenylcarbamate in the presence of methanol (Eq. 44) ... 

More recently, reductive carbonylation of Na2PtCl6 6H20 in methanol, in the presence of alkali acetates or hydroxide, has been shown to proceed... 

The orange-red dianion [TtefCO) ]2-, which has also been obtained by reductive carbonylation in concentrated methanolic sodium hydroxide solution, is better synthesized by reducing preformed [Pt3(CO)6]n2- (n = 3, 4, or 5) with sodium or lithium metal in THF. Using Na/K alloy, the reduction goes still further to give the unstable pink dianion QPtsfCO) 6]2-(vco = 1950, 1745 cm-1), as yet not isolated in the solid state. 

Scheme 4.6 The sequence of reaction steps passed along the reductive carbonylation of [PtCy2- with alkali hydroxides in methanol...

The trinuclear Ru3(CO)12 can be used in combination with [NEtJCl to catalyze the selective reductive carbonylation of aromatic nitro compounds to carbamates. Thus, nitro benzene reacts in toluene with CO and methanol (160- 170°C, 82 bar, 5 hr) to give methyl JV-phenylcarbamate in 93% yield, the catalytic turnover being 92 ... 

A plausible mechanism for the reaction includes several organometallic species that are sensitive to reactive moieties elsewhere in the molecule. If a chloro, chloromethyl, or mesyloxymethyl substituent is attached vicinal to the 1,1 -dibromo moiety, efficient ring opening occurs prior to carbonylation and P,y- and y, -unsaturated acid derivatives are formed. Reductive carbonylation has also been achieved with 1,1-dibromocyclopropanes using an excess of pentacarbonyliron in dimethylformamide with added methanol or sodium methoxide, or cobalt(II) chloride and nickel(ll) cyanide under phase-transfer conditions in a carbon monoxide atmosphere. However, the yield of cyclopropanecarboxylic acid derivatives is low, and when pentacarbonyliron is used the amount of monobromides is fairly high. ... 

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