Oxidation carbonylation, route

A commercially attractive palladium catalyzed oxidative carbonylation route to adipic and sebacic acid has been developed which uses butadiene and the elements of synthesis gas as the raw... 

Oxidative carbonylation. The oxidative carbonylation route is shown in Eqs. (38)-(41). 

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). 

Aromatic polycarbonates are currently manufactured either by the interfacial polycondensation of the sodium salt of diphenols such as bisphenol A with phosgene (Reaction 1, Scheme 22) or by transesterification of diphenyl carbonate (DPC) with diphenols in the presence of homogeneous catalysts (Reaction 2, Scheme 22). DPC is made by the oxidative carbonylation of dimethyl carbonate. If DPC can be made from cyclic carbonates by transesterification with solid catalysts, then an environmentally friendlier route to polycarbonates using C02 (instead of COCl2/CO) can be established. Transesterifications are catalyzed by a variety of materials K2C03, KOH, Mg-containing smectites, and oxides supported on silica (250). Recently, Ma et al. (251) reported the transesterification of dimethyl oxalate with phenol catalyzed by Sn-TS-1 samples calcined at various temperatures. The activity was related to the weak Lewis acidity of Sn-TS-1 (251). 

The oxidative carbonylation reaction of enolizable ketones follows the general routes already illustrated for simple alkenes. Thus, a-methoxycarbonyl-ation may occur either by addition of a Cl - Pd - C02Me species to the enolic... 

This reaction should not be confused with hydrolytic dehalogenation, despite apparent similarities [58] although both hydrolytic and oxidative dehalogenation routes may produce the alcohol and carbonyl derivatives, the product that is formed as the primary or secondary metabolite is different in the two pathways. Further, it is clear that the enzymes involved cannot be identical. 

While the direct carbonylation is well accepted by industry, the reductive and oxidative carbonylations are still in the research and development stage. Using Texaco technology (j, 7/ ) the combined synthesis of ethene and ethanol is feasible via homologation of acids according to Figure 3. Ethene can also be obtained from the reductive carbonylation of methyl acetate to ethyl acetate followed by pyrolysis (2 ). Both routes, so far, lack selectivity. 

A phosgene-free route to aromatic isocyanates, such as M DI and TDI, was reported by Fernandez et al. [42] (Scheme 5.7) According to the patent, the one-pot synthesis involves the use of an immobilized Schiff base type of ligand catalyst that facilitates the oxidative carbonylation of aromatic amines to the corresponding isocyanates. However, 2,2,2-trifluoroethanol (TFE), 1,2-dichlorobenzene, and carbon monoxide were used in this process, so this would not be a totally environmentally friendly process even if these reagents could be recycled and reused. 

A few of these imply the carbonylation of nitroaromahc substrates [41], or the oxidative carbonylation of amines [42], or the reaction of amines with carbonic acid diesters [11] that are currently available, even on an industrial scale, through phosgene-free routes [43]. 

Methyl methacrylate (MMA) is an important commodity since it is polymerized to give poly methylmethacrylate (PMMA), a strong, durable and transparent polymer sold under the trade-names Perspex and Plexiglas. Since the conventional routes to MMA involve either the reaction of acetone with HCN to give the cyanohydrin (which has environmental problems), or the oxidation of isobutene, alternative carbonylation routes to MMA are being developed. One of these is the Lucite Alpha process which is claimed to decrease production costs by ca. 40%. This first synthesizes methyl propionate by a methoxycarbonylation of ethylene (Equation 23), using a palladium catalyst with very high (99.8%) selectivity. In the second step, MMA is formed in 95% selectivity by the reaction of methyl propionate with formaldehyde (Equation 24). 

This process was elaborated as a heterogeneously catalyzed variation by Asahi Chemicals (Japan) in order to open a new route to diisocyanates, not depending on the use of phosgene [120, 134]. Ethyl phenylcarbamate, which in a first step is obtained by catalytic oxidative carbonylation of aniline, CO, oxygen, and ethanol (eq. (17)), is condensed with aqueous formaldehyde to yield methylene diphenyl diurethane. Thermal decomposition leads to methylene diphenyl diisocyanate (MDI), which is one of the most important intermediates for the industrial manufacture of polyurethanes (eq. (18)). The yields and selectivities of the last reaction step seem to be the main reasons why this process is still inferior to the existing ones. 

Of specific potential are several processes which presently experience (or even surpass) the pilot-plant stage vinyl acetate from syngas, precursors of polymers such as polycarbonate and polyurethanes via reductive or oxidative carbonylation, methyl mediacrylates and adipic acid through alternative routes, polypropene and COCs (cf. Section 4.1.14) by means of metallocenes (cf. Section 2.3.1.5) - new routes have been opened in all these cases. The last-named example emphasizes in an almost classical way the principle of tailor-making novel, optimized, homogeneous catalysts. Chapter 3 should again be consulted for details. 

The release of phosgene and toxic solvent has stimulated the development of novel processes. The BASF process for MDI, that employs high temperatures and pressures to increase the rate of reaction, does not release phosgene. Catalytic routes, via oxidative carbonylation of aniline to methyl A-phenyl carbamate (12), using palladium metal... 

Therefore, any possible use of DMC as substitute of phosgene should be based on a different synthesis of DMC, not involving phosgene. Non-phosgene alternative routes for DMC production, basically, have relied on the reaction of methanol with carbon monoxide (oxidative carbonylation) or with carbon dioxide (direct carboxyl-ation with CO2, or indirect carboxylation, using urea or alkylene carbonates as CO2 carriers) (Figure 1.10) [72]. 

Oxidative carbonylation of methanol to DMC, which takes place in the presence of suitable catalysts, has been developed industrially by EniChem (later Polimeri Europa). Carbonylation/transesterification of ethylene oxide to DMC via ethylene carbonate is also an attractive route. However, this route is burdened by the complexity of the two-step process, the co-production of ethylene glycol (even if it... 

The preparation of l,3-oxathiolan-2-one (32) by reaction of 2-thioethanol with phosgene was reported at an early date <4i RTC453> and more recent routes to the same compound involve oxidative carbonylation of di(2-hydroxyethyl)disulfide in the presence of Se and EtsN <74TL2899>, and reaction of 2-thioethanol with diethyl carbonate in the presence of H2SO4 <83URP1016286>. 

Another manufacturing process [9l] for 4,4 -diphenylmethyl diisocyanate (MDI) was introduced by Asahi Chemical. In contrast to the ARCO route, aniline is used for the carbonylation to N-phenylethyl urethane otherwise, the same steps are followed. The oxidative carbonylation of aniline is done in the presence of metallic palladium and an alkali iodide promoter at 150-180°C and 50-80 bar. The selectivity is more than 95% with a 95% aniline conversion ... 

Formation of the 17/-[2]benzopyran system by a 6-endo-dig cyclisation is favoured over the 5-exo-dig route to isobenzofurans in the Pd-catalysed oxidative carbonylation of... 

Because of the toxicity of phosgene, research on nonphosgene routes to isocyanates and polycarbonates has intensified over the past decade. Eni-Chem of Italy has commercialized a process to manufacture dimethyl carbonate (DMC) by oxidative carbonylation of methanol. Dimethyl carbonate can be used as an intermediate for the production of polycarbonates. A description of the nonphosgenation chemistry for producing DMC and polycarbonates is included in Section II.A in this chapter. 

MDI by Carbonylation. Nonphosgene production of MDI can be accomplished by forming urethanes that undergo decomposition to isocyanates. Two routes have been demonstrated for the formation of urethanes using carbon monoxide, reductive carbonylation and oxidative carbonylation. However, there is a disadvantage in the reductive carbonylation route because two-thirds of the carbon monoxide required for the reaction forms... 

CO2, which must be removed from the product gas. The oxidative carbonyl-ation route uses carbon monoxide and oxygen in the presence of an alcohol to form intermediates that are converted to urethanes. This uses carbon monoxide feedstock more effectively and shows more promising economics. 

TDI by Carbonylation. Two routes have been demonstrated for the conversion of dinitrotoluene to TDI by carbonylation. TDI can be formed by either reductive or oxidative carbonylation. The processes, catalysts, and operating conditions are similar, as are the advantages and disadvantages of each route. 

Oxidative carbonylation of alcohols in the presence of CO provides an economically viable route to dialkyl carbonates and/or oxalates (Eqs. (8.4) and (8.5)), both of which have important industrial applications. Dialkyl carbonates (e.g., dimethyl carbonate, propylene carbonate) are excellent solvents for a variety of organic substances [14]. Dialkyl oxalates have utility as solvents, C2 building blocks in fine chemicals synthesis, and intermediates in the manufacture of oxamide (as a fertilizer) [15]. Hydrogenation of dialkyl oxalates provides an alternative route to ethylene glycol that is independent of oil-derived resources [15,16]. 

A system has been described for the formation of dimethyl carbonate via the phosgene-free route of oxidative carbonylation of methanol [(Eq. (8)] catalyzed by PdCl2 in [BMIMKPFjj (110 C, total pressure 10 MPa, 1 h) [48]. Conversions were generally low (< 7%) and did not improve with increased reaction time, although the selectivity to dimethyl carbonate dropped. Dimethoxymethane was the major product but selectivities of dimethyl carbonate of up to 25% were possible with an O2/CO2 ratio of 29 71. Neither the pressure nor the temperature had dramatic effects upon the yield or selectivity, although the reaction was slower at lower temperatures. The reaction was repeated three times under the optimum conditions in a repetitive batch process. The rate remained constant, but there was a slight drop in selectivity. 

Methanol is also an important starting material for further syntheses. Interesting new routes could be based on reactions such as carbonylation, reductive carbonyla-tion, and oxidative carbonylation. Another example is the homologization of methanol to ethanol via acetaldehyde. 

However, the limit for the use of DMC in industrial practice was in its preparation, far from eco-friendly, that involved the reaction of methanol with phosgene. Among the alternative phosgene-free routes to DMC considered in the last two decades, the most attractive is the metal ion-catalyzed oxidative carbonylation of methanol, set up by EniChem in 1983 (2). This technology is now currently used in the industry for the production of DMC. 

Ichikawa et al (35,36) prepared tertiary butyl substituted FePc in zeolite Y via a modified form of the carbonyl route. Zeolite occluded Fe203 was prepared through oxidation and subsequent reduction of adsorbed HFe3(CO)-j. . The complex was synthesized with 4-tButyl-1,2-dicyanobenzene. The disadvantages inherent to the carbonyl method remain present. 

Another route to carbamates has been studied a-fter that dimethylcarbonate was available via the oxidative carbonyl at i on o-f methanol, catalyzed by copperU) chloride C ] ... 

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