Oxidative carbonylation of methanol

The oxidative carbonylation of alcohols and phenols to carbonates can be catalyzed by palladium or copper species [154-213]. This reaction is of particular practical importance, since it can be developed into an industrial process for the phosgene-free synthesis of dimethyl carbonate (DMC) and diphenyl carbonate (DPC), which are important industrial intermediates for the production of polycarbonates. Moreover, DMC can be used as an eco-friendly methylation and carbonylation agent [214,215]. The industrial production of DMC by oxidative carbonylation of methanol has been achieved by Enichem [216] and Ube [217]. 

First of all, DMC is a nontoxic compound since the middle 1980s, in fact, it has not been produced from phosgene, but by catalytic oxidative carbonylation of methanol with oxygen through a process developed by Enichem (Italy) and UBE Industries (Japan) (Scheme 4.3) ... 

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

The oxidative carbonylation of methanol to dimethyl carbonate has found small industrial application (26-27). The reaction can be carried out in two steps following Equation 10 and 11 or also in one step. 

Dimethyl Carbonate. An industrial process to manufacture dimethyl carbonate through the oxidative carbonylation of methanol catalyzed by cuprous chloride has been developed and commercialized by EniChem.197,198 The reaction occurs in two steps. Cupric methoxy chloride is formed in the first oxidation step [Eq. (7.21)], which is then reduced to yield dimethyl carbonate and regenerate cuprous chloride [Eq. (7.22)] ... 

In the presence of trace amounts of water, the tetrameric p,2-oxo complex (182) in 1,2-dimethoxyethane is transformed into a p, -oxo tetrameric complex (183 equation 254), characterized by an X-ray structure.574 In contrast, (182) 572,575 is inactive towards the oxidation of phenols. The reaction of N,N,N, AT -tetramethyl-l,3-propanediamine (TMP) with CuCl, C02 and dioxygen results in the quantitative formation of the /z-carbonato complex (184 equation 255).s76 This compound acts as an initiator for the oxidative coupling of phenols by 02. 6 Such jz-carbonato complexes, also prepared from the reaction of Cu(BPI)CO with 02 [BPI = 1,3 bis(2-(4-methyl-pyridyl)imino)isoindoline],577 are presumably involved as reactive intermediates in the oxidative carbonylation of methanol to dimethyl carbonate (see below).578 Upon reaction with methanol, the tetrameric complex (182 L = Py X = Cl) produces the bis(/z-methoxo) complex (185 equation 256), which has been characterized by an X-ray structure,579 and is reactive for the oxidatiye cleavage of pyrocatechol to muconic acid derivatives.580,581... 

Oxidative Carbonylation of Methanol to Dimethyl Carbonate and Dimethyl Oxalate... 

Extensive efforts to achieve the oxidative carbonylation of methanol in the gas phase using CuCl or Cu(OCH3)Cl complexes supported on active carbon have been undertaken to Dow Chemicals [49, 50], Because of the rapid catalyst deactivation this method has not become an alternative to the Enichem process. 

King, S.T. Reaction mechanism of oxidative carbonylation of methanol to dimethyl carbonate in Cu-Y zelolite. J. Catal. 1996, 161, 530-538. 

Dimethyl carbonate (DMC) is a versatile compound that is an attractive alternative to phosgene [68, 69] and which could be synthesized in a eco-friendly process by catalytic oxidative carbonylation of methanol with oxygen (Enichem, Italy [70] and... 

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... 

In-situ infrared (IR) study of DMC synthesis from the gas-solid oxidative carbonylation Figure 3 shows the IR spectrum of DMC synthesis from the oxidative carbonylation of methanol over 5 wt% CUCI2/HZSM-5. The IR intensity of DMC s carbonyl band at 1766 and 1789 cm was leveled off after 2 min of reaction. A 8.1% yield of DMC was achieved. The key adsorbates observed are Cu+(CO)Cl at 2080 cm and Cu2(CO)4Cl2 at 2052 cm. ... 

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. 

Oxidative carbonylation of methanol to dimethyl carbonate. Dimethyl carbonate (DMC) is made industrially by the phosgenation of methanol, but it can also be produced without the use of phosgene by the oxidative carbonylation of methanol. Enichem has commercialized a process for dimethyl carbonate based on oxidative carbonylation [25]. 

Cu-Catalyzed Oxidative Carbonylation of Methanol for the Synthesis of Dimethyl Carbonate... 

Figure 5.1 Illustration of chloride-free catalysts for the oxidative carbonylation of methanol (a) 2,2 -bipyrimidine-Cu(OAc)2 and (b) a Co"-Schiff base complex.

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. 

Reactions that require phosgene are dangerous, and dimethyl carbonate (DMC) 33 is the most promising phosgene substitute. Current industrial processes for DMC synthesis are oxidative carbonylation of methanol and transesterification of ethylene carbonate with methanol. Hence, the direct reaction of CO2 and methanol (Scheme 58) is regarded as an attractive, next-generation process, but the limitation... 

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. 

Oxidative carbonylation of methanol to dimethyl carbonate PdClj-CuCl Ugo et al. (1980)... 

Dimethylcartx)nate (DMC), a non toxic, non polluting chemical, is achieving increasing importance as a versatile intermediate and product. Of the several synthetic routes to DMC that are available, oxidative carbonylation of methanol appears to be the most attractive. This route, coupled with the use of cuprous chloride as the catalyst led to the development of an industrially viable process, successfully used by EniChem Synthesis. Recent developments allow easy scale up to large capacity plants. 

To avoid the use of the extremely toxic chemical, phosgene, several alternative routes have been considered based on the use of carbon monoxide (oxidative carbonylation) or carbon dioxide (through direct or indirect carboxylation). The two most attractive routes for industrial syntheses were found to be oxidative carbonylation of methanol in the presence of a suitable catalyst (eq.2)... 

Alternative technological implementations of the oxidative carbonylation of methanol include the development of vapor phase processes over heterogeneous supported catalysts (27-22), such as CuClj on active carbon. 

DMC is an environmentally safe reagent now produced by the oxidative carbonylation of methanol (Equation 1) by Enichem (Italy) (6). 

The oxidative carbonylation of methanol to DMC, which takes place in the presence of suitable catalysts, has been developed industrially. 

Another route to carbanrates has been studied after dimethyl carbonate was available via the oxidative carbonylation of methanol, catalysed by copper(I) chloride (eq. 9) [13] ... 

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