Methane oxidative carbonylation

Although turnover of the catalyst is low, even unreactive cyclohexane[526] and its derivatives are oxidatively carbonylated to cyclohexanecarboxylic acid using KiS Og as a reoxidant in 565% yield based on Pd(II)[527]. Similarly, methane and propane are converted into acetic acid in 1520% yield based on Pd(II) and butyric acid in 5500% yield [528],... 

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). 

Considerable challenges still remain in the development of new carbonylation processes for acetic acid manufacture. For example, all of the current processes use iodide compounds, leading to corrosive HI and the need for expensive materials for plant construction. An iodide-free system could potentially impart considerable benefit. Other long term goals include the selective direct conversion of syn-gas or oxidative carbonylation of methane to acetic acid. Organometallic chemists are certain to play a crucial role if these targets are to be achieved. 

Even aliphatic hydrocarbons are susceptible to oxidative carbonylation. From an industrial point of view, the most important process concerns the direct conversion of methane into acetic acid. This transformation has been achieved with Rh(III)-based catalysts using oxygen as the oxidizing agent [149-153], and it is still object of investigations aimed at developing more efficient catalytic systems working under mild conditions. 

Oxidative carbonylation of methane to acetic acid is one of the pursued ways to solve the fundamental problem of direct methane utilization. Partly aqueous systems with RhCU-HCl-KI catalyst mixture were applied with some success for this purpose. However, the reaction proceeds faster in acetic acid as solvent, containing only a small percentage of water [34]. 

Organic constituents that may be found in ppb levels in WP/F smoke include methane, ethylene, carbonyl sulfide, acetylene, 1,4-dicyanobenzene, 1,3-dicyanobenzene, 1,2-dicyanobenzene, acetonitrile, and acrylonitrile (Tolle et al. 1988). Since white phosphorus contains boron, silicon, calcium, aluminum, iron, and arsenic in excess of 10 ppm as impurities (Berkowitz et al. 1981), WP/F smoke also contains these elements and possibly their oxidation products. The physical properties of a few major compounds that may be important for determining the fate of WP/F smoke in the environment are given in Table 3-3. 

The first oxidative carbonylation reactions (cf. Section 2.1.2.5) with methane used superacid catalysts to perform the carbonylation in a Koch-type reaction which involved protolytic oxidation of methane to the methyl cation (eq. (29) [137]) ... 

In addition to Sen s work on the Rh-catalyzed oxidative carbonylation of methane, Grigoryan has also reported a similar reaction in acetic acid [45]. Predictably, the reaction rate is between that observed in pure water and in the perfluoro-... 

Rest and Graham reported in 1984 that the metal carbonyl complexes CpRh(CO)2, CpIr(CO)2, and Cp Ir(CO)2 can be deposited in methane matrices at 12 K and irradiated to give the corresponding methane oxidative addition products [28]. In addition, the dihydride CpIr(CO)H2 could be irradiated in a methane/argon matrix to generate CpIr(CO)(CH3)H by an alternative route [29]. While the dicarbonyl compounds were not efficient producers of the coordinatively unsaturated intermediate, Perutz found that CpRh(CO)(C2H4) lost... 

These oxidative carbonylations also occur with alkanes, although with low conversions of alkane and relatively low turnover numbers. Fujiwara reported that cyclohexane reacts with CO and K S Oj in the presence of palladium acetate and copper acetate in trifluoroacetic acid to form cyclohexane carboxylic acid with about 20 turnovers and about 4% yield based on alkane (Equation 18.24). Fujiwara also reported the carboxylation of methane with KjSjOj as oxidant with V(0)(acac)j as catalyst (Equation 18.25). This reaction occurred in 93% yield based on methane and with 18 turnovers. Sen reported a palladium(II)-catalyzed oxidative carbonylation of methane with hydrogen peroxide as the oxidant. Subsequently, he showed that RhClj catalyzes the conversion of methane, CO, and oxygen to acetic acid at 100 °C in water (Equation 18.26). Periana has reported a somewhat related transformation of methane to acetic acid, although the reaction is conducted in the absence of CO, and both carbon atoms of the acetic acid arise from methane (Equation 18.27). In this case, the CO appears to arise from oxidation of the methaiie, as shown in Scheme 18.5. 

An even cheaper feedstock than ethane is methane. A direct reaction from methane to acetic acid requires first methane oxidation to methanol followed by a carbonylation step. Catalyst systems based on Pd/Cu or RhCls have been reported to show good acetic acid jdelds in academic work, but for a commerdal process the reaction rates are still too slow. Nevertheless, due to the very attractive feedstock basis this route may become a threat to methanol carbonylation in the future if this problem can be convincingly overcome by further process and catalyst development. 

Thus, in agreement with homogeneous direct methane oxidation to acetic acid, methane is initially oxidized to methanol, which can be oxidized to carbon monoxide. The formation of acetic acid takes place through carbonylation of methanol. 

Zerella, M. and Bell, A.T. (2006) Pt-catalyzed oxidative carbonylation of methane to acetic acid in sulfuric acid. 

Fig. 7.38 Plausible mechanism for the oxidative carbonylation of methane via the CH activation reaction.

Oxygen Nitrogen Hydrogen Carbon monoxide Carbon dioxide Methane Hydrogen sulfide Sulfur dioxide Carbon (graphite) Diatomic sulfur Nitric oxide Carbonyl sulfide Hydrogen cyanide Ammonia Nitrous oxide... 

Mesitylene [Benzene, 1,3,5-tnmethyl-], 86 Z Met Gly Gly OEt [Gly cine,V-[Ar-[A-[(phenylmethoxy)carbonyl] -L-methionyl] glycyl] -, ethyl ester], 9 3 Methane, iodo-, hazard note 127 Methyl chlonde polystyrene [Benzene, diethenyl-, polymer with ethenyl-benzene, chloromcthylatcd], 96 Methyl iodide [Methane, iodo-], 79 Methyl mercaptan [Methanethiol], 73 Moffat oxidation, 99... 

Dipyridiue-chromium(VI) oxide2 was introduced as an oxidant for the conversion of acid-sensitive alcohols to carbonyl compounds by Poos, Arth, Beyler, and Sarett.3 The complex, dispersed in pyridine, smoothly converts secondary alcohols to ketones, but oxidations of primary alcohols to aldehydes are capricious.4 In 1968, Collins, Hess, and Frank found that anhydrous dipyridine-chromium(VI) oxide is moderately soluble in chlorinated hydrocarbons and chose dichloro-methane as the solvent.5 By this modification, primary and secondary alcohols were oxidized to aldehydes and ketones in yields of 87-98%. Subsequently Dauben, Lorber, and Fullerton showed that dichloro-methane solutions of the complex are also useful for accomplishing allylic oxidations.6... 

Acetate may also be converted into methane by a few methanogens belonging to the genus Meth-anosarcina. The methyl group is initially converted into methyltetrahydromethanopterin (corresponding to methyltetrahydrofolate in the acetate oxidations discussed above) before reduction to methane via methyl-coenzyme M the carbonyl group of acetate is oxidized via bound CO to CO2. 

---