Oxidation of ethene

Wacker process The oxidation of ethene to ethanal by air and a PdClj catalyst in aqueous solution. The Pd is reduced to Pd in the process but is reoxidized to Pd " by oxygen and Cu. ... 

Very large quantities of oxygen are used in steel manufacture (p. 392). Other important uses include organic oxidation reactions the oxidation of ethene CH2=CH2 to epoxyethane, CH2—CHj, is of... 

Ethanal is produced by the aerial oxidation of ethene in the presence of PdCli/CuC in aqueous solution. The main reaction is the oxidative hydrolysis of ethene ... 

Overall this equates to the direct oxidation of ethene in a 100% atom efficient process. 

Kursawe, A., Honicke, D., Comparison of Ag/Al- and Ag/a-Al Oj catalytic suifaces for the partial oxidation of ethene in microchannel reactors, in Matlosz, M., Ehrfeld, W., Baselt, J. P. (Eds.), Microreaction Technology - IMRET 5 Proc. 5th International Conference on Microreaction Technology, pp. 240-251, Springer-Verlag, Berlin (2001). 

Other methods for the preparation of acetic acid are partial oxidation of butane, oxidation of ethanal -obtained from Wacker oxidation of ethene-, biooxidation of ethanol for food applications, and we may add the same carbonylation reaction carried out with a cobalt catalyst or an iridium catalyst. The rhodium and iridium catalysts have several distinct advantages over the cobalt catalyst they are much fester and fer more selective. In process terms the higher rate is translated into much lower pressures (the cobalt catalyst is operated by BASF at pressures of 700 bar). For years now the Monsanto process (now owned by BP) has been the most attractive route for the preparation of acetic acid, but in recent years the iridium-based CATTVA process, developed by BP, has come on stream. 

Acetaldehyde is the product of the Wacker process. At the end of the fifties oxidation of ethene to ethanal replaced the addition of water to acetylene, because the acetylene/coal-based chemistry became obsolete, and the ethene/petrochemistry entered the commercial organic chemicals scene. The acetylene route involved one of the oldest organometallics-mediated catalytic routes started up in the 1920s the catalyst system comprised mercury in sulfuric acid. Coordination of acetylene to mercury(II) activates it toward nucleophilic attack of water, but the reaction is slow and large reactor volumes of this toxic catalyst were needed. An equally slow related catalytic process, the zinc catalysed addition of carboxylic acids to acetylene, is still in use in paint manufacture. 

The cation-radicals of ethenes, which are the primary products of one-electron oxidation, differ in their reactivity from the corresponding neutral compounds. This widens the possibilities of syntheses. Primary oxidation of ethenes (photochemically, with salts of transition metals or ammo-niumyl salts) makes it possible to obtain cation-radicals, which initiate reactions that are unusual for ethenes in an uncharged state. For instance, the cation-radical of phenylvinyl ether initiates head-to-head cyclodimerization as shown in Scheme 7.19 (Ledwith 1972, Farid and Shealer 1973, Kuwata et al. 1973). 

So far, no reference has been made to the presence of more than one phase in the reactor. Many important chemicals are manufactured by processes in which gases react on the surface of solid catalysts. Examples include ammonia synthesis, the oxidation of sulphur dioxide to sulphur trioxide, the oxidation of naphthalene to phthalic anhydride and the manufacture of methanol from carbon monoxide and hydrogen. These reactions, and many others, are carried out in tubular reactors containing a fixed bed of catalyst which may be either a single deep bed or a number of parallel tubes packed with catalyst pellets. The latter arrangement is used, for exjimple, in the oxidation of ethene to oxiran (ethylene oxide)... 

A reaction of immense industrial importance is the formation of oxacy-clopropane itself (most often called ethylene oxide) by oxidation of ethene with oxygen over a silver oxide catalyst at 300° ... 

Diols are prepared from alkenes by oxidation with reagents such as osmium tetroxide, potassium permanganate, or hydrogen peroxide (Section 11-7C). However, ethylene glycol is made on a commercial scale from oxacy-clopropane, which in turn is made by air oxidation of ethene at high temperatures over a silver oxide catalyst (Section 11-7D). 

Catalytic Oxidation of Ethene to Acetaldehyde and Acetic Acid. -Evnin et al120 studied Pd-doped V2 Os catalysts for the vapor-phase oxidation of ethene to acetaldehyde in a heterogeneous type of Wacker process. From a mechanistic study they establish a redox mechanism with Pd both as the site of the ethene oxidation and of the reoxidation of the catalyst. On the basis of the role of the V4+ ions proposed by these authors, Forni and Gilardi121 substantiated this mechanism by adding tetra- and hexa-valent dopants to the V2 05 and studying the effects on the catalytic reaction. 

Inomata et al.,149 Murakami et al.,24 and Mori et al.150 find that besides the selective exposure of the (V=0) bonds, which was already discussed above, a second effect is that for certain reactions, in particular the oxidation of ethene and benzene the intrinsic activity of these groups also differs, being highest for anatase and lower for A1203. 

The first set of reactions is the mainstay of the petrochemical industry 1 outstanding examples are the oxidation of propene to propenal (acrolein) catalysed by bismuth molybdate, and of ethene to oxirane (ethylene oxide) catalysed by silver. In general these processes work at high but not perfect selectivity, the catalysts having been fine-tuned by inclusion of promoters to secure optimum performance. An especially important reaction is the oxidation of ethene in the presence of acetic (ethanoic) acid to form vinyl acetate (ethenyl ethanoate) catalysed by supported palladium-gold catalysts this is treated in Section 8.4. Oxidation reactions are very exothermic, and special precautions have to be taken to avoid the catalyst over-heating. 

It is convenient to consider the synthesis of vinyl acetate at this point, because it involves the aerobic oxidation of ethene to the unstable intermediate ethenol (H2C=CH(OH)), followed by its immediate esterification with acetic (ethanoic) acid,... 

The symmetrical transition states BTS and CTs are very similar to the transition state calculated for the permanganate oxidation of ethene,47 indicating that the substitutent does not play a major role. All other transition states are very... 

In my opinion (and I am convinced that Ernst Otto Fischer would have agreed), Walter Hafner was one of the best Ph.D. students, probably the best Fischer ever had. After he finished his doctoral research, he joined the Consortium filr Elektrochemische Industrie, a research subsidiary of Wacker-Chemie in Munich, where he laid the foundations for the palladium-catalyzed oxidation of ethene to acetaldehyde, the Wacker process. This process has been licenced to various chemical companies all over the world and initiated an evergrowing area of synthetic organic chemistry. Walter Hafner retired in 1992 and died in 2004. 

In this context it is also worth mentioning that Showa Denko has developed a new process for the direct oxidation of ethene to acetic acid using a combination of palladium(II) and a heteropoly acid [104]. However, the reaction probably involves heteropoly acid-catalyzed hydration followed by palladium-catalyzed aerobic oxidation of ethanol to acetic acid rather than a classical Wacker mechanism. 

Thus the initial reaction rate can be determined in one, single experiment by differentiating the conversion versus axial position curve at z = 0. This method has been used for the selective oxidation of ethene [37]. 

Suzuki reaction the palladium-catalyzed reaction of an aryl or vinyl halide with an aryl boronic acid to give an arylated or vinylated arene. In some cases, primary alkyl halides can react in place of the aryl or vinyl halides Wacker process the palladium-catalyzed oxidation of ethene to acetaldehyde by oxygen... 

The oxidation of ethene by palladium salts in water to give acetaldehyde has been known for 100 years see Oxidation Catalysis by Transition Metal Complexes). It is often called the Wacker Process, after Wacker Chemie GmbH, which first developed the process. The key steps in this oxidation are shown in Scheme 2. Palladium catalyzes the nucleophilic addition of water to ethene, leading to the reduction of Pd to Pd°. Then the palladium is reoxidized back to Pd with Cu salts, giving Cu which in turn is oxidized by oxygen. 

Oxidation of ethene on silver catalysts to yield ethene oxide is a good example of an industrial catalytic process with a high selectivity. In order to confirm a possible correlation between the catalysts affinity towards oxygen and their activity in ethene epoxidation, a heat-flow microcalorimeter equipped with a pulse flow reactor has been used to study the reaction of oxygen at 473 K with a series of silica-supported silver catalysts [71]. At 473 K, adsorption of oxygen at the surface of silver is a fast process incorporation of oxygen into deeper metal layers, though present, is a slow process. 

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