Wacker Chemie oxidation process

In 1960, quickly after the introduction of the Celanese process, Wacker-Chemie commercialized a liquid phase vinyl acetate process which represented and extension of its earlier acetaldehyde process wherein acetic acid was simply substituted for water. (See equation [19]. This chemical transformation is also referred to as oxidative acetoxylation.) As shown in Figure 2, wherein R=Ac, the liquid phase oxidative acetoxylation of ethylene utilized the same catalytic cycle as the Wacker-Chemie acetaldehyde process. 

Production of acetone by dehydrogenation of isopropyl alcohol began in the early 1920s and remained the dominant production method through the 1960s. In the mid-1960s virtually all United States acetone was produced from propylene. A process for direct oxidation of propylene to acetone was developed by Wacker Chemie (12), but is not beheved to have been used in the United States. However, by the mid-1970s 60% of United States acetone capacity was based on cumene hydroperoxide [80-15-9], which accounted for about 65% of the acetone produced. 

Meanwhile, Wacker Chemie developed the palladium-copper-catalyzed oxidative hydration of ethylene to acetaldehyde. In 1965 BASF described a high-pressure process for the carbonylation of methanol to acetic acid using an iodide-promoted cobalt catalyst (/, 2), and then in 1968, Paulik and Roth of Monsanto Company announced the discovery of a low-pressure carbonylation of methanol using an iodide-promoted rhodium or iridium catalyst (J). In 1970 Monsanto started up a large plant based on the rhodium catalyst. 

Catalysts used to convert ethylene to vinyl acetate are closely related to those used to produce acetaldehyde from ethylene. Acetaldehyde was first produced industrially by the hydration of acetylene, but novel catalytic systems developed cooperatively by Farbwerke Hoechst and Wacker-Chemie have been used successfully to oxidize ethylene to acetaldehyde, and this process is now well established (7). However, since the largest use for acetaldehyde is as an intermediate in the production of acetic acid, the recent announcement of new processes for producing acetic acid from methanol and carbon monoxide leads one to speculate as to whether ethylene will continue to be the preferred raw material for acetaldehyde (and acetic acid). 

Discovered by Phillips in 1894,382 the oxidation of ethylene to acetaldehyde by palladium(ll) salts in an aqueous solution was developed into a commercial process about 60 years later by Smidt and coworkers at Wacker Chemie.383,384 These researchers succeeded in transforming this stoichiometric oxidation by a precious metal (equation 150) into a catalytic reaction through the reoxidation of the resulting Pd° by molecular oxygen in the presence of copper salts (equations 151-152). 

The cycle approach for oxidation has been adopted at an industrial level for the Wacker-Chemie process for acetaldehyde production, in which ethylene is first put in contact with the oxidized catalyst solution, containing palladium chloride, and in the second step the solution containing the reduced catalyst is sent to a regeneration reactor containing cupric chloride and inside which also air is fed. The regenerated catalyst solution is returned to the first oxidation stage. Another industrial application is the Lummus process for the anaerobic ammoxidation of o-xylene to o-phthaloni-trile [68]. Du Pont has developed the oxidation of n-butane to maleic anhydride catalyzed by V/P/O, in a CFBR reactor, and built a demonstration unit in Spain [69] however, a few years ago the plant was shut down, due to the bad economics. 

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. 

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. 

Research to convert ethylene directly to acetaldehyde was begun in 1956 at the Consortium fiir Elektrochemische Industrie G.m.b.H., a subsidiary of Wacker Chemie G.m.b.H., under the direction of J. Smidt. The results of this research were summarized (34, 35) in two fundamental publications and in numerous patents. Smidt and co-workers first surveyed the open literature to determine what approaches had been used to oxidize ethylene and what the resulting oxidation products were. Table III summarizes the pertinent literature findings up to 1956. None of the processes published offered much promise for converting ethylene to acetaldehyde directly. In their initial experiments, Smidt et al. (34) passed mixtures of ethylene, oxygen, and hydrogen over a catalyst of palladium deposited on activated carbon, obtaining traces of acetaldehyde. They also found that the acetaldehyde yield was increased when... 

The liquid-phase oxidation of ethylene to acetaldehyde was pioneered by the Consortium fiir Elektrochemische Industrie G.m.b.H. Industrially, the single-stage process was developed mainly by Farbwerke Hoechst A. G. and the two-stage process by Wacker Chemie G.m.b.H. itself. Both processes are licensed by Aldehyd G.m.b.H., jointly owned by Wacker Chemie G.m.b.H. and Farbwerke Hoechst G.m.b.H. The basic patents of these two companies on the Wacker process are listed in Table IV. In addition to these patents, which have given Wacker Chemie G.m.b.H. and Farbwerke Hoechst a dominant role in this field, other companies hold some patents in this area (Table X). How many of the patents listed in Tables IX and X are commercially important cannot be judged, based on the open literature alone. 

The reaction is very effectively catalyzed by and Hg " salts. However, Hg -" partially oxidizes the acetaldehyde formed to acetic acid, and is itself reduced to metallic Hg. In a process carried out at Wacker-Chemie until 1962 [39, 40], the metallic mercury was reoxidized to Hg "" by iron(TII) sulfate. In a separate step, the iron(II) sulfate formed was oxidized back to Fe using nitric acid and was returned to the initial reaction. This process, carried out on a large industrial scale, has also been superseded in the intervening period by a process based on ethylene (Section 2.4.1). 

This is currently the most widespread method for manufacturing acetaldehyde. Initial research and development conducted by the Consortium Jur ElectrocHanische Industrie, a Wacker Chemie affiliated organization, culminated in 1956 in the development of an industrial process with two variants. One of them, proposed by Hoechst, employs oxygen as the oxidant, and the second, examined by Wackert employs air. The commercialization of these two alternatives by Aldehyd, a joint venture, led to the construction of the first industrial plant in 1960. 

The single-stage process was developed by a research group of Hoechst AG (also see [36]). At the time, Hoechst AG owned 50% of the shares of Wacker Chemie. Via the board, they learned at an early time about Wacker s activity on ethylene oxidation and began research on this field. Later on, both companies cooperated and combined their results. 

The first chemical plant to use ethylene oxidation for the manufacture of acetaldehyde was built in Germany by Wacker Chemie in 1959, and the process itself became known as the Wacker process. 

It is most conveniently obtained by the Wacker-chemie s oxidation process. In this process ethylene is oxidised with oxygen in presence of the catalyst solution (Scheme 18). 

The Wacker oxidation was discovered by Smidt and co-workers at Consortium fiir Electrochemie (a subsidiary of Wacker Chemie and Farbwerken Bayer). It is actually a combination of known reactions and thus not a catalytic reaction in the strictest sense (Scheme 1). The first and most basic reaction, the oxidation of ethene in aqueous solution was first discovered by Phillips in 9AP The precipitation of palladium metal from a palladium(II) chloride solution was used as a test for olefins. However, it was the discovery by Smidt and co-workers that the Pd(0) formed could be regenerated by cupric chloride that made the reaction a commercial success. The final step, the oxidation of CuCl to CuCl2 is one of the fastest reactions in inorganic chemistry, The three reactions add up to the simple air oxidation of ethene to ethanal. At one point over two billion pounds a year of ethanal was produced by the Wacker process. Presently, the Monsanto acetic acid process has largely replaced the Wacker procednre.t" ... 

BUTOX A biological process for oxidizing bioethanol to acetic acid. Developed by Wacker Chemie. In 2001, they were ready to build a plant but had not done so by 2008. BUTOX is also the name of a proprietary veterinary medicine. 

The Wacker process, an important industrial procedure now used to make 6 million tons a year of aldehydes, relies on nucleophilic attack on an alkene complex. The fact that aqueous PdCb oxidizes ethylene to acetaldehyde had been known—although not understood—since the nineteenth century the reaction consumes the PdCb as oxidant and deposits metallic Pd(0). It took considerable imagination to see that such a reaction could ever be useful on an industrial scale because PdCla is obviously far too expensive to use stoichiometrically. It is often useful to find a way to convert a stoichiometric to a catalytic process. J. Smidt of Wacker Chemie realized in the late 1950s that it is possible... 

An interesting process for the production of acetaldehyde was based on the work of F. C. Phillips, who showed that ethylene could be oxidized to acetaldehyde by an aqueous palladium chloride solution. The palladium chloride was reduced to metallic palladium. During the late 1950 s, Wacker Chemie introduced a new process for the manufacture of acetaldehyde by direct oxidation of ethylene with air. The palladium metal was converted back to (PdCU) by an acidic solution of cupric chloride, which was, itself, reduced to cuprous chloride. The cupric chloride was regenerated by reaction with air in hydrochloric acid solution. The reaction sequence is shown in the following equations ... 

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