Wacker catalyst system

Isobutylene glycol may also be produced by a direct catalyzed liquid phase oxidation of isobutylene with oxygen in presence of water. The catalyst is similar to the Wacker-catalyst system used for the oxidation... 

A rather interesting application of zeolite-based alkene oxidation catalysis has been demonstrated by Japanese workers (46, 47). In particular, a Pd2 +, Cu2 +Y zeolite was shown to be an active and stable heterogeneous oxidation catalyst which is analogous to the well-known homogeneous Wacker catalyst system containing PdCl2 and CuCl2 (48). Under Wacker conditions (i.e., alkene/02/H20) the zeolite Y catalyst was shown to convert ethylene to acetaldehyde and propylene to acetone with selectivities in excess of 90% with C02 as the major by-product. 

The direct oxidation of ethylene is used to produce acetaldehyde (qv) ia the Wacker-Hoechst process. The catalyst system is an aqueous solution of palladium chloride and cupric chloride. Under appropriate conditions an olefin can be oxidized to form an unsaturated aldehyde such as the production of acroleia [107-02-8] from propjiene (see Acrolein and derivatives). 

A variation of the Pd/Cu Wacker-Hoechst process, termed OK Technology, has been proposed by Catalytica Associates (40—46). This process avoids the use of chlorides and uses a Pd/Cu catalyst system which incorporates a polyoxoanion and a nitrile ligand. 

The Wacker process uses an aqueous solution of palladium(II) chloride, copper(II) chloride catalyst system. 

Asymmetric induction has also been achieved in the cyclization of aliphatic alcohol substrates where the catalyst derived from a spirocyclic ligand differentiates enantiotopic alcohols and alkenes (Equation (114)).416 The catalyst system derived from Pd(TFA)2 and (—)-sparteine has recently been reported for a similar cyclization process (Equation (115)).417 In contrast to the previous cases, molecular oxygen was used as the stoichiometric oxidant, thereby eliminating the reliance on other co-oxidants such as GuCl or/>-benzoquinone. Additional aerobic Wacker-type cyclizations have also been reported employing a Pd(n) system supported by A-heterocyclic carbene (NHC) ligands.401,418... 

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 Wacker-Hoechst process has been studied in great detail and in all textbooks it occurs as the example of a homogeneous catalyst system illustrating nucleophilic addition to alkenes. Divalent palladium is the oxidising agent and water is the oxygen donor according to the equation ... 

This chapter has focused on inorganic and heterogeneous catalysts, because historically these are the major systems with which chemical engineers have been concerned. There are number of important homogeneous catalytic processes such as the Wacker process to make vinyl acetate from ethylene and acetic acid, and there are many acid and base homogeneous catalyst systems. 

One of the earliest uses of palladium(II) salts to activate alkenes towards additions with oxygen nucleophiles is the industrially important Wacker process, wherein ethylene is oxidized to acetaldehyde using a palladium(II) chloride catalyst system in aqueous solution under an oxygen atmosphere with cop-per(II) chloride as a co-oxidant.1,2 The key step in this process is nucleophilic addition of water to the palladium(II)-complexed ethylene. As expected from the regioselectivity of palladium(II)-assisted addition of nucleophiles to alkenes, simple terminal alkenes are efficiently converted to methyl ketones rather than aldehydes under Wacker conditions. 

Moreover, it was disclosed that PdCl2 in combination with N,N-dimethylaceta-mide (DMA) solvent could offer a simple and efficient catalyst system for acid-and Cu-free Wacker oxidation [102]. The reaction is illustrated in Fig. 4.37. A wide range of terminal olefins could be oxidized to form the corresponding methyl ketones in high yields, reaching a TOF up to 17 h-1. The Pd-DMA catalyst layer could be recycled. Furthermore this system is also capable of per-... 

The Wacker-Hoechst process has been practised commercially since 1964. In this liquid phase process propylene is oxidized to acetone with air at 110-120°C and 10-14 bar in the presence of a catalyst system containing PdCl2. As in the oxidation of ethylene, Pd(II) oxidizes propylene to acetone and is reduced to Pd(0) in a stoichiometric reaction, and is then reoxidized with the CuCl2/CuCl redox system. The selectivity to acetone is 92% propionaldehyde is also formed with a selectivity of 2-4%. The conversion of propylene is more than 99%. 

Karakhanov, E. A., Zhuchkova, A. Y., Filippova, T. Y., Maksimov, A. L. Supramolecular cyclodextrin-based catalyst systems in Wacker oxidation. Neftekhimiya 2003,43, 302-307. 

Oxidative carbonvlation of ethylene this process, developed by Union Oil operates in the liquid phase, between 135 and 150°C. at 7.5.106 Pa absolute, with a high ethylene and low carbon monoxide partial pressure, and in the presence of a catalyst system similar to the one used in the Wacker process for manufacturing acetaldehyde. The main reactions are the following ... 

The overall reaction is shown in equation (29). This reaction is similar to the Wacker acetaldehyde process. The same catalyst system is used, except that the vinyl acetate process is carried out in the vapor phase over a heterogeneous solid catalyst, whereas in the acetaldehyde process the catalyst is in solution in the liquid phase. 

Exploration of Basic Catalyst Components The study of direct oxidative acetoxyla-tion of 1,3-butadiene began with the use of Wacker-type homogeneous catalyst Pd(OAc)2-CuCl2 [10]. This catalyst system gave low l,4-diacetoxy-2-butene selectivity, and there was a problem in separating the catalyst. After that, liquid-and vapor-phase methods using a Pd-based catalyst were studied in parallel. Catalyst activity was greatly improved by the addition of Bi or Sb to the Pd catalyst in the gas-phase reaction [11]. However, catalyst activity was reduced by the adhesion of resin by-product derived from unsaturated aldehydes on the catalyst surface. Various improvements have been tried in the gas phase, but catalyst robustness has never met industrial requirements. 

In a later work, both the CuCl/KCl molten salt Wacker oxidation system and a [Bu4N][SnCl3] system (melting point 60 °C) was applied to the electrocatalytic generation of acetaldehyde from ethanol by co-generation of electricity in a fuel cell [56]. In the cell set-up, porous carbon electrodes supported with an ionic liquid catalyst electrolyte were separated by a proton conducting membrane (Fig. 5.6-4), and current efficiency and product selectivity up to 87% and 83%, respectively, were reported at 90 °C. 

In addition to the Wacker oxidation catalysts, supported eutectic molten salt CuCl/KCl-based catalyst systems have also been examined for other processes including, for example, production of synthesis gas from methanol for the use as on-board hydrogen production in vehicles [57] and quantitative combustion of chlorinated hydrocarbons to COx and HCI/CI2 at ambient pressure (200-500 °C) with silica-based systems [58,59]. 

Fig. 5.6-4 Schematic illustration of a supported ionic liquid fuel cell containing the Wacker oxidation system (SMSEC supported molten salt electro-catalyst) for co-generatlon of acetaldehyde and electricity from ethanol [55],...

The use of liquid membranes for controlling chemical reactions such as that just discussed has been proposed for a number of other systems. This type of application, in which liquid membranes are used as heterogeneous catalysts or as reaction moderators, is an area that deserves more study. Ollis et al. and Wolytdc and Ollis studied liquid membranes as heterogeneous catalyst systems using the catalytic oxidation of ethylene to acetaldehyde (Wacker process) as a model. This process entails the following three... 

Karakhanov EA, Buchneva TS, Maksimov AL, Runova EA. Calixarene-based catalyst systems in biphasic Wacker oxidation of oleflns. Neftekhimiya 2003 43(l) 42-9. 

Earlier studies have also shown that a catalyst system consisting of palladium(II) and copper salts plus oxygen for the reoxidation did not work well,t in contrast to the result with the Wacker oxidation. However, if quinone or hydroquinone was added to a mixture of palladium acetate and copper acetate, oxygen could be used as an efficient oxidant for conversion of alkenes into allylic acetates. Thus, cyclohexene gave better than 85% cyclohexenyl acetate (Scheme 10). The combination of oxygen and cobalt or manganese acetate also works, but less well.t ... 

Mitsudome, T., Mizumoto, K., Mizugaki, T., et al. (2010). Wacker-Type Oxidation of Internal Olefins Using a PdCl2/N,N-Dimethylacetamide Catalyst System under Copper-Free Reaction Conditions, Angew. Chem. Int. Ed., 49, pp. 1238-1240. 

Michel, B., Camelio, A., Cornell C., et al. (2009). A General and Efficient Catalyst System for a Wacker-Type Oxidation Using TBHP as the Terminal Oxidant application to Classically Challenging Substrates, J. Am. Chem. Soc., 131, pp. 6076-6077. 

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