Palladium -catalysts, copper® chloride

Hoechst-Uhde (2) A variation of the Wacker process, which makes vinyl acetate from ethylene and acetic acid. The catalyst is an aqueous solution of palladium and copper chlorides. 

Wacker (1) A general process for oxidizing aliphatic hydrocarbons to aldehydes or ketones by the use of oxygen, catalyzed by an aqueous solution of mixed palladium and copper chlorides. Ethylene is thus oxidized to acetaldehyde. If the reaction is conducted in acetic acid, the product is vinyl acetate. The process can be operated with the catalyst in solution, or with the catalyst deposited on a support such as activated caibon. There has been a considerable amount of fundamental research on the reaction mechanism, which is believed to proceed by alternate oxidation and reduction of the palladium ... 

Dimethyl carbonate [616-38-6] and dimethyl oxalate [553-90-2] are both obtained from carbon monoxide, oxygen, and methanol at 363 K and 10 MPa (100 atm) or less. The choice of catalyst is critical cuprous chloride (66) gives the carbonate (eq. 20) a palladium chloride—copper chloride mixture (67,68) gives the oxalate, (eq. 21). Anhydrous conditions should be maintained by removing product water to minimize the formation of by-product carbon dioxide. 

A one-stage process for producing vinyl acetate directly from ethylene has also been disclosed. In this process ethylene is passed through a substantially anhydrous suspension or solution of acetic acid containing cupric chloride and copper or sodium acetate together with a palladium catalyst to yield vinyl acetate. 

This reaction is similar to 13-1 and, like that one, generally requires activated substrates. With unactivated substrates, side reactions predominate, though aryl methyl ethers have been prepared from unactivated chlorides by treatment with MeO in HMPA. This reaction gives better yields than 13-1 and is used more often. A good solvent is liquid ammonia. The compound NaOMe reacted with o- and p-fluoronitrobenzenes 10 times faster in NH3 at — 70°C than in MeOH. Phase-transfer catalysis has also been used. The reaction of 4-iodotoluene and 3,4-dimethylphenol, in the presence of a copper catalyst and cesium carbonate, gave the diaryl ether (Ar—O—Ar ). Alcohols were coupled with aryl halides in the presence of palladium catalysts to give the Ar—O—R ether. Nickel catalysts have also been used. ... 

Palladium catalysts, 10 42 14 49 16 250 Palladium-catalyzed carbonylation, 13 656 Palladium chloride/copper chloride, supported catalyst, 5 329 Palladium compounds, 19 650-654 synthesis of, 19 652 uses for, 19 653-654 Palladium films, 19 654 Palladium membranes, 15 813 Palladium monoxide, 19 651 Palladium oxide, 19 601... 

The metal-catalysed autoxidation of alkenes to produce ketones (Wacker reaction) is promoted by the presence of quaternary ammonium salts [14]. For example, using copper(II) chloride and palladium(II) chloride in benzene in the presence of cetyltrimethylammonium bromide, 1-decene is converted into 2-decanone (73%), 1,7-octadiene into 2,7-octadione (77%) and vinylcyclohexane into cyclo-hexylethanone (22%). Benzyltriethylammonium chloride and tetra-n-butylammo-nium hydrogen sulphate are ineffective catalysts. It has been suggested that the process is not micellar, although the catalysts have the characteristics of those which produce micelles. The Wacker reaction is also catalysed by rhodium and ruthenium salts in the presence of a quaternary ammonium salt. Generally, however, the yields are lower than those obtained using the palladium catalyst and, frequently, several oxidation products are obtained from each reaction [15]. 

A route not yet commercialized is the reaction of ethylene, carbon monoxide, and air to give AA. The ethylene is dissolved in acetic acid. The process talces place at 270°F and 1100 psi in the presence of palladium chloride-copper chloride catalyst. Yields are 80—85%. If the by-product and corrosion problems can be licked, the process will probably catch on. 

The reaction of zinc homoenolate 9 with acid chlorides in ethereal solvents containing 2 equiv of HMPA rapidly produces 4-ketoesters in high yield Eq. (44) [33]. A palladium catalyst [40] (or less effectively a copper catalist) [28] accelerates the reaction. This is in contrast to the cyclopropane formation in a nonpolar solvent see (Eq. 22 above). 

Palladium(II) acetylacetonate-Tri-phenylphosphine, 233 Palladium catalysts, 62, 65, 170, 185, 208, 230, 241, 251 Palladium(II) chloride, 9, 234 Palladium(II) chloride-Copper(II) chloride, 235... 

When either an alcohol or an amine function is present in the alkene, the possibility for lactone or lactam formation exists. Cobalt or rhodium catalysts convert 2,2-dimethyl-3-buten-l-ol to 2,3,3-trimethyl- y-butyrolactone, with minor amounts of the 8-lactone being formed (equation 51).2 In this case, isomerization of the double bond is not possible. The reaction of allyl alcohols catalyzed by cobalt or rhodium is carried out under reaction conditions that are severe, so isomerization to propanal occurs rapidly. Running the reaction in acetonitrile provides a 60% yield of lactone, while a rhodium carbonyl catalyst in the presence of an amine gives butane-1,4-diol in 60-70% (equation 52).8 A mild method of converting allyl and homoallyl alcohols to lactones utilizes the palladium chloride/copper chloride catalyst system (Table 6).79,82 83... 

Dicarboxylation reactions of alkenes can be carried out such that predominately 1,2-addition of the two ester functions occurs (equation 61). The reaction takes place under mild conditions (1-3 bar, 25 C) in alcohol. It is stoichiometric in palladium, since the palladium(II) catalyst is reduced to palladium(O) in the process, but by use of an oxidant (stoichiometric copper chloride or catalytic copper chloride plus oxygen equation 62 and 63) the reaction becomes catalytic in palladium. In the reoxidation process, water is generated and the build-up of water increases the water gas shift reaction at the expense of the carboxylation. Thus a water scavenger such as triethyl orthoformate is necessary for a smooth reaction. 

To overcome the problems encountered in the homogeneous Wacker oxidation of higher alkenes several attempts have been undertaken to develop a gas-phase version of the process. The first heterogeneous catalysts were prepared by the deposition of palladium chloride and copper chloride on support materials, such as zeolite Y [2,3] or active carbon [4]. However, these catalysts all suffered from rapid deactivation. Other authors applied other redox components such as vanadium pentoxide [5,6] or p-benzoquinone [7]. The best results have been achieved with catalysts based on palladium salts deposited on a monolayer of vanadium oxide spread out over a high surface area support material, such as y-alumina [8]. Van der Heide showed that with catalysts consisting of H2PdCU deposited on a monolayer vanadium oxide supported on y-alumina, ethene as well as 1-butene and styrene... 

A PEG-SCCO2 system has also been used in the aerobic oxidation of styrene (Figure 8.7). In the presence of cuprous chloride co-catalyst the reaction favours acetophenone formation, whereas in the absence of copper benzaldehyde is favoured. The catalyst could be recycled five times and it was suggested that the PEG acts to prevent the palladium catalyst from decomposing and also assists in product separation. 

The oxidation of propylene has been chosen as a probe reaction to study the catalytic activity of Cu Pd -TSM. The olefin oxidation in an acidic solution of Cu(II) and Pd(U) chlorides, well known as the Wacker reaction, is achieved when olefins are selectively oxidized to ketones or aldehydes by hydrated Pd, leaving Pd . The Pd is oxidized back to Pd by 2Cu, and the resulting Cu is reoxidized by dissolved oxygen. Because the corrosive nature of the catalyst solution is a serious disadvantage for practical use, supported copper-palladium catalysts have been proposed to operate the reaction in a gas flow reactor (40). 

---