Ethylene, palladium® chloride

Metal-Halogen Counpounds. One of the few examples of an olefin insertion into a metal-halogen compound has been reported by Tsuji. The reaction, which also supports the idea that sigma-bonded metal-carbon compounds are intermediates in the palladium chloride-olefin oxidation reaction, was the addition of carbon monoxide to the ethylene palladium chloride 7r-complex in nonaqueous solvents to produce a moderate yield of 3-chloropropionyl chloride (96). 

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). 

The palladium chloride process for oxidizing olefins to aldehydes in aqueous solution (Wacker process) apparendy involves an intermediate anionic complex such as dichloro(ethylene)hydroxopalladate(II) or else a neutral aqua complex PdCl2 (CH2=CH2)(H2 0). The coordinated PdCl2 is reduced to Pd during the olefin oxidation and is reoxidized by the cupric—cuprous chloride couple, which in turn is reoxidized by oxygen, and the net reaction for any olefin (RCH=CH2) is then... 

In recent years vinyl acetate has been prepared in large quantities by oxidation of ethylene. If ethylene is passed into a solution of palladium chloride in acetic acid containing sodium acetate, then vinyl acetate, ethylene diacetate and acetaldehyde are produced, the vinyl acetate being obtained in good yields by the reaction shown in Figure 14.3... 

The oxidation of ethylene to acetaldehyde by palladium chloride in water has been known since the nineteenth century.80 However, the reaction requires the use of a stoichiometric amount of PdCl2, resulting in Pd(0) deposit. Anderson, in 1934, observed a similar reaction (but... 

Palladium-catalyzed oxidation of hydrocarbons has been a matter of intense research for about four decades. The field was initiated by the development of the aerobic oxidation of ethylene to acetaldehyde catalyzed by palladium chloride and co-catalyzed by cupric chloride (the Wacker process, equation l)1. 

The catalyst is the key to this reaction and in this case is an aqueous solution of palladium chloride (PdCl2) and cupric chloride (CuCh). There is a complex, but well understood, mad scramble of ions and molecules that takes place as chlorine temporarily separates from the palladium and the copper and facilitates ethylene s reacting with oxygen. 

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 oxidation of olefins to carbonyl compounds by palladium (II) ion can be regarded as an addition of a palladium hydroxide group to the olefin followed by a hydrogen shift. Kinetic evidence suggests the following mechanism for the oxidation of ethylene by palladium chloride in aqueous solution containing excess chloride ion 21, 49, 99). 

Palladium chloride or the chloropalladite ion catalyze the oxidation of olefins to aldehydes or ketones, presumably by forming unstable palladium-olefin complex intermediates 196). A reaction of great industrial importance is the palladium chloride/cupric chloride catalyzed oxidation of ethylene to acetaldehyde 195). The first stage is presumably the oxidative hydrolysis of ethylene,... 

Monosubstituted and 1,2-disubstituted olefins can be oxidized to aldehydes and ketones by palladium chloride and similar salts of noble metals.367 1,1-Disubstituted olefins generally give poor results. The reaction is used industrially to prepare acetaldehyde from ethylene... 

In tonnage production, acetaldehyde may be manufactured by (1) the direct oxidation of ethylene, requiring a catalytic solution of copper chloride plus small quantities of palladium chloride, (2) the oxidation of ethyl alcohol with sodium dichromate, and (3) the dry distillation of calcium acetate with calcium formate. 

WACKER REACTION. The oxidation of ethylene to acetaldehyde in the presence of palladium chloride and cupric chloride. 

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. 

Acetic acid is manufactured by three processes acetaldehyde oxidation, //-butane oxidation, and methanol carbonylation.Ethylene is the exclusive organic raw material for making acetaldehyde, 70 percent of which is further oxidized to acetic acid or acetic anhydride. The single-stage (Wacker) process for making acetaldehyde involves cupric chloride and a small amount of palladium chloride in aqueous solution as a catalyst. 

A Wacker catalyst is used in this process, similar to that for the manufacture of acetic acid. Since the acetic acid can also be made from ethylene, the basic raw material is solely ethylene. A liquid-phase process has been replaced by a vapor-phase reaction run at 70 to 140 psi and 175 to 200°C. Catalysts may be (1) carbon-palladium chloride-cupric chloride (C-PdCl2-CuCl2), (2) palladium chloride-alumina (PdCl2-Al203), or (3) palladium-carbon-potassium acetate (Pd-C-KOAc). The product is distilled into water, acetaldehyde that can be recycled to acetic acid, and the pure colorless liquid, which is collected at 72°C. The yield is 95percent. 

Over 35 years ago, Richard F. Heck found that olefins can insert into the metal-carbon bond of arylpalladium species generated from organomercury compounds [1], The carbopalladation of olefins, stoichiometric at first, was made catalytic by Tsutomu Mizoroki, who coupled aryl iodides with ethylene under high pressure, in the presence of palladium chloride and sodium carbonate to neutralize the hydroiodic acid formed (Scheme 1) [2], Shortly thereafter, Heck disclosed a more general and practical procedure for this transformation, using palladium acetate as the catalyst and tri-w-butyl amine as the base [3], After investigations on stoichiometric reactions by Fitton et al. [4], it was also Heck who introduced palladium phosphine complexes as catalysts, enabling the decisive extension of the ole-fination reaction to inexpensive aryl bromides [5],... 

One of the first examples of this type of reaction and perhaps the one most investigated and best understood, is the oxidation of ethylene to acetaldehyde by aqueous palladium chloride. 

The aqueous palladium chloride oxidation of ethylene to acetaldehyde has been developed into an important commercial process. The discovery of how to make the reaction catalytic with respect to palladium chloride was, perhaps, as important to the process as the discovery of the oxidation reaction itself. This process known as the Wacker-Process, employs cupric chloride as a catalyst for the oxygen (air) reoxidation of... 

Vinyl ethers can be obtained from ethylene and alcohols with palladium chloride 7> by a mechanism that is probably very similar to that in the ethylene oxidation to acetaldehyde. 

In the absence of water, palladium chloride and ethylene react to form vinyl chloride 12> presumably by way of an adduct which eliminates the elements of [HPdCl]. 

The invention of the Wacker process was a triumph of common sense. It had been known since 1894 that ethylene is oxidized to acetaldehyde by palladium chloride in a stoichiometric reaction (Figure 27). However, it was not until 1956 that this reaction was combined with the known reoxidation reactions of palladium by copper and, in turn of copper by oxygen. The total process developed by Wacker and Hoechst between 1957 and 1959 can be depicted as an exothermic catalytic direct oxidation to yield acetaldehyde. 

In 1938 Kharasch and co-workers described a method generally applicable for preparing mono-olefin palladium complexes (14 ). Palladium (II) chloride reacted with warm benzonitrile to form the complex bis(benzonitrile)-palladium chloride, and the latter reacted directly with olefins such as ethylene, styrene, cyclohexene, etc., as follows ... 

Alcohols in ethylene carbonate containing sodium acetate and palladium chloride are oxidized by oxygen at room temperature in 62-98% yields [70]. Oxygen passed at room temperature under irradiation through a solution of catalytic amounts of chloroplatinic acid and cuprous chloride in alcohols produces ketones in yields of up to 98% [57], Other catalysts used for this purpose are platinum [55], platinum-on-charcoal [56], and, better still, platinum oxide [56]. Such oxidations are carried out usually at room temperature and give fair to high yields. 

Among the most significant developments in the field of catalysis in recent years have been the discovery and elucidation of various new, and often novel, catalytic reactions of transition metal ions and coordination compounds 13, 34). Examples of such reactions are the hydrogenation of olefins catalyzed by complexes of ruthenium (36), rhodium (61), cobalt (52), platinum (3, 26, 81), and other metals the hydroformylation of olefins catalyzed by complexes of cobalt or rhodium (Oxo process) (6, 46, 62) the dimerization of ethylene (i, 23) and polymerization of dienes (15, 64, 65) catalyzed by complexes of rhodium double-bond migration in olefins catalyzed by complexes of rhodium (24,42), palladium (42), cobalt (67), platinum (3, 5, 26, 81), and other metals (27) the oxidation of olefins to aldehydes, ketones, and vinyl esters, catalyzed by palladium chloride (Wacker process) (47, 48, 49,... 

For each mole of acetaldehyde formed, one mole of palladium chloride was reduced to metallic palladium. To make this process industrially attractive, it must be conducted so that palladium chloride acts as a catalyst rather than as an oxidant—i.e., so that the metallic palladium formed is reoxidized to palladium chloride and can be reused for the principal reaction. This was the second fundamental recognition, which helped make this process commercial. The search for proper oxidants for metallic palladium was facilitated by the observation of Smidt et al. (34) that if cupric or ferric chloride were added to palladium chloride in the vapor-phase oxidation of ethylene to acetaldehyde, the acetaldehyde yield was increased. Therefore, these compounds were also used in the liquid-phase oxidation. In such a system, the following reactions will occur in the presence of oxygen and hydrochloric acid, the latter being formed by the reaction above (34). 

During the following 15 years, only small advances were achieved in increasing catalyst efficiencies. Independently, Fenton [9a] at Union Oil and Nozaki [9b] at Shell Development Company (USA) discovered several related palladium chlorides, palladium cyanides, and zero-valent palladium complexes as catalysts. Sen and co-workers [10] reported that cationic bis(triphenyl-phosphine)-palladium tetrafluoroborate complexes in aprotic solvents such as dichloromethane, produced ethylene/carbon monoxide copolymers under very mild conditions. The reaction rates were, however, very low, as were the molecular weights. 

The next step, however is discussed contradictorily. In the first experiments it was already found that chloride and hydrogen ions inhibit the reaction between ethylene and palladium chloride [1, 10, 13] and it was concluded that an OH ion would attack the complexed olefin. This was confirmed by kinetic studies carried out by Moiseev et al. [14-16] and Henry [17, 18], leading to eq. (9) where K is the equilibrium constant for eq. (8) and k an overall rate constant. 

In a stereochemical study f-Cethylenel-da (C2H2D2) [32] was reacted with palladium chloride and cupric chloride under extreme conditions, i. e., extremely high chloride ion concentration as cupric and lithium chlorides. Under such conditions 2-chloroethanol was formed as the main product from ethylene, besides some acetaldehyde [33] (see Section 2.4.1.5.1) this is not the normal product of the Wacker reaction. In the above study the formation of cis-, 2-dideuterioethylene oxide, evidently via 1,2-dideuterio-2-chloroethanoI, suggests trans addition of water (nnh-hydroxypalladation). 

In the single-stage process (Figure 2) a mixture of ethylene and oxygen is passed through an aqueous solution of copper chloride and palladium chloride placed in a towerlike reactor (a). Acetaldehyde is formed according to eq. (6). 

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