Oxidations 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... 

This elimination is reminiscent of the last step in the aqueous palladium chloride oxidation mentioned above and this reaction also may involve multiple hydride addition-elimination steps. Minor amounts of the normal products and Markovnikov products are also generally found in these reactions. Cupric chloride can be used as a reoxidant although the yields are generally lower than with an all acetate, non-catalytic reaction. 

Palladium catalysts are useful alternatives to Adams platinum oxide catalyst described in Section 111,150. The nearest equivalent to the latter is palladium chloride upon carbon and it can be stored indefinitely the palladium salt is reduced to the metal as required ... 

METHOD 2 Without a doubt, this is the current world favorite for making P2Ps. This method is known as the Wacker oxidation and involves mixing safrole (or any other allylbenzene), palladium chloride, cuprous chloride and dimethylformamide in an oxygen atmosphere to get MD-P2P very quickly and in a totally clean manner [11, 12]. There s also a very nice review in ref. 13. 

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). 

Oxidative Garbonylation. Carbon monoxide is rapidly oxidized to carbon dioxide however, under proper conditions, carbon monoxide and oxygen react with organic molecules to form carboxyUc acids or esters. With olefins, unsaturated carboxyUc acids are produced, whereas alcohols yield esters of carbonic or oxalic acid. The formation of acryUc and methacrylic acid is carried out in the Hquid phase at 10 MPa (100 atm) and 110°C using palladium chloride or rhenium chloride catalysts (eq. 19) (64,65). 

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... 

Palladium catalysts have been prepared by fusion of palladium chloride in sodium nitrate to give palladium oxide by reduction of palladium salts by alkaline formaldehyde or sodium formate, by hydrazine and by the reduction of palladium salts with hydrogen.The metal has been prepared in the form of palladium black, and in colloidal form in water containing a protective material, as well as upon supports. The supports commonly used are asbestos, barium carbonate, ... 

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... 

It has long been known that ethene can be oxidized to acetaldehyde in the presence of palladium chloride and water. This reaction was of no practical value since it required molar amounts of precious metal. 

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. 

An increased chloride ion concentration in the palladium-catalyzed oxidation of 1,3-cyclohexadiene resulted in a highly stereo- and regioselective 1,4-chloroacetoxylation35. The product selectivity was also high. Thus, palladium-catalyzed chloroacetoxylation afforded an 89% isolated yield of chloroacetate 29 which was >98% cis (Scheme 5). Only 1-2% of diacetate was observed in the crude product. 

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 reaction is highly exothermic as one might expect for an oxidation reaction. The mechanism is shown in Figure 15.1. Palladium chloride is the catalyst, which occurs as the tetrachloropalladate in solution, the resting state of the catalyst. Two chloride ions are replaced by water and ethene. Then the key-step occurs, the attack of a second water molecule (or hydroxide) to the ethene molecule activated towards a nucleophilic attack by co-ordination to the electrophilic palladium ion. The nucleophilic attack of a nucleophile on an alkene coordinated to palladium is typical of Wacker type reactions. 

The electrochemical Wacker-type oxidation of terminal olefins (111) by using palladium chloride or palladium acetate in the presence of a suitable oxidant leading to 2-alkanones (112) has been intensively studied. As recyclable double-mediatory systems (Scheme 43), quinone, ferric chloride, copper acetate, and triphenylamine have been used as co-oxidizing agents for regeneration of the Pd(II) catalyst [151]. The palladium-catalyzed anodic oxidation of... 

The more expedient, direct catalytic oxidation route to acetone was developed in Germany in the 1960s. If you had been in charge of building the acetone business from scratch, you d probably not have built any IPA-to-acetone plants if you had known about the Wacker process. It s a catalytic oxidation of propylene at 200—250°F and 125—200 psi over palladium chloride with a cupric (copper) chloride promoter. The yields are 91-94%. The hardware for the Wacker process is probably less than for the combined IPA/acetone plants. But once the latter plants were built, the economies of the Wacker process were not sufficient to shut them down and start all over. So the new technology never took hold in the United States. 

Palladium. Palladium catalysts are much like platinum, but a little more versatile. Palladium oxide is made by heating palladium chloride with sodium nitrate to fusion at 575-600°. Use palladium oxide (an equimolar amount) in the formulas already given for reducing with platinum oxide. Below is a reduction with palladium-carbon. 

Palladium catalysts resemble closely the platinum catalysts. Palladium oxide (PdO) is prepared from palladium chloride and sodium nitrate by fusion at 575-600° [29,30]. Elemental palladium is obtained by reduction of palladium chloride with sodium borohydride [27, 31], Supported palladium catalysts are prepared with the contents of 5% or 10% of palladium on charcoal, calcium carbonate and barium sulfate [32], Sometimes a special support can increase the selectivity of palladium. Palladium on strontium carbonate (2%) was successfully used for reduction of just y, (5-double bond in a system of oc, / , y, (5-unsaturated ketone [ii]. 

C(l) in 355 is in the oxidation state of an aldehyde or a ketone in 1-alkylated products. The necessary solvolytic attack of the enol carbamate double bond requires substoichio-metric amounts of a catalyst such as mercuric acetate or palladium chloride and one equivalent of acid (e.g. methanesulphonic acid) for binding the liberated diisopropylamine. 

Palladium oxide is prepared by heating palladium sponge in oxygen at 350°C. The oxide is obtained as a black powder. The oxide also may be prepared specially for catalytic use by heating a mixture of palladium chloride and potassium nitrate at 600°C and then leaching out water-soluble residue. A hydrated form of the oxide, which is acid soluble can be prepared by precipitation from solution, for example, by hydrolysis of palladium nitrate. The brown hydrated oxide converts to black anhydrous oxide on heating. Its solu-bdity in acids decreases with lowering of water content. 

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). 

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). 

Contrary to the ionic mechanism suggested by Tsuji, an insertion mechanism explains the facts much better. An external attack of carbon monoxide at the most positive carbon atom of propylene in a palladium chloride complex, as Tsuji proposed, would be expected to produce 3-chloro-2-methylpropionyl chloride rather than the observed product, 3-chlorobutyryl chloride. Since oxidation of propylene by Pd (II) ion gives acetone rather than propionalydehyde, a CO insertion reaction and elimination should produce the observed compound, 3-chlorobutyryl chloride... 

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,... 

Torisawa [17] developed an alternative oxidative amidation of aldehydes using palladium chloride (PdCl2)-xantphos complex as a catalyst. The use of hydrogen peroxide (H2O2)-urea complex as oxidant prevents the formation of imine from the carbinolamine intermediate and minimizes the level of benzoic acid side... 

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... 

---