Palladium-catalyst oxidants copper® acetate

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... 

In fact, the role of copper and oxygen in the Wacker Process is certainly more complicated than indicated in equations (151) and (152) and in Scheme 10, and could be similar to that previously discussed for the rhodium/copper-catalyzed ketonization of terminal alkenes. Hosokawa and coworkers have recently studied the Wacker-type asymmetric intramolecular oxidative cyclization of irons-2-(2-butenyl)phenol (132) by 02 in the presence of (+)-(3,2,10-i -pinene)palladium(II) acetate (133) and Cu(OAc)2 (equation 156).413 It has been shown that the chiral pinanyl ligand is retained by palladium throughout the reaction, and therefore it is suggested that the active catalyst consists of copper and palladium linked by an acetate bridge. The role of copper would be to act as an oxygen carrier capable of rapidly reoxidizing palladium hydride into a hydroperoxide species (equation 157).413 Such a process is also likely to occur in the palladium-catalyzed acetoxylation of alkenes (see Section 61.3.4.3). 

Esters 106 (R = Me, Et or Pr = Et, Pr, r-Bu or PhCHi) of aliphatic carboxylic acids react with lithium acetylides 107 (R = H, C5 Hi i or Ph) in the presence of boron trifluoride etherate in THE to give acetylenic ketones 108 (equation 18). Palladium-[tetrakis(triphenylphosphine)]-copper(I) iodide catalyses the oxidative addition-decarboxylation of propargyl methyl carbonates, e.g. 109, with terminal alkynes to yield 1,2-dien-4-ynes (allenylacetylenes) 110. The regiochemistry of the palladium-catalyzed addition of phenylacetylene to the allenic ester 111 depends on the nature of the catalyst used palladium(III) acetate-triphenylphosphine yields a 81 19 mixture of adducts 112 and 113, while in the presence of tetrakis(carbomethoxy)palladacyclopentadiene-tris(2,4,6-trimethoxyphenyl)phosphine the ratio is reversed to 9 91 k... 

As noted above, the oxidative reaction of ethylene with acetic acid forms vinyl acetate (Equation 16.107), and this reaction has been conducted on industrial settings in both the liquid phase and in the gas phase with a supported palladium catalyst. Allyl alcohol is also produced by palladium-catalyzed oxidations. The reaction of pro-pene with acetic acid in the presence of a combination of palladium and copper forms allyl acetate (Equation 16.108), which is hydrolyzed to the alcohol. Cyclic olefins also undergo allylic oxidation, in this case to generate allylic esters. A variety of combinations of palladium acetate and co-oxidants and additives give rise to this allylic ester in good to excellent yields. Equation 16.109 summarizes results for the reactions of cyclohexene. ... 

These oxidative carbonylations also occur with alkanes, although with low conversions of alkane and relatively low turnover numbers. Fujiwara reported that cyclohexane reacts with CO and K S Oj in the presence of palladium acetate and copper acetate in trifluoroacetic acid to form cyclohexane carboxylic acid with about 20 turnovers and about 4% yield based on alkane (Equation 18.24). Fujiwara also reported the carboxylation of methane with KjSjOj as oxidant with V(0)(acac)j as catalyst (Equation 18.25). This reaction occurred in 93% yield based on methane and with 18 turnovers. Sen reported a palladium(II)-catalyzed oxidative carbonylation of methane with hydrogen peroxide as the oxidant. Subsequently, he showed that RhClj catalyzes the conversion of methane, CO, and oxygen to acetic acid at 100 °C in water (Equation 18.26). Periana has reported a somewhat related transformation of methane to acetic acid, although the reaction is conducted in the absence of CO, and both carbon atoms of the acetic acid arise from methane (Equation 18.27). In this case, the CO appears to arise from oxidation of the methaiie, as shown in Scheme 18.5. 

Also, catalytic systems were studied by early workers. With palladium chloride or palladium acetate as catalyst, and copper(ll) chloride as oxidant, complicated reaction... 

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 ... 

Since, as shown in equation (34), palladium metal is precipitated as a byproduct of the reaction, it is necessary to reoxidize it back to the Pd " " state. This is accomplished with a palladium-copper couple, as depicted in equations (35) and (36), which is driven by oxygen. The reaction is carried out by contacting a mixture of ethylene and oxygen with a mixture of acetic acid, lithium acetate, and the palladium-copper couple at temperatures of 80 to 150 °C. The vapor-phase process is carried out under pressure at high temperatures (120 to 150 °C) using a fixed-bed palladium catalyst [218]. The oxidative acylation of ethylene can also be used for the preparation of the higher vinyl esters, although it is not currently used for that purpose, due to the low demand for those materials. 

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. 

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 ... 

The palladium catalysed substitution reaction of allylic systems has also been utilised in the formation of five membered rings. Intramolecular nucleophilic attack of the amide nitrogen atom on the allylpalladium complex formed in the oxidative addition of the allyl acetate moiety on the catalyst led to the formation of the five membered ring (3.63.). In the presence of a copper(II) salt the intermediate pyrroline derivative oxidized to pyrrole.80... 

Very simple experimental conditions (palladium(II) chloride (catalyst, 0.1 equivalent) copper(II) chloride (oxidant, 3 equivalents) and sodium acetate (buffer, 3 equivalents) in acetic acid under carbon monoxide at normal pressure and temperature) are necessary for this asymmetric route to saturated fused heterocycles with defined stereochemistry. 

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