Moiseev reaction

This reaction Moiseev reaction, cf. also Section 3.3.14.4 [2] was discovered in 1960 [1] and commercialized by Bayer, Hoechst, and some other companies [2] it can be performed both in the liquid and gas phase. The current industrial process for vinyl acetate monomer (VAM) is based on the gas-phase version with the formally heterogeneous Pd(Au-modified) catalyst. 

Route a is the Moiseev reaction-, the industrial Wacker oxidation (route b) is Pd-catalyzed and produces acetaldehyde by ethylene oxidation in aqueous solution [4, 8, 9]. 

What is the oxidation product of ethylene by O2 (Wacker process) in acetic acid (Moiseev reaction) Write the reaction mechanism. 

The oxidation of ethylene by palladous acetate in acetic acid has been examined by Moiseev et This reaction shows mixed stoichiometry ... 

Moiseev et al., who proposed initially that ethylidene diacetate was produced from addition of acetic acid to vinyl acetate, later showed this to be impossible from the result of reaction in CH3CO2D, preferring the following mechanism ... 

Solutions of Moiseev s giant Pd colloids [49,161-166] were shown to catalyze a number of reactions in the quasi homogeneous phase, namely oxidative ace-toxylation reactions [162], the oxidative carbonylation of phenol to diphenyl carbonate [166], the hydrogen-transfer reduction of multiple bonds by formic acid [387], the... 

The complex [A] is essentially the intermediate inferred in the mechanism proposed by Stern (60) to explain his results from the reaction between propene and PdCl2 in the presence of acetic acid. The kinetics of essentially the same reaction have been carefully investigated by Moiseev et al. (61) and a thorough study of each step in the reaction was recently reported by Henry (62). Henry, assuming that PdClg in an aqueous system exists in the form of [PdCl ] -, proposed that the steps in the reaction were as follows ... 

The selective oxidation of saturated hydrocarbons is a reaction of high industrial importance. Besides a variety of other oxidants, hydrogen peroxide as a very clean oxidant has also been used for these purposes . As an example, in 1989 Moiseev and coworkers reported on the vanadium(V)-catalyzed oxidation of cyclohexane with hydrogen peroxide (Scheme 146) . When the reaction was carried out in acetic acid cyclohexanol and cyclohexanone were formed, bnt conversions were very poor and did not exceed 13%. Employing CF3COOH as solvent, complete conversions could be obtained within 5 min-ntes. Here, cyclohexyl trifluoroacetate was the main product (85% of the products formed) resulting from the reaction of cyclohexanol (the primary product of the oxidation) with CF3COOH. 

In 1960, Moiseev and coworkers reported that benzoquinone (BQ) serves as an effective stoichiometric oxidant in the Pd-catalyzed acetoxylation of ethylene (Eq. 2) [19,20]. This result coincided with the independent development of the Wacker process (Eq. 1, Scheme 1) [Ij. Subsequently, BQ was found to be effective in a wide range of Pd-catalyzed oxidation reactions. Eor example, BQ was used to achieve Wacker-type oxidation of terminal alkenes to methyl ketones in aqueous DMF (Eq. 3 [21]), dehydrogenation of cyclohexanone (Eq. 4 [22]), and alcohol oxidation (Eq. 5 [23]). In the final example, 1,4-naphthoquinone (NQ) was used as the stoichiometric oxidant. 

Soon after the invention of the Wacker process the formation of vinyl acetate by the oxidative acetoxylation of ethylene using Pd(OAc)2 was discovered by Moiseev [16], and the industrial production of vinyl acetate based on this reation was developed. At present, vinyl acetate is produced commercially by a gas-phase reaction of ethylene, acetic acid and O using Pd catalyst supported on alumina or silica (eq. 1.11). 

Smidt, J. and Sieber, R. (1959) Reactions of palladium dichloride with olefinic double bonds. Angew. Chem., 71, 626. Moiseev, I.I., Levanda, O.G. and Vargaftik, M.N. (1974) Kinetics of olefin oxidation by tetrachloropalladate in aqueous solution. /. Am. Chem. Soc., 96, 1003. 

Alternatively, it may occur by 1,2-elimination of HPdCl followed by reverse readdition and reductive elimination. Moiseev and Vargaftik533 prepared the o-bonded complex independently by reaction of PdCl2 with 3-chloromercuri-ethanol and showed that it afforded acetaldehyde on decomposition ... 

The essence of the Wacker process is the invention of the reoxidation process for Pd° by using CuCh as a cocatalyst. Cu" salts are good reoxidants, but chlorination of carbonyl compounds takes place with CuCh. For example, chloroacetaldehyde is a by-product of the Wacker process. Chlorohydrin is another by-product from the reaction of ethylene with PdCh and CuCb. - Thus, a number of other reoxidants were introduced. When CuCl, pretreated with oxygen, is used, no chlorination of ketones takes place and the rate of the reaction is higher. - Also Cu(N03)2 and Cu(OAc)2 have been used. Oxidation of cy-clopentene with PdCl2/Fe(C104)3 combined with electrochemical oxidation was carried out. Benzoqui-none was used at first by Moiseev et al and later by many other researchers as a good reoxidant, but a stoichiometric amount is necessary. The oxidation of alkenes can be carried out smoothly with catalytic... 

Because of the ability of PdCl2 in aqueous systems to catalyze the oxidation of simple olefins to the corresponding aldehyde or ketone (268), considerable attention has been devoted to the study of the nature of the complex in solution and of the kinetics of the oxidation reaction. This subject has been thoroughly reviewed (4, 556). Moiseev and coworkers 414, 467, 468) have established that the complex equilibria in solution are as represented by Eqs. (6) and (7)... 

In keeping with this mechanism, Moiseev and Vargaftik reported that when the reaction was carried out in CH3COOD, no deuterium was incorporated in the ethylidene diacetate (197). However, no experimental... 

The formation of vinyl acetate from ethylene was first reported by Moiseev et al. (31), The compound was obtained by reaction of ethylene with PdCl2 in an acetic acid solution containing sodium acetate. Whether in this medium vinyl acetate formation occurs via the monomeric [PdCla C2H4] TT-complex, postulated as intermediate in the Wacker acetaldehyde process, or via the dimer (C2H4 PdCl2)2, previously described by... 

Anderson (2) and Kharasch (22, 23), was not established. [The complexes described by Anderson and Kharasch are believed today to be dimers of [PdCb C2H4] (7, 25, 28)]. Moiseev et al. left both possibilities open. Stern and Spector (37) favored the dimeric intermediate. They obtained vinyl acetate in 22 mole % yield, by reaction of ethylene with PdCl2 in isooctane containing acetic acid and NaoHP04. 

Moiseev and Vargaftik (36) have reported that deuterium is not incorporated into either vinyl acetate or ethylidene diacetate (III) when the vinyl acetate synthesis reaction is carried out in deuteroacetic acid. They considered this observation as evidence for a process such as Reaction 4 in which the final carbonium ion (VII) is forming products either by losing a proton or by reacting with acetate to give ethylidene diacetate (III). 

The next step in the reaction scheme—decomposition of the a-bonded alkylpalladium (XIV or XV)—has caused some controversy. To account for the results of several deuterium-labelling studies (15, 36, 54), a. palladium-assisted hydride transfer reaction (Reaction 4) has been proposed (36, 54). A number of inconsistencies in the studies using 2-deuteropro-pylene as substrate (54) have been discussed (i). In addition, the formation of a free carbonium ion such as VII [as proposed by Moiseev (36)], while accounting well for the formation of ethylidene diacetate, is much less satisfactory in accounting for the production of the unsaturated esters in an acetate-acetic acid medium. A simple elimination of -hydrogen (Reactions 13a and b) could also account for the products formed. While not necessary for the reaction, chloride assistance for proton removal is a possibility and has been postulated previously for a similar reaction (i, 37). 

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. 

For the last step a reductive elimination, whether through a carbonium ion intermediate by heterolysis [12] or by a concerted reaction [23] forming the hydrate of acetaldehyde, is more a philosophical question (eqs. (21) and (22)). Both routes would explain the findings of Moiseev and Vargaftik [22] that in... 

Acetoxylations (oxyacylations) have to be seen in context with olefin oxidation to carbonyl compounds (Wacker process, Section 2.4.1). With the lowest olefin, ethylene, acetaldehyde is formed. In water-free acetic acid no reaction takes place. Only in the presence of alkali acetates - the acetate ion shows higher nu-cleophilicity than acetic acid - ethylene reacts with palladium salts (eq. (1)) to give vinyl acetate, the expected product, as first reported by Moiseev et al. [1]. Stem and Spector [2] independently used [HP04] as base in a mixture of isooctane and acetic acid. This reaction could be exploited for a commercial process to produce vinyl acetate and closed the last gap replacing acetylene by the cheaper ethylene, a petrochemical feed material, for the production of large-tonnage chemical intermediates. 

Other authors found other rate expressions. Thus, Moiseev et al. [28] found at high sodium acetate concentration a dependence according to eq. (8) while sodium acetate accelerates the reaction at low concentration (also found by Grover et al. [29]). They interpreted the activation by sodium acetate in terms of the formation of a mononuclear Pd complex from polynuclear palladium chloride according to eqs. (9) and (10). 

Moiseev has proposed that the analogous reaction between ethylene tmd acetic acid to vinylacetate takes place on the Pd surface [130]. 

The Moiseev proposal is that reaction occurs on the Pd surface via an adsorbed... 

One final report of alkane activation has been reported by Moiseev. The mechanism of the reaction was not investigated, but this system might be classified as an electrophilic activation of methane, either of the Shilov type or of the concerted four-center type (Fig. lc) where X=triflate. Reaction of methane with cobalt(III)triflate in triflic acid solution leads to the formation of methyltriflate in nearly stoichiometric quantities (90% based on Co) (Eq. 18). Carbon dioxide was also observed, but not quantified. Addition of 02 led to catalysis (four turnovers) [79]. 

In the well-known Wacker process ethylene is converted to acetaldehyde by aerobic oxidation in an aqueous medium in the presence of PdCl2 as catalyst and CuCl2 as cocatalyst [7], Terminal olefins afford the corresponding methyl ketones. Oxidative acetoxylation of olefins with Pd(II) salts as catalysts in acetic acid was first reported by Moiseev and coworkers [8], The addition of an alkali metal acetate, e. g. NaOAc, was necessary for the reaction to proceed. Palladium black was also found to be an active catalyst under mild conditions (40-70 °C, 1 bar) in the liquid phase, if NaOAc was added to the solution before reducing Pd(II) to Pd black, but not afterwards [9,10]. These results suggested that catalytic activity... 

Two research groups, a Russian one with Moiseev et a/. [ 11 -13] and an American one with Henry [14,15], published an identical rate equation for reaction (9.2)... 

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