Acetaldehyde and vinyl acetate

Ethylene can be oxidized to a variety of useful chemicals. The oxidation products depend primarily on the catalyst used and the reaction conditions. Ethylene oxide is the most important oxidation product of ethylene. Acetaldehyde and vinyl acetate are also oxidation products obtained from ethylene under special catalytic conditions. 

Kinetic Studies Provide Only Limited Mechanistic Information. While such studies are invaluable and frequently indicate the nature of pre-rate-determining steps, they provide almost no information concerning such vital fast steps as electron transfers and rearrangements. For example, despite extensive studies of the kinetics of acetaldehyde and vinyl acetate syntheses, it is clear only that olefin, nucleophile, and palladium combine in a complex. The nature of the rate-determining step as well as the details of post-rate determining product forming steps remains uncertain (7,94). In some cases—e.g., the metal-catalyzed autoxi-dation of thiols to disulfides—re-oxidation of metal to its catalytically... 

Both reactions were at the origin of the boom in palladium chemistry, scientifically as well as industrially. To render the previously cited reactions catalytic, the reduced form of Pd is reoxidized with the Cu2+/Cu+ redox couple, with the reduced form of copper finally being reoxidized with dioxygen. This chemistry is performed industrially with the chloride salts of Pd2+ and Cu2+ with ethylene as a feed, either in an aqueous or acetic acid medium. Products are acetaldehyde and vinyl acetate, respectively. 

Supported liquid-phase catalysts (SLPCs) combine the salient features of both homogeneous and heterogeneous catalysis for enhanced catalytic and/or process efficiency (337). SLPC catalysts, in which a liquid-phase (homogeneous) catalyst is dispersed within a porous support, have been used in Wacker-type ethylene oxidation for acetaldehyde and vinyl acetate production (337, 338). In the former case, a traditional homogeneous Wacker catalyst (vide supra) consisting of a chlorinated solution of Pd and Cu chlorides retained on a support with monomodal pore size distribution... 

Liquid phase oxidation of hydrocarbons by molecular oxygen forms the basis for a wide variety of petrochemical processes,3 "16 including the manufacture of phenol and acetone from cumene, adipic acid from cyclohexane, terephthalic acid from p-xylene, acetaldehyde and vinyl acetate from ethylene, propylene oxide from propylene, and many others. The majority of these processes employ catalysis by transition metal complexes to attain maximum selectivity and efficiency. 

The liquid phase processes resembled Wacker-Hoechst s acetaldehyde process, i.e., acetic acid solutions of PdCl2 and CuCl2 are used as catalysts. The water produced from the oxidation of Cu(I) to Cu(II) (Figure 27) forms acetaldehyde in a secondary reaction with ethylene. The ratio of acetaldehyde to vinyl acetate can be regulated by changing the operating conditions. The reaction takes place at 110-130°C and 30-40 bar. The vinyl acetate selectivity reaches 93% (based on acetic acid). The net selectivity to acetaldehyde and vinyl acetate is about 83% (based on ethylene), the by-products being CO2, formic acid, oxalic acid, butene and chlorinated compounds. The reaction solution is very corrosive, so that titanium must be used for many plant components. After a few years of operation, in 1969-1970 both ICI and Celanese shut down their plants due to corrosion and economic problems. 

An interesting approach to overcome these limits and thus combine the advantages of homogeneous and heterogeneous catalysis is that of supported liquid phase catalysts (SLPC or SLP). In SLPC the organometallic complex active components are dissolved in a small quantity of liquid phase dispersed in the form of an isle or film on the surface of supports. A SLPC has been applied successfully for several chemical transformations [113], particularly in the Wacker-type ethylene oxidation to acetaldehyde and vinyl acetate production by ethylene acetoxylation [114], and in other reactions catalyzed by Pd-complexes such as the Heck reaction [115]. 

The oxidative functionalization of olefins through ir-olefin complexes of palladium also has a long history, including the industrial production of acetaldehyde and vinyl acetate. Related reactions, including the conversion of olefins to vinyl ethers and enamines, have been studied in more recent times for fine chemical synthesis. These oxidative C-0 and C-N bond formations have been conducted with a variety of oxidants, including Oj, and have been studied as both intermolecular and intramolecular processes. 

The process is similar to the catalytic liquid-phase oxidation of ethylene to acetaldehyde. The difference hetween the two processes is the presence of acetic acid. In practice, acetaldehyde is a major coproduct. The mole ratio of acetaldehyde to vinyl acetate can he varied from 0.3 1 to 2.5 1. The liquid-phase process is not used extensively due to corrosion problems and the formation of a fairly wide variety of by-products. 

Poly(vinyl alcohol) (PVA) is a polymer of great interest because of its many desirable characteristics specifically for various pharmaceutical, biomedical, and separation applications. PVA has a relatively simple chemical structure with a pendant hydroxyl group (figure la). The monomer, vinyl alcohol, does not exist in a stable form, rearranging to its tautomer, acetaldehyde. Therefore, PVA is produced by the polymerization of vinyl acetate to poly(vinyl acetate) (PVAc) followed by the hydrolysis to PVA (figure 2). Once the hydrolysis reaction is not complete, there are PVA with different degrees of hydrolysis (figure lb). For practical purposes, PVA is always a co-polymer of vinyl alcohol and vinyl acetate [1]. 

PRATT, H. R. C. and Glover, S. T. Trans. Inst. Chem. Eng. 24 (1946) 54. Liquid-liquid extraction Removal of acetone and acetaldehyde from vinyl acetate with water in a packed column. 

Vinyl ethers are important raw materials in the production of glutaraldehyde, as well as of vinyl polymer materials which contain oxygen and are expected to degrade easily in Nature. The [IrCl(cod)]2 catalyzes an efficient exchange reaction between vinyl acetate 57 and alcohols or phenols 58, leading to the corresponding vinyl ethers 59 (Equation 10.11) [27]. Usually, the acid-catalyzed exchange reaction between alcohols and vinyl acetate results in alkyl acetates 60, and also to vinyl alcohol 61 which is readily isomerized to acetaldehyde 62. 

By-products formed during their preparation (e.g., ethylbenzene and divinyl-benzenes in styrene acetaldehyde in vinyl acetate) added stabilizers (inhibitors) autoxidation and decomposition products of the monomers (e.g., perox-... 

Under the same reaction conditions, acetaldehyde and butyraldehyde displayed near-complete conversion (greater than 95%). The photocatalytic oxidation of the alcohol 1-butanol displayed similarly high conversion levels, although conversion of methanol was somewhat lower. The oxygenated compounds methyl-t-butyl ether (MTBE), methyl acrylate, 1,4 dioxane, and vinyl acetate displayed conversion levels ranging from 92% to 100%. The lowest conversion levels of the oxygenated compounds studied were seen with the ketones used [acetone and 2-butanone (methylethylketone)], which displayed conversions of approximately 80%. The initial conversion levels seen with -hexane were similar... 

Oxidation of ethylene in alcohol with PdCl2 in the presence of a base gives the acetal of acetaldehyde and vinyl ether [39,40]. The reaction of alkenes with alcohols... 

Ethylene is readily absorbed by solutions of PdCl2 in acetic acid,5,4 but the presence of acetate ions (as NaOAc or LiOAc) is essential for reaction.S34a,b Van Helden et a/.53Sa found that ethylene at 1 atm reacts with Pd(OAc)2 at 70°C to form palladium metal and vinyl acetate (40-50%), together with acetaldehyde, ethylidene diacetate, and acetic acid. The rate of reaction increases considerably in the presence of sodium acetate and the selectivity to vinyl acetate is much higher (80-90%). 

Acetaldehyde is an intermediate in acetic acid and vinyl acetate production. Since 1916 it has been produced from the addition of water to acetylene, a reaction catalyzed by divalent mercury in sulphuric acid (20%)/water. Acetylene was made from coal. In Germany in particular, a lot of research was carried out on the use of acetylene as a chemical feedstock. 

Synthesis of (-I-) calanolide A (Scheme 8-11) was achieved by enzyme catalyzed resolution of the aldol products ( )-53. Compound 7 with acetaldehyde by aldol reaction in the presence of LDA/TiCU stereoselectively produced a mixmre of ( )-53 and ( )-54 (94% yield), the ratio of which was 96 4. ( )-53 was then resolved by lipase AK-catalyzed acylation reaction in the presence of tert-butyl methyl ether and vinyl acetate at 40 °C to obtain 41% yield of (+)-55 and 54% yield of the acetate (—)-56. Mitsunobu cyclization of (+)-55 in the presence of tri-phenylphosphine and dielthyl azodicarboxylate afforded 63% yield of (-l-)-43 with 94% ee as determined by chiral HPLC. Luche reaction on (+)-43 with CeCla 7H2O and triphenyl phosphine oxide and NaBH4 in the presence of ethanol at 30 °C gave the crude product. It was purified by column chromatography on silica gel to give 78% yield of a mixture containing 90% of (+)-calanolide A and 10% (+)-calanohde B, which were further separated by HPLC. 

Homogeneous Acetaldehyde and acetic anhydride react in liquid phase in the presence of a catalyst to give ethylidene diacetate, which decomposes to acetic acid and vinyl acetate. 

This is a kinetic resolution that works by enantioselective acylation of the unwanted enantiomer of the alcohol. The reaction is therefore an ester exchange and vinyl acetate is an efficient acetate transfer agent since the other product is vinyl alcohol better known as the enol of acetaldehyde so the reaction is irreversible. 

The equilibrium between acetaldehyde and vinyl alcohol is overwhelmingly in the direction of acetaldehyde. In fact, monomeric vinyl alcohol evidently has not been isolated. Yet poly (vinyl alcohol) is an important item of commerce. It is manufactured by the controlled hydrolysis of polymeric vinyl esters. In fact, a major fraction of the industrial homopolymer of poly(vinyl acetate) is used to... 

Evolving Production of the Acetyls (Acetic Acid, Acetaldehyde, Acetic Anhydride, and Vinyl Acetate) A Mirror for the Evolution of the Chemical Industry... 

In this chapter, we will discuss the evolution of processes for the production of the acetyl chemicals - acetic acid (AcOH), acetic anhydride (AC2O), acetaldehyde (AcH), and vinyl acetate (VA). These four materials coevolved in a series of synergistic relationships which ultimately led to the modem acetyl stream which now exceeds 6 X 10 kg/yr of acetyl (as acetic acid equivalents) per year and will be discussed in evolutionary context with each other. Opportunities and resultant innovations in the chemical industry are normally created when lower cost raw materials become available or existing products fail... 

The chemistry is more complex than would appear on the surface. When acetic anhydride reacts with acetaldehyde, it forms EDA in an equilibrium that favors EDA (Equation [8]), but a subsequent disfavorable equilibrium follows which forms acetic acid and vinyl acetate (Equation [9]). These equilibrium constants indicate that EDA is the most thermodynamically favored product. In the presence of acids, these equilibria occur rapidly. Using LeChatelier s principle, if the most volatile product, acetaldehyde, is continuously removed you can shift the equilibrium until only acetic anhydride remains which can then be distilled independently. (The equilibrium between EDA and vinyl acetate would prove to be pivotal in the later development of a vinyl acetate process.)... 

We have examined a number of materials in terms of toxic gas evolution during pyrolysis or combustion. For example, the products from fibreglass insulations included isocyanic acid and hydrogen cyanide, while the support backing and adhesive of a made-up panel produced acetic acid, acetaldehyde and vinyl chloride as well. The effect of a fire in a confined space such as a surface ship or submarine can be imagined. The products come from thermal decomposition of polymer coatings etc, and while the experimental conditions may not duplicate those of a fire, the information is very useful. 

The synthesis of starch acetate from starch and vinyl acetate witli acetaldehyde as a byproduct... 

By-products formed during their preparation (e.g., ethylbenzene and divin-ylbenzenes in styrene acetaldehyde in vinyl acetate) added stabilizers (inhibitors) autoxidation and decomposition products of the monomers (e.g., peroxides in dienes, benzaldehyde in styrene, hydrogen cyanide in acrylonitrile) impurities that derive from the method of storage of the monomer (e.g., traces of metal or alkali from the vessels, tap grease etc.) dimers, trimers, and polymers that are generally soluble in the monomer, but sometimes precipitate, for example, polyac-rylOTiitrile from acrylonitrile. Likewise, in polycondensation reactions it is important to remove reactive impurities because they can cause considerable interference during the polyreaction. 

A comprehensive set of data on the contacting of water and vinyl acetate was obtained by Pratt and Glover (65), with acetone and acetaldehyde as distributed solutes. Fig. 10.40. The water preferentially wet the packing, and when dispersed formed the rivulets on the packing previously described. In addition to the empirical correlations of the figure, Pratt and Glover... 

When one is discussing oxidation of olefins with dual metal catalysts it is difficult to avoid the subject of the Wacker reaction. This extremely important synthetic method using various mixtures of metal salts (Pd/Cu, Pd/Fe, Rh/Fe, etc.) allows the preparation of acetaldehyde or vinyl acetate from ethylene equations (1) and (2), as well as many other useful synthetic procedures. Reactions (1) and (2) occur, however, via nucleophilic attack of coordinated water or acetate, equations (319)-(321), followed by j3-hydrogen elimination. 

In the chemical industry, mercury is used as a catalyst for the manufacture from acetylene of acetaldehyde, vinyl chloride and vinyl acetate. Mercury acetate has been used in paints. The intention has been to protect boats against attack of mold fungus. Mercury fulminate Hg(ONC)2 was earher used in detonators, but is nowadays replaced by lead azide. 

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