Ethene to vinyl acetate

But how ubiquitous actually are alkalis in the promotion of reactions catalyzed at metal surfaces An examination of recent authoritative sources [6,7] shows that the majority of medium-to large-scale processes do not employ alkali promoters, even when one includes nonmetallic (i.e., metal oxide) catalysts. In a number of cases (e.g., steam reforming of naphtha) it seems clear that the role of alkali is simply to reduce the acidity of the oxide support. There are famous cases, of course, where the presence of alkali species on the catalytically active metal surface is critically important to the chemistry. Notable are ethene epoxidation (Ag-Cs), ammonia synthesis (Fe-K), acetoxylation of ethene to vinyl acetate (Pd, Pd/Au-K), and Fischer-Tropsch synthesis (Fe, Co, Ru-K). The first three are major industrial... 

The fact that gold is active under very mild conditions means that its potential as a selective oxidation catalyst is high, and many selective oxidation processes are important in the chemical industry [1,2]. Papers have been published on the selective oxidation of propene to propene oxide in the presence of hydrogen, oxidation of sugars and aldehydes to acids, and the oxidation of alcohols and other hydroxyl-compounds. Au-Pd catalysts have been used to oxidize ethene to vinyl acetate in the presence of acetic acid and oxygen and this is a process used by a number of manufacturers worldwide. The selective oxidation of hydrogen to hydrogen peroxide, rather than water, is also catalyzed efficiently by supported Au-Pd catalysts [49]. 

Using ethene in ethanoic acid at 70-80 C it is possible to prepare vinyl acetate (ethenyl ethanoate) in good yields. 

Rhodium complexes catalyze the oxidative coupling of benzene with ethene to produce styrene directly.45,45a,45b Using Rh(ppy)2(OAc) (ppyH = 2-phenylpyridine), the reaction of benzene with ethene in the presence of 02 and Cu(OAc)2 in benzene and acetic acid at 180 °C gives styrene and vinyl acetate in 77% and 23% selectivities, respectively. 

Ethanal is only used as an intermediate to acetic acid and its derivatives and in the near future production of ethanal will be replaced by other routes based on methanol and syn-gas to give acetic acid and acetic anhydride. Vinyl acetate can also be made via syn-gas routes, but the major producer in Europe employs a direct Wacker route with a heterogeneous palladium catalyst (former Hoechst ethene, acetic acid -from syn-gas-, and oxygen). 

The first examples of ortho cycloaddition can be found in a U.S. patent of Ayer and Buchi [1], Benzonitrile and 2-methylbut-2-ene are reported to yield 7,8,8-trimethylbicyclo[4.2.0]octa-2,4-diene-l-carbonitrile upon irradiation under nitrogen with a mercury resonance arc. Similar reactions, all leading to derivatives of bicyclo[4.2.0]octa-2,4-diene-l-carbonitrile occurred when benzonitrile was irradiated in the presence of 2,4,4-trimethylpent-l-ene, ethyl vinyl ether, vinyl acetate, methyl vinyl ketone, and methyl acrylate. The addend pairs para-tolunitrile/oct-l-ene, ort/m-dicyanobenzene/2-methylbut-2-ene, para-dicyanobenzene/but-l-ene, 2,3-dimethylbenzonitrile/propene, and 3,4,5-trimethylbenzonitrile/ethene likewise produced ortho photocycloadducts. 

The industrial synthesis of vinyl acetate [14] via palladium-catalyzed oxidative coupling of acetic acid and ethene using direct 02 reoxidation has already been mentioned (Scheme 3, d). Some NaOAc is required in the reaction medium, and catalysis by Pd clusters, as alternative to Pd(II) salts, was proposed to proceed with altered reaction characteristics [14]. Similarly, the alkenyl ester 37 (Table 5) containing an isolated vinyl group yields the expected enol acetate 38 [55] whereas allylphenol 39 cyclizes to benzofuran 40 with double bond isomerization [56]. 

The first set of reactions is the mainstay of the petrochemical industry 1 outstanding examples are the oxidation of propene to propenal (acrolein) catalysed by bismuth molybdate, and of ethene to oxirane (ethylene oxide) catalysed by silver. In general these processes work at high but not perfect selectivity, the catalysts having been fine-tuned by inclusion of promoters to secure optimum performance. An especially important reaction is the oxidation of ethene in the presence of acetic (ethanoic) acid to form vinyl acetate (ethenyl ethanoate) catalysed by supported palladium-gold catalysts this is treated in Section 8.4. Oxidation reactions are very exothermic, and special precautions have to be taken to avoid the catalyst over-heating. 

It is convenient to consider the synthesis of vinyl acetate at this point, because it involves the aerobic oxidation of ethene to the unstable intermediate ethenol (H2C=CH(OH)), followed by its immediate esterification with acetic (ethanoic) acid,... 

The commercial process for vinyl acetate production has evolved over the years. Early in the 1930s, Wacker developed a process based upon the gas-phase conversion of acetylene and acetic acid over a zinc acetate catalyst supported on activated carbon. Later, in 1960s, a more economically favourable gas-phase process was introduced involving the acetoxylation of ethene over a Pd-based silica supported catalyst. Ethene, acetic acid and oxygen reacted to form vinyl acetate and water [122,237-242] ... 

However, earlier findings [247] showed that very highly dispersed palladium catalysts had very low activity for VA formation. This was attributed to the very small particles being inaccessible to the ethene feed due to their being completely embedded within the acetic acid/acetate liquid layer (ethene has very low solubility in acetic acid). Vinyl acetate formation may therefore be restricted to the larger Pd-Au alloy particles accessible to gaseous ethene. This... 

Diels-Alder reactions of cyclopentadiene with different alkenes proceed at different rates. Cyclopentadiene reacts with acrolein in ether at room temperature (24 h) to give a 95% yield of 27.59 contrasts with the reaction of cyclopentadiene and ethene in ether to give a 74% yield of norbornene (28), but required heating to 200°C in an autoclave at 5800 psi pressure or 32 h. The presence of an electron releasing group on the alkene causes the reaction to proceed with greater difficulty. Vinyl acetate reacted with cyclopentadiene at 190°C in an autoclave (10 h, neat) to give only 25% of 29. 

The major route for the industrial production of vinyl acetate, the monomer of polyvinyl acetate (emulsion paints, adhesives) and its hydrolysis product, polyvinyl alcohol (textiles, food packaging) is closely related to the Wacker acetaldehyde process, but the industrial catalysts are heterogeneous. A mixture of ethene, oxygen and acetic acid is passed over a palladium catalyst supported on alumina at 100-200°C. The overall reaction is H C=CH2-hCHjCO H-hyO ->H2C=CHC02CH3 -hH O. Ethene is no longer cheap, so that work is being pursued to make vinyl acetate from synthesis gas (p. 384). 

The practically most important copolymer is made from ethene and propene. Titanium- and vanadium-based catalysts have been used to synthesize copolymers that have a prevailingly random, block, or alternating structure. Only with Ziegler or single site catalyst, longer-chain a-olefins can be used as comonomer (e.g., propene, 1-butene, 1-hexene, 1-octene). In contrast to this, by radical high-pressure polymerization it is also possible to incorporate functional monomers (e.g., carbon monoxide, vinyl acetate). The polymerization could be carried out in solution, slurry, or gas phase. It is generally accepted [173] that the best way to compare monomer reactivities in a particular polymerization reaction is by comparison of their reactivity ratios in copolymerization reactions. 

At elevated temperatures, ethene can be copolymerized with a number of unsaturated compounds by radical polymerization [174-180] (Table 7). The commercially most important comonomers are vinyl acetate [181], acrylic acid, and methacrylic acid as well as their esters. Next to these carbon monoxide is employed as a comonomer, as it promotes the polymer s degradability in the presence of light [182]. 

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