Oxidation to acetaldehyde

In contrast with the well-known Embden-Meyerhof-Pamass glycolysis pathway for the conversion of hexose sugars to alcohol, the steps in conversion of ethanol to acetic acid remain in some doubt. Likely, ethanol is first oxidized to acetaldehyde and water (39). For further oxidation, two alternative routes are proposed more likely, hydration of the acetaldehyde gives CH2CH(OH)2, which is oxidized to acetic acid. An alternative is the Cannizzaro-type disproportionation of two molecules of acetaldehyde to one molecule of ethanol and one molecule of acetic acid. Jicetobacter... 

Equation 1 is referred to as the selective reaction, equation 2 is called the nonselective reaction, and equation 3 is termed the consecutive reaction and is considered to proceed via isomerization of ethylene oxide to acetaldehyde, which undergoes rapid total combustion under the conditions present in the reactor. Only silver has been found to effect the selective partial oxidation of ethylene to ethylene oxide. The maximum selectivity for this reaction is considered to be 85.7%, based on mechanistic considerations. The best catalysts used in ethylene oxide production achieve 80—84% selectivity at commercially useful ethylene—oxygen conversion levels (68,69). 

Isomerization of ethylene oxide to acetaldehyde occurs at elevated temperatures ia the presence of catalysts such as activated alumina, phosphoric acid, and metallic phosphates (75). Iron oxides also catalyze this reaction. Acetaldehyde may be found as a trace impurity ia ethylene oxide. 

Catalysts such as iron oxides cause isomeriza tion of the ethylene oxide to acetaldehyde with the evolution of heat. The acetaldehyde has a much lower autoignition temperature in air than does ethylene oxide, and the two effects may lead to hot-spot ignition (190,191). 

Compared with these methods, the palladium-catalyzed oxidation of 1-olefins described here is more convenient and practical. The industrial method of ethylene oxidation to acetaldehyde using PdCl2-CuCl 2-O2 original reaction of this type. The oxidation of various olefins has been carried out. ... 

In the course of the reaction, the Pd " ions are reduced to Pd metal, and ethylene is oxidized to acetaldehyde ... 

The catalyst is similar to that of the Wacker reaction for ethylene oxidation to acetaldehyde, however, this reaction occurs in presence of carbon monoxide. 

A direct route for acetone from propylene was developed using a homogeneous catalyst similar to Wacker system (PdCl2/CuCl2). The reaction conditions are similar to those used for ethylene oxidation to acetaldehyde. ... 

Alcohol dehydrogenase is a cytoplasmic enzyme mainly found in the liver, but also in the stomach. The enzyme accomplishes the first step of ethanol metabolism, oxidation to acetaldehyde, which is further metabolized by aldehyde dehydrogenase. Quantitatively, the oxidation of ethanol is more or less independent of the blood concentration and constant with time, i.e. it follows zero-order kinetics (pharmacokinetics). On average, a 70-kg person oxidizes about 10 ml of ethanol per hour. 

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. 

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 results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

The conversion of a chemical with a given molecular formula to another compound with the same molecular formula but a different molecular structure, such as from a straight-chain to a branched-chain hydrocarbon or an alicyclic to an aromatic hydrocarbon. Examples include the isomerization of ethylene oxide to acetaldehyde (both C2H40) and butane to isobutane (both C4H10). 

The substrate in most reactions of this type is an alcohol, which becomes oxidized to an aldehyde or ketone, e.g. ethanol is oxidized to acetaldehyde. Some reactions employ the alternative phosphorylated cofactor NADP+ the phosphate does not function in the oxidation step, but is merely a recognition feature helping to bind the compound to the enzyme. The full structures of NAD+ and NADP+ are shown in Box 11.1. 

In addition to alcohol dehydrogenase, ethanol can be oxidized to acetaldehyde by the microsomal mixed-function oxidase system (cytochrome P450 2 El), as illustrated in Figure 35.1. Although this microsomal ethanol-oxidizing system probably has minor impor-... 

Alcohols. In a reaction reminiscent of diazonium ion chemistry, 26 is reduced by ethanol to 13 (R = H). The ethanol is oxidized to acetaldehyde (72UP1). Like water, decomposition of 26 in f-butanol gives nitrogen in quantitative yield, but the other product is intractable. 

Consequently, under these conditions, ethanol may be totally oxidized to carbon dioxide via the first reaction, partially oxidized to acetaldehyde via the second reaction, dehydrogenized... 

Ethylene can be oxidized to acetaldehyde in high yields similar to the Wacker-process if electrogenerated palladium(ll) is used as catalyst. In this way the copper(II) catalyzed air oxidation of palladium(O) is replaced by the electrooxidation according to Eq. (40). 

Oxidation with Palladium in the Homogeneous Phase. The most thoroughly studied reaction concerning the transformation of alkenes to carbonyl compounds is their oxidation catalyzed by palladium in homogeneous aqueous media.243 244 494-503 As a rule, ethylene is oxidized to acetaldehyde, and terminal alkenes are converted to methyl ketones.504 505... 

In the presence of nitrogen oxides, ethyl alcohol is readily oxidized to acetaldehyde and this chemical change can upset the nitration reaction, if the add contains appreciable amounts of nitrogen dioxide. 

Lactic Acid. Qualitative and even semiquantitative data are obtained by paper chromatography. Quantitative procedures where lactic acid is oxidized to acetaldehyde and the acetaldehyde determined colorimetri-cally are available (4,13, 22, 90). 

The wine yeast, Saccharomyces fermentati, is able to form a film or veil on the surface of dry white wines of about 15-16% alcohol. This yeast produces agreeable smelling and tasting substances which dissolve in the wine and give it the aroma and flavor characteristic of Spanish fino sherries. To provide itself with energy for growth while in the film form on the surface of the wine, the yeast utilizes some of the oxygen from the atmosphere above the wine in the partially filled butt or barrel to oxidize some of the ethyl alcohol from the wine. The ethyl alcohol of the wine is not completely metabolized to carbon dioxide and water, however, but is oxidized to acetaldehyde—probably the principal compound in the complex mixture responsible for the aroma of this type of appetizer wine. 

The selectivity of ethylene oxidation was found to be independent of feed composition at zero conversion. This was interpreted to mean that each of the two parallel processes is initiated by a similar type of transformation. Selectivity at zero conversion appeared to approach, a value considerably different from 100%. Therefore the Initial rate of carbon dioxide formation does not approach zero, as it should if it has to arise exclusively from ethylene oxide. The initial rate of ethylene oxide oxidation was found to depend on the partial pressure of both ethylene oxide and oxygen. Orzechoweki and Mac-Cormack concluded from this, in conflict with Twigg s earlier proposal,1771 that isomerization of ethylene oxide to acetaldehyde ie not a significant step in its further oxidation, Ethylene oxide could undergo oxidation either on the catalyst surface or in the gas phase by ooffision with an adsorbed oxygen atom.127 ... 

The chemical reactions in the preparation appear to be as follows. (1) The alcohol is oxidized to acetaldehyde, and (2) the nitrous acid which is formed attacks the acetaldehyde to form a nitroso derivative which goes over to the more stable, tautomeric, isonitroso form. 

One of the earliest uses of palladium(II) salts to activate alkenes towards additions with oxygen nucleophiles is the industrially important Wacker process, wherein ethylene is oxidized to acetaldehyde using a palladium(II) chloride catalyst system in aqueous solution under an oxygen atmosphere with cop-per(II) chloride as a co-oxidant.1,2 The key step in this process is nucleophilic addition of water to the palladium(II)-complexed ethylene. As expected from the regioselectivity of palladium(II)-assisted addition of nucleophiles to alkenes, simple terminal alkenes are efficiently converted to methyl ketones rather than aldehydes under Wacker conditions. 

Since methyl dioxolane can amount to as much as ten percent of the dioxane, a termination of this kind could account for the low yield from regenerated ions but this scheme puts a lot of weight on the presence of dioxolane, a product which could, after all, arise by direct rearrangement of oxide to acetaldehyde. Furthermore, the zero order dependence on monomer does not necessarily rule out direct reaction between oxonium ion and monomer for it will be recalled that Meerwein observed that the inner oxonium salt complexed very strongly with a molecule of ether. If reaction were to occur between an ion and a monomer molecule held in this way, the rate could be independent of the monomer concentration. 

TPPS)Fe-O-Fe(TPPS)]8" 2 [Fe"(TPPS)]4" Solvent water + ethanol Xilr = unspecified ethanol oxidized to acetaldehyde [255]... 

For long time, Pd has been used mainly as a heterogeneous catalyst for the hydrogenation of unsaturated bonds. A revolution in Pd chemistry occurred with the development of homogeneous Pd catalysts. The first example was the invention of the Wacker process in 1959, by which ethylene is oxidized to acetaldehyde using PdCl2 and CuCl2 as catalysts in aqueous solution (eq. 1.10) [13]. 

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