Acetate formation from acetaldehyde oxidation

C. A. McDowell and J. B. Farmer, Fifth Symposium (International) on Combustion, p. 453, op. ciL, have shown the formation of peracetic acid as the principal initial product in the photosensitized and thermal oxidation of acetaldehyde. (See also earlier papers of McDowell and Farmer.) J. Grumcr, ibid, p. 447, also showed that, at low O2 content, C2H4, C He, CO, CH4, CH,OH, CHsCHO, and CH,CH2CHO were important products from propane pyrolysis in the range 350 to 475 C. He also found considerable amounts of acetic acid from the oxidation of CHaCHO in mixtures at 130 to 450 C having about 3 per cent O2. Such I0W-O2 mixtures are, of course, ideal for observing sensitized pyrolysis reactions. 

Infrared spectroscopy has also been employed to follow the formation of acetaldehyde and acetic acid on Pt during ethanol electro-oxidation. On the basal planes, acetaldehyde could be observed starting at about 0.4 V (vs. RHE), well before the onset of CO oxidation, while the onset of acetic acid formation closely follows CO2 formation [Chang et al., 1990 Xia et al., 1997]. This is readily explained by the fact that both CO oxidation and acetic acid formation require a common adsorbed co-reactant, OHads, whereas the formation of acetaldehyde from ethanol merely involves a relatively simple proton-electron transfer. 

Pd2+ salts are useful reagents for oxidation reactions of olefins. Formation of acetaldehyde from ethylene is the typical example. Another reaction is the formation of vinyl acetate by the reaction of ethylene with acetic acid (16, 17). The reaction of acetic acid with butadiene in the presence of PdCl2 and disodium hydrogen phosphate to give butadienyl acetate was briefly reported by Stem and Spector (110). However, 1-acetoxy-2-butene (49) and 3-acetoxy-l-butene (50) were obtained by Ishii and co-workers (111) by simple 1,2- and 1,4-additions using PdCl2/CuCl2 in acetic acid-water (9 1). 

From the mass spectrometric data and Eqs. (27) and (28), it is possible to calculate the relative current due to the formation of caibon dioxide, acetaldehyde and finally acetic acid from the ethanol oxidation reaction. These partial currents are shown in Fig. 36 for Pt/C, PtRu/C and PtsSn/C catalysts. " This figure clearly presents the efficiency of the three different catalysts towards the formation of reaction products resulting from the electro-oxidation of ethanol. This quantitative analysis allows us to evaluate the total number of exchanged electrons during the oxidation reaction and the global current efficiency (Aq) and product yield (Wq) of the reaction calculated from the total charge involved for each partial current (Table 4). 

Auld and Hantzsch, from acetaldehyde and mercuric oxide in slightly alkaline solution, obtained a base, trimercuridialdehyde hydroxide, which readily polymerised to a white powder, (CJTgOgHgg), . The latter decomposes without znelting at about 100° C, and is insoluble in the usual organic solvents, decomposed by dilute hydrochloric acid with formation of acetaldehyde and mercuric chloride, but not affected by dilate acetic acid. The investigators state that this is a delicate test for the presence of small quantities of acetaldehyde, since it detects the presence of one part of aldehyde in 6000 parts of water. ... 

However, if in nonaqueous solutions (discussed next) the oxidations also proceed through oxypalladation adducts, then the two mechanisms of decomposition of the oxypalladation adducts would predict diflFerent products. First, let us consider the mechanism of Jira, Sedlmeier, and Smidt (Reactions 50-53). In this case OH in II (Reaction 52) is replaced by OR. Decomposition via Reaction 55 is impossible, so II must decompose by solvolysis. This would give 1,1-disubstituted ethanes from ethylene oxidation. On the other hand, the first suggestion (Reaction 48) would probably be more consistent with formation of the vinyl compounds since hydride elimination should be completed if a rapid rearrangement of electrons to give acetaldehyde cannot occur. Evidence exists that 1,1-disubstituted ethanes are the initial products in methanol, and in acetic acid it is claimed that both vinyl acetate and 1,1-diace-toxyethane are initial products this suggests that in this solvent competition exists between palladium (II) hydride elimination and acetate attack. However, until now there have been no detailed studies of the oxidation under conditions where 1,1-disubstituted products are formed. More work is needed before the course of the reaction under these conditions is completely understood. 

Some of the substances are of greater concern than the others due to its relative quantities or to its flavored characteristic [1]. As an example, ethanol is the major compound in the group of alcohols being responsible for the formation of various other substances, such as acetaldehyde, resulting from ethanol oxidation, and it is the most abundant of the carbonylic compounds in distilled beverages. For the same reason, acetic acid is the major compound within its group, the carboxylic acids. 

The most important reactions that occur in catalytic aftertreatment of emissions from an ethanol-fuelled diesel engine are listed in Table 2. For a catalyst involved in this type of pollution control one of the most important qualifications is the selectivity towards complete oxidation of ethanol. This is indicated by the formation of acetaldehyde, which is the major by-product formed. Over some of the catalysts other by-products such as acetic acid, diethyl ether, methane and ethylene are also formed, but to a much lower extent. The low-temperature... 

By using pumice, asbestos, or copper as catalysts, Clock 14 claims the formation of acetaldehyde, acetic acid, and ethanol from the oxidation of ethane. The fact that practically the same conditions of operation are used for ethane as were used for methane oxidation makes it seem rather doubtful that products having the same number of carbon atoms as the original ethane should have been obtained in view of the fact that methane is much more resistant to oxidation than ethane and requires more severe treatment. 

Acetaldehyde to Acetic Acid. The formation of acetic acid furnishes an excellent example of liquid-phase oxidation with molecular oxygen. Acetic acid may be obtained by the direct oxidation of ethanol, but the concentrated acid is generally obtained by oxidation methods from acetaldehyde that may have been formed by the hydration of acetylene or the oxidation of ethanol. The oxidation usually occurs in acetic acid solution in the presence of a catalyst and at atmospheric or elevated pressures. Temperatures may range up to lOO C, depending upon conditions, but are usually lower. 

Besides maleic anhydride, the products of Kernos and Moldavskii contained formic and acetic acids, formaldehyde, acetaldehyde, methyl vinyl ketone, and furan. Formation of these intermediates was proposed by the scheme shown in Fig. 7. This scheme was devised from a study of vapor phase oxidation of individual materials all the intermediates and products shown were identified. Crotonaldehyde is a principal inter-... 

Oxidation of ethylene in alcohol with PdCl2 in the presence of a base gives the acetal of acetaldehyde as a major product and vinyl ether as a minor product. Methoxypalladation is the first step. Then hydride shift is followed by attack of methoxy anion to form the acetal of acetaldehyde. No deuterium incorporation is observed in the acetal formed from ethylene and MeOD, indicating that the hydride shift takes place as shown by 8 (path c). Formation of methyl vinyl ether can be understood by jS-H elimination. The elimination is a main path with higher alkenes. 

On a pure Pf/C catalyst, Rousseau et showed that the electro-oxidation of ethanol at the anode of a DEFC working at 80°C mainly led to the formation of acetaldehyde, acetic acid and carbon dioxide, with chemical yields of 47.5%, 32.5% and 20.0%, respectively. By comparing the mass yield and the faradic yields, they concluded that no other products were formed in a significant amount. This result confirms that Pt is able to break the C-C bond to some extent In situ infrared measurements on ethanol adsorption and electro-oxidation at platinum electrodes have clearly shown that the adsorbed CO species are formed from 0.3 V vs RHE at the platinum surface moreover Iwasita and Pastor found some traces of CH4 at potentials lower than 0.4 V vs RHE. Previous studies showed that the initial steps of ethanol adsorption and oxidation on Pt can follow two different modes ... 

There is strong evidence that TPP, in functioning as a coenzyme, combines directly with the substrate to form an active intermediate. This may be regarded as a further step in the metabolism of thiamine and the way in which the combination takes place is suggested by the thiamine-catalyzed nonenzymic formation of acetoin and acetic acid from diacetyl and acetaldehyde. It has been shown, by using C -labeled acetaldehyde, that this is not an oxidation-reduction but rather a transfer reaction. 

The complete electrooxidation of ethanol to CO2 releases 12 electrons and two molecules of CO2 per molecule of ethanol. Alas, in aqueous acid medium at room temperature, the partial oxidation of ethanol is the most favorable route, leading to the formation of acetaldehyde and acetic acid releasing of 2 and 4 electrons, respectively (see Figure 3.1). Whereas acetaldehyde can be further oxidized to acetic acid and CO2, acetic acid is a dead-end product of the electrooxidation of ethanol in acid medium. The formation of CO2 implies the scission of the C—C bond, a process which seems to be the bottleneck step for the complete oxidation of ethanol. Many aspects of the electrooxidation of ethanol still remain unclear in particular it not yet understood how the cleaving of the C—C bond proceeds. The nature of the ethanol adsorbate(s) and the intermediate adsorbed species leading to the cleavage of the C—C bond are also still under debate. Some authors propose that C—C scission can happen directly from ethanol whereas others claim that acetaldehyde (or acetyl) species are formed before C—C scission. The nature of the active site for the cleavage of the C—C scission is also under debate. 

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