Acetaldehyde radical mechanism

Homogeneous Oxidation Catalysts. Cobalt(II) carboxylates, such as the oleate, acetate, and naphthenate, are used in the Hquid-phase oxidations of -xylene to terephthaUc acid, cyclohexane to adipic acid, acetaldehyde (qv) to acetic acid, and cumene (qv) to cumene hydroperoxide. These reactions each involve a free-radical mechanism that for the cyclohexane oxidation can be written as... 

Peroxynitrite reacts with heme proteins such as prostacycline synthase (PGI2), microperoxidase, and the heme thiolate protein P450 to form a ferryl nitrogen dioxide complex as an intermediate [120]. Peroxynitrite also reacts with acetaldehyde with the rate constant of 680 1 mol 1 s" 1 forming a hypothetical adduct, which is decomposed into acetate, formate, and methyl radicals [121]. The oxidation of NADH and NADPH by peroxynitrite most certainly occurs by free radical mechanism [122,123], Kirsch and de Groot [122] concluded that peroxynitrite oxidized NADH by a one-electron transfer mechanism to form NAD and superoxide ... 

However, the ethylene and acetaldehyde appearing among the final products may also originate through non-radical mechanisms, namely ft elimination processes that are prevalent for these alkoxygermanes (equations 41 and 42). 

The fact that the decomposition of ozonides is catalyzed by finely divided metals (silver, platinum, palladium) and metal salts such as ferrous sulfate suggests a free-radical mechanism.23 2-Butene ozonide is broken down with dilute ferrous sulfate solution into acetic acid and acetaldehyde.23... 

Ethanolamine ammonia lyase. EAL converts ethanol-amine to acetaldehyde, with loss of ammonia. EAL depends upon adenosylcobamides, such as coenzyme B12 (3), but a range of other adenosylcobamides are also accepted as cofactors, while cobalamins with /3-ligands other than the 5 -deoxy-5 -adenosyl group (of AdoCbl) are inhibitors. Active EAL is multimeric and has an apparent molecular mass of about 560 600kDa. Similar to the mechanism of DD, a radical mechanism is proposed for the isomerization of the vicinal amino-alcohol substrates (ethanolamine, (/f)- and (5)-aminopropanol) by EAL, starting with the abstraction of an H atom from the C-1 position of the substrates. 

It was proved by a separate experiment that isotope mixing in a mixture of methane and methane-i proceeds very slowly even above 600 °C. Thus, it must be concluded that, in the pyrolysis, the formation of the partially deuterated methanes is a result of free radical reactions and not of the secondary exchange of the methanes. Consequently, these results support the free radical mechanism of the acetaldehyde decomposition. 

As shown in the pyrogram of poly(L-lactide), the main pyrolysis products are CO and acetaldehyde. The pyrolysis probably takes place by a free radical mechanism including the following reactions ... 

Highly strained systems sueh as bicyelobutane (14) and [1.1. l]propellane (15) readily underwent addition of bromotrichloromethane across the central bond by a radical mechanism. Benzoyl peroxide eatalyzed a number of addition reactions to the extremely strained central bond of [l.l.l]propellane (15). Examples were acetaldehyde, cyanogen bromide, deuteriochloroform, diphenyl disulfide, diphenyl diselenide, iodine, and tert-butyl hypochlorite.Radical chain addition of various organic disulfides to [l.l.ljpropellanes (15), initiated by 2,2 -azobis(iso-butyronitrile) gave the normal adducts across the strained central bond and homologs that contained two or more bicyclo[l.l.l]pentane moieties. 

It is generally conducted in the liquid phase, in the presence of manganese, cohalt or copper salts (acetatesX by a chain free radical mechanism involving the intermediate formation of peracetic add. This may either decompose to form acetaldehyde and oxygen, or react with the components of the reaction medium to yield a mixed metallic complex of the acetaldehyde and the peradd.. -... 

Aldehydes are considerably more reactive toward OH radicals than alkanes, so that the aldehydes produced are subject to further oxidation. Thereby additional NO is converted to N02. To give an example, let R, stand for CH3 so that RjCHO represents acetaldehyde. The mechanism for acetaldehyde oxidation may be written as follows ... 

Using the combination of molecular oxygen, acetaldehyde and N-hydroxyphthalimide (the last compounds is a component - in addition to a metal complex - of the catalyst in the Ishii oxidation reaction), it is possible to oxidize alkylaromatic hydrocarbons and cycloalkanes in acetonitrile at room temperature [40a]. The reaction occurs via a radical mechanism depicted in Scheme II.5. 

The principal studies of acetaldehyde oxidation are those of Bogdanovskii and Shlygin, who have proposed an electron-radical mechanism which is of the form ... 

The resistance of poly(ethylene terephthalate) to photochemical degradation is very good. Some thermal degradation occurs when the polymer is heated above the melting point, the principal products being carbon dioxide, acetaldehyde and terephthalic acid. The reaction may proceed by either the molecular or free radical mechanism shown below ... 

Chlorine dioxide oxidizes triethylamine to the secondary amine and acetaldehyde (equation 63) a free-radical mechanism was proposed... 

Supercritical CO2 is a non-polar, aprotic solvent and promotes radical mechanisms in oxidation reactions, similar to liquid-phase oxidation. Thus, wall effects might occur as known, e.g. from olefin epoxidation with 02 or H202 which may decrease epoxide selectivities. The literature covers the synthesis of fine chemicals by oxidation either without catalysts (alkene epoxidation, cycloalkane oxidation, " Baeyer-Villiger oxidation of aldehydes and ketones to esters ), or with homogeneous metal complex catalysts (epoxidation with porphyrins, salenes or carbonyls ). Also, the homogeneously catalysed oxidation of typical bulk chemicals like cyclohexane (with acetaldehyde as the sacrificial agent ), toluene (with O2, Co +/NaBr ) or the Wacker oxidation of 1-octene or styrene has been demonstrated. 

Ethoxyethylperoxyls were prepared by a variety of methods and react to give ethyl acetate, ethanol, acetaldehyde and ethyl formate. (Table V). There was no evidence for the formation of di-(1-ethoxyethyl) peroxide, a result that is not entirely incompatible with Diaper s work in view of the large difference in the size the peroxy radicals studied by the two groups of workers. The absolute yields of the products were difficult to ascertain with any degree of certainty because of secondary reactions. The high yield of ethyl formate is, however, diagnostic for the intermediacy of alkoxy radicals and indicates that at least 20 of the self-reactions of 1-ethoxyethylperoxyls occur via the radical mechanism. 

This agrees with experimental findings on the decomposition of acetaldehyde. The appearance of the three-halves power is a wondrous result of the quasisteady hypothesis. Half-integer kinetics are typical of free-radical systems. Example 2.6 describes a free-radical reaction with an apparent order of one-half, one, or three-halves depending on the termination mechanism. 

Solution The procedure is the same as in the acetaldehyde example. ODEs are written for each of the free-radical species, and their time derivatives are set to zero. The resulting algebraic equations are then solved for the free-radical concentrations. These values are substituted into the ODE governing RCl production. Depending on which termination mechanism is assumed, the solutions are... 

Reduction of vinyl radicals by to the corresponding anion also has been observed (216). When purified acetylene is bubbled through Fenton s reagent, acetaldehyde is formed as a product, presumably via the following mechanism ... 

For n-alkanes, n-alcohols, 1-chloroalkanes, n-ethers, and chloroethenes, the carbon chain length influences the reactivity, and the clear linear correlations indicate that the attack mechanism of these pollutants by OH or Cl radicals occurs via the same pathway. However, such correlations do not hold true for aromatics, ketones, and aldehydes, for reasons discussed in our previous paper [3]. We also estimated missing values of kci by analogy for ethylbenzene, we take kci = 1.5e-10 cm molecule S, greater than that for m-xylene, but smaller than the 2.0e-10 cm molecule- s-i value for very reactive compoxmds. Also we estimate a similar value for butyraldehyde kci = le-10 cm molecule- s-, only 10% larger than kci of acetaldehyde to remain consistent with the equivalent koH value. 

A possible free-radical chain mechanism for the thermal decomposition of acetaldehyde (to CH4 and CO) is the Rice-Herzfeld mechanism (Laidler and Liu, 1967) ... 

The mechanism of this reaction involves free radical oxidation of butane to butane hydroperoxide, which decomposes to acetaldehyde via P scissions. It is similar to the oxidation of cyclohexane to cyclohexanol and cyclohexanone, which will be discussed in Chapter 11, Section 4. 

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