Acetaldehyde pyrolysis

Since the conversion of C2H5 into C2H4 + H is indeed the slow step in the ethane pyrolysis, the occurrence of this reaction does explain the non-zero rates at maximal inhibition and the increase in rate at high NO concentrations. On the other hand, for reactions like the acetaldehyde pyrolysis the g - P transition is not rate limiting, and the Norrish-Pratt mechanism then gives no explanation for the behavior. Also, the Norrish-Pratt mechanisms as originally written down do not explain the large amounts of products such as H2O, N2 and N2O that are found in the ethane pyrolysis. 

The CH3 radicals are present in significant amounts in the acetaldehyde pyrolysis, being chain-carriers in the ethane pyrolysis, on the other hand, the CH3 radical concentration will be low, so that not much CH3NO will be formed. 

Acetonitrile, CH3CN, is formed in the ethane pyrolysis, but not in the acetaldehyde pyrolysis. These facts are easily explained if the main source of CH3CN is... 

In the acetaldehyde pyrolysis little C2H5 is present, so that little CH3CN can be formed. 

The results of Come et obtained at 520 °C in the investigation of acetaldehyde pyrolysis, are compatible with the pressure dependence of methyl recombination below 100 torr. 

The decompositions of the formyl and acetyl radicals are certain to be in the fall-off region at the pressures used in the investigations of the acetaldehyde pyrolysis. However, the complexity of the mechanism impedes any conclusion to be drawn from this system. 

The series of elementary steps below has been proposed to describe acetaldehyde pyrolysis to methane and CO. Derive the steady-state rate expression making the usual long-chain approximation i.e., that the chain length is very high. What comprises the apparent activation energy ... 

Decomposition. Acetaldehyde decomposes at temperatures above 400°C, forming principally methane and carbon monoxide [630-08-0]. The activation energy of the pyrolysis reaction is 97.7 kj/mol (408.8 kcal/mol) (27). There have been many investigations of the photolytic and radical-induced decomposition of acetaldehyde and deuterated acetaldehyde (28—30). 

Interestingly, the Fischer indole synthesis does not easily proceed from acetaldehyde to afford indole. Usually, indole-2-carboxylic acid is prepared from phenylhydrazine with a pyruvate ester followed by hydrolysis. Traditional methods for decarboxylation of indole-2-carboxylic acid to form indole are not environmentally benign. They include pyrolysis or heating with copper-bronze powder, copper(I) chloride, copper chromite, copper acetate or copper(II) oxide, in for example, heat-transfer oils, glycerol, quinoline or 2-benzylpyridine. Decomposition of the product during lengthy thermolysis or purification affects the yields. 

Non-catalyzed reactions have also been performed. For instance, the pyrolysis of glycerol in steam was studied in a laminar flow reactor in the temperature range 923-973 K. Acrolein is the principal product along with acetaldehyde and CO [21]. Reported yields were as high as 52% when pyrolysis was carried in steam at 923 K and atmospheric pressure. 

Table 8.1 shows the stochastic model solution for the petrochemical system. The solution indicated the selection of 22 processes with a slightly different configuration and production capacities from the deterministic case, Table 4.2 in Chapter 4. For example, acetic acid was produced by direct oxidation of n-butylenes instead of the air oxidation of acetaldehyde. Furthermore, ethylene was produced by pyrolysis of ethane instead of steam cracking of ethane-propane (50-50 wt%). These changes, as well as the different production capacities obtained, illustrate the effect of the uncertainty in process yield, raw material and product prices, and lower product... 

Reactions lla-e add up to Reaction 10. Reactions lla-b have been shown above to be catalyzed by Rh/CH3l. Reaction 11c, i.e. acid-catalysed pyrolysis of EDA to acetaldehyde and acetic anhydride, is well documented (9). Both reaction lid, hydrogenation of aldehyde, and Reaction lie, carbonylation of alcohols, are of course well known. The reaction sequence is in agreement with the fact that EDA and AH, especially in short-duration experiments, are detected as by-products. Acetaldehyde is also observed in small quantities, but no ethanol is found. Possibly, Reactions lid and He occur concertedly. We have separately demonstrated that both EDA and AH are suitable feeds to produce propionic acid under homologation reactions conditions. We thus demonstrated... 

Neither the thermal nor the cobalt-catalyzed decomposition of 3-butene-2-hydroperoxide in benzene at 100 °C. produced any acetaldehyde or propionaldehyde. In the presence of a trace of sulfuric acid, a small amount of acetaldehyde along with a large number of other products were produced on mixing. Furthermore, on heating at 100°C., polymerization is apparently the major reaction no volatile products were detected, and only a slight increase in acetaldehyde was observed. Pyrolysis of a benzene or carbon tetrachloride solution at 200°C. in the injection block of the gas chromatograph gave no acetaldehyde or propionaldehyde, and none was detected in any experiments conducted in methanol. 

All these reactions are endothermic and have high activation energies. The observation that acetaldehyde concentration rises during the pic darret while that of formaldehyde decreases suggests that only the last reaction is important and that formaldehyde is formed by oxidation (e.g., of CH3) rather than by pyrolysis. 

Ethane occurs in natural gas, from which it is isolated. Ethane is among the chemically less reactive organic substances. However, ethane reacts with chlorine and bromine to form substitution compounds. Ethyl iodide, bromide, or chlorides are preferably made by reaction with ethyl alcohol and the appropriate phosphorus halide. Important ethane derivatives, by successive oxidation, are ethyl alcohol, acetaldehyde, and acetic acid. Ethane can also be used for the production of aromatics by pyrolysis (Fig. 1). 

The a-aminocarbonyls are not only precursors of pyrazines, but can also lead to pyrroles,242 as well as imidazoles and oxazoles.243 Pyrolysis-GC-MS is relatively readily available and provides a productive technique. As mentioned previously, Wnorowski and Yaylayan212 had shown that, although more products are formed on pyrolysis than in aqueous media, most of the products identified in aqueous systems are present in pyrolysates with identical label distribution, even though the proportions may differ. Pyrolysates (250 °C, 20 s) of model systems of carbonyl and [2-13C]Gly or Ala were analysed. In the butanedione-Gly system, acetaldehyde and formaldehyde formed by decomposition of the carbonyl are unlabelled, but formaldehyde by Strecker degradation is labelled. 2,4,5-Trimethyloxazole was found to be unlabelled, being formed from acetaldehyde, but 4,5-dimethyloxazole was 15% mono-labelled, i.e., 15% of the precursor formaldehyde had been derived by Strecker degradation. 

Li, D., H. Haneda, S. Hishita, N. Ohashi and N.K. Labhsetwar (2005b). Fluorine-doped TiOj powders prepared by spray pyrolysis and their improved photocatalytic activity for decomposition of gas-phase acetaldehyde. Journal of Fluorine Chemistry, 126(1), 69-77. 

The pyrolysis of isoquinamine (XIII) to yield acetaldehyde has also been recorded (22). This fission may also proceed via a cyclic intermediate. 

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