Acetaldehyde and higher aldehydes

General features of the ignition regions of acetaldehyde, propion-aldehyde, iso- and n-butyraldehyde and acrolein have been described by Newitt et al. [110]. These authors were able to show that there was a generar similarity in the ignition behaviour of these aldehydes, although 

A further region is recognized by the presence of a pic d arret , an abrupt but weak emission of light occurring towards the conclusion of reaction. A mechanistic interpretation of this has yet to be given, but this phenomenon indicates a high radical concentration at this stage of reaction. 

Flow systems offer the special advantage that by a suitable choice of initiating temperature and flow conditions, a spatial separation along the 

Cool flames were somewhat more difficult to establish with propion-aldehyde than with acetaldehyde and it was necessary to use a higher initial tube temperature (270 C). In its general features, this system resembled that of acetaldehyde, although the second stage flame was less sharply defined. The analytical data were more complex and considerable production of ethylene occurred, presumably via (42), the ethyl radicals being the result of C2H5 CO dissociation. 

Recently Halstead et aL [122, 122a] have proposed a model for acetaldehyde cool flame combustion which is basically similar to that described above. Their treatment accounts for the periodicity and the self-quenching which is attributed to a thermal switch in which the decomposition of CH3CO 

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A side reaction occurring with acetaldehyde and higher aldehydes containing a-hydro-gens is aldol condensation [Hashimoto et al., 1976, 1978 Yamamoto et al., 1978], Aldol reaction can be extensive at ambient temperatures and higher but is avoided by polymerization at low temperature. 

Competing side reactions in cationic polymerization of carbonyl monomers include cyclotrimerization and acetal interchange. Cyclotrimerization is minimized by low-polarity solvents, low temperatures, and initiators of low acidity. Acetal interchange reactions among different polymer chains do not occur except at higher temperatures. Acetaldehyde and higher aldehydes are reasonably reactive in cationic polymerization compared to formaldehyde. Haloaldehydes are lower in reactivity compared to their nonhalogen counterparts. 

Acetaldehyde and higher aldehydes ALD Peroxy radicals with carbonyl groups ... 

Similarly, with acetaldehyde and propionaldehyde as the starting materials, one gets the 2,4-dimethyl-6-ethyl- and 2-ethy 1-4,6-dimethyl derivatives (33,37), In the presence of acetaldehyde, the higher aldehydes give various substituted... 

Polymerization of aldehyde by typical cationic catalysts such as sulfuric acid and titanium tetrachloride is considered to reflect the steric factor. Acetaldehyde gave an isotactic-rich amorphous polymer whereas propionaldehyde and higher aldehydes gave isotactic crystalline ones. The yield of polymer and the stereospecificity of polymerization increased with the increase in the bulkiness of the alkyl group of the aldehyde (Table 7). 

Fig. 8D.7 Aldehyde metabolism, showing key role of acetaldehyde in formation of branched-chain and higher aldehydes, and diacetyl and acetoin...

The kinetics of cationic polymerization of acetaldehyde or higher aldehydes in solution are even less understood. No rate data on acetaldehyde polymerization with BF3 in ether are available [6]. It is only known that after an induction period of 5—15 min a vigorous polymerization occurs which is completed in a few minutes. No attempts were made to control the temperature during this uncontrolled reaction and polymer precipitated. Other cationic polymerizations of acetaldehyde with less... 

The use of ozone in the oxidation of the heavier hydrocarbons is subjected to the same restrictions surrounding its industrial use as with the natural gas hydrocarbons, chiefly cost. Consequently, even less work has been done with it in regard to the heavy hydrocarbons than is true of methane. Where ozonized air is passed into boiling n-hexane a series of oxidation products results consisting of aldehydes (formaldehyde, acetaldehyde in preponderance and higher aldehydes up to hexoic), fatty acids probably also up to six carbon atoms, and a mixture of esters.88... 

Although acetaldehyde is the primary aldehyde present in wines, there are reports of hydroxymethylfurfural, furfural, and higher aldehydes. Acetal and acetone are also found in some wines. 

Formalin added to 2 moles of acetoacetanilide in ethanol, stirred until soln. is effected, and the product isolated after 4-5 days a, -diacetylglutaranilide. Y 90%.—Acetaldehyde gives much lower yields and higher aldehydes fail to react in the absence of a catalyst. F. e. s. B. D. Wilson, J. Org. Chem. 28, 314 (1963). 

Potassium Cyanide Method. Romijn also devised this method of formaldehyde determination which is considered by Mutschin to be as. accurate as the sodium sulfite, alkaline peroxide, and iodimetric methods for pure solutions of formaldehyde, and superior to them in the presence of acetoner acetaldehyde, benzaldehvde, higher aldehydes, and ketones. The procedure is based on the quantitative formation of cyanohi drin when formaldeh de is treated vith a solution containing a -known excess of potassium cyanide. 

Yeast (qv) metabolize maltose and glucose sugars via the Embden-Meyerhof pathway to pymvate, and via acetaldehyde to ethanol. AH distiUers yeast strains can be expected to produce 6% (v/v) ethanol from a mash containing 11% (w/v) starch. Ethanol concentration up to 18% can be tolerated by some yeasts. Secondary products (congeners) arise during fermentation and are retained in the distiUation of whiskey. These include aldehydes, esters, and higher alcohols (fusel oHs). NaturaHy occurring lactic acid bacteria may simultaneously ferment within the mash and contribute to the whiskey flavor profile. 

The noncatalytic oxidation of propane in the vapor phase is nonselec-tive and produces a mixture of oxygenated products. Oxidation at temperatures below 400°C produces a mixture of aldehydes (acetaldehyde and formaldehyde) and alcohols (methyl and ethyl alcohols). At higher temperatures, propylene and ethylene are obtained in addition to hydrogen peroxide. Due to the nonselectivity of this reaction, separation of the products is complex, and the process is not industrially attractive. 

Hydrogenolysis of esters to aldehydes or alcohols needs high temperatures and high pressures. Moreover, it leads to the formation of acids, alcohols, and hydrocarbons. In contrast, bimetallic M-Sn alloys (M = Rh, Ru, Ni) supported on sihca are very selective for the hydrogenolysis of ethyl acetate into ethanol [181]. For example while the selectivity to ethanol is 12% with Ru/Si02, it increases up to 90% for a Ru-Sn/Si02 catalyst with a Sn/Ru ratio of 2.5 [182]. In addition, the reaction proceeds at lower temperatures than with the classical catalysts (550 K instead of temperatures higher than 700 K). The first step is the coordination of the ester to the alloy (Scheme 46), and most probably onto the tin atoms. After insertion into the M - H bond, the acetal intermediate decomposes into acetaldehyde and an ethoxide intermediate, which are both transformed into ethanol under H2. 

In 1972, Eiter and his group reported the synthesis of a-alkoxy dialkyl N-nitrosamines (11),which can be obtained easily in 20-50 g quantities. This synthetic scheme works well when formaldehyde was used. In those cases when higher aliphatic aldehydes are used (e.g. acetaldehyde), the yields decreased to 3-5%. The a -alkoxy dialkyInitrosamines always contained the trimeric paraldehyde as impurity. When acetaldehyde and... 

In a survey of chemical plants (without prior hypothesis) in the German Democratic Republic, nine cancer cases were found in a factory where the main process was dimerization of acetaldehyde and where the main exposures were to acetaldol (3-hydroxybu-tanal), acetaldehyde, butyraldehyde, crotonaldehyde (IARC, 1995) and other higher, condensed aldehydes, as well as to traces of acrolein (lARC, 1985). Of the cancer cases, five were bronchial tumours and two were carcinomas of the oral cavity. All nine patients were smokers. The relative frequencies of these tumours were reported to be higher than those expected in the German Democratic Republic. [The Working Group noted the mixed exposure, the small number of cases and the poorly defined exposed population.]... 

This is in marked contrast to the higher aldehydes which oxidize much more readily, at temperatures as low as 100° C.—e.g., acetaldehyde (55). The mechanism by which formaldehyde reduces the induction period in hydrocarbon oxidation below 300° C. is not evident. An inhibiting effect is explicable on the basis of removal of free radicals, as Lewis and von Elbe (32) have pointed out. This could occur by CH20 -f R — RH -f HCO. HCO is then oxidized to the relatively inert CH03 which diffuses to the wall and is destroyed. Above 300° C. formaldehyde is oxidized more rapidly, giving rise to free radicals, and it is not surprising to find that the induction period in some hydrocarbon oxidations is shortened. 

Aldehyde content is considered an important flavor note included in the standard of identities for citrus oils. The flavor strength of an oil is based on the aldehyde content, where higher is better. The two major aldehydes are acetaldehyde and octanal. The quantification of aldehydes is based on the reaction of citral in the sample with a hydroxylamine solution, followed by titration with KOH in the presence of ethyl orange indicator. It is modified from AOAC Method 955.32 (AOAC, 1990c Redd et al., 1986). This method was originally developed for lemon oils however, it is applicable to other citrus oils. 

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