Acetaldehyde, thermal activation

In general, acidic proteinoids are more active than lysine-rich proteinoids for this reaction. Thermal poly(glutamic acid, threonine) and thermal Poly(glutamic acid, leucine) are the most active of these tested 20>. The activity is gradually decreased by progressive acid hydrolysis20. Compared with natural enzymes, the activity of proteinoid is weak. However the decarboxylation of pyruvic acid by proteinoid obeys Michaelis-Menten kinetics as expressed by the Lineweaver-Burk plot201. In this reaction a small amount of acetaldehyde and acetoin are formed in addition to acetic acid and C02 201. 

Another study on the use of Fe showed that the oxidation rate of acetaldehyde was improved with Ti02 catalysts doped with Fe and Si s)mthesized by thermal plasma (Oh et al., 2003). A Fe content lower than 15% rendered higher activities than the untreated catalyst. The catalyst preparation technique involved a complex procedure using a plasma torch, with all this likely leading to an expensive photocatalyst of mild prospects for large-scale applications. 

During polymerization, ester interchange between the vinyl ester and a glycol-terminated molecule eliminates acetaldehyde, the stable keto-form of the vinyl ester function. Activation energies for the thermal degradation of PET range [39] between 32 and 62 kcal mole . ... 

An example of a DHS application is the determination of aroma-active compounds in bambuu shoots. In this study, compoimds such as p-cresol, methional, 2-heptanoI, acetic acid, ( ,Z)-2,6-nonadienal, linalool, phenyl acetaldehyde, were extracted from the bambuu shoot samples and analysed by GC. The required sample amount was 10 g, and the extraction temperature was 60°C, using a 30 min extraction time. The stripped analytes were first trapped into a cooled adsorbent tube (VOCARB 3000, at 0 °C), and then thermally desorbed to GC. In DTD, the sample amount required for the analysis is typically smaller than in solid head-space (SHS). In the determination volatile components such as camphor, 1,8-cineoIe and 2,3,S,S-tetramethyl-4-methylene-2-cyclopenten-l-one, from Lavandula luisieri, only 10-20 mg of (dry) plant sample was required for the analysis. The volatiles were desorbed fi om the sample under a helium flow and then cryofocused on a Tenax TA trap at -30 °C. The trap was then quickly heated and the desorbed volatiles were transferred directly to the GC column through a heated fused-silica line (85). 

It not infrequently happens that a chain reaction and a molecular reaction take place concurrently and make contributions of comparable magnitude to the total observed chemical change. In the thermal decomposition of acetaldehyde vapour, for example, there are probably two major mechanisms, a direct molecular rearrangement CH3CHO = C0-[-CH4, and a chain process similar to (3) above. The activation energy, Ui, for the formation of radicals is very much higher than that for the rearrangement, Ii, and in consequence the number of molecules which initiate chains is smaller in about the ratio than the number which suffer simple... 

The thermal degradation rate of PET has been determined by the change in the characteristic melt viscosity, by the concentration of end COOH and OH groups as well as by the rate of release of acetaldehyde. The data obtained show that the process proceeds by first-order kinetics and by random chain scission. The activation energy calculated for the thermal degradation of PET by changes in the intrinsic viscosity is 260.4 kj/mol. 

Typical aminocarboxyhc acids, unsaturated fatty acids bound in hpids, sugars and some other food components are precursors of many important sensory-active carbonyl compounds. Amino acids produce aldehydes mainly as secondary products of alco-hohc or lactic acid fermentations and during thermal processes by Strecker degradation. Formaldehyde (methanal) is formed from glycine, acetaldehyde (ethanal) from alanine propanal and butanal arise from threonine (Figure 8.3), 2-methylpropanal from valine. 

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