Ketone, thermal degradation

Many impurities are present in commercial caprolactam which pass into the liquid wastes from PCA manufacture from which caprolactam monomer may be recovered. Also, the products of die thermal degradation of PCA, dyes, lubricants, and other PCA fillers may be contained in the regenerated CL. Identification of die contaminants by IR spectroscopy has led to the detection of lower carboxylic acids, secondary amines, ketones, and esters. Aldehydes and hydroperoxides have been identified by polarography and thin-layer chromatography. 

Dreier et al. [44] determined sterols in lacustrine sediments. Samples of wet lacustrine sediments were heated under anoxic conditions at 150, 175, 200 and 250°C for five days at 175°C for five days with influx of potassium hydroxide and methanol to remove sterols and at 175°C for 12, 18, 24 and 48h, after which extraction was performed. Heating the sediment increased the amounts of extractable sterols provided that the temperature did not exceed 200°C, because degradation became rapid above that temperature. The behaviour of sterol ketones was similar, but the temperature limit was slightly higher. The various levels of the sterols extracted are tabulated 4-methylsterols had a high stability towards thermal degradation under the conditions used. 

Found in processed truffles but absent in fresh truffles were two furans (compound 4 and 7) and a pyrazine (compound 24). Furans are well known to result from the thermal degradation of carbohydrates while alkyl pyrazines result from the reaction of amino acids and alpha-diketones. A number of methyl ketones were also observed in the canned product which were absent in the fresh product. Methyl ketones are known to result from the thermal decomposition of beta-keto acids (17-19) -... 

Other investigators (7-9) have identified a large number of carbonyls from heated fat. The remaining meat aroma components derived by heating lipids are esters, lactones, alkan-2-ones (methyl ketones), benzenoids and other alkylfurans. Several investigators have analyzed volatile compounds formed during thermal degradation of fatty acids (10-12). 

The volatiles from cooked meat contain large numbers of aliphatic compounds including aldehydes, alcohols, ketones, hydrocarbons and acids. These are derived from lipids by thermal degradation and oxidation (J7) and many may contribute to desirable flavor. In addition, the aldehydes, unsaturated alcohols and ketones produced in these reactions, as well as the parent unsaturated fatty acids, are reactive species and under cooking conditions could be expected to interact with intermediates of the Maillard reaction to produce other flavor compounds. 

Other compounds. Rice-Herzfeld mechanisms appear to be the rule in thermal degradation of many other types of organic compounds, among them aldehydes [21,43,52-54] and ketones [21,55], Many of these reactions are approximately first order. Decomposition of acetaldehyde, quite extensively studied, is of order one-and-a-half, easily explained with a Rice-Herzfeld mechanism and eqn 9.18 or 9.19... 

Thermal degradation of poly(ethylene-co-carbon monoxide) takes place by chain scission, yielding alkenes and ketone fragments. Around 500° C the decomposition products consist of CO, H2O, ethene, and series of ketones with the general structure R-[-CO-CH2-CH2-]n-CO-R where R, R = -CH3, -CH2-CH3 or -CH=CH2 [2, 3]. 

The DTA of the PVA-PEG beads (Fig. 2a) shows three endothermic peaks at 51, 221 and 317 °C. The first one is associated with the loss of physisorbed water. The other two peaks are assigned to evolution of water and other volatile compounds (aldehydes, ketones and ethers), as a result of the thermal degradation of the PVA and PEG [12]. 

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