Thermal degradation decarboxylation

The use of aliphatic monomers for hyperbranched polyesters has been debated because aliphatic monomers are said to be prone to thermal degradation reactions such as decarboxylation, cyclization, or dehydration [77]. The only commercial hyperbranched polymer is a hydroxy-functional aliphatic polyester, Boltorn, available from Perstorp AB, Sweden. 

Processes such as decarbonylation, decarboxylation, elimination of water, and several other reactions may also occur prior to ionization, i.e., as non-mass spectral reactions, typically as a result of thermal degradation upon heating of the sample to enforce evaporation. In such a case, the mass spectrum obtained is not that of the analyte itself, but of its decomposition product(s). Sometimes, those thermal reactions are difficult to recognize, because the same neutral loss may also occur by a true mass spectral fragmentation of the corresponding molecular ion. 

Thermal degradation prior to ionization can cause decarbonylation or decarboxylation of the analyte. Decarbonylation, for example, is observed from a-ketocarboxylic acids and a-ketocarboxylic acid esters, whereas decarboxylation is typical behavior of P-oxocarboxylic acids such as malonic acid and its derivatives and di-, tri-, or polycarboxylic acids. 

Studies on the thermal degradation of the cellulose structure have shown that oxidation reactions at 160-180 °C are more important than decarboxylation, but that this state may change at 190 °C (28). 

Side reactions that might occur during direct polyesterification include loss of functionality by decarboxylation of an acidic end group, thermal degradation of ester linkE es, the formation of ether linkages, and cyclization reactions. 

A scheme for the formation of guaiacols from ferulic acid has also been proposed by Manley et al. (1974). The biosynthesis of various phenolic acids from p-coumaric acid (H.84) was studied by Friedrich (1976). Formation pathways for simple phenols in food flavors have been reviewed (Maga, 1978a). The two primary pathways could be the decarboxylation of phenolic carboxylic acids and the thermal degradation of lignin. Secondary pathways include bacterial, fungal, yeast enzymic and glycosidic reactions. 

Figure 10.17 shows the FTIR gas-phase spectrum measured during the 180°C experiment. Clearly present in this this spectrum are absorptions due to C02 (2364 cm-l), S02 (1376 cm-1) and an azido effect (2132 cm-l). The presence of C02 is pointing at decarboxylation of the acid group. The presence of S02 is indicating that at 180°C already a further thermal degradation of the ASB molecules occurs. The azido absorption (2132 cm-l) and the absorptions at 1765, 1348 en 1177 cm-l indicate that a part of the ASB spontaneously evaporates. 

In addition to caprolactam and water, considerable quantities of carbon dioxide, ammonia, carbon monoxide, methane, and so on, are released via secondary reactions during the thermal degradation of aliphatic polyamides. Thus decarboxylation of the terminal COOH groups of polyamides results in release of carbon dioxide. Ammonia forms because of the self-interaction of terminal amino groups [2, 6] ... 

The thermal degradation of poly(butylene terephthalate) was examined with the aid of a laser microprobe and mass spectrometry [506]. A complex multistage decomposition mechanism was observed that involves two reaction paths. The initial degradation takes place by an ionic mechanism. This results in an evolution of tetrahydrofuran. This is followed by concerted ester pyrolyses reactions that involve intermediate cyclic transition states and result in formation of 1,3-butadiene. Simultaneous decarboxylations occur in both decomposition paths. The latter stages of decomposition are... 

The poly(amides), like the poly(esters) show much greater thermal stability than many of the addition polymers. Although there has been evidence of decarboxylation during thermal degradation [24] the rates of production are slow. 

PhenoHc acids are precursors of a number of simple phenols, which result from the activities of microorganisms or during thermal processes. The main products of thermal degradation of cinnamic acids are 4-vinyl phenols that arise as decarboxylation products. The subsequent reactions yield the corresponding 4-formyl phenols, 4-ethyl phenols, 4-(prop-2-en-l-yl) phenols, 4-acetyl phenols... 

Another experiment was conducted (Reed 1990 Reed and Hajash 1992) using only unbuffered 0.01 M oxalic acid (no solid) to monitor potential reaction with the experimental system and/or thermal degradation of the oxalate. In this experiment, which ran for s30 days at 100°C and 345 bar, oxalate in the reacted solution remained near initial values and was apparently not removed by reaction with the system, precipitation, or decarboxylation. The pHf was also essentially constant at 2.1. Reaction with the experimental system was limited to minor leaching of Fe (<7 ppm) and Ni (<10ppm). Ti was below detection limits (<2ppm). 

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