Amylose pyrolysis

Because of its practical importance, significant effort was made to understand the pyrolysis of starch rather than one of its components. Data are also available on amylose pyrolysis alone, but much less on amylopectin. However, the pyrolysis products of these compounds are expected to be the same. Starch pyrolysis generates... 

Besides the compounds indicated in Tables 7.4.1 and 7.4.2, there are several other pyrolysis products of starch (and amylose) reported in literature [53]. They were either not seen in the pyrograms from Figures 7.4.1 and 7.4.2 or not identified. A complementary list of compounds detected in amylose pyroiysate [53] obtained in similar conditions (510° C) as those for Tables 7.4.1 or 7.4.2 are given in Table 7.4.3. 

Bryce and Greenwood studied the kinetics of formation of the major volatile fraction from potato starch, and its components. They limited their interest to the temperature range from 156 to 337 and to the formation of water, as well as of carbon mon- and di-oxide. The results revealed the following facts. Stability toward pyrolysis within the first 20 minutes of the process falls in the order amylose < starch < amylopectin < cellulose. Autocatalysis is absent, as shown by Puddington. Both carbon mon- and di-oxide are evolved as a consequence of each of two first-order reactions. The initial one is fast, and the second is slow. The reasons are not well understood, but they probably involve some secondary physical effects. The amount of both carbon oxides is a direct function of the quantity of water produced from any polysaccharide, which, furthermore, is independent of the temperature. The activation energy for the production of carbon mon-and di-oxide reaches 161.6 kJ/mol, and is practically independent of the polysaccharide formed. At the limiting rates, the approximate ratios of water carbon dioxide carbon monoxide were found to be 16 4 1 for amylopectin, 13 3 1 for starch, 10 3 1 for amylose, and 16 5 1 for cellulose. 

The extent to which starch and cellulose form volatile decomposition products in the absence of inorganic material may be seen from the results shown in Table IV for the percentage weight of polysaccharide remaining after pyrolysis under vacuum. Although differences between starch and its components are small, cellulose is relatively more stable. The general order of thermal stability appears to be amylose < starch < amylo-pectin < cellulose. 

It has now been shown that, in addition to levoglucosan, the pyrolysis of amylose at about 300° results in the formation of 1,4 3,6-dianhydro-D-glucopyranose. ... 

At the limiting rates, the molar ratio C02 C0 H20 was starch, 13 3 1 amylose, 10 3 1 amylopeetin, 16 4 1 and cellulose, 16 5 1. These differences may reflect differences in thermal stability. At lower temperatures, each ratio differed from this value. The ratios of H20 C02 and H2O CO both decreased with rising temperature of pyrolysis, whereas the ratio C02 C0 remained essentially constant. The ratio for C02 C0 of 3 1 found for potato starch is in agreement with that reported by Pudding-ton. ... 

Early work had indicated that the course of starch pyrolysis is also altered when such simple salts as sodium chloride and sodium carbonate are present. In an attempt to investigate this phenomenon in more detail, Bryce and Greenwood studied the kinetics of the decomposition of amylomaize starch (high-amylose, maize starch) in the presence of two series of salts one having a common cation (NaH2P04, Na2B407, NaCl,... 

Although the essential features of the structural modifications undergone by amylose on pyrolysis are now established, full investigations of the dextrinization of the more complicated, amylopectin component have yet to be attempted. The most useful approach in this aspect of the field is to correlate the changes in such physical properties as molecular size with alterations in chemical structure. 

Reductic acid, separated as its lead salt, has been isolated from the pyrolysis products of cellulose by reaction at 450 C in the presence of oxygen. Amylose, maltose, and D-glucose also gave reductones. A mass spectrometer with a data system was required to study the products of the direct pyrolysis of cellulose and cellulose which had been treated with a fire-retardant. The amount of products evolved at any point during, or throughout, the entire pyrolysis could be analysed. 

Products from the pyrolysis of cellulose in the absence of a catalyst were found to be mainly derivatives of 1,6-anhydro-D-glucoseand other, unsaturated, products. One product, formed in 1.4% yield, was found to be 1,5-anhydro-4-deoxy-D- /yc ro-hex-l-en-3-ulose. This product was also formed during the pyrolysis of amylose, amylopectin, and laminarin. A further product from cellulose, probably formed as an oxidation product, was 3,5-dihydroxy-2-methyl-4/f-pyran-4-one. Sixty-three compounds were detected in the condensate of smoke produced by pyrolysis of cellulose. These compounds included furans, cyclic ketones, lactones, benzene derivatives, aliphatic ketones, and aldehydes. One of the major products was 2-hydroxy-3-methyl-cyclopenten-l-one. 

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