Degradation probability

Most structural work on xylan has been done on that from esparto grass and the principal attack made by way of the methyl ether. Xylan can be methylated by heating with methyl iodide and silver oxide,92-93 but complete etherification is difficult and considerable degradation probably occurs. On the other hand, complete etherification is attained by methylation in two operations with potassium hydroxide and dimethyl sulfate to give a dimethylxylan in almost quantitative yield70 showing [< ]22d — 92° in chloroform. Methylation with potassium hydroxide appears to proceed more readily than with sodium hydroxide.70-92... 

Treatment of 15 with l,5-diazabicyclo[5.4.0]undec-5-ene (DBU) in benzene resulted in /3-elimination, but under these conditions, the liberated 2,3,4,6-tetra-O-methyl-D-glucose was further degraded, probably with formation of 3-deoxy-2,4,6-tri-0-methyl-D-erc/fhro-hex-2-enopyranose. In order to prevent this degradation, the reaction of 15 with DBU was carried out in the presence of acetic anhydride. The reaction mixture gave, after chromatography on silica gel, methyl (methyl 4-deoxy-2,3-di-0-methyl-a-L-threo-hex-4-enopyranosid)uron-ate (65) and a mixture of the 1-acetates of 2,3,4,6-tetra-O-methyl-a- and -/3-D-glucose (66). 

Chromanones may or may not be attacked by aqueous or ethanolic alkali depending on the substituents. 7-Methoxychromanone is quite stable to alkali but 7-methoxy-2,2-dimethylchromanone (647) is degraded, probably to an acrylophenone (648), which may itself be cyclized to the chromanone by treatment successively with aqueous sodium hydroxide and hydrochloric acid. 

The effect of the presence of dialkyl phosphoric acid was moderate, with an increase of the malonamide degradation probably by hydrolysis, as has been observed in specific hydrolysis experiments (71). 

Activation by substituentB other than carbonyl or carboxyl functions has a like effect on the glycosidic linkage, and the alkaline degradation probably proceeds by a similar mechanism. Helferich and Lutzmann14 described the reducing property of ethyl 2-(/3-D-glucopyranosyloxy)-ethanesulfonate (XI), and Helferich and Hase16 found that 2-nitroethyl... 

At 360°C-370°C, an important increase in the apparent initial viscosity begins that corresponds to the complete degradation of the initial material and to the carbonization of the system. The foamed material appears to be constituted by solid particles only. From 450°C-460°C, the viscosity value is more stable and increases slightly. At this temperature, a char oxidation/degradation probably starts. Complementarity, the viscosity can be analyzed versus temperature and versus time (Figure 10.10) in order to better visualize the mechanical and thermal stabilities of the protective intumescent layer and to have a better understanding of the carbonization process. 

The acidic hydrolysis of the PVFA/VTS-silica hybrids is combined with loss of the grafted polymer content. It is assumed that part of the grafted PVFA chains undergo degradation, probably because of the rigorous acidic conditions. 

Changing the structure of the polymer from regioregular to regio-random significantly accelerates the degradation, probably due to the higher triplet yield of the regiorandom polymer. 

Cornstarch processed with cyclic sodium trimetaphosphate is used to make cold-water jellies. Phosphorylated varieties of this kind are resistant to hydrolysis and degradation (probably due to cross-linking), and are used as thickening agents in cooked foods. 

HOAC-AC2O. This one-carbon degradation probably proceeds via... 

The degradation probably starts with the formation of a phenoxy radical at position which is stabilized by several resonance forms (Fig. 301). These forms may react with OH radicals or water and may undergo further oxidation. As a consequence the whole molecule may be degraded lastly to COg, acetic acid and succinic acid. 

The low RBC ATP concentration is the most probable explanation for the hemolysis (1). In vitro studies of adenosine metabolism by intact patient s RBC showed as expected, a markedly decreased ATP synthesis from adenosine moreover, metabolic studies of adenylic nucleotides labelled with radioactive adenine indicate that AMP degradation (probably by hydrolysis of the phosphate ester followed by deamination of adenosine) is abnormally elevated in the patient s erythrocytes. Thus, the low RBC ATP concentration appears to be secondary to both a diminished synthesis of AMP from adenosine and an excessive catabolism of AMP. 

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