Thermolytic degradation

Silaallenes 613 have been proposed by Ishikawa, Kumada and coworkers as transient reactive intermediates in the photolytic or thermolytic degradation of alkynyldi-silanes 614 as minor byproducts, the main product being silacyclopropenes 615184,192,287 (equation 203). 

Tiwari, S. K., Nema, S. K., and Agarwal, Y. K. 1998. Thermolytic degradation behavior of inorganic ion-exchanger incorporated Nafion-117. Thermochimica Acta 317 175-182. 

Oxidation in the atmosphere begins photolytically with radiation from the sun rather than thermolytically thus, atmospheric chemistry differs between day and night. In the daytime, the most common initiation step for VOC degradation involves photolysis of ozone by the sun s ultraviolet light, leading to hydroxyl (HO ) radical generation ... 

The lower amount of ring strain renders thietane molecules more resistant to thermolytic and photolytic degradation. Nonetheless, to prevent decomposition, they still must be stored in the dark and at room temperature. 

Both silene isomers 278 and 279 are ideal precursors for the generation of silylene 284, since their interconversion to 284 is spontaneous (in the case of 278) or can be easily induced by irradiation (in the case of 279). There are numerous well-established methods to prepare transient silylenes 279. Three important examples are shown in equation 69, namely the photolytic generation from a trisilane 280153, thermolytic or photolytic decomposition of cyclic silanes 28114,154,155 and degradation of diazidosilanes 282153,156. The photolysis of the diazido silane 282 is an especially clean reaction which has been used in several spectroscopic studies157. The photolysis of w-diazo compounds 283 is the only frequently used reaction path to silenes 284 via a carbene-silene rearrangement8. 

There are many HPLC methods that are developed during the process of drug development. The chromatographer needs to understand the aim of analysis in order to make judicious choices prior to the commencement of method development and the implications it may have on the final method that is developed. The following should be considered method development time, the maximum run time for analysis, the number of samples expected per week, the complexity of the mixture, the structure of the main analyte (physicochemical properties), possible degradation pathways (i.e., hydrolysis, oxidative, photolysis, dethydration, thermolytic, racemization), and whether the analyte or analytes are ionizable. 

The temperature/humidity conditions used may be more severe than the typical accelerated stability testing conditions in order to generate potential degradation products in a reasonable time. The typical forced degradation conditions include thermolytic, hydrolytic, oxidative, photolytic (in excess of ICH conditions), high pH (alkaline conditions), and low pH (acidic conditions). Outlined in Table 9-25 and Table 9-26 are some solid-state and solution forced degradation studies, respectively, that could be conducted. In the following... 

There are four major degradation pathways that an analytical chemists must focus on for pharmaceutical analysis thermolytic (heat), hydrolytic (water), oxidative (oxygen, light, peroxide), and photolytic (UV and Vis light). 

TABLE 4 Recommended Conditions for Assessing Hydrolytic,Thermolytic, and Photolytic Degradation Pathways... 

The key to the strategy outlined above is to have well-designed stress testing studies that form all potential degradation products. Thorough stress testing studies need to evaluate the four main degradation pathways of pharmaceuticals (1) hydrolytic, (2) thermolytic, (3) photolytic, and (4) oxidative. 

Uncovering the potential hydrolytic, thermolytic, and photolytic degradations is relatively straightforward. The conditions outlined in Table 4 are suggested as practical stress conditions for assessing these pathways. The oxidative pathways are a bit trickier, and will be discussed in more detail later in this chapter. 

Ferrous ion-catalyzed degradation of f-butyl peracetate can be replaced by either photochemical or thermolytic breakdown procedures, of which the former, using light of >300 nm, is a better means of methyl radical... 

No distinction of the polymer additives, residual monomers and thermolytically produced degradation products, all of which arise in differing temperature regions. 

The hard segments are relatively stable towards thermal oxidation. Degradation of the urethane segment typically does not occur below its thermolytic decomposition temperature. Aromatic isocyanates are generally less susceptible to thermal degradation than aliphatic isocyanates [1]. 

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