Oxidative degradation case studies

Sealants obtained by curing polysulfide liquid polymers with aryl bis(nitrile oxides) possess stmctural feature of thiohydroximic acid ester. These materials exhibit poor thermal stability when heated at 60°C they soften within days and liquefy in 3 weeks. Products obtained with excess nitrile oxide degrade faster than those produced with equimolar amounts of reagents. Spectroscopic studies demonstrate that, after an initial rapid addition between nitrile oxide and thiol, a second slower reaction occurs which consumes additional nitrile oxide. Thiohydroximic acid derivatives have been shown to react with nitrile oxides at ambient temperature to form 1,2,4-oxadiazole 4-oxides and alkyl thiol. In the case of a polysulfide sealant, the rupture of a C-S bond to form the thiol involves cleavage of the polymer backbone. Continuation of the process leads to degradation of the sealant. These observations have been supported by thermal analysis studies on the poly sulfide sealants and model polymers (511). 

Oxidation. Oxidative studies are designed to reveal the primary oxidative degradation products due to oxidation. Oxidative degradants in drug substances and drug products normally are the result of reaction with molecular oxygen. As in the case of acid/base hydrolysis, appropriate controls are necessary. 

Hong, J., Lee, E., Carter, J. C, Masse, J. A., and Oksanen, D. A. (2004), Antioxidant-accelerated oxidative degradation A case study of transistion metal ion catalyzed oxidation in formulation, Pharm. Dev. Tech., 9(2), 171-179. 

Arylmercuric halides may be used in place of diarylmercurials. Excellent yields, often 90-98%, were obtained in many cases. Table III lists some examples. Oxidative degradation studies of selected products showed that the aryl carbon atom originally attached to mercury was the one that became bonded to the apical carbon atom of the cluster. This reaction was much less useful in the preparation of alkyl derivatives, because of very long reaction times (1-2 weeks) giving at best moderate yields (Table III). The reaction of a-haloalkylmercurials with HCCo3(CO)9 occurred... 

On the other hand Price and Sears [107] studied the reactions of nitryl chloride with various aromatic compounds in the presence of aluminium chloride, and found that phenol, anisole and naphthalene tended to undergo oxidative degradation. In the case of naphthalene they obtained a 31% yield of a- nitronaphthalene, whereas with anisole and phenol they were able to isolate only traces of nitro compounds without any evidence of chlorination. 

A relatively recent field of study, which, will be expanded upon later, is that of transition metal substituted polyoxometallates.43 The fact that they are, in most cases, completely inorganic means that they are inherently robust to oxidative degradation, hence, offering good prospects for industrial application. 

H2O2 Degradation and Toxicity Reduction of Textile Azo Dyes Remazol Black-B, a Case Study, J. Adv. Oxid. Technol. 2, No. 3 442-448. 

After hydrolysis, oxidation is the next most common pathway for dmg breakdown. However, whereas the hydrolytic degradation of dmgs has heen thoroughly studied, their oxidative degradation has received comparatively little attention. Indeed, in cases where simultaneous hydrolytic and oxidative degradation can occur, the oxidative process has usually been eliminated by storage under anaerobic conditions without an investigation of the oxidative mechanism. 

Case Study A.4 Scaled-up Oxidative Degradation and Isolation Using Solid-Phase Extraction and Preparative HPLC... 

Case Study A.6 Scaled-Up Oxidative Degradation, Preparative HPLC,... 

Case Study A.8 Scaled-Up Oxidative Degradation and Preparative Isolation NMR Characterization Critical to Differentiate Between Two Possible Structures... 

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