Degradation mechanism, decomposition products

A combined method including TLC, HPLC, GC-MS and FTIR was employed for the study of the mechanism of the degradation of Navitan Fast Blue S5R by Pseudomonas aeruginosa. The culture medium containing the dye and its decomposition products was centrifuged and analysed by HPLC. The lyophilized supernatant was investigated by TLC... 

Aryl halides are often susceptible to photochemical degradation. As described in Chapter 10 later in this book, cleavage of the C-X bond occurs with low quantum yield for aryl chlorides (132), higher quantum yields for aryl bromides and iodides (133), and high quantum yields for some aryl fluorides (e.g., fluoroquinolones) (134). Aryl chlorides are photolabile to homolytic and/or heterolytic dechlorination (43). For sertraline hydrochloride, decomposition of the aryl dichloride moiety occurs in solution when exposed to light (ultraviolet and fluorescent conditions). As shown in the following proposed mechanism, the major photochemical decomposition products include mono-chloro- and des-chloro-sertraline via homolytic cleavage (Fig. 91) (86). 

Among the volatile compounds listed in Table II, only thiazole compounds are derived from the thermal degradation of thiamin. 5-(2-hydroxyethyl)-4-methylthiazole and 4-methyl-5-vinylthiazoIe are well-known thermal degradation products of thiamin. 5-(2-Chloro-ethyl)-4-methylthiazole may form through the interaction of 5-(2-hydroxyethyl)-4-methylthiazole with hydrogen chloride. However, the most abundant product, 4-methylthiazole, has never been identified as a decomposition product of thiamin. The mechanism for its formation is not clear. 

Schonherr [43] has described the combination of decomposition in a thermogravimetry oven and FTIR spectroscopy for the identification of base polymers in elastomers, as exemplified for nitrile rubber, and has presented infrared spectra for decomposition products of various rubbers. The same author [36] studied use of the integrated TG-FTIR system for the identification of sixteen vulcanised rubbers in mechanical goods reporting the characteristic infrared spectra of the degradation products at temperatures ranging from 334 °C to 635 °C. 

When PVC is pyrolyzed, the main decomposition product is hydrochloric acid, along with small amounts of saturated and unsaturated hydrocarbon side products. PVC is easily degraded through the effect of heat, light and mechanical energy. In order to improve the low stability of this plastic, a series of additives are incorporated into the PVC melt. The most important additives for the processing of PVC are the plasticizers, which may be incorporated at elevated temperatures to give mixtures stable at room temperature. 

Only with such modern analytical tools is it possible to give correct answers to the many problems occurring in interactions between plastics and food. Some of the results obtained with ill-suited analytical methods for high molecular additive mixtures can be re-evaluated in this manner. In addition, answers can be given about the mechanism of degradation and the nature of decomposition products (Chapter 3). Last but not least a much faster determination of low migrants concentrations is possible in many cases. This is an important assumption for quality assurance with low thresholds of concentrations for regulation. 

DuPont s Biomax product is a standard PET with the addition of three aliphatic monomers to allow degradation to take place. Comparable to PLA, the degradation mechanism is described as an initial attack of water to the special monomers, which are sensitive to hydrolysis. Although it appears that Biomax sufficiently disintegrates under composting conditions, the process of decomposition of the material was too slow to meet accepted standards. 

A new macroscopic degradation mechanism of polymers studied by Murata et al. [6] was suggested with two distinct mechanism in the thermal degradation of PE, PP and PS. One is a random scission of polymer links that causes a decomposition of macromolecnles into the intermediate reactants in liquid phase, and the other is a chain-end scission that caused a conversion of the intermediate reactants into volatile prodncts at the gas-liqnid interface. There are parallel reactions via two mechanisms. The random scission of polymer links causes a reduction in molecular weight of macromolecules and an increase of the number of oligomer molecules. The chain-end scission causes a dissipation of oligomer molecules and a generation of volatile products. 

In a variety of organic syntheses, metallacycloalkanes with different ring sizes are important reactive intermediates. They are formed in different ways, as pointed out in Section II,A. Several degradation mechanisms are responsible for their decomposition, which results in the formation of organic products and the corresponding catalytically active species. Stabilization of metallacycloalkanes results on introduction of a donor atom adjacent to the metal. 

Decomposition of PA-6 and PA-66 produces NH3, H2O, CO, CO2, and hydrocarbons. The addition of magnesium hydroxide decreases the amounts of volatiles produced but the chemical components and their proportions are very similar to unfilled polymers. The addition of zeolites to polypropylene changes the mechanism of degradation depending on the zeolite type, its morphology, and dispersion but, in the investigation, the composition of the decomposition products was not determined. ... 

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