Platinum direct thermal decomposition

Pyrolysis involves the thermal decomposition, degradation, or cracking of a large molecule into smaller fragments. Pyrolysis GC is an excellent technique for identifying certain types of compounds which cannot be analyzed by derivatization, e.g., polymers. The pyrolysis temperamre is typically between 400°C and 1000°C. A number of analytical pyrolyzers have been introduced and are commercially available. The devices consist of platinum resistively heated and Curie point pyrolyzers. The carrier gas is directed through the system, and the platinum wire is heated to a certain temperature. The material decomposes, and the fragmentation products are analyzed. ... 

Isothermal (flash pyrolysis). The temperature of the sample is suddenly increased (10-100 ms) to reach the thermal decomposition level (500 - 800°C). This process can be carried out by means of a platinum or platinum-rhodium filament heated by an electrical current directly coupled to the injector port of the GC. Some pyrolysis fragments are obtained in a very short time and can be directly sent to the column and detector. In spite of this short time for the pyrolysis, it is possible to indicate three different phases (a) heating (10 -10 s), (b) stabilization of the maximum temperature, and (c) cooling. However, the main drawback of this technique is the lack of equilibrium between temperatures with the pyrolyzer. 

An alternative is the reaction of the respective sesquioxides with (NH4)Hp2, in analogy to the ammonium chloride (bromide) route. In principle, this is a two-step procedure with the formation of a ternary fluoride first and, secondly, its thermal decomposition (see below). When elemental fluorine is available, the direct fluorination of the rare earths or any of their salts is also a possibility. Ternary fluorides are obtained by a solid state reaction of the respective binary components in sealed gold or platinum tubes. 

We have demonstrated (a) the diversity of mechanistic pathways that exists for the thermal decompositon of metal alkoxides, and (b) how the preferred pathway is a function of the nature of the alkoxide ligand. A perhaps surprising conclusion that emerges from the study is that neither M-OR nor MO-R bond homolysis plays a direct role in these decompositions. It should be noted, however, that we have only examined the alkoxides of oxophilic metal ions that are not easily reduced. It is conceivable that for the later transition metal ions that are both less oxophilic and more reducible, decompositon pathways that lead to the reduction of the metal ion may become more important. These include -hydrogen abstraction followed by reductive elimination (cf., eq. 6), as well as M-OR bond cleavage. Note that P-hy(6ogen abstraction has been demonstrated to be quite facile for the platinum-group metal alkoxides. 

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