Thermal decomposition solid-phase products

Thermal reactions (dehydration, thermal decomposition, solid state reactions) play an important part in the production of inorganic materials from minerals, gels and related raw materials. Solid state NMR can provide useful insights into the progress of these reactions and their mechanistic details, as well as information on phase transformations and other high-temperature phenomena. 

TABLE 3.2. The Composition of Solid-Phase Products of Thermal Decomposition of Ni-Containing Precursors (7-exp - 643 K)... 

Typical characterization of the thermal conversion process for a given molecular precursor involves the use of thermogravimetric analysis (TGA) to obtain ceramic yields, and solution NMR spectroscopy to identify soluble decomposition products. Analyses of the volatile species given off during solid phase decompositions have also been employed. The thermal conversions of complexes containing M - 0Si(0 Bu)3 and M - 02P(0 Bu)2 moieties invariably proceed via ehmination of isobutylene and the formation of M - O - Si - OH and M - O - P - OH linkages that immediately imdergo condensation processes (via ehmination of H2O), with subsequent formation of insoluble multi-component oxide materials. For example, thermolysis of Zr[OSi(O Bu)3]4 in toluene at 413 K results in ehmination of 12 equiv of isobutylene and formation of a transparent gel [67,68]. 

A. J. B. Robertson [23] found that the decomposition of cyclonite at a temperature above its melting point (between 213 and 299°C) proceeds as a first order reaction. At 213°C, half the substance decomposes in 410 sec, and at 299°C in 0.25 sec. The gaseous decomposition products contain chiefly N2, N20, NO, CO and C02. According to A. J. B. Robertson the activation energy E of the thermal decomposition of cyclonite at these temperatures is 47,500 cal, log 21=18.5. The reaction rate in the liquid phase is approximately ten times greater than in the solid phase (below the melting point.)... 

Thus far we ve been discussing homogeneous equilibria, in which all reactants and products are in a single phase, usually either gaseous or solution. Heterogeneous equilibria, by contrast, are those in which reactants and products are present in more than one phase. Take, for example, the thermal decomposition of solid calcium carbonate, a reaction used in manufacturing cement ... 

Aminoquinolines 62 have been prepared in a two-step, one-pot, three-component reaction of 2-azidobenzophenones, secondary amines and arylac-etaldehydes [110]. The microwave-assisted reaction proceeded via the initial formation of enamines 59. Subsequent addition of 2-azidobenzophenones 60 afforded the triazoline intermediates 61, which underwent thermal rearrangement and cyclocondensation to furnish 2-aminoquinolines 62 (Scheme 41). Direct comparison with conventional thermal conditions demonstrated the superiority of microwave dielectric heating in terms of yields (73% vs. 31% of heterocycle 63 after 10 min at 180 °C). Furthermore, the formation of by-products due to decomposition of azide 60 was diminished in the microwave-assisted synthesis. Purification of the products was achieved using solid-phase extraction techniques. 

Organoindium substances are important, especially for the production of materials by metal-organic chemical vapor-phase deposition (MOCVD). This technique involves the thermal decomposition of mixtures of an organoindium compound and a compound such as phosphine (PH3), leading to the deposition of ordered layers of InP. The resulting compound can be used in the formation of semiconductors and solid-state optical devices (similar to silicon), see also Inorganic Chemistry. 

FIGURE 25. The heterogeneous gas-phase dehydrochlorination of /1-chloroethyazide on solid potassium rm-butoxide yielding vinyl azide, and the subsequent thermal decomposition of the latter to 27/-azirine. The double-oven apparatus is equipped with cold traps for the by-product tert-butyl alcohol and the end product 2/7-azirine. The PES ionization patterns of the pure compounds were used for optimization of the reaction conditions. Reproduced by permission of Verlag der Zeitschrift der Naturforschung from Reference 215... 

Solid state reactant Thermal decompositions of a solid Oxidation or reduction of a solid Precipitation Solution heating or cooling Evaporative salting-out Chemical reaction with insoluble product Hydrothermal synthesis Forced insolubility Dissolution reprecipitation Evaporative Condensation Gas phase reaction with solid product Thermal decompositions Oxidation or reduction reactions Combination reactions with a solid product Solvent removal Spray drying Freeze drying Spray roasting Sol-gel synthesis Melt solidification... 

So far, we have discussed equilibria only for systems in the gas phase, where all reactants and products are gases. These situations represent homogeneous equilibria. However, many equilibria involve more than one phase and are called heterogeneous equilibria. For example, the thermal decomposition of calcium carbonate in the commercial preparation of lime occurs by a reaction involving both solid and gas phases ... 

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