Nonoxidative decomposition

The oxidation of alkenes and cycloalkenes and their halogen derivatives with at least one hydrogen or halogen atom at the double bond leads to carboxylic acids. Ozonolysis usually requires the oxidative decomposition of the ozonide. The oxygen content of the ozonide is not sufficient for the formation of two molecules of acids or one dicarboxylic acid. The nonoxidative decomposition of cyclohexene ozonide gives an aldehyde-acid or its derivatives [1108]. It comes, therefore, as a surprise that carboxylic acids are claimed as products of the decomposition of ozonides by hydrogenation over the Lindlar catalyst [55] (equation 108). 

Metal organic decomposition (MOD) is a synthesis technique in which metal-containing organic chemicals react with water in a nonaqueous solvent to produce a metal hydroxide or hydrous oxide, or in special cases, an anhydrous metal oxide (7). MOD techniques can also be used to prepare nonoxide powders (8,9). Powders may require calcination to obtain the desired phase. A major advantage of the MOD method is the control over purity and stoichiometry that can be achieved. Two limitations are atmosphere control (if required) and expense of the chemicals. However, the cost of metal organic chemicals is decreasing with greater use of MOD techniques. 

Vapor-Phase Techniques. Vapor-phase powder synthesis teclmiques, including vapor condensation, vapor decomposition, and vapor—vapor, vapor—Hquid, and vapor—soHd reactions, employ reactive vapors or gases to produce high purity, ultrafine, reactive ceramic powders. Many nonoxide powders, eg, nitrides and carbides, for advanced ceramics are prepared by vapor-phase synthesis. 

Nonoxidative Processing of Hydrocarbons 2.3.1 Thermal Decomposition of Methane... 

Decomposition of methane to H2 and carbon over Ni/Si02 was carried out in a membrane reactor (membrane 90Pd-10Ag) [106]. The use of the membrane reactor allowed increasing the H2 yield by shifting the reaction equilibrium toward the products. An excellent review of the literature data on nonoxidative methane activation over the surface of transition metals was recently published by Choudhary et al. [107]. 

When the rate of the chemical reaction occurring at the surface is the rate-limiting step, the principles we have described to this point apply. The reaction rate can have any order, and the gas reacts with the ceramic substrate to produce products. Although our discussion to this point has focused on oxide ceramics, there are a number of nonoxide ceramics, such as carbides, nitrides, or borides, that are of importance and that undergo common decomposition reactions in the presence of oxygen. These ceramics are particularly susceptible to corrosion since they are often used at elevated temperatures in oxidizing and/or corrosive enviromnents. For example, metal nitrides can be oxidized to form oxides ... 

This technique is not so easily extended to nonoxides. Sulphur, for example, does not form the cross-linking bonds needed to form the sol-gel as readily as does oxygen. However, a related method has been used, albeit to a very small extent, to form CdS films. It is based on the thermal decomposition (at ca. 300°C) of a Cd-thiourea complex, which is formed as a film by slowly withdrawing the substrate from a methanolic solution of a Cd salt and thiourea [196]. 

Chemical Catalysts. Vazo or 2,2 -azobisisobutyronitrile catalyst (2) is preferred over peroxide catalysts because of its low decomposition temperature and its nonoxidizing nature. Vazo will not bleach dyes dissolved in the monomer during polymerization. 

The decomposition is complete by 300°C, and the Zr02 powder (mean particle size 5 nm) is collected by means of an electrostatic precipitator. Nonoxide ceramic powders such as SiC are prepared by the decomposition (CH3)2SiCl2" and CHsSiHs. ... 

Flash-vacuum pyrolysis of bis(dialkylamino)cyclopropanes can cause a nonoxidatively induced cycloelimination to give cycloalkenes and amidines. Thus, decomposition of 7,7-dimor-pholinobicyclo[4.1.0]heptane (8) at 700°C (10 Torr) gives heterocyele 9 and cyelohexene in good yield. The corresponding pyrrolidino and piperidino compounds are similarly cleaved to give 2,3,4,5-tetrahydro-6-pyrrolidinopyridine and 3,4,5,6-tetrahydro-7-piperidino-2//-azepine, respectively. The intermediacy of diaminocarbenes has been proposed for the formation of these heterocycles. 

The aqueous corrosion of ceramics may involve a charge-transfer or electrochemical dissolution process. However, in many cases, dissolution or corrosion may take place with no charge transfer yet may be determined by one or more electrochemical factors such as absorbed surface charge or electronic band bending at the surface of narrow-band-gap semiconducting ceramics. The aqueous corrosion of ceramics is important in a number of areas. One of the most important is the stability of passive oxide films on metals. The stability of ceramics is a critical aspect in some aqueous photoelectrochemical applications (12), an example being the photoelectrolytic decomposition of water. Structural, nonoxide ceramics such as SiC or Si3N4 are unstable in both aqueous acid and alkaline environments the latter is virtually unstudied, however. 

Mechanism of Nonoxidative Thermal Dehydrochlorination. This subject is still very controversial, with various workers being in favor of radical, ionic, or molecular (concerted) paths. Recent evidence for a radical mechanism has been provided by studies of decomposition energetics (52), the degradation behavior of PVC-polystyrene (53) or PVC-polypropylene (54) mixtures, and the effects of radical traps (54). Evidence for an ionic mechanism comes from solvent effects (55) and studies of the solution decomposition behavior of a model allylic chloride (56). Theoretical considerations (57,58) also suggest that an ionic (El) path is not unreasonable. Other model compound decompositions have been interpreted in terms of a concerted process (59), but differences in solvent effects led the authors to conclude that PVC degrades via a different route (59). 

ZnPg-. Orange to red needles, d (x-ray) 3.51. Sublimes without decomposition in an atmosphere containing phosphorus vapor insoluble in nonoxidizing acids. Crystal structure tetragonal space group or Df. 

Such a reaction of Fe(CO)5 (at 293-363 K, PVP) without ultrasonic radiation proceeds very slowly and only after few days there, a material is formed with very low Fe content (2%, the isolated particles 2-5 nm in size). It is of interest that the sonochemical decomposition of Fe(CO)5 does not proceed in the presence of PVP if THF is used as the solvent, but the reaction is very effective when anisole is used as the solvent and PFO is used as the polymer matrix [93]. A black product formed contains up to 10% (in mass) of the spheric particles of nonoxidized Fe (mainly y-Fe, with little content of a-Fe) with 1-12 nm in size (the mean diameter is 3nm, as shown in Figure 3.7). It is likely that the big particles present the flocks of little ones ( 2-2.5nm). The sonochemical synthesis allows us to produce the functionalized amorphous nanoparticles of ferric oxide with 5-16 nm in diameter [94]. The ultrasonic irradiation in the PFO presence allows us to also produce the stabilized nanoparticles of copper, gold, and so on. In the literature the findings are not about the bimetallic particle formation in the ultrasonic fields by carbonyl metal reduction in the polymer matrices presence (as, for example, in the case of the carbon-supported Pt-Ru from PtRu5C(CO)i6 reduced clusters [95]). 

There are three types of solid-state reaction (i) chemical decomposition, (ii) chemical reaction between solids, and (iii) chemical reduction. The first two reactions will be introduced, while the third one is commonly used for nonoxides... 

Co2(CO)g] and [Co4(CO)i2] are air-sensitive however, large crystals of these compounds do not undergo noticeable oxidation in a short period of time. Solutions of these carbonyls rapidly undergo decomposition. The halogens quantitatively oxidize [Co2(CO)g] and [ 04(00)12] to Co(II) salts. Oxidizing acids oxidize [Co2(CO)g] to Co(II) compounds and nonoxidizing acids react with this carbonyl only slowly and partially. 

Table 6.4 Temperature at the onset of decomposition and weight retention at 500 and 800°C for cured PFA nanocomposites under nonoxidative degradation in N2.

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