Potential, chemical decomposition

Impurities in drug substances and drug products continue to be a source of great concern, discussion, debate, and research. " These concerns and debates typically center on the potential safety risks associated with impurities due to contamination and the setting of acceptance criteria. However, the bulk of the work being performed in the pharmaceutical industry, with respect to impurities, is focused on the isolation, identification, qualification and quantification of impurities that are found as a result of the manufacturing process or through chemical decomposition. On the... 

We continue the discussion of multicomponent crystals placed in the potential chemical gradient of a component. Let us investigate what happens when a nearly stoichiometric compound crystal is brought between different potentials of its nonmetallic component (e.g., AO B203 between two different oxygen potentials). These two potentials are chosen to fall inside the stability field of the spinel phase so that the spinel will be neither reduced nor oxidized thermodynamically. We will demonstrate that the spinel can nevertheless decompose in the oxygen potential gradient. This decomposition is a purely kinetic effect and has therefore been named kinetic decomposition. 

Curie point pyrolysis mass spectrometry has also been valuable in providing information about the chemical types that are evolved during the thermal decomposition of coal (Tromp et al., 1988) and, by inference, about the nature of the potential chemical types in coal. However, absolute quantification of the product mixtures is not possible, due to the small sample size, but the composition of the pyrolysis, product mix can give valuable information about the metamorphosis of the coal precursors and on the development of the molecular structure of coal during maturation. However, as with any pyrolysis, it is very important to recognize the nature and effect that any secondary reactions have on the nature of the volatile fragments, not only individually but also collectively. 

Extensive studies of the redox chemistry of [ Co3(CO)9 2 n-C(C=C)mC ] (m = 0, 271 1, 286) have been made independently by the groups of Robinson439 and Osella481,482 and the electrochemical behavior of the C2 and C4 complexes has been compared with that of Co2(CO)6 2(p-r 2-PhC2C2Ph).482,483 Two distinct one-electron reduction processes are found, of which the first shifts to more negative potentials as the carbon chain is lengthened. This is consistent with effective electronic communication between the redox centers. This is attenuated when a Co2(CO)6 group is attached to the carbon chain. All scans contain a wave due to the [Co(CO)4] anion formed by chemical decomposition. 

The deposition of silver sulphide is detrimental as it contaminates the silver deposit and the solution, interferes with the kinetics of silver deposition and tends to cause chemical instability of the fixer. At extremely negative cathode potentials, cathodic decomposition of the fixer may result in emission of toxic hydrogen sulphide ... 

The paramagnetic products of the one-electron oxidation, [CpReH2 P(p-XCgH4)3 2], are stable and the reversible potential shows a linear dependence with Hammett s Op parameter. These compounds, however, have not been isolated and have only been characterized, besides their cyclic voltammetric properties, by UV-visible spectroscopy for X = H and by the nature of the chemical decomposition products (see section 6.5.2). Two isolated members of this class were described later by Herrmann. The silver oxidation of Cp ReH(X)(PMe3)2 (X = H or Cl) yield salts of the corresponding cations, isolated as the triflate for X = H and the hexafluoroantimonate for X = Cl. No characterization other than elemental analysis and IR (no mention of Re-H frequencies) was given, however... 

Chemical decomposition is usually observed in solid reactions, such as carbonate, hydroxides, nitrate, acetate, oxalates, alkoxides and so on, when they are heated at a certain temperature. The decomposition leads to the formation of a new solid product, together with one or more gaseous phases, which is usually used to produce powders of simple oxides in most cases and complex oxides sometimes. Although this method has not been widely reported for the synthesis of transparent ceramic powders, it could be a potential technique for such a purpose, due to its various advantages, such as simple processing, inexpensive raw materials, and capability of large scale production. In fact, the calcination step involved in most wet-chemical processing routes, especially chemical precipitation or co-precipita-tion, is chemical decomposition, either from carbonates or hydroxides, as discussed later. 

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