Lead oxides, decompositions

Malinin et al. [634,647] have studied rates of decompositions of lead oxides. The reaction of Pb304 at 840 K yields some 15% atomic oxygen, obeys the Avrami—Erofe ev equation [eqn. (6), n = 2] and values of E are 320 and 190 kJ mole-1 at atmospheric pressure and in vacuum, respectively. 

The S=N bond in sulphilimines is relatively sensitive to hydrolysis and so the oxidation of these compounds to sulphoximines must be carried out under mild conditions. For example, attempted oxidation of many sulphilimines with potassium permanganate usually leads to decomposition without formation of the required product17S. It should be noted, however, that once the sulphoximine is formed the S=N bond is much more stable and hence less readily available for reaction. 

Lead oxide reacts violently with numerous metals such as sodium powder (immediate ignition), aluminium (thermite reaction, which is often explosive), zirconium (detonation), titanium, some metalloids, boron (incandescence by heating), boron-silicon or boron-aluminium mixtures (detonation in the last two cases). Finally, silicon gives rise to a violent reaction unless it is combined with aluminium (violent detonation). It also catalyses the explosive decomposition of hydrogen peroxide. 

The formation of peroxides and formaldehyde in the high-purity polyoxyethylene surfactants in toiletries has been shown to lead to contact dermatitis [31], Peroxides in hydrogenated castor oil can cause autoxidation of miconazole [32], Oxidative decomposition of the polyoxyethylene chains occurs at elevated temperature, leading to the formation of ethylene glycol, which may then be oxidized to formaldehyde. When polyethylene glycol and poloxamer were used to prepare solid dispersions of bendroflumethiazide, a potent, lipophilic diuretic drug, the drug reacted with the formaldehyde to produce hydroflumethiazide [33],... 

Simpson, M. B. H., Kautsch. Gummi, Kunstst., 1980, 33, 83 -85 Dispersions of lead oxide in fluoroelastomers underwent severe exothermic decomposition when heated above the normal mixing temperature of below 200°C, forming elemental lead. 

The charge carriers may reduce or oxidize the semiconductor itself leading to decomposition. This poses a serious problem for practical photoelectrochemical devices. Absolute thermodynamic stability can be achieved if the redox potential of oxidative decomposition reaction lies below the valence band and the redox potential of the reductive decomposition reaction lies above the conduction band. In most cases, usually one or both redox potentials lie within the bandgap. Then the stability depends on the competition between thermodynamically possible reactions. When the redox potentials of electrode decomposition reactions are thermodynamically more favored than electrolyte redox reactions, the result is electrode instability, for example, ZnO, Cu20, and CdS in an aqueous electrolyte. 

Confinement—Deflagration rates of substances such as azo compounds, peroxides, and certain lead oxides may accelerate by pressure increase, especially when the governing decomposition reaction is gas-phase controlled [28]. Initiation of a deflagration at the bottom or at the center of a closed or partially closed vessel may lead to an increase of eh deflagration rate by a factor of more than 100 in comparison with top initiation. Autocatalytic decomposition by a volatile catalyst is enhanced by confinement. 

Ellis and coworkers studied the effect of lead oxide on the thermal decomposition of ethyl nitrate vapor.P l They proposed that the surface provided by the presence of a small amount of PbO particles could retard the burning rate due to the quenching of radicals. However, the presence of a copper surface accelerates the thermal decomposition of ethyl nitrate, and the rate of the decomposition process is controlled by a reaction step involving the NO2 molecule. Hoare and coworkers studied the inhibitory effect of lead oxide on hydrocarbon oxidation in a vessel coated with a thin fQm of PbO.P l They suggested that the process of aldehyde oxidation by the PbO played an important role. A similar result was found in that lead oxide acts as a powerful inhibitor in suppressing cool flames and low-temperature ignitions.P l... 

Ellis, W. R., Smythe, B. M., and The-harne, E. D., The Effect of Lead Oxide and Copper Surfaces on the Thermal Decomposition of Ethyl Nitrate Vapor,... 

Reaction of 3,5-disubstituted-1,2,4-trioxolanes (89) with oxidants (usually under basic conditions) leads to carboxylic acids (Equation (14)). This reaction is often carried out as the work up procedure for alkene ozonolysis, avoiding the need to isolate the intermediate ozonide. Typical oxidants are basic hydrogen peroxide or peracids and this type of oxidative decomposition is useful for both synthetic and degradative studies. 

It is not necessary that the reaction should always lead to decomposition of the ligand. If the central ion can give a stable complex with one lower (or higher) oxidation number, the product of a intramolecular redox reaction may be a complex with a central metal ion of different oxidation number. 

Nitrogen Pentasulphide, NaS5.—Nitrogen pentasulphide is formed by the decomposition of the yellow sulphide, N4S4, and its derivatives. It is formed, for example, when the yellow sulphide is exploded by friction, when the compounds of N4S4 with the halogens or with nitrous or nitric acid are boiled with water, and also when N4S4 is heated carefully with lead oxide.6... 

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