Oxidation by oxygen

CHa CHlCH CHO. Colourless lachrymatory liquid with a pungent odour. B.p. 104 "C. Manufactured by the thermal dehydration of aldol. May be oxidized to crotonic acid and reduced to crolonyl alcohol and 1-butanol oxidized by oxygen in the presence of VjOj to maleic anhydride. It is an intermediate in the production of l-butanol from ethanol. 

The introduction of additional alkyl groups mostly involves the formation of a bond between a carbanion and a carbon attached to a suitable leaving group. S,.,2-reactions prevail, although radical mechanisms are also possible, especially if organometallic compounds are involved. Since many carbanions and radicals are easily oxidized by oxygen, working under inert gas is advised, until it has been shown for each specific reaction that air has no harmful effect on yields. 

In the first step, propylene is introduced at 10—40°C into nitric acid, the concentration of which is kept at 50—75 wt % and molar ratio to propylene at 0.01—0.5, and converted into a-nitratolactic acid and lactic acid. a-Nitratolactic acid is oxidized by oxygen in the second step in the presence of a catalyst at 45—100°C to produce oxahc acid dihydrate. The overall yield based on propylene is greater than 90% and the conversion of propylene, 77.5%. The outhne of the process is shown in Figure 2. The RhcJ)ne-Poulenc process can be characterized by the coproduction of lactic acid. 

Potassium Superoxide. Potassium, mbidium, and cesium form superoxides, MO2, upon oxidation by oxygen or air. Sodium yields the peroxide, Na202 lithium yields the oxide, Li20, when oxidized under comparable conditions. Potassium superoxide [12030-88-5] KO2 liberates oxygen in contact with moisture and carbon dioxide (qv). This important property enables KO2 to serve as an oxygen source in self-contained breathing equipment. 

Generated by spontaneous dissociation of the dimer. Stable for several days at room temperature. Oxidized by oxygen. 

Two other methods worth discussing are wet air oxidation and regeneration by steam. Wet oxidation may be defined as a process in which a substance in aqueous solution or suspension is oxidized by oxygen transferred from a gas phase in intimate contact with the liquid phase. The substance may be organic or inorganic in nature. In this broad definition, both the well known oxidation of ferrous salts to ferric salts by exposure of a solution to air at room temperature and the adsorption of oxygen by alkaline pyrogallol in the classical Orsat gas analysis would be considered wet oxidations. 

The nickel supported catalysts formed in this way have some specific features (144)- The catalysts containing about 3% of Ni are paramagnetic. When varying the nickel content from 0.1 to 20%, all the nickel the reduced catalyst (the exposed surface area of nickel was about 600 m2/g Ni) is oxidized by oxygen. The activity in benzene hydrogenation is very high and increases in proportional to the nickel content in the catalyst. 

In addition to effects on the concentration of anions, the redox potential can affect the oxidation state and solubility of the metal ion directly. The most important examples of this are the dissolution of iron and manganese under reducing conditions. The oxidized forms of these elements (Fe(III) and Mn(IV)) form very insoluble oxides and hydroxides, while the reduced forms (Fe(II) and Mn(II)) are orders of magnitude more soluble (in the absence of S( — II)). The oxidation or reduction of the metals, which can occur fairly rapidly at oxic-anoxic interfaces, has an important "domino" effect on the distribution of many other metals in the system due to the importance of iron and manganese oxides in adsorption reactions. In an interesting example of this, it has been suggested that arsenate accumulates in the upper, oxidized layers of some sediments by diffusion of As(III), Fe(II), and Mn(II) from the deeper, reduced zones. In the aerobic zone, the cations are oxidized by oxygen, and precipitate. The solids can then oxidize, as As(III) to As(V), which is subsequently immobilized by sorption onto other Fe or Mn oxyhydroxide particles (Takamatsu et al, 1985). 

At sufficiently high concentration of iron(iri) and copper(II), the induced oxidation by oxygen is eliminated because all the HO2 radicals are oxidized by steps (55) or (56). In such cases F approaches infinity and Xas becomes equal to 1, i.e. arsenic(III) is oxidized according to equation B. Consequently, iron(II) is reformed at the same rate as it is oxidized. 

Paik CH, Jarvi TD, O Grady WE. 2004. Extent of PEMFC cathode surface oxidation by oxygen and water measured by CV. Electrochem Solid State Lett 7 A82-A84. 

Corrosion, a type of redox reaction, can cause cars and buildings to rust. Rusting happens when iron is oxidized by oxygen in the air. This process happens when —... 

This conclusion is in agreement with experiments in which a smootb quartz and cellulose were used as substrates. For above materials the transfer of excitation energy of the dye into the substrate is low which is confirmed by intensive luminescence of adsorbed tripaflavine. Note, that the activation energy of emission of singlet oxygen is close for zinc oxide oxidized by oxygen atoms, quartz and cellulose and amounts to 5-10 kcal/mol [83]. 

Precious metals such as silver and gold, which are seldom oxidized even at high temperatures, are often refined by cupellation, a process for removing from them base metal impurities such as lead and tin, with which they are associated in many ores. Hot lead and tin are easily oxidized. In the cupellation process, a crude, impure precious metal is placed in a shallow cup or crucible made of bone ash, known as a cupel, and is then heated by a blast of hot air. At high temperatures, the base metal impurities are oxidized by oxygen in the hot air, and the oxides thus formed are absorbed by the porous bone ash. The Chaldeans are said to have been the first to have utilized (ca. 2500 b.c.e.) cupellation to remove lead and purify silver from lead-silver ores. 

The first chemiluminescent paracyclophanes have been described recently 208> the compounds 138 and 139 both contain a phthalhydrazide group as that part of the molecule producing the excitation energy which is transferred to the substituted benzene resp. anthracene moiety. 139 chemiluminesces with about double the amount of 2.3-anthracene dicarboxylic hydrazide on oxidation by oxygen/potassium tert. butoxide... 

Oxidized LDL are considered to be one of the major factors associated with the development of atherosclerosis. The earliest event is the transport of LDL into the arterial wall where LDL, being trapped in subendothelial space, are oxidized by oxygen radicals produced by endothelial and arterial smooth muscle cells. The oxidation of LDL in the arterial wall is affected by various factors including hemodynamic forces such as shear stress and stretch force. Thus, it has been shown [177] that stress force imposed on vascular smooth muscle cells incubated with native LDL increased the MDA formation by about 150% concomitantly with the enhancement of superoxide production. It was suggested that oxidation was initiated by NADPH oxidase-produced superoxide and depended on the presence of metal ions. 

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