Oxidation with oxygen or air

Oxidation. Acetaldehyde is readily oxidized with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid AND DERIVATIVES). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the liquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is believed to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21-0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or ozone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directly by liquid-phase oxidation at 5 -50°C with a cobalt salt catalyst (37) (see Peroxides AND peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of -xylene to terephthalic acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

Effect of Ozone in Autoxidations. To appreciate this effect what is called the oxidation yield has been determined (abbreviated RO,-from the French equivalent of oxidation yield, rendement d oxydation ). This value relates the amount of supplementary oxygen bound when one passes from the oxidation with oxygen (or air) alone to the oxidation with oxygen (or air) containing a known percentage of ozone, all other conditions remaining identical. The amount of reacted oxygen can be found by analysis of the oxidation products after the experiments. 

Diels and coworkers have shown that, when n-arafemo-hexulose phenyl-osazone is oxidized with oxygen (or air) in an alkaline medium, a dehydro-osazone is obtained which possesses two hydrogen atoms fewer than the parent osazone. On acetylation, the compound gives a triacetate, and its hydrazine residues could not be removed with p-nitrobenzaldehyde, suggesting their involvement in ring formation. The authors supported this view by the findings that dehydro-osazones cannot be obtained from methylphenylosazones or from the Diels anhydro-osazone (which, at that time, was believed to be a pyrazole compound). 

The nitrosyl process (See chapter 10.2.2) is one way to recover chlorine from hydrogen chloride by oxidizing with oxygen or air. 

Another method of manufacture involves the oxidation of 2-isopropylnaphthalene ia the presence of a few percent of 2-isopropylnaphthalene hydroperoxide/i)ti< 2-22-(y as the initiator, some alkaU, and perhaps a transition-metal catalyst, with oxygen or air at ca 90—100°C, to ca 20—40% conversion to the hydroperoxide the oxidation product is cleaved, using a small amount of ca 50 wt % sulfuric acid as the catalyst at ca 60°C to give 2-naphthalenol and acetone in high yield (70). The yields of both 2-naphthalenol and acetone from the hydroperoxide are 90% or better. 

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. 

Nakajima and coworkers [30] observed that, in the presence of CuCl(OH).-TMEDA with oxygen or air as the oxidant, 2-naphthol 103a is transformed into l,l -bi-2,2 -naphthol 104a. A wide variety of substrates undergo oxidative coupUng in excellent yields (Scheme 28). It is worth noting that the reaction requires as little as 1 mol % of the catalyst. 

Coal with a mean particle size of less than 3 mm is slurried with water and then oxidized with oxygen or mixtures of oxygen and air at temperatures ranging from 100° to 300° C, at partial oxygen pressures ranging from 0.1 to 10 MPa and reaction periods ranging from 5 to 600 minutes [425]. In the absence of catalysts, such as alkaline bases, the main products of oxidation are humic acids. 

Potassium reacts with oxygen or air forming three oxides potassium monoxide, KaO potassium peroxide, KaOa and potassium superoxide, KOa. The nature of the product depends on oxygen supply. In limited supply of oxygen potassium monoxide is formed, while in excess oxygen, superoxide is... 

C. G. Vayenas and R. D. Farr, Science 208, 593 (1980), describe a solid electrolyte fuel cell in which ammonia is the fuel and is catalyt-ically converted at 1000 K with oxygen (or air) to nitric oxide. The idea is that the energy released in this step in industrial nitric acid production (Section 9.4) could be recovered directly as electricity. 

Evaluate data and assess results Prior to carrying out oxidation experiments, the mass balance of a compound should be examined under the conditions of aeration with oxygen or air, so that other elimination processes can be excluded. For example stripping of a compound can be determined by absorption of the off-gas in water or other appropriate liquid in gas wash bottles. 

The fuel cell is positioned within the magnet. Fuel gas (hydrogen) and oxidant gas (oxygen or air) are fed to the cell. For investigation of water transport in PEMFCs by MRI, it is preferable to operate PEMFCs in elevated temperature with humidity control, because both operating temperature and relative humidify (RH) inherently affects water transport in PEMFCs. Tsushima et al.27-29... 

The times of the complete oxidation of alkanes with oxygen or air under the action of nanosecond pulsed discharges have been determined 222 The kinetics of liquid-phase oxidation of isomeric methoxy(l-methylethyl)benzenes with oxygen to the corresponding hydroperoxides has been studied. The overall activation energies of the oxidation and initiating properties of some of the hydroperoxides were determined 223... 

Activation of aluminum in a cavity, ball or vibration mill. This activation technique should be used in nitrogen and in 5% solution of triethylaluminum in n-heptane, because aluminum suspension is easily transported through pipes and activated aluminum is protected from oxidation (with oxygen in air) during transportation and storage. Besides, wet grinding is less explosive than dry. Aluminum powder should be activated in the mill for 20-30 hours. The aluminum ground in a vibration mill is the most active. 

The most dramatic results obtained so far with gold catalysts have been with the liquid phase processes. They are conducted with oxygen or air, often using water as solvent, and are therefore felt to be environmentally benign. Particular success has been obtained with reducing sugars (Section 8.3.2) and other aldehydes (Section 8.3.3), and with alcohols and other hydroxy-compounds (Sections 8.3.4-8.3.7). Reactions that use soluble gold complexes to catalyse selective oxidation are reported in Chapter 12. 

Dry ashing is the process of oxidizing an organic sample with oxygen or air at high temperature, leaving the inorganic component for analysis. 

The ethylene oxidation rate is proportionhUo the oxygen concentration. This means that the air-to-ethylene ratio has a predominant influence on the conversion and yield. For practical purposes, however, the optimal ethylene concentration is determined by the flammability limits of the mixtures with oxygen or air, and by the olefin loss in tbe off-gases. 

Acetaldehyde monoperacetate normally decomposes, to yield 97 per cent anhydride and water and 3 per cent add. However, the hydrolysis takes place rapidly, so that acetic anhydride is merely the forerunner of the add in the oxidation of acetaldehyde. The difficulty of the operation, which takes place in the liquid phase with oxygen or air, at moderate temperature (45 to 60°Q and low pressure (0.1 to 0.4.106 Pa absolute), thus consists in preventing the hydrolysis of acetic anhydride from developing. 

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