Excess-oxidant oxidation

Oxidation of Coal and Coal Macerals. Extraction residues were oxidized as outlined in the experimental section. Two oxidation procedures were adopted - i). excess oxidant oxidation and ii). oxidant starved oxidation (partial oxidation). 

Chitins and chitosans from a variety of sources have simple e.s.r. spectra, provided they have been isolated and purified under controlled conditions to avoid excessive oxidative oxidation.The primary product of the thermal degradation of chitin, 2-acetamido-l,6-anhydro-2-deoxy-/3-D-glucopyranose, has been detected and isolated on a preparative scale. ... 

In addition to predicting the exhaust composition of both gases and soHds, the abiHty of these chemical equiHbrium programs to do adiabatic calculations makes them useful for computing supplemental fuel requirements and the effect of excess oxidant on temperature. 

Titration Indicators. Concentrations of arsenic(III) as low as 2 x 10 M can be measured (272) by titration with iodine, using the chemiluminescent iodine oxidation of luminol to indicate the end point. Oxidation reactions have been titrated using siloxene the appearance of chemiluminescence indicates excess oxidant. Examples include titration of thallium (277) and lead (278) with dichromate and analysis of iron(II) by titration with cerium(IV) (279). 

In contrast to most extmsion processes, extmsion coating involves a hot melt, ca 340°C. The thin web cools rapidly between the die and nip even at high linear rates. Both mechanical and chemical bonding to substrates are involved. Mechanical locking of resin around fibers contributes to the resin s adhesion to paper. Some oxidation of the melt takes place in the air gap, thereby providing sites for chemical bonding to aluminum foil. Excessive oxidation causes poor heat-sealing characteristics. 

Red Brass Alloys. In forming red brass alloys, which iaclude leaded red and leaded semired brasses, caution should be exercised to prevent gas absorption by flame impingement or the melting of oily scrap, or metal loss through excessive oxidation of the melt surface. To prevent excessive 2iac volatilization, the melt must be poured as soon as it reaches the proper temperature. The melt should be finally deoxidized and cast at ca 1065—1230°C as measured with a pyrometer. Fluxing is usually not needed if clean material has been melted. 

Special low fusing porcelain veneers are appHed to pure (unalloyed) titanium dental castings. It is important that firing be done either in a vacuum or inert atmosphere to protect the metal surface from excessive oxidation. The strength of the metal-ceramic bond is apparently adequate although the bonding is thought to involve primarily a mechanical rather than a chemical component. 

Chromium is the most effective alloying element for promoting resistance to oxidation. Table 3.10 gives temperatures at which steels can be used in air without excessive oxidation. In atmospheres contaminated with sulfur, lower maximum temperatures are necessary. 

As already noted (p. 1073), the platinum metals are all isolated from concentrates obtained as anode slimes or converter matte. In the classical process, after ruthenium and osmium have been removed, excess oxidants are removed by boiling, iridium is precipitated as (NH4)2lrCl6 and rhodium as [Rh(NH3)5Cl]Cl2. In alternative solvent extraction processes (p. 1147) [IrClg] " is extracted in organic amines leaving rhodium in the aqueous phase to be precipitated, again, as [Rh(NH3)5Cl]Cl2. In all cases ignition in H2... 

This is essential to avoid both the excessive oxidation of the reactants and the danger of a sodium-sparked fire. 

All attempts to oxidize either cis- or trans-di-t-butylthiirane oxides failed122 (see equation 20). Reagents investigated included m-chloroperbenzoic acid, sodium peroxide, hydrogen peroxide, ozone and aqueous potassium permanganate. The cis oxide was resistant to oxidation (apparently steric hindrance), and the trans isomer was consumed with excess oxidizing agent but no identifiable products could be isolated. 

A 250-mL, two-necked, round-bottomed flask equipped with a magnetic stirbar, thermometer, and a reflux condenser fitted with a rubber septum and balloon of argon is charged with a solution of methyltrioxorhenium (MTO) (0.013 g, 0.05 mmol, 0.1% mol equiv) in 100 mL of methanol (Note 1). Urea hydrogen peroxide (UHP) (14.3 g, 152 mmol) is added (Notes 1, 2, 3, 4), the flask is cooled in an ice bath, and dibenzylamine (9.7 mL, 50.7 mmol) is then added dropwise via syringe over 10 min (Notes 1, 5). After completion of the addition, the ice bath is removed and the mixture is stirred at room temperature (Note 6). A white precipitate forms after approximately 5 min (Note 7) and the yellow color disappears within 20 min (Note 8). Another four portions of MTO (0.1% mol equiv, 0.013 g each) are added at 30-min intervals (2.5 hr total reaction time). After each addition, the reaction mixture develops a yellow color, which then disappears only after the last addition does the mixture remain pale yellow (Note 9). The reaction flask is cooled in an ice bath and solid sodium thiosulfate pentahydrate (12.6 g, 50.7 mmol) is added in portions over 20 min in order to destroy excess hydrogen peroxide (Note 10). The cooled solution is stirred for 1 hr further, at which point a KI paper assay indicates that the excess oxidant has been completely consumed. The solution is decanted into a 500-mL flask to remove small amounts of undissolved thiosulfate. The solid is washed with 50 mL of MeOH and the methanol extract is added to the reaction solution which is then concentrated under reduced pressure by rotary evaporation. Dichloromethane (250 mL) is added to the residue and the urea is removed by filtration through cotton and celite. Concentration of the filtrate affords 10.3 g (97%) of the nitrone as a yellow solid (Note 11). 

Methemoglobinemia Intake of excess oxidants (various chemicals and drugs) Genetic deficiency in the NADH-dependent methemoglobin reductase system (MIM 250800) Inheritance of HbM (MIM 141800)... 

The apparent first-order rate coefficient obtained using excess oxidant increased exponentially with increase in acidity in the range 5 N < [H30" ] < 12 N. The reaction is first-order with respect to added manganous ions (k increasing sharply), but the activation energy (11.0 kcal.mole ) remains unchanged. At appreciable catalyst concentrations the reaction becomes almost zero-order with respect to bromide ion. The mechanism appears to be a slow oxidation of Mn(II) to Mn(III) followed by a rapid reduction of the latter by bromide. This reaction is considered further in the section on Mn(II)-catalysis of chromic acid oxidations (p. 327). 

Abel has assumed that the reaction between arsenite and molecular oxygen is catalyzed by a chromium intermediate. He suggested that chromium(IV) is converted by oxygen into chromium(VI) which causes the excess oxidation of arsenic(III). However, this mechanism is also devoid of experimental support. 

Steel making, broadly speaking, is an oxidation process in which impurities such as carbon, silicon, manganese, phosphorus and sulfur present in the pig iron are removed to specified levels. It can be anticipated from the Ellingham diagram that at about 1600 °C, the elements C, Si, and Mn would oxidize preferentially before iron undergoes excessive oxidation. The oxidation reactions may be represented by... 

FIGURE 6.41 Oxidation of 3-oxa-chromanol 59 in aqueous media (excess water present), leading to acetophenone 61 with an equimolar amount of oxidant, and further to para-quinone 62 in the presence of excess oxidant. 

An occasional batch of zinc dust failed to effect the desired reduction, possibly because of excessive oxide deposition on the surface of the zinc. It is suggested, therefore, that the surface of the zinc dust be cleaned with dilute hydrochloric acid just before amalgamation. 

Thenard, J., Compt. rend., 1844, 18, 652 A mixture with excess oxide can be exploded by sparking. 

The complex, containing excess oxide over amine, exploded at below 0°C when... 

Mild allylic oxidation of the A-2-crotyl-substituted thiadiazolidinone 1,1-dioxide 140 by sodium metaperiodate/ ruthenium trichloride hydrate (RuC13) gave the aldehyde 141. Excess oxidizing agent afforded the carboxylic acid 142 (Equation 26) <1999EJ02275>. 

Metal-excess oxides can change composition by way of metal interstitials or oxygen vacancies. The formation of cation interstitials in a nonstoichiometric oxide MO can be represented by... 

The analysis of oxygen-excess oxides is similar to that for metal-rich phases just given. For example, the creation of oxygen excess by cation vacancies can be written ... 

Thus, the conductivity increases as the partial pressure of oxygen increases, which is the opposite behavior to that of the metal-excess oxides. 

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