Fast oxidation

Flame Retardants. Because PVC contains nearly half its weight of chlorine, it is inherently flame-retardant. Not only is chlorine not a fuel, but it acts chemically to inhibit the fast oxidation in the gas phase in a flame. When PVC is diluted with combustible materials, the compound combustibiHty is also increased. Por example, plastici2ed PVC with > 30% plastici2er may require a flame retardant such as antimony oxide, a phosphate-type plastici2er, or chlorinated or brominated hydrocarbons (145,146). 

Occasionally it happens that the oxo compound, produced by oxidation, forms a hydrate which is further oxidized to a dihydroxy compound. Attention must be given to the possibility (so far unreported) that when the hydrated species is in equilibrium with a trace of the ring-opened structure a sufficiently fast oxidation rate of the amino-aldehyde (i.e. the acyclic structure) could lead to the incorrect conclusion that the original material was not cyclic. 

The very fast oxidation of the radical precludes its detection and identification by esr however, reacting mixtures are capable of initiating polymerisation of acrylonitrile. The oxidations of allylic alcohols by V(V) perchlorate are ca. thirty times faster than those of saturated alcohols. This is supporting evidence for radical intermediates in view of the expected delocalisation of the free electron... 

On the basis of these results it can be stated that the fast oxidation of thiocyanate by peroxy acids gives rise to the induced reduction of hydrogen peroxide. In order to elucidate the mechanism of this interesting reaction let us have a look at reactions of thiocyanate with peroxy compounds of different types. 

This type of catalyst is not limited to nickel other examples are Raney-cobalt, Raney-copper and Raney-ruthenium. When dry, these catalysts are pyrophoric upon contact with air. Usually they are stored under water, which enables their use without risk. The pyrophoric character is due to the fact that the metal is highly dispersed, so in contact with oxygen fast oxidation takes place. Moreover, the metal contains hydrogen atoms and this adds to the pyrophoric nature. Besides the combustion of the metal also ignition of organic vapours present in the atmosphere can occur. Before start of the reaction it is a standard procedure to replace the water by organic solvents but care should be taken to exclude oxygen. Often alcohol is used. The water is decanted and the wet catalyst is washed repeatedly with alcohol. After several washes with absolute alcohol the last traces of water are removed. 

Avoiding the fast oxidation acidic medium was applied, the hydrogenation was carried out in methanol-water mixture containing a stoichiometric amount of hydrochloric acid, 4 mole with respect to 1 mole 4,6-bisphenylazo resorcinol. Under... 

Together with the fast oxidation (at low temperatures) of NO to N02, the plasma causes the partial HC oxidation (using propylene, the formation of CO, C02, acetaldehyde and formaldehyde was observed). Both the effects cause a large promotion in activity of the downstream catalyst [86]. For example, a "/-alumina catalyst which is essentially inactive in the SCR of NO with propene at temperatures 200°C allows the conversion of NO of about 80% (in the presence of NTP). Formation of aldehydes follows the trend of NO concentration suggesting their role in the reaction mechanism. Metal oxides such as alumina, zirconia or metal-containing zeolites (Ba/Y, for example) have been used [84-87], but a systematic screening of the catalysts to be used together with NTP was not carried out. Therefore, considerable improvements may still be expected. 

The interception of the oxidized dye by the electron donor in the electrolyte (i.e., iodide) occurs within 10ns. The rate of the reaction leading to the regeneration of the dye ground state was found to depend strongly on the nature and the concentration of the cations present in the solution. Small cations such as Li+, Mg2+, and La3+ can intercalate into the oxide surface, thereby favoring fast oxidation of iodide by the oxidized state of the sensitizer. 

This expression is valid for oxidation with the excess of bromide ions over cobalt ions (the conditions of fast oxidation of Co3+). The experimental data agree with this dependence. The kp, kp, and Kkp values for three hydrocarbons (343 K, acetic acid) are presented below [206]... 

Soluble copper salts were found to possess the outstanding inhibiting activity in the presence of iron salts [50], This copper antioxidant activity is believed to be the result of the fast oxidation of catalytically active ferrous ions by cupric ions... 

In agreement with literature results (45,46), independent experiments confirmed that the addition of an aliquot of a CuCl acetonitrile solution to an H202 solution induced the immediate decay of H202 at pH 9.0 (44). Most likely, the OH radical produced is involved in fast oxidation of the H2C-R, SQ-R - or even the Q-R forms of the substrate and the stoichiometry shown in Eq. (54) is not valid anymore. The formation of free radicals was excluded under acidic conditions (36) implying that the Fenton-type decomposition of H202 may gain significance only in alkaline solution. 

Although a number of precautions have been mentioned for the control of sulfide by precipitation as FeS, this methodology is often considered not only acceptable but also cheap and efficient. Added iron salts may also be reused in the treatment process. Under aerobic conditions in the wastewater treatment plant, the amorphous FeS is fast oxidized, and the iron can be used for chemical removal of phosphate. 

The influence of steric effects on the rates of oxidative addition to Rh(I) and migratory CO insertion on Rh(III) was probed in a study of the reactivity of a series of [Rh(CO)(a-diimine)I] complexes with Mel (Scheme 9) [46]. For a-diimine ligands of low steric bulk (e.g. bpy, L1, L4, L5) fast oxidative addition of Mel was observed (103-104 times faster than [Rh(CO)2l2] ) and stable Rh(III) methyl complexes resulted. For more bulky a-diimine ligands (e.g. L2, L3, L6) containing ortho-alkyl groups on the N-aryl substituents, oxidative addition is inhibited but methyl migration is promoted, leading to Rh(III) acetyl products. The results obtained from this model system demonstrate that steric effects can be used to tune the relative rates of two key steps in the carbonylation cycle. 

Complexes between tertiary aliphatic amines (triethylamine, tribenzylamine) and bromine are of interest also for their high reactivity. The Et3N/Br2 complex cannot be isolated because of the very fast oxidation-reduction process of equation 16. 

We suggest that these results can be explained if the aggregation process in these solid TTF polymers proceeds by means of a two-step mechanism (Figure 7) in which the fast oxidative electron transfer step is followed by a slow process of ion clustering/reorganization which is favored by a low viscosity environment. This mechanism is consistent with the fact that the starting neutral homopolymer shows no spectroscopic evidence for site-site interaction between the pendant donors. The absorption spectrum of the polymer is... 

Fibre Slow oxidative (type I) Fast oxidative (type Ha) Fast glycolytic (type lib)... 

The compounds BajInjOj, Agl and PbFj illustrate ionic conductivity in stoichiometric compounds. The first is a fast oxide-ion conductor above a first-order order-disorder transition at 930 °C that leaves the Bain array unchanged the second is a fast Ag -ion conductor above a first-order transition at which the I -ion array changes from close-packed to body-centred cubic and the third exhibits a smooth transition to a fast F ion conductor without changing the face-centred-cubic array of Pb " ions. 

An useful alternative to the already known retropinacol reactions is presented by Liu and co-workers [7], This works demonstrates that pinacols bearing (dimethylamino)phenyl substiments can be subjected to fast oxidative fragmentation via photoinduced electron transfer with chloroform as the electron acceptor in yields up to 80%. The extremely fast dechlorination of the chloroform radical anion inhibits back-electron transfer and thus leads to effective fragmentation of the pinacol radical cation (Scheme 8). 

Substituents stabilising a carbonium ion influence the course of the anodic oxidation of carboxylic acids by promoting fast oxidation of the radical intermediate to the carbonium ion. Subsequent chemical steps are those expected of this ionic intermediate and the overall process is termed the non-Kolbe reaction. Reaction at... 

FeOOH precipitates as platy crystals. When formed by fast oxidation of Fe(OH)2 at pH 12 well formed hexagonal plates result, whereas simultaneous precipitation/oxi-dation gives thin plates which are often rolled up (Feitknecht, 1959). Feroxyhyte (5 -FeOOH) produced by rapid oxidation (e.g. with H2O2) of FeQ2 solution at pH 8 also forms thin platy crystals around 100 nm in size (Fig. 4.27, upper). As the pH is lowered, the crystals become smaller and develop a grassy appearance (Carlson Schwertmann, 1980). Natural feroxyhyte from the Clara Mine in the Black Forest occurred as vermiform aggregates (Fig. 4.27, lower) (Walenta, 1997). 

This is frequently the required mode of operation for fast oxidation reactions because the heat release is too fast to provide efficient heat exchange. Most combustion processes are nearly adiabatic (your home furnace and your automobile engine), and many catalytic oxidation processes such as NH3 oxidation in HNO3 synthesis are nearly adiabatic. 

Artemisinin is a natural endoperoxide-containing sesquiterpene, isolated from a plant used in traditional Chinese medicine. Acetalic artemisinin derivatives (arte-mether, artesunate) are very active against chemo-resistant forms of Plasmodium falciparum, and are clinically used for the treatment. However, they suffer from an unfavourable pharmacological profile. They are quickly metabolised by fast oxidative metabolism, hydrolytic cleavage and glucuronidation. 

---