Further Oxidation Reactions

A further oxidative reaction, in this case accompanied by rearrangement, has also been observed18 in the reaction of 4-benzylalkylamino-azobenzenes with Schiff s bases. Thus, reaction of the methyl-substituted azobenzene 15 with Schiff s base (16) gives at 40° to 45°C the expected stilbene 17. However, at higher temperature this product undergoes oxidative rearrangement to the A-ethylketimine (18). 

A further oxidation reaction occurs when sulfur dioxide is changed to sulfur trioxide in the air ... 

FURTHER OXIDATION REACTIONS OF CARBON MONOXIDE IN HOMOGENEOUS SYSTEMS... 

During their residence time in the atmosphere, mineral dusts become coated by sulfates, nitrates, and other species (Dentener et al. 1996 Buseck and P6 sfai 1999 Zhang and Carmichael 1999 Song and Carmichael 1999 Buseck et al. 2000). These coatings are formed through chemical reactions such as the oxidation of SO2 and NO2 at the gas-solid interface, as well as by condensation of sulfuric and nitric acids. Once coated, the hygroscopic dusts act as cloud condensation nuclei and further oxidation reactions can take place in the aqueous medium (Wurzler et al. 2000). Subsequent evaporation of the cloud droplet yields a coated particle. 

Hence, experimental rate constant measurements in combination with theoretical simulations show a pronounced size and structure selective activity of anionic silver clusters toward molecular oxygen due to cooperative effects. In particular, for Ag clusters with odd n, a weakly bound first O2 promotes the adsorption of a second O2 molecule which is then (for n = 3, 5) differently bound with the O2 bond elongated to 1.32 A and thus potentially activated for further oxidation reactions such as CO combustion, which have indeed been observed for larger cluster sizes [361]. 

Even better results are obtained by a post-synthesis treatment of TS-1 with both hydrogen peroxide and ammonium hydrogen fluoride, NH4HF2. Upon such a treatment (H202/F/Ti = 10 2.5 1 60 °C 4h), a substantial amount of titanium (up to 75% of the initial value) is removed. Nevertheless, the crystalline structure of the zeolite remains unchanged and the catalytic activity does not decrease. On the contrary, it actually increases since the turnover frequency of residual titanium atoms rises from 31 to 80 h . Even more importantly, at 8.6% benzene conversion the selectivities, both on benzene and on hydrogen peroxide, also increase from 83 to 94% and from 67 to 83% respectively, with formation of catechol (4%) and hydroquinone (2%) as the only by-products, without any evidence of further oxidation reactions [19]. 

Oxidative amino acid side-chain modifications do not result in a stable end product of the oxidation process, but very often highly reactive intermediates are formed. These include chemically reactive groups, like ketones and aldehydes, or the formation of protein hydroperoxides. The presence of such protein hydroperoxides leads to a process called protein peroxidation. Here secondary reactions occur if the protein hydroperoxide decomposes and initiates further oxidative reactions, again forming oxidized protein forms. 

Taylor20 observed that temperature changes often produce fundamental differences in the adsorptive behavior, and suggested that an elevation in temperature can produce an activated condition so that molecules become adsorbed in a special state. This special state may lead to a strong chemisorption, as is the case with oxygen molecules adsorbed as surface oxides on carbon. These molecules do not enter into further oxidation reactions. In other cases, adsorbed molecules in the special state are able to participate in further reactions and at lower temperatures than in the absence of a catalyst. 

PEO and polymethyl vinyl ether were UV irradiated in hydrogen peroxide solutions. Hydroxy and hydroperoxy radicals accelerate the oxidative degradation of these polymers. Hydroxy and possibly hydroperoxy radicals can abstract hydrogen from methylene groups in both polymers. As a result of further oxidative reactions, different carbonyl, hydroxy and hydroperoxy groups are formed (297). 

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