Oxidation 978 INDEX

Disappearance of the deep blue colour and precipitation of cuprous oxide indicates reducing agents such as ... 

Chemical analysis of niobium oxide indicated that the purity of the final product depends strongly on the purity of the initial solution. Account should be taken of about 0.02-0.03% wt. cationic impurities, introduced due to interactions with metal parts of the equipment. The main added impurities are Fe, Ni, Cr, which originate mostly from the stainless steel filter. The purity of the final product can be significantly increased by using a filter made of niobium or other appropriate material. Nevertheless, the material obtained using a stainless steel filter is sufficient for use in ceramic applications or as an initial material for carbide manufacture. 

The presence of free bromine, and consequently the end-point, can be detected by its yellow colour, but it is better to use indicators such as methyl orange, methyl red, naphthalene black 12B, xylidine ponceau, and fuchsine. These indicators have their usual colour in acid solution, but are destroyed by the first excess of bromine. With all irreversible oxidation indicators the destruction of the indicator is often premature to a slight extent a little additional indicator is usually required near the end point. The quantity of bromate solution consumed by the indicator is exceedingly small, and the blank can be neglected for 0.02M solutions. Direct titrations with bromate solution in the presence of irreversible dyestuff indicators are usually made in hydrochloric acid solution, the concentration of which should be at least 1.5-2M. At the end of the titration some chlorine may appear by virtue of the reaction ... 

Both benzothieno[3,2-b]pyridine 5-oxide (31) and thieno[3,2-b 4,5-b ]dipyridine 5-oxide (32) exhibit competitive loss of oxygen either as an atom or as carbon monoxide after initial skeletal rearrangement, e.g. to sulfenate esters (equation 10)18b. These results together with some data for Y-oxides indicate that the presence of an intense [M — 16] + peak is not diagnostic for the latter only. 

FIGURE 10.7 The elements in and close to the diagonal line of metalloids typically form amphoteric oxides (indicated by the red lettering). 

The reason for the effectiveness of triphenylphosphine is at present uncertain, although its eventual isolation as triphenylphosphine oxide indicates that it may well function as a scavenger for the thallium(III) released in the metal-metal exchange reaction. 

Fig. 5.1 Compounds 389 and 390 xanthones from Gentianaceae showing their formation and a graph of oxidation indices...

In 1960, Montanari and Balenovic and their coworkers described independently the first asymmetric oxidation of sulfides with optically active peracids. However, the sulphoxides were formed in this asymmetric reaction (equation 130) with low optical purities, generally not higher than 10%. The extensive studies of Montanari and his group on peracid oxidation indicated that the chirality of the predominantly formed sulphoxide enantiomer depends on the absolute configuration of the peracid used. According to Montanari the stereoselectivity of the sulphide oxidation is determined by the balance between one transition state (a) and a more hindered transition state (b) in which the groups and at sulphur face the moderately and least hindered regions of the peracid,... 

Fig. 9 Illustrations of the charge transport in duplex 37/38, a in the absence and b in the presence of BamH I. Horizontal arrows and the numbers shown on the site of guanine oxidation indicate the band intensity relative to that of G24 in the protein bound duplex... 

Melroy and co-workers88 recently reported on the EXAFS spectrum of Pb underpotentially deposited on silver (111). In this case, no Pb/Ag scattering was observed and this was ascribed to the large Debye-Waller factor for the lead as well as to the presence of an incommensurate layer. However, data analysis as well as comparison of the edge region of spectra for the underpotentially deposited lead, lead foil, lead acetate, and lead oxide indicated the presence of oxygen from either water or acetate (from electrolyte) as a backscatterer. 

Alcohols, like hydrocarbons, are oxidized by the chain mechanism. The composition of the molecular products of oxidation indicates that oxidation involves first the alcohol group and the neighboring C—H bond. This bond is broken more readily than the C—H bond of the corresponding hydrocarbon, since the unpaired electron of the formed hydroxyalkyl radical interacts with the p electrons of the oxygen atom. 

This is not exactly the order as the electronic conductivity of the oxides, indicating that electrocatalytic activity of mixed ionic and electronic conducting (MIEC) oxides depends on other properties such as the oxygen exchange and ionic conductivities. 

The mean value of the standard molar energy of combustion of 4-cyanopyridine N-oxide indicated refers to reaction 7.58 at 298.15 K ... 

The appearance of a single two-electron oxidation indicates that the C2H4 spacer does not permit any electronic communication between the two ferrocenyl sites. 

---