Oxides and oxo compounds

The amphoteric nature of AS2O3 and the trends in properties of several of the oxides and oxoacids 

AS2O3 (diarscnic trioxide) is the most important compound of As (Panel, p. 549). It is made 

The structural relationships in Bi203 are more complex. At room temperature the stable form is monoclinic a-Bi203 which has a polymeric layer structure featuring distorted, 5-coordinate Bi in pseudo-octahedral iBiOs units. Above 717°C this transforms to the cubic 5-form which has a defect fluorite structure (Cap2, p. 118) with randomly distributed oxygen vacancies, i.e. [Bi203D]. The /S-form and several oxygen-rich forms (in which some of the vacant sites are filled 

The solubility of AS2O3 in water, and the species present in solution, depend markedly on pH. In pure water at 25°C the solubility is 2.16g per 100 g this diminishes in dilute HCl to a minimum of 1.56 g per 100 g at about 3 m HCl and then increases, presumably due to the formation of chloro-complexes. In neutral or acid solutions the main species is probably pyramidal As(OH)3, arsenious acid , though this compound has never been isolated either from solution or otherwise (cf. carbonic acid, p. 310). The solubility is much greater in basic solutions and spectroscopic evidence points to 

Arsenites of the alkali metals are very soluble in water, those of the alkaline earth metals less so, and those of the heavy metals are virtually insoluble. Many of the salts are obtained as meta-arsenites, e.g. NaAs02, which comprises polymeric chain anions formed by comer linkage of pyramidal ASO3 groups and held together by Na ions  

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Chemical properties of gallium fall between those of aluminum and indium. It forms mostly the binary and oxo compounds in -i-3 oxidation state. It forms a stable oxide, Ga203 and a relatively volatile suboxide, Ga20. 

Insertion of a methyl group at the site where nucleophilic attack occurs during hydration considerably hinders the reaction and lowers the percentage of covalently hydrated species at equilibrium. Covalent hydrates are converted by mild oxidation into oxo compounds. 

Quantitative investigations of the reactions of oxide ions and oxo-compounds in high-temperature ionic solvents are, therefore, of considerable scientific and applied importance. The interactions of such kinds are referred to as acid-base ones, according to Lewis. Since 1939, when Lux proposed a definition of acids as oxide ion acceptors and bases as donors of O2-, such acid-base interactions came to be called oxoacidity . The most general scheme of a Lux acid-base interaction is presented by the following equation ... 

The hydroxy- and oxo-compounds derived from di- and tri-saccharides after the sequence of periodate oxidation, sodium borohydride reduction, and acid hydrolysis have been identified by g.l.c. of their 0-trimethylsilyl ether derivatives, thus giving useful information for linkage analysis. ... 

Gallium forms mostly binary and oxo compounds in a +3 oxidation state for example, gallium forms a stable Ga203, and a volatile suboxide of Ga20. 

Amino-6-chloro-4-methyl- and 3-amino-6-chloro-5-methyl-pyridazine and 3-amino-6-methylpyridazin-4(l//)-one are transformed with sodium nitrite in the presence of acid into the corresponding oxo compounds. If concentrated hydrochloric acid is used, in some instances the corresponding chloro derivatives are obtained as side products. On the other hand, 3-, 4-, 5- and 6-aminopyridazine 1-oxides and derivatives are transformed into stable diazonium salts, which can easily be converted into the corresponding halo derivatives. In this way 3-, 4-, 5- and 6-bromopyridazine 1-oxides, 5-chloropyridazine 1-oxide, 3,4,5-trichloropyridazine 1-oxide and 6-chloropyridazine 1-oxide can be obtained. 

The 6- and 7-quaternary salts of pyrido[2,3-d]pyridazine are reduced by borohydride with subsequent air oxidation to 5,6- and 7,8-dihydro oxo derivatives respectively (77BSF919), whilst the [3,4-d] analogues give the corresponding 1,2- and 3,4-dihydro oxo compounds 72CR(C)(275)1383). ... 

This oxidation state is sparse in the case of Mn but is important in the pharmaceutical applications of Tc, and an extensive chemistry has been developed. Some fluoro complexes of Tc and Re such as the salts of [MFe] are known, but oxo compounds predominate and, in [MOCls] and [MOX4] (X = Cl, Br, I) for instance, other halides are also able to coordinate. [MOX4] is square pyramidal with apical M=0 and the moiety is reminiscent... 

The above method is unsatisfactory when hydration takes place at two alternative sites in the molecule, although one hydrate is usually present in only a very small proportion, at equilibrium. Which oxo compound is preferentially formed in such a case depends on the rates of oxidation at the different sites and on the rate of isomerization of the water molecule from one position to the other, hence this method does not indicate which is the thermodynamically more stable hydrate. 

The spectra of 1,3,5-, 1,3,7-, and 1,3,8-triazanaphthalerie cations revealed that they were predominantly hydrated, and mild oxidation to the corresponding 4-oxo compounds indicated that hydroxylation took place on C-4. Ring-chain tautomerism in the cation was excluded, at least during the first 45 min after mixing, because negative aldehyde tests were obtained with p-nitrophenylhydrazine. 1,3,6-Triazanaphthalene, under the same conditions, gave a yellow precipit-... 

Sequential O-deacetylation, 0-isopropylidenation, and acetylation transformed 80 into compound 81. O-Deacetylation of 81, and ruthenium te-traoxide oxidation of the product, gave the 2-oxo compound 82, which was converted into 83 by hydrogenation over a platinum catalyst and acetylation. ... 

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