Oxide anions

In tenns of an electrochemical treatment, passivation of a surface represents a significant deviation from ideal electrode behaviour. As mentioned above, for a metal immersed in an electrolyte, the conditions can be such as predicted by the Pourbaix diagram that fonnation of a second-phase film—usually an insoluble surface oxide film—is favoured compared with dissolution (solvation) of the oxidized anion. Depending on the quality of the oxide film, the fonnation of a surface layer can retard further dissolution and virtually stop it after some time. Such surface layers are called passive films. This type of film provides the comparably high chemical stability of many important constmction materials such as aluminium or stainless steels. 

The benzylidene derivative above is used, if both hydroxyl groups on C-2 and C-3 are needed in synthesis. This r/vzns-2,3-diol can be converted to the sterically more hindered a-cpoxide by tosylation of both hydroxy groups and subsequent treatment with base (N.R. Williams, 1970 J.G. Buchanan, 1976). An oxide anion is formed and displaces the sulfonyloxy group by a rearside attack. The oxirane may then be re-opened with nucleophiles, e.g. methyl lithium, and the less hindered carbon atom will react selectively. In the following sequence starting with an a-glucoside only the 2-methyl-2-deoxyaltrose is obtained (S. Hanessian, 1977). 

Exceptions are salts of oxidizing anions, which decompose with oxidation of the ammonium ion to nitrous oxide [10024-97-2], N2O, or nitrogen, N2. 

Methoxy-2,6-dimethylpyridine 4-Hydroxy-2,6-diraethylpyridine-l-oxide anion l-Hydroxy-2,6-dimethyl-4-pyridone 4-Methoxy-2,6-dimethylpyridine-l-oxide... 

Anionic polymerization of alkylene sulfides was extensively studied by Sigwalt and collaborators. In contrast to propylene oxide, anionic polymerization of pro-... 

The retro Diels-Alder reaction is strongly accelerated when an oxide anion substituent is incorporated at positions 1 and 2 of the six-membered ring which has to be cycloreversed, namely at one terminus carbon of the original diene or at one sp carbon of the dienophile [51] (Equation 1.22). 

The first example of an oxide-anion accelerated retro Diels Alder reaction was reported by Papies and Grimme [52]. The adduct 19 (Equation 1.23) treated with tetra-w-butylammonium fluoride (TBAF) in THE at room temperature is immediately converted into 20, in contrast to the parent 21 (Equation 1.24) which undergoes cycloreversion into 22 at 100 °C. The dramatic oxide-anion acceleration (> 10 ) was ascribed to the loss of basicity of about 8pK, units in the transformation of alcoholate ion of precursor 19... 

An example of the effect of oxide-anion associated with the 2n component (i.e. position 1, Equation 1.22) is illustrated in Equation 1.25 [53]. The potassium salt of 1,4-dihydro-11 -hydroxy-9,10-dihydro-9,10-ethanoanthracene undergoes more facile debridging (remotion of ethylene) than the 11-deoxygenated parent compound. 

Bunnage M. E. Nicolaou K. C. The Oxide Anion Accelerated Retro-Diels-Alder... 

Solids containing oxidized anions (carbonates, sulfates, hydroxides, and oxides) are the dominant forms of Cu in airborne particulate matter. In the few studies that have addressed the reactions of these particles in atmospheric washout, about 50% of the copper has been found to be soluble. Since the solubility is strongly dependent on pH, acid precipitation and acidification of receiving waters may have a significant effect on the form and fate of airborne copper. 

By convention, the chemical formulas of many ionic compounds do not explicitly state the charges of the ions. It is not necessary to do so when the species involved form ions with only one possible charge. However, many metals form more than one type of stable cation. For example, copper forms two different oxides, black CuO and red C112 O. The oxide anion has a -2 charge, so for the first compound to be neutral the copper cation must bear a +2 charge. In C112 O, each copper ion must have +1 charge. 

Cr03 As a transition metal, chromium forms more than one stable cation. Name the metal first, using a Roman numeral to designate chromium s charge. Each of the three oxide anions has a -2 charge. To maintain net charge neutrality, Cr must be +6, so the name of the compound is chromium(VI) oxide. 

Metallic iron is made up of neutral iron atoms held together by shared electrons (see Section 10.7). The formation of rust involves electron-transfer reactions. Iron atoms lose three electrons each, forming Fe cations. At the same time, molecular oxygen gains electrons from the metal, each molecule adding four electrons to form a pair of oxide anions. As our inset figure shows, the Fe cations combine with O anions to form insoluble F 2 O3, rust. Over time, the surface of an iron object becomes covered with flaky iron(ni) oxide and pitted from loss of iron atoms. 

Magnesium atoms are oxidized in this reaction, so some other species must be reduced. Oxygen molecules accept the electrons lost by the magnesium atoms. Each oxygen atom gains two electrons from a magnesium atom, generating two oxide anions O2 + 4 e 2 O... 

Magnesium cations and oxide anions attract each other strongly, forming the ionic solid, MgO. Notice that in the balanced redox reaction there is no net change in the number of electrons two Mg atoms lose four electrons, and one O2 molecule gains four electrons. 

In the reaction of 1,3-dithiane oxide anions with iV-acylimidazoles the optimum procedure involved a sodium hexamethyldisilazide/butyllithium mixture as base [101]... 

G. Metal Cluster and Metal Oxide Anion Reactions.226... 

Acid-Base Chemistry of Metal Oxide Anions... 

The true role of incorporation of anions in the formation of anodic alumina is being intensively discussed. Baker and Pearson183 have considered the anion effect in modifying the structure of anodic oxides to be due to the coordinative ability of anions to replace alumina tetrahedra in the body of the oxides. Dorsey184,185 has postulated that in porous oxides, anions stabilize the network of alumina tetrahedra and octahedra. 

The substitution by two Nd for three AE ions in the solid solutions should provoke one cation vacancy formation for attaining electroneutrality. The created vacancies render the nearby oxide anions coordinatively unsaturated and more basic what was supported by C02-TPD data. The more pronounced shift of Tmilx in the SG samples confirmed the better incorporation of Nd. 

According to detailed XRD analyses, the two catalyst preparation procedures under study formed solid solutions. The application of sol-gel method led to improved selectivity to olefins in the reaction of propane ODH, compared to the simple procedure of evaporation and decomposition. However, the propane conversion on the sol-gel catalysts was lower at the same experimental conditions, while the catalysts surface area was higher. Moreover, the sol-gel samples presented higher basicity as shown by C02 TPD. It could be explained by a better incorporation of Nd into the AEO lattice, creating cationic vacancies for attaining electroneutrality and thus rendering the nearby oxide anions coordinatively unsaturated and more basic. 

The crystal structure of [Fe(Cp)2]2[Ni(mnt)2]2[Fe(Cp)2] is composed by segregated stacks of pairs of cations, [Fe(Cp)2]+, and zig-zag dimerized anions stacks, with a neutral [Fe(Cp)2] molecule laying beside each anionic dimer [65]. In the case of [Co(Cp)2][Ni(dmit)2], the crystal structure consists of layers composed by two types of chains formed by the [Ni(dmit)2] anions, through short S—S contacts. Cation pairs are located between the anionic stacks [68], In the crystal structure of [Co(Cp)2][Ni(dmit)2]3 2MeCN, the partially oxidized anions form... 

As known, compounds of the (R3Sn)2X type enter readily into various exchange reactions.62 No intermediate silicon organophosphorus betaine 61 with the oxide anionic center was detected in the reactions of thiobetaines 20a, with (R3Sn)20 in ether at room temperature.84,96,100 In solutions they... 

All studied model compounds can distinctly be divided into three groups (Table VII). The first group is composed of substances in which the sulfur, selenium or cyclopentadienyl anion acts as an anionic center. They exist only in open betaine forms, and their PES do not contain local minima corresponding to cyclic isomers. The second group contains compounds with arsonium cationic and oxide anionic centers and silicon and germanium betaines with arsonium and amide centers. They exist as cyclic isomers and their PES have no local minima corresponding to the open forms. Finally, the third group consists of six studied compounds with phosphonium cationic and oxide or amide anionic centers and arsonium-imide betaine. Their PES have minima for both cyclic and open forms separated by low barriers. 

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