Oxygen anions

The unique chemical behavior of KO2 is a result of its dual character as a radical anion and a strong oxidizing agent (68). The reactivity and solubiHty of KO2 is gready enhanced by a crown ether (69). Its usefiilness in furnishing oxygen anions is demonstrated by its appHcations in SN2-type reactions to displace methanesulfonate and bromine groups (70,71), the oxidation of benzyHc methylene compounds to ketones (72), and the syntheses of a-hydroxyketones from ketones (73). [Pg.519]

The reactivity of mercury salts is a fimction of both the solvent and the counterion in the mercury salt. Mercuric chloride, for example, is unreactive, and mercuric acetate is usually used. When higher reactivity is required, salts of electronegatively substituted carboxylic acids such as mercuric trifiuoroacetate can be used. Mercuric nitrate and mercuric perchlorate are also highly reactive. Soft anions reduce the reactivity of the Hg " son by coordination, which reduces the electrophilicity of the cation. The harder oxygen anions leave the mercuric ion in a more reactive state. Organomercury compounds have a number of valuable synthetic applications, and these will be discussed in Chapter 8 of Part B. [Pg.371]

Figure 7-5. Bry4nsted-type plot for nucleophilic reactions of p-nitrophenyl acetate. Key , simple imidazoles in 28.5 ethanol at JO°C. p = 0.80 (data from Ref. 197] O, oxygen anions, in water at 25°, P = 0.95 for linear portion [data from Ref. 119, 198] O, a effect nucleophiles. Several of the nucleophiles are identified.

Oxygen anion resonance. This means of stabilizing hydration depends on the resonance shown in 39b-c, which is akin to 2,4-dihydroxypyridine anion resonance. An example of its occurrence (e.g. 24) is mentioned in Section III,E, l,d. This resonance bears a close resemblance to the pteridine anion resonance shown in formula 21,... [Pg.36]

Acid-treated clays were the first catalysts used in catalytic cracking processes, but have been replaced by synthetic amorphous silica-alumina, which is more active and stable. Incorporating zeolites (crystalline alumina-silica) with the silica/alumina catalyst improves selectivity towards aromatics. These catalysts have both Fewis and Bronsted acid sites that promote carbonium ion formation. An important structural feature of zeolites is the presence of holes in the crystal lattice, which are formed by the silica-alumina tetrahedra. Each tetrahedron is made of four oxygen anions with either an aluminum or a silicon cation in the center. Each oxygen anion with a -2 oxidation state is shared between either two silicon, two aluminum, or an aluminum and a silicon cation. [Pg.70]

The four oxygen anions in the tetrahedron are balanced by the -i-4 oxidation state of the silicon cation, while the four oxygen anions connecting the aluminum cation are not balanced. This results in -1 net charge, which should be balanced. Metal cations such as Na", Mg ", or protons (H" ) balance the charge of the alumina tetrahedra. A two-dimensional representation of an H-zeolite tetrahedra is shown ... [Pg.70]

A proposed mechanism for the oxidation of propylene to acrolein is by a first step abstraction of an allylic hydrogen from an adsorbed propylene by an oxygen anion from the catalytic lattice to form an allylic intermediate ... [Pg.216]

Special characteristics can be developed in individual materials depending on the cations present and their arrangement relative to each other and to the oxygen anions. The most important of these characteristics is low, medium or high reversible thermal expansion. The properties of some commercially available glass-ceramics are summarised in Table 18.6. [Pg.883]

Whether or not the highly electropositive alkali metals or magnesium form an ionic instead of a covalent bond to the oxygen of the enolate is less important. Even if there is a contact ion pair of the metal cation and the oxygen anion, the geometry of the six-membered chair transition state, as outlined above, will be maintained. [Pg.459]

Oxygen anions are thus now attracted to the electrode with the positive charge or the electrode which has been made positive by anodic polarization. Backspillover will continue untill the charge is neutralized. Similarly oxygen anions will be repelled from the negatively charged or cathodically polarized electrode to enter into the YSZ structure. The charges q+ and q. thus disappear and thus TV and TV vanish. [Pg.221]

As shown on Figure 9.1 when the circuit is opened (I = 0) the catalyst potential starts increasing but the reaction rate stays constant. This is different from the behaviour observed with O2 conducting solid electrolytes and is due to the fact that the spillover oxygen anions can react with the fuel (e.g. C2H4, CO), albeit at a slow rate, whereas Na(Pt) can be scavenged from the surface only by electrochemical means.1 Thus, as shown on Fig. 9.1, when the potentiostat is used to impose the initial catalyst potential, U r =-430 mV, then the catalytic rate is restored within 100-150 s to its initial value, since Na(Pt) is now pumped electrochemically as Na+ back into the P"-A1203 lattice. [Pg.437]

Some insulating oxides become semiconducting by doping. This can be achieved either by inserting certain heteroatoms into the crystal lattice of the oxide, or more simply by its partial sub-stoichiometric reduction or oxidation, accompanied with a corresponding removal or addition of some oxygen anions from/into the crystal lattice. (Many metal oxides are, naturally, produced in these mixed-valence forms by common preparative techniques.) For instance, an oxide with partly reduced metal cations behaves as a n-doped semiconductor a typical example is Ti02. [Pg.322]

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