Alkali cationized species

Alkali-cationized species are generally more stable than the protonated species because of the reduced mobility of the charge away from the alkali metal however, in the case of the presence of an acidic site, proton migration to a basic site may occur, producing an anion site able to solvate the alkali ion (i.e., salt). On the other hand, this means that cationized zwitterionic forms are generated that are destabilized, owing to the protonated site that induces ion dissociation with alkali metal retention in the product ions. 

It is extensively used industrially as a catalyst, notably in the oxidation of sulphur dioxide to the trioxide in sulphuric acid manufacture. It is an essentially acidic oxide, dissolving in alkalis to give vanadates however, addition of acid converts the anionic vanadate species to cationic species, by processes which are very complex, but which overall amount to the following ... 

The sizes of the voids decrease in order Cs, Rb, Na, K These differences are ascribed to the different influence of cation on the surrounding reactive species that changes the nature of alkali cation - aluminosilicate anion complexes. On the other hand, in the case that the cations are introduced in the matrix by ion exchange, (procedure b) the r3 lifetimes are approximately the same for all the cations (Table 2) and the size of cation does not have such pronounced influence. The calculated radii are shown in Table 4. 

Role of alkali and NH cations in the crystallization of ZSM-5 Introduced in an aqueous (alumino) silicate gel (sol), the bare alkali cations will behave in various ways firstly, they will interact with water dipoles and increase the (super) saturation of the sol. Secondly, once hydrated, they will interact with the aluminosilicate anions with, as a result, the precipitation of the so formed gel (salting-out effect). Thirdly, if sufficiently small, they also can order the structural subunits precursors to nucleation species of various zeolites (template function-fulfilled by hydrated Na+ in the case of ZSM-5 (11,48)). ... 

Part of the alkali metal trend may be due to changes in lattice parameter. The lattice parameter for PTA is related to the cationic species separating the Keggin ions. For anhydrous PTA, the lattice constant is 10.8 A. while for Csj-PTA it expands to 13.7 A.10 For the hexahydrate, the lattice parameter is intermediate at 12.5 A.2... 

The authors proposed the following picture of the silylene anion-radical formation. Treatment of the starting material by the naphthalene anion-radical salt with lithium or sodium (the metals are denoted here as M) results in two-electron reduction of >Si=Si< bond with the formation of >SiM—MSi< intermediate. The existence of this intermediate was experimentally proven. The crown ether removes the alkali cation, leaving behind the >Si - Si< counterpart. This sharply increases electrostatic repulsion within the silicon-silicon bond and generates the driving force for its dissociation. In a control experiment, with the alkali cation inserted into the crown ether, >Si — Si< species does dissociate into two [>Si ] particles. 

The constant rate of reaction at high activities of silicic acid can be explained by IEX reactions. Exchange reactions between a monovalent alkali cation M+ (e.g., Na+) and H+ species can be written in the following manner ... 

This is in agreement with the observed increase in methanol decomposition during the intervention, which may well arise from the presence of an excellent hydrogen acceptor, such as carbon dioxide. [11,12,16,17]. Together with the presence of alkali cation, co-adsorption of methanol and carbon dioxide could possibly form a methyl carbonate species which would rapidly undergo decomposition to carbon monoxide and hydrogen. 

Multisite crown ethers (30) and (31) are polymacrocycles. These molecules are potentially like cryptands in view of the possibilities for forming inclusion-like species. The photoresponsive crowns provide an excellent example of this aspect, and consist of two crown ethers, as in (30a and 30b), attached via a photosensitive azo linkage. This molecule undergoes reversible isomerization (likened to a butterfly motion), shown in equation (13). The cis form gives a stable 1 1 cation ligand complex with the larger alkali cations (actually a 1 2 cation crown ratio). Concentrations of (30b) in solutions are thus noted to be enhanced by the addition of these cations.100,101 Other multisite crowns have been prepared from diphenyl- and triphenyl-methane dyes, e.g. (31).102... 

The semiempirical quantum chemical consideration led to the conclusion that the discrepancy can be a consequence of ion-pair formation (Zuilhof Lodder 1995). In the case of cyclo-octatetraene, the ion-pairing phenomenon deserves more detailed explanation. While the dianion of cyclo-octatetraene is completely planar and meets all the requirements of aromaticity, the anion radical of cyclo-octatetraene is a nonaromatic species and is not completely planar. In the equilibria just considered, both the anion radical and the dianion had alkali cations as counterparts. The dialkali salt of the dianion has two cations symmetrically located over and beneath the octagonal plane. Distortions from ion pairing between the dianion plane and these two alkali cations are reciprocally compensated. With the... 

Amphoteric oxides (oxides which dissolve in acids to give cationic species, and also in alkalis to give anionic hydroxo- or oxo-anions) have slightly negative values (between -5 and 0). The a value for H20 is arbitrarily set equal to zero. The enthalpy change AH0 for the reaction between the basic oxide B and the acidic oxide A is given approximately by -(aA - aB)2 in kj mol-1, where the stoichiometric unit corresponds to the transfer of one mole of oxide ion from B to A. For example, from Table 9.1 we would predict AH° for the reaction ... 

The extractant is typically present in 5-20% (by mass) concentration and is selected to give almost complete extraction at pH 4 or above. The metal species M may subsequently be stripped to the aqueous phase in purified and enriched form using a dilute mineral acid which drives the equilibrium in Eq. (5) to the left. While Eq. (5) refers to cationic species, anionic species can be extracted with solutions of amines. Stripping is carried out with strong aqueous alkali. 

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