Oxide amphoteric nature

The amphoteric nature of the oxide is illustrated by its abiUty to form siUcates and aluminates in the dry state at elevated temperatures... 

Sn02, cassiterite, is the main ore of tin and it crystallizes with a rutile-type structure (p. 961). It is insoluble in water and dilute acids or alkalis but dissolves readily in fused alkali hydroxides to form stannates M Sn(OH)6. Conversely, aqueous solutions of tin(IV) salts hydrolyse to give a white precipitate of hydrous tin(IV) oxide which is readily soluble in both acids and alkalis thereby demonstrating the amphoteric nature of tin(IV). Sn(OH)4 itself is not known, but a reproducible product of empirical formula Sn02.H20 can be obtained by drying the hydrous gel at 110°, and further dehydration... 

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

The amphoteric nature of hydrated thorium oxide has been established. Microgram scale preparation of Cm02, which has a face-centred cubic... 

Chlorine monofluoride oxide, 18 328-330 force field of, 18 329, 330 infrared spectrum of, 18 328, 329 stretching force constants for, 18 330 synthesis of, 18 328 Chlorine nitrate fluorination of, 18 332 preparation of, 5 54 Chlorine oxides, 46 109-110, 158 fluorination of, 18 348 Chlorine oxyfluorides, 18 319-389, see also specific compounds adduct formation, 18 327, 328 amphoteric nature of, 18 327, 328 bond lengths, 18 326 bond strengths, 18 323-327 geometry of, 18 320-323 ligand distribution, 18 323 reactivity of, 18 327, 328 stretching force constants, 18 324-327 Chlorine pentafluoride oxide, 18 345, 346 Chlorine trifluoride, reaction with difluoramine, 33 157... 

In conclusion, it should be noted that the Barton-Zard condensation formally might be considered as a tandem SnH-Sn ipso process (see Section III.B.3). However, the corresponding crH-complcx is stabilized here not via elimination of any auxiliary leaving group or oxidation but by means of an intramolecular nucleophilic attack on an isonitrile fragment. This is due to the amphoteric nature of isocyanoacetate ion acting at first as a nucleophile and then as an electrophile. 

Aqueous corrosion of tin results in production of oxides of tin. The oxides and hydroxides of tin are stable in the pH range 3-10. The amphoteric nature of the oxides results in attack by mineral acids to produce stannous or stannic salts, stannites and stannates in basic solutions. While borates and bicarbonate render stability to the oxide... 

The N-hydroxy structure (26) was preferred123 to an iV-oxide representation on account of the amphoteric nature of the product and because the derived acetate formed a well-defined hydrochloride salt. Hydrogenation of these N-hydroxyimidazoles over Raney nickel gives imidazoles in 60-94% yields.122 The reaction has been adapted for the preparation of 4-mercaptoimidazoles, using an a-ketothionamide (27) with an aldimine.124... 

Solubility of MgO, CaO, and Fc203 decreases as the pH increases, while the rest of the oxides show an amphoteric nature, i.e., their solubihty has a minimum in between the entire pH range and increases at lower as well as higher pH. 

The two most characteristic properties of the stannylenes are their behaviour as Lewis acids and Lewis bases, and their ready oxidative addition to give Sn(IV) compounds. The amphoteric nature provides the model for the structure of the dimers, the distannenes, and for the oligomerisation that occurs with the less hindered examples two dative bonds are assumed to be formed between the doubly-occupied sp2 orbital and the vacant p orbital, affording a trans non-planar distannene (equation 21-9). These structures are discussed in more detail below. 

Use of the classical two-pKn model to describe the local isotherm for proton adsorption on an amphoteric oxide in the presence of an indifferent electrolyte complicates the situation considerably. The two pK values represent, in an artificial way, the amphoteric nature of the oxide (see secs. 4.4. and 4.8.). Equation (77) and (79) have to be extended with a second summation or integration to account for both logK distributions. Only when it is assumed that ApK is the same for all different site types a more simple relation is found. The latter assumption is however rather arbitrary. As there are no physical arguments in favour of using the two-pKn model a good advise is not to use this model. 

Many different complexes of elements in a given oxidation state may exist in water. The amphoteric nature of Al(III) and Fe(III) results from the formation of a series of dissolved species, MOH, M(OH)J, M(0H)3, and other forms, in addition to the more common M ". The speciation of soluble A1 and Fe is thus a sensitive function of pH. 

Some oxides and hydroxides are able to react with both acids and bases, thereby functioning as both bases and acids, respectively. Water is probably the most common example, but in this section we consider the amphoteric nature of metal oxides and hydroxides. Aluminium oxide, AI2O3, reacts with acids (equation 6.39) and with hydroxide ion (equation 6.40). 

The oxides and hydroxides of the metals of Group 3 and higher tend to be only weakly basic, and most display an amphoteric nature. Most of these compounds are so slightly soluble in water that their acidic or basic character is only obvious in their reactions with strong acids or bases. 

This lead compound exists in two polymorphic forms tetragonal (P-PbO) and orthorhombic (a-PbO). The solubility of the two forms in water at 25 °C is 0.0504 g for a-PbO and 0.1065 g for 3-PbO [6]. Lead oxide forms lead hydroxides, 3Pb0-H20 and 5PbO H2O [7,8]. Lead oxide is hydrated forming Pb(OH)2, a compound of amphoteric nature. It dissociates to HPb02 and Pb(OH) ions. In the battery industry, lead oxide is obtained by partial thermal oxidation of lead and is ealled leady oxide , as it eontains between 73% and 85% PbO, the remaining part being non-oxidized lead. The basie eonstituent of leady oxide is tet-PbO, but orthorhombie PbO is also present, up to 5—6%. Leady oxide is used for tbe preparation of the pastes for lead—aeid battery plate production. 

Synthesis and antimicrobial activity of 3-formyl analogs of norfloxacin, ciprofloxacin, and pefloxacin have been reported [93]. These studies have shown definitive evidence that the 3-formyl analogs of quinolones function as prodrugs and are oxidized in vivo to carboxylic acids. The higher bioavailability of formyl derivatives may be due to a change in physical and chemical properties by the lack of their amphoteric nature, compared to the parent zwitterionic compounds. 

The solubility of zinc carbonates, oxides, hydroxides, and so forth rapidly increases at either high pH or low pH because of the amphoteric nature of zinc compounds. Basic zinc carbonate, therefore, is soluble at both ends of the pH scale, but is only slightly soluble in the middle range (Garrett et al. 1979). 

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