Stannous ions

The main binary tin fluorides are stannous fluoride and stannic fluoride. Because the stannous ion,, is readily oxidized to the stannic ion,, most reported tin and fluorine complexes are of tin(IV) and fluorostannates. Stannous fluoroborates have also been reported. 

Arsenious oxide, trivalent antimony (73), sulfurous acid (74), hydrogen sulfide (75), stannous ion, and thiocianate (76) have been recommended for the titration of iodine. However, none of these appears to have a greater sensitivity for the deterrnination of minute quantities of iodine than thiosulfate. Organic compounds such as formaldehyde (77), chloral hydrate (78), aldoses (79), acetone (70,80), and hydroquinone have also been suggested for this purpose. 

Pure tin is completely resistant to distilled water, hot or cold. Local corrosion occurs in salt solutions which do not form insoluble compounds with stannous ions (e.g. chloride, bromide, sulphate, nitrate) but is unlikely in solutions giving stable precipitates (e.g. borate, mono-hydrogen phosphate, bicarbonate, iodide) . In all solutions, oxide film growth occurs and the potential of the metal rises. Any local dissolution may not begin for several days but, once it has begun, it will continue, its presence being manifested... 

In plain tinplate cans for acid foods, tin provides cathodic protection to steel (3,4). The slow dissolution of tin prevents steel corrosion. Many investigators (5-1I) have defined this mechanism in detail and have shown that the tin dissolution rate is a function of the cathodic activity of the base steel, the steel area exposed through the tin and the tin-iron alloy layers, and the stannous ion concentration. Kamm et al. showed that control of the growth of the tin—iron alloy layer provides a nearly continuous tin-iron alloy layer and improves the corrosion resistance of heavily coated (over 45 X 10"6 in. tin) ETP for mildly acid food products in which tin provides cathodic protection to steel (12). The controlled tin-iron alloy layer reduces the area of steel exposed to the product. ETP with the controlled alloy is designated type K, and since 1964, 75 type K ETP has been used to provide the same protection as 100 ETP provided previously (13). 

The reduction of persulphate by stannous ions is strongly affected by dissolved oxygen The anaerobic oxidation is first-order in both oxidant and reduc-tant with E 11.9 kcal.mole and AS = —19.4 eu . 

One also sees that at room temperature the two peaks of the quadru-pole split pattern are different in intensity. This difference disappears at 77°K. It is an example of what is known as the Gordanskii effect 10) and is caused by the fact that the amplitude of vibration is different, parallel to the surface and normal to the surface, so that the effective resonant fraction is different for the two halves of the quadrupole splitting. This effect has been extensively studied by the Russians. In a recent paper, Suzdalev and others report a study of tin in the surface of silica gel 18), They put calcium ions in the surface of silica gel, then replaced them with divalent tin by ion exchange. The result was a mixture of stannous and stannic ions, and of course, the use of the Mossbauer effect made it possible to determine accurately the relative amounts of the two. They studied the amplitude of vibration of the two kinds of atoms and found, for example, for the stannous ions, the r.m.s. amplitude of vibration parallel to the surface was 0.07 A., and the r.m.s. amplitude of vibration perpendicular to the surface was about twice as great—about 0.13 A. Karasev and others have also worked on the chemistry of adsorbed... 

From the relationship of the chemical shift with the 5 electron density, Lees and Flinn (16) found a shift of 0.277 cm./sec. for the ideal (55 ) stannous ion. The 5 electron density can also be calibrated from the correlation of the NMR coupling constant with the Mossbauer chemical shift. This is shown in Figure 4 for the methylstannanes, using the... 

Nucleation is performed by immersion of a sensitized nonconductor into the nucleating solution for 0.5 to 2min. The surface reaction between the stannous ions, Sn +,... 

A few well-controlled clinical studies suggested a potential plaque-inhibiting effect for dentifrices containing staimous fluoride. However, these results were most likely due to the stannous ion rather than to fluoride the positive charge of the stannous ion may interfere with bacterial membrane function, bacterial adhesion, and glucose uptake, thereby inhibiting the formation of plaque. 

Red blood cell labeling inhibition. Tobacco decreased the labeling of blood elements with technetium-99m and plasma proteins. This effect possibly resulted from either a direct or an indirect effect (reactive oxygen species [ROS]) of tobacco by oxidation of the stannous ion, possible damages caused in plasma membrane and/or possible chelating action on the stannous and/or pertechnetate ions . 

The oxidation of aromatic hydroxylamines with peracids in the presence of cupric ions produces nitroso compounds. In the rigorous absence of metallic ions, azoxy compounds are formed [32]. On the other hand, the air oxidation is strongly accelerated by metals, the approximate order of activity based on a kinetic study being cupric s ferric > manganous > nickel chromic > cobaltous ions. Silver and stannous ions appear to have no effect [33]. 

The role of stannous ions in the "mTc chelate have been examined and it has been shown that they are not essential for bone uptake185). 

Monocapped boronic acid adducts of Tc(III) /m(dioxime) (BATO) (X — Cl, Br dioxime = dimethylglioxime, cyclohexanedione dioxime R = CF13, C4Fl9) have been prepared by template synthesis starting with pertechnetate and stannous ion [NBu4][TcOCl4] or M2[TcXO] (M = NH4, X = C1, Br), yielding seven-coordinate... 

For the formation of tin complexes it is necessary to have stannous ions in solution, and for this to happen the electrons released by the oxidation of tin may be consumed by hydrogen evolution at the iron centers in the pores of the tin plate. As tin dissolves more of the steel surface is available for the hydrogen evolution reaction and... 

In a method that predates the Stock system, two different endings are used to distinguish the valences of metals. The ending -ic is used to represent the larger valence number. The ending -ous is used to represent the smaller valence number. Thus, the ions Sn2+ and Sn4+ are named stannous ion and stannic ion. To use this system, you need to know the Latin name of an element. For example, the two ions of lead are the plumbous and plumbic ions. See Table 3.6 for more examples. 

Stannous fluoride Viscosity, pH (2.8-4.0), stannous ion content, total tin content, and assay Well-closed containers... 

It is of interest to note that if the equilibrium constant of the system consisting of two metals and their simple ions could be determined experimentally and the standard potential of one of them were known, the standard potential of the other metal could be evaluated by means of equation (34). This method was actually used to obtain the standard potential of tin recorded in Table XLIX. Finely divided tin and lead were shaken with a solution containing lead and tin perchlorates until equilibrium was attained the ratio of the concentrations of lead and stannous ions in the solution was then determined by analysis. The standard potential of lead being known, that of tin could be calculated. 

This low value of the equilibrium constant means that when equilibrium is attained in the ferrous-ferric and stannous-stannic mixture, the concentrations (activities) of ferric and stannous ions must be negligibly small in comparison with those of the ferrous and stannic ions. In other words, when these two systems are mixed, reaction occurs so that the ferric ions are virtually completely reduced to ferrous ions while the stannous are oxidized to stannic ions. This fact is utilized in analytical work for the reduction of ferric to ferrous ions prior to the estimation of the latter by means of dichromate. 

The next step is to balance the ecjnation for the reaction. In balancing the equation for an oxidation-reduction reaction it is often vise to write the electron reactions separately (as they would occur in an electrolytic cell), and then to add them so as to cancel out the electrons. For example, ferric ion, Fe- +", oxidi/es stannous ion, Sn, to stannic ion, Sn + + + + that is, from the bipositive state to the quadripositive state. The ferric ion is itsell reduced to ferrous ion, Fe++. The two electron reactions are... 

The consideration of the electrode leactions lias shown that two ferric ions are required to oxidize one stannous ion, because the reduction of ferric ion requires only one electron, whereas in the oxidation of stannous ion tw o electrons are given up. 

The stannous ion is an active reducing agent, which is easily oxidized to stannic chloride, SnCl4, or, in the presence of excess chloride ion, to the complex chlorostannate ion, SnClg. ... 

Ferric ion in solution can be reduced to ferrous ion by treatment with metallic iron or by reduction with hydrogen sulfide or stannous ion. 

In the classical case, R is sulphite and Ox sulphate. Three classes of related reactions have been recognised. To the first belong the sulphite, thiosulphate and stannous ion reactions, and with these (4) is always faster than (3) so that the starch-iodine colour emerges very suddenly when all the reductant is exhausted (by excess iodate). The second type can attain equal rates of iodine production, through (2) and (3), and decomposition (4). Starch-iodine colour is seen at about that point, with partial removal of the reductant e.g. arsenite, ferrocyanide, Fe(II) complexed with oxalate or EDTA). In the third type, reaction (3) is so much faster than (4) that the necessary iodide concentration to give starch-iodine colour is only attained late in reaction. Iodine is then present early but the blue colouration only develops later. A number of organic reductants fall into this class. The rates of colour development in the normal reaction system have been treated in semiquantitative fashion . ... 

Mochida I., Noguchi H., Fujitsu H., Seiyama T., and Takeshita K. (1977) Reactivity and selectivity in the reductive elimination of halogen from haloalkanes by chromous, cuprous, and stannous ions. Can. J. Chem. 55, 2420-2425. 

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