Stannous complexes

Rutin and several other flavonoid glycosides exhibit antioxidant properties and affect the flexibility and permeability of blood capillaries. Rutin (formerly vitamin P) is thus used in pharmaceutical preparations and food supplements. Together with other substances called bioflavonoids (see Section 5.15), rutin increases levels of ascorbic acid in various animal organs, either by protection against oxidation catalysed by metal ions, or by increased ascorbic acid utilisation in the body. Natural sources of ascorbic acid containing flavonoids (such as rosehips with a considerable amount of rutin) are thus more effective than synthetic vitamin C. A complex of rutin with iron causes dark discoloration of asparagus in tins, and the stannous complex of rutin is yeUow. 

Tin(ll) chloride, SnCl2, stannous chloride. M.p. 247 - C. While solid (Sn plus gaseous HCl), forms hydrates (SnCl2,2H20 is tin salt) from Sn and aqueous HCl. Acts as acceptor in complexes and forms complexes with transition metals. Used as a mordant. 

Tm II)fiuoride, Snp2, stannous fluoride. M.p. 213°C. Formed from Sn and aqueous HF. Forms complexes, e.g. MSnFj. Used in toothpastes. 

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. 

Solutions of anhydrous stannous chloride are strongly reducing and thus are widely used as reducing agents. Dilute aqueous solutions tend to hydrolyze and oxidize in air, but addition of dilute hydrochloric acid prevents this hydrolysis concentrated solutions resist both hydrolysis and oxidation. Neutralization of tin(II) chloride solutions with caustic causes the precipitation of stannous oxide or its metastable hydrate. Excess addition of caustic causes the formation of stannites. Numerous complex salts of stannous chloride, known as chlorostannites, have been reported (3). They are generally prepared by the evaporation of a solution containing the complexing salts. 

Stannic chloride is made by the direct chlorination of tin at 110—115°C. Any stannous chloride formed in the process is separated from the stannic chloride by volatilization and subsequently chlorinated to stannic chloride. The latter is inert to steel in the absence of moisture and is shipped in plain steel dmms of special design. Because prolonged contact with the skin causes bums, goggles and protective clothing should be used in the handling of stannic chloride. Stannic chloride, like stannous chloride, also forms many complexes (3). 

Phosphate. Phosphoms occurs in water primarily as a result of natural weathering, municipal sewage, and agricultural mnoff The most common form in water is the phosphate ion. A sample containing phosphate can react with ammonium molybdate to form molybdophosphoric acid (H2P(Mo202q)4). This compound is reduced with stannous chloride in sulfuric acid to form a colored molybdenum-blue complex, which can be measured colorimetrically. SiUca and arsenic are the chief interferences. 

Tin anodes dissolve by etching corrosion in acid baths based on stannous salts, but in the alkaline stannate bath they undergo transpassive dissolution via an oxide film. In the latter the OH" ion is responsible for both film dissolution and for complexing the tin. Anodes must not be left idle because the film dissolves and thereafter corrosion produces the detrimental divalent stannite oxyanion. Anodes are introduced live at the start of deposition, and transpassive corrosion is established by observing the colour of the film... 

Samples are hydrolyzed with hydrochloric acid and stannous chloride solution at elevated temperature, and the evolved carbon disulfide is drawn with an air steam through two gas washing tubes in series containing lead acetate and sodium hydroxide solutions and an absorption tube containing an ethanolic solution of cupric acetate and diethanolamine. Lead acetate and sodium hydroxide remove hydrogen sulfide and other impurities. In the absorption tube, the carbon disulfide forms two cupric complexes of Af,Af-bis(2-hydroxyethyl)dithiocarbamic acid with molecular ratios Cu CS2 of 1 1 and 1 2. These complexes are measured simultaneously by spectrophotometry at 453 nm. 

The allylation of aldehydes can be carried out using stannous chloride and catalytic cupric chloride or copper in aqueous media." In-situ probing provides indirect (NMR, CV) and direct (MS) evidence for the copper(I)-catalyzed formation of an allyltrihalostannane intermediate in very high concentration in water (Scheme 8.6). Hydrophilic palladium complex also efficiently catalyzes the allylation of carbonyl compounds with allyl chlorides or allyl alcohols with SnCl2 under aqueous-organic... 

A general mode of access to polyhydric complexes of Tc(V) is reduction of pertechnetate with two equivalents of stannous chloride in aqueous solution of the excess O-donor ligand, e.g. ... 

The O-donor complexes of Tc(V) exhibit moderate and differential stability in aqueous solution. In the presence of reducing agents, such as stannous chloride, they are reduced to mainly undefined products of Tc in a lower oxidation state. However, at the low technetium concentration of "mTc that is used in nuclear medicine, the rate of the reduction process is very low. This makes it possible to prepare Tc(V) radiopharmaceuticals with O-donor ligands by the usual procedure, in which an excess of reducing agent over technetium is unavoidably used. The Tc(V) complexes also tend either to be easily oxidized or to disproportionate [23],... 

Let us consider again an isotopic exchange reaction of the type shown in equation 11.53, such as, for instance, the already treated equilibrium between stannous chloride and an aqueous complex... 

The complex hydride reductions of nitriles to aldehydes compare favorably with the classical Stephen reduction which consists of treatment of a nitrile with anhydrous stannous chloride and gaseous hydrogen chloride in ether or diethylene glycol and applies to both aliphatic and aromatic nitriles [183,285, 1152]. An advantage of the Stephen method is its applicability to polyfunctional compounds containing reducible groups such as carbonyl that is reduced by hydrides but not by stannous chloride [1153]. 

Stannous chloride reduction of the cilcoholysis products led to the chelate complex PtBrs (oS). A reaction scheme and the proposed structures of the compounds PtBrs (oSX)—(oS) (X = Br, OMe, OEt, 0"Pr, 0 Bu) are shown in Fig. 8. The structure of the ethoxy derivative has been confirmed by X-ray diffraction analysis 13). 

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