Tin metal

Tin(II) chloride is slowly oxidised in air. but keeping a piece of tin metal in the solution prevents this. 

Ethyl indole-2-carboxylate (45.2 g, 0.238 mmol) was dissolved in abs. EtOH (450 ml) in a 11 polyethylene container and cooled in a dry icc-cthanol bath. The solution was saturated with dry HCl gas until the volume increased to 875 ml, Granular tin metal (84.2g, 0.7l0mmol) was added to the slurry and... 

Stannous fluoride probably was first prepared by Scheele in 1771 and was described by Gay-Lussac and Thenard in 1809. Commercial production of stannous fluoride is by the reaction of stannous oxide and aqueous hydrofluoric acid, or metallic tin and anhydrous hydrogen fluoride (5,6). Snp2 is also produced by the reaction of tin metal, HP, and a halogen in the presence of a nitrile (7). 

Alkyltin Intermedia.tes, For the most part, organotin stabilizers are produced commercially from the respective alkyl tin chloride intermediates. There are several processes used to manufacture these intermediates. The desired ratio of monoalkyl tin trichloride to dialkyltin dichloride is generally achieved by a redistribution reaction involving a second-step reaction with stannic chloride (tin(IV) chloride). By far, the most easily synthesized alkyltin chloride intermediates are the methyltin chlorides because methyl chloride reacts directiy with tin metal in the presence of a catalyst to form dimethyl tin dichloride cleanly in high yields (21). Coaddition of stannic chloride to the reactor leads directiy to almost any desired mixture of mono- and dimethyl tin chloride intermediates ... 

The other important direct alkylation processes involve reaction of electron-rich olefinic compounds with either tin metal or stannous chloride (tin(II) chloride) in the presence of stoichiometric amounts of hydrogen chloride (22). Butyl acrylate (R = C Hg) was used commercially in this process to prepare the estertin or P-carboalkoxyethyltin chlorides as iHustrated in the foUowing. 

Cost bilizers. In most cases the alkyl tin stabilizets ate particularly efficient heat stabilizers for PVC without the addition of costabilizers. Many of the traditional coadditives, such as antioxidants, epoxy compounds, and phosphites, used with the mixed metal stabilizer systems, afford only minimal benefits when used with the alkyl tin mercaptides. Mercaptans are quite effective costabilizets for some of the alkyl tin mercaptides, particularly those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyl tin mercaptide ate currendy the most efficient stabilizers for PVC extmsion processes. The level of tin metal in the stabilizer composition can be reduced by up to 50% while maintaining equivalent performance. Figure 2 shows the two-roU mill performance of some methyl tin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. 

Other Uses. The production of finished shapes from iron powder by compacting and sintering utilizes about 100,000 t of iron powder aimuaHy copper powder (2—10 wt %) is normally added as a sintering aid. Addition of 2% tin powder or equal amounts of tin and copper powder considerably lowers the sintering temperature and time of sintering at a cost saving. The tin addition also improves dimensional control. Iron powder plus 10 wt % powdered lead—tin metal is pressed and siatered to make pistons for use ia automotive hydrauHc brake cylinders. 

Stannic and stannous chloride are best prepared by the reaction of chlorine with tin metal. Stannous salts are generally prepared by double decomposition reactions of stannous chloride, stannous oxide, or stannous hydroxide with the appropriate reagents. MetaUic stannates are prepared either by direct double decomposition or by fusion of stannic oxide with the desired metal hydroxide or carbonate. Approximately 80% of inorganic tin chemicals consumption is accounted for by tin chlorides and tin oxides. 

Anhydrous stannous chloride, a water-soluble white soHd, is the most economical source of stannous tin and is especially important in redox and plating reactions. Preparation of the anhydrous salt may be by direct reaction of chlorine and molten tin, heating tin in hydrogen chloride gas, or reducing stannic chloride solution with tin metal, followed by dehydration. It is soluble in a number of organic solvents (g/100 g solvent at 23°C) acetone 42.7, ethyl alcohol 54.4, methyl isobutyl carbinol 10.45, isopropyl alcohol 9.61, methyl ethyl ketone 9.43 isoamyl acetate 3.76, diethyl ether 0.49, and mineral spirits 0.03 it is insoluble in petroleum naphtha and xylene (2). 

Stannous Chloride Dihydrate. A white crystalline soHd, stannous chloride dihydrate is prepared either by treatment of granulated tin with hydrochloric acid followed by evaporation and crystallisation or by reduction of a stannic chloride solution with a cathode or tin metal followed by crystallisation. It is soluble in methanol, ethyl acetate, glacial acetic acid, sodium hydroxide solution, and dilute or concentrated hydrochloric acid. It is soluble in less than its own weight of water, but with much water it forms an insoluble basic salt. 

Soluble Sta.nna.tes, Many metal staimates of formula M Sn(OH) are known. The two main commercial products are the soluble sodium and potassium salts, which are usually obtained by recovery from the alkaline detinning process. They are also produced by the fusion of stannic oxide with sodium hydroxide or potassium carbonate, respectively, followed by leaching and by direct electrolysis of tin metal in the respective caustic solutions in cells using cation-exchange membranes (27). Another route is the recovery from plating sludges. 

Stannous Sulfate. Stannous sulfate (tin(Il) sulfate), mol wt 214.75, SnSO, is a white crystalline powder which decomposes above 360°C. Because of internal redox reactions and a residue of acid moisture, the commercial product tends to discolor and degrade at ca 60°C. It is soluble in concentrated sulfuric acid and in water (330 g/L at 25°C). The solubihty in sulfuric acid solutions decreases as the concentration of free sulfuric acid increases. Stannous sulfate can be prepared from the reaction of excess sulfuric acid (specific gravity 1.53) and granulated tin for several days at 100°C until the reaction has ceased. Stannous sulfate is extracted with water and the aqueous solution evaporates in vacuo. Methanol is used to remove excess acid. It is also prepared by reaction of stannous oxide and sulfuric acid and by the direct electrolysis of high grade tin metal in sulfuric acid solutions of moderate strength in cells with anion-exchange membranes (36). 

Triben2yltin chloride [3151 -41 -5] is a unique example of a triorganotin chloride that can be prepared directiy from the organic haUde and tin metal ... 

Many organic hahdes, especially alkyl bromides and iodides, react direcdy with tin metal at elevated temperatures (>150° C). Methyl chloride reacts with molten tin metal, giving good yields of dimethyl tin dichloride, which is an important intermediate in the manufacture of dimethyl tin-ha sed PVC stabilizers. The presence of catalytic metallic impurities, eg, copper and zinc, is necessary to achieve optimum yields (108) ... 

The reaction of higher alkyl chlorides with tin metal at 235°C is not practical because of the thermal decomposition which occurs before the products can be removed from the reaction zone. The reaction temperature necessary for the formation of dimethyl tin dichloride can be lowered considerably by the use of certain catalysts. Quaternary ammonium and phosphonium iodides allow the reaction to proceed in good yield at 150—160°C (109). An improvement in the process involves the use of amine—stannic chloride complexes or mixtures of stannic chloride and a quaternary ammonium or phosphonium compound (110). Use of these catalysts is claimed to yield dimethyl tin dichloride containing less than 0.1 wt % trimethyl tin chloride. Catalyzed direct reactions under pressure are used commercially to manufacture dimethyl tin dichloride. 

The direct reaction of tin metal with higher haloalkanes is less satisfactory even when catalysts are used, except with alkyl iodides. The reaction of... 

Tin metal also reacts directly with a number of activated organic haUdes, including aHyl bromide, benzyl chloride, chloromethyl methyl ether, and P-halocarboxyhc esters and nitriles giving fair-to-good yields of diorganotin dihaUdes (97,111—114). 

In 1975, the estimated world aimual production of tin chemicals represented the consumption of 12,000—14,000 t of tin metal or 5% of total tin consumption (196). In 1978, ca 20,000 t/yr was consumed worldwide, with equal amounts represented by inorganic tin and organotin compounds (197). It is estabhshed that worldwide production of organotins rose from ca 50 t in 1950 to a possible 30,000—35,000 t in 1980. 

In pyrolysis employing molten tin, a flow of the urea on the surface is eventually converted to a sheet of cmde CA 15—20 mm thick. After reaching the edge of the tin bath, the moving sheet falls into a mill. The resultant powdered cmde CA (contaminated with tin metal) is subjected to acid hydrolysis to convert aminotriazines (30—40%) to CA. Tin losses can amount to 15 kg/1 product. 

Boron, as barium metaborate, is marketed as a mildew preventative for paints (273). Borax is used as a wood preservative, and an organic boron, 2,2 -(l-methyltrimethylenedioxy)-bis(4,4,6-trimethyl)-l,3,2-dioxaborinane (Biobor JF) [14697-50-80] is a biocide for jet fuel (274). Whereas tin metal is used to coat steel cans used as food containers, organic tin in the form of tributyl tin compounds have proven to be powerfiil antimicrobials, and have found use in antifouHng coatings for ship bottoms, paints, and wood preservatives (275). 

Self-Tfst K.4A When tin metal is placed in contact with a solution of Fe3+ ions, it reduces the iron to iron(II) and is itself oxidized to tin(II) ions. Write the net ionic equation for the reaction. 

The halostannanes can also be generated in situ by reactions of allylic halides with tin metal or stannous halides. 

Mediated by Tin. In 1983, Nokami et al. observed an acceleration of the reaction rate during the allylation of carbonyl compounds with diallyltin dibromide in ether through the addition of water to the reaction mixture.74 In one case, by the use of a 1 1 mixture of ether/water as solvent, benzaldehyde was allylated in 75% yield in 1.5 h, while the same reaction gave only less than 50% yield in a variety of other organic solvents such as ether, benzene, or ethyl acetate, even after a reaction time of 10 h. The reaction was equally successful with a combination of allyl bromide, tin metal, and a catalytic amount of hydrobromic acid. In the latter case, the addition of metallic aluminum powder or foil to the reaction mixture dramatically improved the yield of the product. The use of allyl chloride for such a reaction,... 

Another element that exhibits allotropy because of variations in the crystal structure is tin. The common allotrope is tin metal, also known as a alpha) tin, which is stable at ambient temperatures. The other allotrope, which generally occurs as a gray powder and is known as p beta) tin, but also as tin pest, is formed only at very low temperatures when tin cools down to temperatures below -18°C, the ordinary allotrope, a tin, is converted to p tin, and the transformation is irreversible under ordinary temperatures. Tin objects exposed to temperatures below -18°C in very cold regions of the world, for example, are generally severely damaged when part of the tin converts to tin pest. In extreme cases, when exposure to low temperatures extends for long periods of time, the allotropic conversion may result in the transformation of tin objects into heaps of gray p-tin powder. 

Pure tin exhibits two common forms in the solid state — a gray tin and a white tin. At temperatures above 13°C or 55°F, the more stable form of tin is the denser white tin. At lower temperatures, the white tin is slowly converted to the gray form, a more powdery substance. Prolonged exposure to the cold winter temperatures of northern Europe contributed to the loss of integrity and disintegration of many cathedral organ pipes. As a consequence of the progressive nature of the structural transformation, as the white tin metallic surface becomes covered with... 

This reaction is irreversible. In the next cycles tin metal forms lithium-tin alloys with different stoicheometiy ... 

Nevertheless, /1-carbonylalkyltin chlorides are obtained347 in high yields by reactions of the carbonyl-activated alkenes RR,C=CR"-C(R",)=0 with HC1 and SnCl2, yielding compounds of the type 118, while with tin metal and HC1 compounds of the type 119 are obtained. 

Survival of the ions is assisted by the solvent. Complexes with bridging tin atoms, and mixed complexes, are particularly interesting. Oxidation of the latter is followed by cleavage of either of the tin-metal bonds as in the following example ... 

Based on a report from the London International Tin Institute, Publication No. 665 (1986), the annual consumption of tin metal as organotin chemicals in the U.S.A., Europe and Japan is summarized in Table 632. Chemical formulae of commonly used organotin chemicals are summarized in Table 732. 

---