TIN COMPOUND

Organotin stabilisers (containing alkyl groups, notably methyl, butyl or octyl) have been widely used in PVC pipe for many years, and are approved for use in potable water pipe both in the USA and some European countries. This is because they are effective at low dose levels, and the quantities leached out of pipes after the first few flushings are much lower than the recommended maximum human exposure level. 

The type of tin compound favoured in PVC stabilisers varies in different parts of the world. In Europe, 60% of the tin stabilisers used are octyl compounds, including those used in potable water pipes, and 30% butyl. In North America, where tin is widely used in pipe, foam and window profiles, 50% of the tin stabilisers are methyl, and most of the rest are butyl. Methyl and octyl compounds are FDA approved in some cases and allowed in food packaging. In Asia, 50% of tin stabilisers are methyl, and 40% octyl. In Japan, octyl tin is preferred for food packaging and potable water pipe, while butyl tin is used in construction applications. 

It had been customary to use loadings of 2 to 3% in the case of the first generation dialkyltin/long-chain mercaptan stabilisers, which meant putting as much as 5400 ppm tin into the PVC. Since then there has been a substantial reduction in tin content. The amount of tin in PVC stabilised with third generation monoalkyl tin combined with short chain or functionalised mercaptides or sulfides is only about 172 to 1800 ppm, depending on the tin content of the stabiliser used. This assumes low loadings of 0.04 to 0.75 %. 

Nevertheless, Greenpeace frequently draws the attention of the public to its concerns about tin in PVC. The toxicity of organotin compounds varies considerably dibutyl tin chloride has one of the lowest oral LD50 values, although others are eye irritants. Dover Chemical has suggested that Doverlube TriCal, its new calcium stearate product, can be used as a secondary stabiliser to reduce the amoimt of tin needed. 

Ceca markets two tin-based stabilisers, Thermolite 190 and 191, for rigid PVC applications, including calendered sheets in packaging and blister packs, extruded and blow-moulded containers, bottles and injected articles. They need a lower dose than other types of tin mercaptan. 

As organotin compounds (organostannanes) undergo smooth Pd-catalysed transmetallation, aryl halides react with a wide variety of aryl-, alkenyl- and alkylstannanes [139]. Coupling with allylstannane is the first example [140]. The reaction is called the Migita-Kosugi-Stille or Stille coupling. Aryl, alkenyl, allyl, alkynyl and benzyl 

The cross-coupling of aromatic and heteroaromatic stannanes has been carried out extensively [144], Tin compounds of heterocycles, such as the oxazole 316 [145], the thiophene (318) [146], furans and pyridines [147], can be coupled with aryl halides. 

Optimum conditions for the coupling of the alkenyl triflates 330 with the arylstannanes 331 have been studied. Ligandless Pd complexes such as Pd(dba)2 are most active in the reaction of the enol triflate. PI13P inhibits the reaction. NMP as a polar solvent gives the best results. The use of tri(2-furyl)phosphine and Ph As in the coupling of stannanes with the halides and triflates increases the rate of the transmetallation of the stannanes to Pd, which is thought to be the rate- 

Instead of enol triflate, the enol phosphate 334, derived from lactone 333, is used for the coupling to afford the cyclic enol ether 335. No coupling of phenyl phosphate 

Copper and Ag salts have been found to be good cocatalysts. The effect of some additives and ligands on the cross-coupling of the stannylpyridine 336 has been studied [158]. However, it seems likely that these effects are observed case by case. Probably transmetallation of Cu(I) with tin reagents generates organocopper, which undergoes facile transmetallation with the Pd species. 

having valence of +2 and +4, forms staimous (tin(II)) compounds and stannic (tin(IV)) compounds. Tin compounds include inorganic tin(II) and tin(IV) compounds complex stannites, MSnX., and staimates, M2SnX, and coordination complexes, organic tin salts where the tin is not bonded through carbon, and organotin compounds, which contain one-to-four carbon atoms bonded direcdy to tin. 

Of the large volume of tin compounds reported in the Hterature, possibly only ca 100 are commercially important. The most commercially significant inorganic compounds include stannic chloride, stannic oxide, potassium staimate, sodium staimate, staimous chloride, stannous fluoride, stannous fluoroborate, stannous oxide, stannous pyrophosphate, stannous sulfate, stannous 2-ethyUiexanoate, and stannous oxalate. Also important are organotins of the dimethyl tin, dibutyltin, tributyltin, dioctyltin, triphenyl tin, and tricyclohexyltin families. 

If tin and sulfur are heated, a vigorous reaction takes place with the formation of tin sulfides. At 100—400°C, hydrogen sulfide reacts with tin, forming stannous sulfide however, at ordinary temperatures no reaction occurs. Stannous sulfide also forms from the reaction of tin with an aqueous solution of sulfur dioxide. Molten tin reacts with phosphoms, forming a phosphide. Aqueous solutions of the hydroxides and carbonates of sodium and potassium, especially when warm, attack tin. Stannates are produced by the action of strong sodium hydroxide and potassium hydroxide solutions on tin. Oxidizing agents, eg, sodium or potassium nitrate or nitrite, are used to prevent the formation of stannites and to promote the reactions. 

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. 

Halides. The tin haUdes of the greatest commercial importance are stannous chloride, stannic chloride, and stannous fluoride. Tin hahdes of less commercial importance are stannic bromide [7789-67-5], stannic iodide [7790-47-8], stannous bromide [10031-24-0], and stannous iodide [10294-70-9] ( )  

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The small amount of tin found in canned foods is quite harmless. The agreed limit of tin content in U.S. foods is 300 mg/kg. The trialkyl and triaryl tin compounds are used as biocides and must be handled carefully. 

Tin-cobalt alloys Tin compounds Tin-copper alloys Tin crystals Tincture Tinctures... 

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