Methyl tin

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. 

Neurotoxicity is the major end-point for the methyl-tins, with a NOAEL of approximately 0.6 mg/kg body weight based on neuropathology for dimethyltin limited data for monomethyltin preclude the derivation of a NOAEL. No neurotoxicity was found with dibutyltin or mono- and dioctyltins no information is available for monobutyltin. 

Fig. 5. Crystal structure of bis[di-(trimethylsilyl)methyl]tin(II) (14). Reprinted with permission from J. Chem. Soc., Chem. Commun, 1976, 261. Copyright by The Chemical Society...

A number of natural waters, from in and around the area of Tampa Bay, Florida, were analysed for tin content. All samples were analysed without pretreatment. Samples that were not analysed immediately were frozen until analysis was possible. Polyethylene bottles, 500 ml volume, were used for sample acquisition and storage. The results of the analyses appear in Table 10.1. The average total tin content of fresh, saline, and estuarine waters are 9.1,4.2, and 12 ng/1, respectively. Approximately 17-60% of the total tin present was found to be in the methylated forms. The saline waters appear to have the highest percentage of methylated tin compounds 60% of the total tin present... 

Cyclic stannanes can be generated by reaction of stannylenes with alkynes112. For example, bis[bis(trimethylsilyl)methyl]tin reacts with cyclooctyne to provide A1,18-9,10-(distanna-9,9,10,10-tetrakis[bis(trimethylsilyl)methyl])bicyclo[6,2,0]-decene, 69. This reaction is a typical oxidative addition on stannylenes. 

Braman and Tompkins first reported methylated tin compounds in environmental materials43. Saline water, estuary water, fresh water, rain water and tap water were analyzed for methyltin compounds tin levels were at ng 1 1. Average total tin concentration of human urine (11 samples) was 1 i-gSn 1 1, and those of methyltin, dimethyltin and trimethyltin were 90, 73 and 42 ngSnl-1, respectively. Methyltin compounds were also observed in shell samples at the 0.1 ng g 1 level. About 17-60% of the total tin was present in monomethyltin form43. 

Butylation of methyl tin species before solvent extraction and the use of atomic absorption spectrometry shortens the extraction procedure and reduces detection limits to about O.lng [102],... 

Under similar conditions As(III) was not oxidized on Fe(III) oxide. Although such an oxidation is favored thermodynamically, it was reasoned (lj) that the kinetics of the process on the Fe(III) oxide are too slow. The role of manganese dioxide in the methylation of tin(II) and methyl tin(IV) ions has been studied (18). It was found that Sn(II) and Sn(IV) form methyl tin ions by CH transfer. Of particular importance was the... 

Peroxo-/i-oxo-bis bisOrimcLhy]si]y])methyl tin (316) is an organotin analog of the FOZ of a symmetrically tetraalkylated olefin (278). It is obtained in low yield by oxidation of the corresponding silylated dialkyltin in the presence of a molybdenum catalyst. The structure was elucidated by XRD analysis and has some characteristic features (a) The 0—0 distance is unusually long (154.3 pm) as compared to that of similar transition metal... 

Recently, Olah and co-workers reported a new route to tributyl(trifluoro-methyl)tin via in situ formation and capture of the trifluoromethyl anion by trialkyltin oxide [106]. Reaction of trimethyl(trifluoromethyl)silane with tribu-tyltin oxide in the presence of catalytic TBAF in THF afforded the corresponding tributyl(trifluoromethyl)tin in good yield (Scheme 38). This reaction system was first reported by Warner and Buchwald [107]. 

The substitution of the unsymmetrical tetraalkyl, MeSnBu, 3, by mercuric iodide was shown to involve only the cleavage of the methyl-tin bond, and hence the overall rate coefficient for the substitution is also that for the cleavage of the methyl-tin bond. Rate coefficients and activation parameters (given in Table 5) are compared with those for the symmetrical tetraalkyls, in Table 6. 

Substitution of a number of tetraalkyltins was examined, and it was shown that only those tetraalkyls that contained at least one methyl-tin group underwent substitution. It was therefore deduced32 that in mixed tetraalkyltins (such as Et2SnMe2) only the methyl group was cleaved from the tin atom. Rate coefficients for reaction of a number of tetraalkyltins with dimethyltin dichloride are given in Table 24, together with activation parameters where determined. 

STATISTICALLY CORRECTED SECOND-ORDER RATE COEFFICIENTS (l.mole" .sec- ) FOR THE CLEAVAGE OF METHYL-TIN BONDS BY DIMETHYLTIN DICHLORIDE IN SOLVENT METHANOL AT 25 °C... 

THE CLEAVAGE OF METHYL-TIN AND ETHYL-TIN BONDS BY IODINE IN SOLVENT METHANOL AT 20 °C AND IONIC STRENGTH 0.025 Af35... 

In addition to synthetic organotin compounds, methylated tin species can be produced biologically in the environment. Figure 12.6 gives some examples of the many known organotin compounds. 

Hydrostannation of alkynes is one of the simplest and direct routes to vinylstannanes which have great versatility as building blocks in syntheses. However, a variety of regio and stereo isomers are usually formed.17-22 Until now, the selectivities are controlled by using different types of tin hydrides described above.26,92 For aryl-subsutituted alkynes, radical stannylation leads to the regioselective formation of the /3-adducts but with poor stereoselectivity. The addition of bulky tris[(phenyl dimethylsilyl)methyl]tin hydride indicates that these reactions take place with complete kinetic or thermodynamic stereoselectivity (Equation (30)).93... 

Vibrational (IR and Raman), UV-visible, photoelectron, NMR, and Mossbauer spectroscopy have all been reported for bis(bistrimethylsilyl-methyl)tin(II) and analogous tin(II) amides. Since an unusual tin-tin double bond has been proposed for the solid state of [Sn[CH(SiMe3)2]2]2 the Raman spectrum of this compound was of interest. Unfortunately, the compound decomposed in the laser beam however, an intense band at 300 cm-1 has been assigned as the Ge—Ge stretching frequency for the analogous germanium compound (68). 

There have been numerous reports of the chemical shifts of methyl groups attached to metals and metalloids (see Tables I to III all tables are collected at the end of this chapter, see pp. 166-206), but very few discussions of the chemical shift data. The chemical shifts of some siloxanes have been discussed in terms of changes in the paramagnetic term (76). The chemical shifts of [Me Sn(SMe)4 ] have also been discussed 218). As n increases the methyl-tin, chemical shift moves to low field, but it was concluded from the behavior of the Sn chemical shifts that the electron-withdrawing capacity of the SMe group(s) does not play the most important lole in the variation of the chemical shifts of the nuclei. 

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