Methyltins

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 same group198 characterized the complexes of methyltin halides with dibenzyl, diethyl and methyl benzyl sulphoxides. R3SnCl forms complexes with one and R2SnCl2 with two donor molecules, and trigonal bipyramidal and octahedral structures, respectively, were suggested for these complexes as shown in Scheme 16. 

Mono- and disubstituted methyltin, butyltin, and octyltin compounds... 

Methyltins are less likely than the butyl- and octyl-tins to partition to sediments, soils, and organic carbon. Modelled data for K c suggest much lower capacity for binding to organic carbon than do measured values, often by several orders of magnitude. Measured data have been used in preference to model environmental fate of the compounds. The compounds also bind strongly to clay minerals, montmorillonite in particular. 

Tributyltin is well established as an aromatase inhibitor, and dibutyltin appears to have some potency also (exact characterization of the endocrine disrupting capacity of dibutyltin alone is difficult because of the presence of tributyltin as an impurity). Monobutyltin and mono- and dioctyltins have no aromatase inhibiting capacity in in vitro tests. No data are available for this end-point for the methyltins. 

The BUSES model provides an estimate of the organic carbon/water partition coefficient (Koc) based on the octanol/water partition coefficient (Kow)- From these data, it is evident that the methyltins are less likely to partition onto organic carbon (in sediments, soils, biota) than are the butyl- and octyltin compormds due to then-lower partition coefficients and higher water solubilities. The 7/oc value can then be used to derive sohds/water partition coefficients in suspended matter, in sediment, and in soil using values of 10%, 5%, and 2% for organie carbon, representing typical organic carbon contents of suspended matter, sediment, and soil, respeetively. 

In the EU, a total of 12 779 tonnes of inorganic tin in 2001 was used in the production of the various organotin compounds, as well as in the production of inorganic tin compounds. It should be further noted that the above tonnage applies only to butyltin and octyltin compounds methyltin compounds, while used in the EU, are produced only outside the EU and are imported. 

Sn -I- 2RI R2Snl2 (where R is the alkyl group and I is the anion). Methyltin stabilizers are produced by direct synthesis in the United States. Dibutyltin dichloride is manufactured from crude tetrabutyltin and tin tetrachloride and is usually catalysed with aluminium trichloride (Blunden Evans, 1989 Gaver, 1997 Thoonen et al, 2001). 

Methyltin compounds, in addition to being used as stabilizers in PVC products, can also be produced via natural processes in the environment. Thus, as with butyltin compounds, it is not possible to exactly attribute the source of methyltin compounds in the environment. 

Summer et al. (2003) also reviewed the concentrations of methyltin compounds in the environment (Table 13). No higher values were found in later literature. As indicated above, methyltin compounds can be produced naturally in the environment by microorganisms (Maguire, 1991). 

There is some evidence to suggest that methyltin compounds bind to sewage sludge. Concentrations... 

Similar calculations have been undertaken for the mono- and dimethyltin compounds and the mono- and dioctyltin compounds. All of the calculations and input data used are the same (in terms of quantities used at a site, losses to air, and percentages lost to wastewater). It is assumed that the stabilizer compounds contained either 50% each of monomethyltin trichloride and dimethyltin dichloride (for the methyltins) or 50% each of monooctyltin trichloride and dioctyltin dichloride (for the octyltin compounds). 

By comparison with the measured data presented above, it can be seen that the local PECs are generally below, or in the order of, the maximum values measured in the aquatic environment. By way of exception, the values reported for methyltins, and in particular dimeth-yltin dichloride, from stabilizer production using the Technical Guidance Document (CEC, 2003) equations are significantly higher than the maximum measured values reported in the environment. 

Arakawa Wada (1993) dosed rats with mono-methyltin trichloride or dimethyltin dichloride for 10 days at 5 mg/kg body weight per day and reported no effects on thymus weight this is the only study examining immunotoxic end-points for the methyltins. 

No data are available on endocrine-related effects of methyltins. 

Elf Atochem NA (1996) Toxicity of a methyltin chloride mixture in rats. Homer, NY, ClinTrials BioResearch (CTBR), for Elf Atochem North America (Project No. 97307). 

Figge K, Koch J (1973) Migration of the methyltin stabilizer Advastab TM-181-FS from rigid PVC in the fat stimulant HB 307. NATEC, Gesellschaft fiir naturwissenschaftliche dienste mbH, April. 

Oldersma H, HanstveitAO, de Haan HPM (2004a) Methyltin tiis (2-ethylhexylmercaptoacetate) (CAS 57583-34-3 MMT(EHMA)) Determination of the effect on the growth of the fresh water green alga Scenedesmus subspicatus. Zeist, TNO Chemistry, 10 June (revised final 12 August) (Report No. V5307/02). 

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