Dialkyltins

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 commercially important routes to alkyltin chloride intermediates utilize an indirect method having a tetraalkjitin intermediate. Tetraalkyltins are made by transmetaHation of stannic chloride with a metal alkyl where the metal is typicaHy magnesium or aluminum. Subsequent redistribution reactions with additional stannic chloride yield the desired mixture of monoalkyl tin trichloride and dialkyltin dichloride. Both / -butjitin and / -octjitin intermediates are manufactured by one of these schemes. 

Trialkyltin methoxides react with anhydrous hydrogen peroxide in ether to give the rather unstable bis(trialkyltin) peroxides, RsSnOOSnRs (214). Under the same conditions, dialkyltin dimethox-ides give polymeric peroxides, (RzSnOO), but, if an aldehyde is present, monomeric peroxides of the following structure are obtained (215). 

Sodium dicyanoethylenedithiolate reacts with trimethyl- or triphenyl-tin chloride to give anionic trialkylstannadithiacyclopentenes, but dialkyltin dichlorides undergo dealkylation (231). 

The dialkyltin compounds show a similar trend of decreasing toxicity with increasing length of the alkyl chain, and certain di-n-octyltin derivatives have been used for many years in food-contact applications, as described in Section V. 

It may, therefore, be seen that the mammalian toxicity of the lower dialkyltin compounds, unlike that of their trialkyltin counterparts, is markedly dependent upon the nature of the X groups this is probably true for species other than mammals (e.g., fungi) if the mode of action is similar. 

The dialkyltin dichloride formed by reaction of the dialkyltin stabilizer with the polymer, or with the hydrogen chloride liberated, is itself... 

Dibutyltin diacetate, dilaurate, and di-(2-ethylhexanoate) are used as homogeneous catalysts for room-temperature-vulcanizing (RTV) silicones. The dialkyltin compounds bring about the cross-linking of the oligomeric siloxanes, to produce flexible, silicone rubbers having a host of different uses, such as electrical insulators and dental-impression molds. Recent work has also shown (560) that various dibutyltin dicar-boxylates catalyze both the hydrolysis and gelation of ethyl silicate under neutral conditions. 

Dimethyltin dichloride is used in the glass industry as an alternative to stannic chloride for coating glass with a thin film of stannic oxide 562). The dialkyltin compound vapor is brought into contact with the glass surface at temperatures of 500-600°C, where decomposition and oxidation occurs. 

The vast majority of in vivo tests show no geno-toxicity of mono- and dialkyltins. Results from in vitro tests are variable, with little indication of DNA reactivity. There are, however, indications of clastogenicity and effects on spindle formation in mitosis in vitro. 

Table 7 Measured half-lives of dialkyltin compounds in soils. ...

WHO (2004) concluded that The mono- and disubstituted compounds that may leach from PVC water pipes for a short time after installation are primarily immunotoxins although they appear to be of low general toxicity, some are developmental toxins in rodents. The data available are insufficient to permit the proposal of guideline values for individual dialkyltins or the mono derivatives, although the concentrations observed in drinking-water are several orders of magnitude lower than the doses reported to cause developmental effects in rats and mice. ... 

Penninks AH, Seinen W (1980) The lymphocyte as target of toxicity a biochemical approach to dialkyltin induced immunosuppression. Proceedings of the International Conference on the Immunological System as Target for Toxic Damage. Advances in Immunopharmacology, 2 41-60. 

Thoonen S, Deelman BJ, van Koten G (2001) Platinum- and palladium-catalysed Kocheshkov redistribution of dialkyltin dichlorides or tetraalkyltins with tin tetrachloride. Chemical Communications, 18 1840-1841. 

WHO (2004) Dialkyltins in drinking water. Background document for the development of WHO Guidelines for drinking-water quality. Geneva, World Health Organization (WHO/SDEA/VSH/ 03.04/109 http //vwvw.vvho.int/water sanitation health/dwq/ chemicals/dialkyltins.pdf). 

While additive analysis of polyamides is usually carried out by dissolution in HFIP and hydrolysis in 6N HC1, polyphthalamides (PPAs) are quite insoluble in many solvents and very resistant to hydrolysis. The highly thermally stable PPAs can be adequately hydrolysed by means of high pressure microwave acid digestion (at 140-180 °C) in 10 mL Teflon vessels. This procedure allows simultaneous analysis of polymer composition and additives [643]. Also the polymer, oligomer and additive composition of polycarbonates can be examined after hydrolysis. However, it is necessary to optimise the reaction conditions in order to avoid degradation of bisphenol A. In the procedures for the analysis of dialkyltin stabilisers in PVC, described by Udris [644], in some instances the methods can be put on a quantitative basis, e.g. the GC determination of alcohols produced by hydrolysis of ester groups. 

On-line SFE-pSFC-FTD, using formic or acetic acid modified CO2 as an extraction solvent, was used to analyse a dialkyltin mercaptide stabiliser in rigid PVC (Geon 87444) [114]. Hunt et al. [115] reported off-line SFE-pSFC-UV analysis of PVC/(DIOP, chlorinated PE wax, Topanol CA), using methanol as a modifier. Individual additives are unevenly extracted at lower pressures and temperatures, where extraction is incomplete. Topanol CA, the most polar of the three PVC additives studied, could not be fully extracted in the time-scale required (15-20min), even at the highest CO2 temperature and pressure obtainable. However, methanol-modified CO2 enhances extraction of Topanol CA. PVC film additives (DEHP, fatty acids, saturated and aromatic hydrocarbons) were also separated by off-line SFE-preparative SFC, and analysed by PDA and IR [116]. 

It should be noted that dicyclopentadienyltin does not give any detectable reaction with 2,3-dimehtyl-1,3-butadiene, in contrast to the dialkyltin compound 154). According to Eq. (31) 6- or 9-membered ring compounds are formed. The dicyclopentadienyl compound in Eq. (31) can also be replaced by the unstable stannylens 154). 

A number of recent studies have been concerned with the effects of commercial heat stabilizers on the photodegradation of PVC. During irradiation at room temperature under air with 253.7-nm light, several dialkyltin dicarboxylates were found to increase the rates of the photooxidation and cross-linking of the polymer (62). However, at 0°C under air in a sunshine weatherometer, photooxidation was shown to be retarded by certain dibutyltin dicarboxylates (63). The latter result was also obtained in experiments involving the use of dibutyltin maleate with irradiation in the (280-400)-nm wavelength region at 38°C under air (50,51,64, 5,66). 

Varying effects have been observed as well for stabilizers of the dialkyltin bis("isooctyl" thioglycolate) type. These substances accelerate PVC photooxidation (62,66) and cross-linking (62) under some conditions. Moreover, the dioctyl... 

---