Organotin stabilizers

Stabilizer Ba/Zn stabilizer, Ca/Zn stabilizer, SnS stabilizer, organotin (small... 

There are three major types of tin stabilizers (organotin stabilizers), distinguished by their respective alkyl groups n-octyl, n-butyl, and methyl ... 

Sulfur-containing stabilizers (organotin mercaptides and sulfides). 

Baerlochar U.S.A. BAEROSTAB Oroanotin Stabilizers Organotin Mercaptides (Continued) ... 

Ultimately, as the stabilization reactions continue, the metallic salts or soaps are depleted and the by-product metal chlorides result. These metal chlorides are potential Lewis acid catalysts and can greatiy accelerate the undesired dehydrochlorination of PVC. Both zinc chloride and cadmium chloride are particularly strong Lewis acids compared to the weakly acidic organotin chlorides and lead chlorides. This significant complication is effectively dealt with in commercial practice by the co-addition of alkaline-earth soaps or salts, such as calcium stearate or barium stearate, ie, by the use of mixed metal stabilizers. 

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 ... 

Additionally, organotin mercaptides can act as antioxidants, as they can sequester free-radical degradation mechanisms (48). The one drawback of mercaptide-based tin stabilizers is the discoloration of the sulfur after exposure to uv-radiation. Special precautions or formulations need to be developed for outdoor apphcations. 

Table 7. Typical Commercially Significant Organotin PVC Stabilizers...

Polyvinyl chloride/Polyvinyl acetate Good prevent yellowing. High-molecular-weight organotin stabilizers improve radiation stability color-corrected radiation formulations are available. Less resistant than PVC. 

The organotins have a wide range of uses, which are largely specific for the different organotins. Thus, mono-and disubstituted organotin compounds are not suitable as biocides, and trisubstituted organotin compounds are not suitable as PVC stabilizers. 

The mono- and disubstituted organotins considered here are used as stabilizers in PVC or as catalysts for the production of electrodeposited coatings (mainly in motor vehicle primers), sihcone rubbers, esterification and powder coatings, and polyurethanes, as well as for coating glass. 

The production figure for organotin PVC stabilizer in 1996-1998 in Japan was 6983-8649 tonnes per year (Chemical Daily Co., Ltd, 1999, as communicated to the Final Review Board by Dr J. Sekizawa). 

Within a commercial organotin product, there will always be some quantity of related substances in addition to the substance itself In some cases, the performance of these products relies upon the presenee of more than one related substance (e.g. mono- and disubstituted octyltin stabilizers), whereas in others, the related substances are present as an inevitable impurity. For example, tributyltin chloride will contain impurities of mono-, di-, and tetrabutyltins, as well as tin tetrachloride (Parametrix, 2002a,b). 

Similarly, while the main products used as stabilizers in PVC are mono- and disubstituted compounds, owing to the chemistry involved in their production, trisubstituted organotin compounds will comprise a small fraction of the total amount. This could be significant in assessing the toxicity of the compounds (see below). 

Over 90% of organotin stabilizers are used in rigid PVC. Table 3 provides details of the estimated quantities of methyl-, butyl-, and octyltin stabilizers used in rigid and flexible PVC applications, whereas Table 4 details the types of applications in which the PVC products are used. 

Table 3 Use of organotin stabilizer types in rigid and flexible PVC in Europe (2001). ...

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