Dialkyltin stabilizers

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

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 ... 

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... 

Certain dioctyltin compounds are used for clear PVC materials. Dialkyltin carboxylate and dialkyltin mercaptide heat stabilizers are used in the PVC industry in many application34. 

Dialkylthallium(III) derivatives, 24 634 Dialkyl thiodipropionates, 3 111-112 Dialkyltin compounds, as PVC stabilizers, 24 821... 

Narula and Gupta76 have measured the thermodynamic stepwise stability constants for the formation of complexes of dialkyltin(TV) ions, R2Sn2+ (R = Me or Bu ), with hydroxamic acids, RCONHOH (R = Ph, Me2CH, Me) potentiometrically in 75% dioxane-water media. This has been followed by determination of formation constant of Af-arylhydroxamic acids-dialkyltin(IV) ions.77... 

Henninghausen G, Lange P. 1980. Immunotoxic effects of dialkyltins used for stabilization of plastics. Pol J Pharmacol Pharm 32 119-124. 

Early attempts at producing dialkyltin compounds yielded polymers. More recently, Neumann has found several synthetic routes to reactive R2Sn intermediates which can be trapped by oxidative-addition reactions (J). In the absence of trapping agents the divalent tin compound polymerizes. Lappert and co-workers have shown that the bulky bistri-methylsilylmethyl ligand stabilizes the divalent tin species toward polymerization. This stable divalent tin species thus provides an excellent starting material for investigating a wide variety of oxidative-addition reactions, as shown in Fig. 10 (78). 

The dialkyltins can be used as stabilizers in PVC pipes. They normally leach in very low concentrations, but if control were required, this would be through product specification. 

It is also worth mentioning here that two compounds containing a Zn Sn coordinate bond have been reported. The first of these is the sole example of a dialkyltin species (see Tin Organometallic Chemistry) stabilized by coordination to zinc-/3-diketonate. It was obtained by reaction of bis[3-dimethylamino)propyl]zinc with bis(dibenzoylmethanato)tin (equation 37) and its molecular structure shows a Zn Sn bond length of 2.634 A. The second compound is... 

The first generation tin mercaptide stabilizers were dialkyltin long-chain mercaptans (1), traditional mercaptoacetate products (2), and mercaptoacetic ester products, having an average tin content of 18% in the stabilizer. When a stabilizer with a high content of a monoalkyltin compound derived from a mercaptoethanol ester (3), was demonstrated to provide outstanding early color and color retention in white pipe, the industry quickly accepted this departure from traditional mercaptoacetate products. 

The two possible reactions of organotin mercaptide stabilizers, both ending in the formation of dialkyltin dichloride, are shown in Schemes 3.3.1 and 3.3.2. 

The formation of dialkyltin dichloride may thus be considered, as a first approximation, to be a measure of the total stabilizer conversion. Accordingly the diagram in Figure 3.3.6 shows the correlation between the stabilizer conversion and the time of heat treatment at 180 °C. 

However, differences in performance do exist, which are dependent on the alkyl substituent present and which must be taken into consideration by stabilizer manufacturers when developing new products, and by end users when formulating and processing PVC compounds with these products. In the case of dialkyltin bis(t-octylmercaptoacetate), as the alkyl chain length decreases from octyl to methyl, the... 

Organotin stabilizers also have a widespread use some examples are dialkyltin dicarboxylate, dialkyltin bis(maleate ester), dialkyltin bis(alkyl-mercaptan), dialkyltin(S,S -mercaptoacid ester) and dialkyltin 0-mercapto-propionate. The last one is supposed to exist in the solid state as a kind of telomer... 

Polyvinyl fluoride can be thermally stabilized with mixtures of phenyl phosphites (e.g., triphenyl phosphite) and low molecular weight epoxy resins. Other methods include the addition of the dolomite series and the zinc salt of an organic acid l or a dialkyltin bis 3> -sulfolanylmercaptide). PO... 

The existence of a ligand exchange reaction between dialkyltin dimercaptides and dicarboxylates (typical poly(vinyl chloride) stabilizers) and dialkyltin dichlorides is demonstrated by 1H and 13C NMR. Dibenzyl- and dibutyltin dimercaptides undergo the reaction instantaneously and quantitatively at 25° C to yield dialkylchlorotin mercaptides. Dialkyltin dicarboxylates and dimethyltin dimercaptides appear to participate in an equilibrium exchange reaction with dialkyltin dichlorides in which the individual components are not identifiable by NMR at 25°C. These results are discussed as they pertain to poly(vinyl chloride) stabilization. 

These exchange reaction phenomena may be general for all types of organotin PVC stabilizers. In the cases where an equilibrium exchange reaction is observed (dimethyltin dimercaptides and dialkyltin dicar-boxylates), the equilibrium at PVC processing temperatures may be far toward the dialkylchlorotin species and thus the mechanism is still operative. 

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