Alkyltin compounds

With functionally substituted, alkyltin compounds, the functional substituent may become involved in the cleavage process, resulting in an intramolecular reaction, e.g.. 

The relative reactivities of alkyltin compounds towards tert-butoxyl radicals, ketone triplets, and succinimidyl radicals are dominated by the steric effect of the alkyl ligands (R" > R"), but that towards bromine atoms follows the reverse sequence (R" < R ). 

Tin-tin bonds are usually best prepared by reducing an Sn-0 or Sn-N bonded compound with a tin hydride. For example, trimethyl (diethylamino)tin is reduced by alkyltin trihydrides to give decaorganotetratins (256). 

As discussed in section 2, the alkyltin component of organotin compounds is relatively stable to environmental degradation processes such as hydrolysis, compared with the association with the relative ligand (such as an isooctyl mercaptoacetate group). Thus, in water, most of the derivatives are reported to dissociate to the constituent alkyltin (usually as the chloride or the oxide) and the relevant anion (KemI, 2000). 

Arakawa Y, Wada O (1993) Biological properties of alkyltin compounds. In Sigel H, Sigel A, eds. Metal ions in biologioal systems. Vol. 9. New York, NY, Marcel Dekker, pp. 101-136. 

The concentration at which a steep rise in this curve begins has been termed as the critical or threshold concentration (2,3). Figure 6 shows such typical curves for PTF and BTF in n-hexane. Despite the fact that different shear rates are involved in capillary viscometry, it can be qualitatively said that at a given concentration, PTF viscosified n-hexane better than BTF. It is clear from Figure 6 that the critical concentration for these two compounds is above 0.7%, while analogous tri-n-alkyltin fluorides showed a critical concentration of less than 0.4% (3). This may be due to the presence of bulky Me3Si-groups nearer to the Sn-F bond, which causes some steric hindrance to auto-association. 

A method for the preparation of dendritic Sn by the electrolysis of alkyltin complexes has been described. Bu2SnBr2 and BusSnBr form as intermediates143. The method is aimed at recovery of elemental tin from residues of tin compounds and for reuse in the preparation of tin halides. 

Compounds of the type CpSnX3 (X = alkyl, Cp, Cl) are very photosensitive compared with alkyltin compounds, and on irradiation show strong E.S.R. spectra of the Cp-radical54. The equivalent silicon and germanium compounds do not show this reactivity (reaction 34). 

Nucleophiles react by attack at the tin center. The reaction of the trialkynyltin compounds RSnfC CR T with primary or secondary alcohols gives the alkyltin trialkoxides, RSn(ORz)3, and controlled hydrolysis gives the closo-clusters [(RSn)12(/730)i4(/r20H)6](0H)2 (Equation (86)).24 The spacer-bridged hexaalkynyldistannanes are... 

Hattori [77] extracted alkyl and alkyltin compounds from sediments with methanoic hydrochloric acid and then, following mixture with sodium chloride and water, the mixture was extracted with benzene and converted to hydrides with sodium borohydride and analysed by gas chromatography using an electron capture detector. Down to 0.02mg kg 1 organotin compounds in sediments could be determined with a recovery of 70-95%. 

Epler et al. [82] used laser enhanced ionisation as a selective detector for the liquid chromatographic determination of alkyltin compounds in sediments. The analysis was performed on a 1-butanol extract of the sediment. 

The procedures described in section 13.4.2.1 [76-78] have been applied to the determination of alkyltin compounds in marine sediments. 

In addition to all the good features of the Stille couplings, there are a few problems with the use of RSnMles or RSn(n-Bu)3 in aqueous solutions. These compounds are rather volatile and water-insoluble but this can be overcome with the aid of co-solvents. However, the products of the reaction still contain alkyltin species which are toxic and environmentally unacceptable. Furthermore, only one of the four Sn-C units take active part in the... 

The most toxic of the organotin compounds are the trialkyltins, followed by the dialkyltins and monoalkyltins. The tetraalkyltins are metabolized to their tri-alkyltin homologs their effects are those of the trialkyltins, with severity of effects dependent on the rate of metabolic conversion, hr each major organotin group, the ethyl derivative is the most toxic. ... 

Costabilizers. In most cases the alkyltin stabilizers are 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 alkyltin mercaptides. Mercaptans are quite effective costabilizers for some of the alkyltin mercaptides, particulady those based on mercaptoethyl ester technology (23). Combinations of mercaptan and alkyltin mercaptide are currently the most efficient stabilizers for PVC extrusion 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-roll mill performance of some methyltin stabilizers in a PVC pipe formulation as a function of the tin content and the mercaptide groups at 200°C. The test formulation contains 100 parts of PVC (Fikentscher K = 65), 1.2 parts of paraffin wax, 0.6 parts of calcium stearate, and 0.4 parts of methyltin-based stabilizers. 

The basic metal salts and soaps tend to be less cosdy than the alkyltin stabilizers for example, in the United States, the market price in 1993 for calcium stearate was about 1.30— 1.60, zinc stearate was 1.70— 2.00, and barium stearate was 2.40— 2.80/kg. Not all of the coadditives are necessary in every PVC compound. Typically, commercial mixed metal stabilizers contain most of the necessary coadditives and usually an epoxy compound and a phosphite are the only additional products that may be added by the processor. The required costabilizers, however, significandy add to the stabilization costs. Typical phosphites, used in most flexible PVC formulations, are sold for 4.00— 7.50/kg. Typical antioxidants are bisphenol A, selling at 2.00/kg -nonylphenol at 1.25/kg and BHT at 3.50/kg, respectively. Pricing for ESO is about 2.00— 2.50/kg. Polyols, such as pentaerythritol, used with the barium—cadmium systems, sells at 2.00, whereas the derivative dipentaerythritol costs over three times as much. The p-diketones and specialized dihydropyridines, which are powerful costabilizers for calcium—zinc and barium—zinc systems, are very cosdy. These additives are 10.00 and 20.00/kg, respectively, contributing significandy to the overall stabilizer costs. Hydrotalcites are sold for about 5.00— 7.00/kg. 

Alkyltin compounds carrying a leaving group at the y-position undergo 1,3-elimination to produce cyclopropanes9. y,<5-Epoxyalkyltin derivatives are converted to cyclopropyl-methyl alcohols under catalysis of a Lewis acid (equation 5)10. y-Hydroxyalkyl selenides... 

Cationic alkyltin species, characteristics, 3, 820 Cationic aluminum catalyst system, in epoxide homopolymerization, 11, 603 Cationic aluminum compounds... 

A theoretical interpretation of substituent effects in unassociated alkyltin compounds has recently been given. (89)... 

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