Organotin Replacements

Tin Chemistry Fundamentals, Frontiers and Applications 6.2.13 Organotin Replacements... 

Replacement of Labile Chlorines. When PVC is manufactured, competing reactions to the normal head-to-tail free-radical polymerization can sometimes take place. These side reactions are few ia number yet their presence ia the finished resin can be devastating. These abnormal stmctures have weakened carbon—chlorine bonds and are more susceptible to certain displacement reactions than are the normal PVC carbon—chlorine bonds. Carboxylate and mercaptide salts of certain metals, particularly organotin, zinc, cadmium, and antimony, attack these labile chlorine sites and replace them with a more thermally stable C—O or C—S bound ligand. These electrophilic metal centers can readily coordinate with the electronegative polarized chlorine atoms found at sites similar to stmctures (3—6). 

Excess alkylating reagent is required if the tetraorganotin is desired as the exclusive product. In commercial practice, the stoichiometry is kept at or below 4 1, since the cmde product is usually redistributed to lower organotin chlorides in a subsequent step and an ether is used as the solvent (86). The use of diethyl ether in the Grignard reaction has been generally replaced with tetrahydrofuran. 

Synthesis of 3,5-disubstituted pyridazines by regioselective [4 + 2] cycloadditions with ethynyltributyltin and subsequent replacement of the organotin substituent [160]... 

Heat stabilisers for PVC act by HC1 scavenging and include organotins, mixed metal salt blends, and lead compounds. The latter account for nearly 64 % of volume (in 1994), followed by barium/cadmium and organotin compounds. Cadmium-based heat stabilisers are rapidly being replaced due to environmental concerns. Barium/zinc and calcium/zinc compounds show a high growth rate. It is expected that methyltin stabilisers will soon dominate the growing PVC pipe market. 

A second method is the replacement of a chiral leaving group of an (optically unstable) organotin compound (a triorganotin menthoxide for instance) by a more nucleophilic reagent (a Grignard reagent or lithium aluminum hydride for instance). 

R2SnCl2 +F RSnCl3 + F (R = Ph, Me, n-Bu, f-Bu) 19F and 119Sn NMR. Intermolecular and intramolecular dynamics of a CH2C12 solution of chlorinated organotin compounds and fluoride ions lead to multiple replacement reactions. Complex ions such as [Ph2SnCl3-KFn], n = 1-3 are formed, that are stereochemically rigid at —100 °C and fluxional at — 80 °C. 159... 

At raised temperature and CO pressure, terminal acetylenes can replace the organotin derivatives, giving acetylenic ketones (equation 114).491 Some of these reactions occur at normal pressure. Aryl, heterocyclic and vinyl bromides and iodides could be used. These reactions again required a stoichiometric quantity of base. The complexes (102), [PdCI2L2] (L = l,l -bis(diphenylphosphino)ferrocene) and [PdI(Ph)(AsPh3)2] were used as catalysts. The mechanism was not discussed. 

All alternative detection schemes fail in at least one of the above criteria, and mass spectrometric detection has replaced other detectors even in applications in which they were well established, such as ECD for the gas chromatographic determination of organochlorine pesticides,61 or atomic emission detection (AED) or FPD in the GC analysis of organotin (OT) compounds.62... 

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