Organotin reactions

Many organotin reactions are catalysed by platinum or palladium compounds, and this has stimulated interest in compounds containing an Sn-Pt or Sn-Pd bond. The chemistry of the SnPt compounds is much the more thoroughly developed, and, if complexes... 

Sandosham J, Benneche T, Moeller B, Undheim K (1988) Syntheses of 5-aIkenylpyrimidines by organotin reactions. Acta Chem Scand B 42 455 61... 

The ketimine 736 is prepared by the reaction of the imidoyl chloride 735 with organotin reagents[604,605]. 

Various organotin reagents react with acyl and aroyl halides under mild conditions without decarbonylation to give carbonyl compounds[390,39l]. Alkyl- or alkenyltin reagents react with acyl and aroyl chlorides to give ketones[548.733,734]. One example is the preparation of the a,/3-dnsaturated 7-keto esters 860 and 861, carried out under a CO atmosphere[735]. The reaction has been applied intramolecularly to the synthesis of the macrocyclic keto... 

The ester 870 is prepared by the cross-coupling of the chloroformate 869 with an organotin reagent. Some chloroformates are easily decomposed by a Pd catalyst, and hence the reaction should be carried out by slow addition of the chloroformates. Similarly, the amide 872 is prepared by the reaction of the carbamoyl chloride 871 [742]. The coupling of alkylcopper with ethyl chloroformate catalyzed by Pd affords esters[743]. 

Polyhydric alcohol mercaptoalkanoate esters are prepared by reaction of the appropriate alcohols and thioester using -toluenesulfonic acid catalyst under nitrogen and subsequent heating (16,17). Organotin mercapto esters are similarly produced by reaction of the esters with dibutyltin oxide (18). Pentaerythritol can be oxidized to 2,2-bis(hydroxymethyl)hydracryhc acid [2831-90-5] C H qO, ... 

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). 

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. 

The organotin maleate and maleate half-ester derivatives also exhibit this bleaching effect reportedly by a Diels-Alder addition reaction (18). The reaction is specific to the organotin maleates other organotin carboxylates containing normal dieneopltiles fail to produce similar results (19). 

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 reaction is of practical importance in the vulcanization of siUcone mbbers (see Rubber compounding). Linear hydroxy-terrninated polydimethyl siloxanes are conveniently cross-linked by reaction with methyldiethoxysilane or triethoxysilane [998-30-1]. Catalysts are amines, carboxyflc acid salts of divalent metals such as Zn, Sn, Pb, Fe, Ba, and Ca, and organotin compounds. Hydroxy-terrninated polysiloxanes react with Si—H-containing polysiloxanes to... 

In practice, these cleavage reactions are difficult to control, and usually mixtures of products form, even with stoichiometric quantities of reagents. Selectivity improves at lower temperatures, higher dilutions, and in the presence of polar solvents, eg, pyridine. This method is not used to prepare the lower alkylated—arylated organotins outside the laboratory. 

These reactions proceed rapidly and in good yield with primary alkyl and phenyl organotin compounds at ca 200°C. The reactions proceed at lower temperatures if anhydrous aluminum chloride is used as a catalyst. 

When R is a lower alkyl, the organotin trichloride can be easily separated from the reaction mixture by extraction with dilute aqueous hydrochloric acid, in which it is soluble. This reaction also works well with unsymmetrical tetraorganotins and has been practiced commercially (85). 

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. 

Toxic Reactions of the Skin Irritation is the most common reaction of the skin. Skin irritation is usually a local inflammatory reaction. The most common skin irritants are solvents dehydrating, oxidizing, or reducing compounds and cosmetic compounds. Acids and alkalies are common irritants. Irritation reactions can be divided into acute irritation and corrosion. Necrosis of the surface of the skin is typical for corrosion. Acids and alkalies also cause chemical burns. Phenols, organotin compounds, hydrogen fluoride, and yellow phosphorus may cause serious burns. Phenol also causes local anesthesia, in fact it has been used as a local anesthetic in minor ear operations such as puncture of the tympanous membrane in cases of otitis. ... 

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