A STUDY OF THE DISPROPORTIONATION EQUILIBRIUM FOR ALLYLDIBUTYLTIN(IV)CHLORIDE AS AN APPROACH TO UNDERSTANDING THE ROLE OF ORGANOTINS IN THE AQUATIC ENVIRONMENT

The equilibrium: 2 Bu(2)(CH2=CHCH2)SnCl reversible arrow Bu(2)Sn(CH2=C HCH2)(2)+Bu(2)SnCl(2) takes place when the allyltin chloride is stirre d in water. This has been chosen as a model to understand the extent a s well as the mechanistic pathways of the disproportionation reactions 2 R(3)SnX reversible arrow R(4)Sn+R(2)SnX(2) which are thought to occ ur in the aquatic environment. The behaviour of Bu(2)(CH2=CHCH2)SnCl h as been studied in various media: water, water-acetone, water-ethanol and water-hexane. It has also been ascertained that Bu(2)(CH2=CHCH2)Sn Cl is a product arising at room temperature from the scrambling of Bu( 2)Sn(CH2=CHCH2)(2) and Bu(2)SnCl(2) either neat, in organic solvents o r also in the presence of water. Equilibrium [1] has been interpreted as arising from a bimolecular interaction between the electrophilic aq uo-cation [Bu(2)(CH2=CHCH2)Sn(H2O)(n)](+) and the nucleophilic molecul e Bu(2)(CH2=CHCH2)SnCl. Kinetic studies on R(3)SnMe/Me(2)SnX(2) (X=Cl, NO3) systems in alcoholic solvents (R=Me, Et, n-Pr, i-Pr, n-Bu) suppo rt the assumption that, in dissociating media, redistribution processe s can be promoted by ionic electrophilic Species.