Direct synthesis and stabilities of unsymmetrical triorganotin compounds
The syntheses of a variety of triorganotin bromides of general formula RBu2SnBr were attempted by reaction of dibutyltin dibromide, an alkyl bromide (RBr), tin and tetrabutylammonium bromide. With the exception of tributyltin bromide which was prepared as a fairly pure compound where R was a butyl group, all other products were mixtures of organotin bromides. In order to identify the compounds of the type RBu2SnBr in these products, tetraorganotins of general formula, RBu2PeSn, were prepared as GLC standards by a sequence of selective dephenylation and alkylation starting from dibutyldiphenyltin. The solubility of the organotin bromide products in aqueous sodium chloride solution was investigated by atomic absorption spectroscopy. In general, solubility was enhanced by functional groups such as ethers in the sidechain R due to hydrogen bonding, while it was lowered by the presence of longer chain organic groups. The stability of organotin bromide mixtures containing propyl, isobutyl and 3-butenyl groups was assessed in sterile, artificial seawater in darkness for periods of approximately one year. No decomposition was detected under these conditions. Decomposition was effected by placing organotin bromides in aqueous sodium hydroxide solution with UV irradiation by a medium pressure mercury vapour lamp. It was found that organic groups such as 2-butoxyethyl showed significant decomposition while those with functional groups situated well away from the tin centre or no functional groups showed no appreciable tin-carbon bond cleavage. Ozone reacted with the organotin bromides at tin-carbon bonds, in general giving tetraorganodistannoxane products, and also at functional groups, for example a sulphide was converted to the corresponding sulphoxide and sulphone. The syntheses of a range of symmetrical triorganotin bromides were also attempted with varying results.