Bis(tributyltin) oxide as a wood preservative: Its chemical nature in timber

Tributyltin compounds have been used for many years as wood preservatives. This study has provided, for the first time, an explanation for the previously reported dealkylation and/or volatilization of the tributyltin species in, and from, timber. Thus ¹¹⁹Sn NMR studies have shown that, on impregnation into timber, bis(tributyltin) oxide, (Bu₃Sn)₂O, is rapidly converted to other tributyltin species, Bu₃SnOX, and that these subsequently undergo disproportionation to Bu₄Sn and Bu₂Sn(OX)₂ compounds. We have additionally demonstrated that Bu₄Sn, so produced, is not persistent in timber and is lost by volatilization. Since the rate of disproportionation of the Bu₃SnOX species should be dependent upon the nature of the X group, it should be possible to affect significantly, if not to stop, this process by the use of alternative tributyltin fungicides, e.g. tributyltin methanesulphonate. However, tributyltin fungicides have been used successfully in wood preservation for at least 25 years. Therefore, it must be concluded that, even after disproportionation in timber, in service, sufficient preservative action is retained to prevent decay of wood under the conditions of natural exposure.