Tributyltin (TBT) compounds are organic derivatives of tetravalent tin. They are characterized by the presence of covalent bonds between carbon atoms and a tin atom and have the general formula (n-C4H9)3Sn-X (where X isan anion). The purity of commercial tributyltin oxide (TBTO) is generally above 96%; the principal impurities are dibutyltin derivatives and, to a lesser extent, tetrabutyltin and other trialkyltin compounds. TBTO is a colourless liquid with a characteristic odour and a relative density of 1.17 to 1.18.