The same reactor as used in Preparation Example 1 was charged with 12.1 g (0.5 mole) of magnesium, 102.4 g (0.5 mole) of n-dodecyl chloride and 200 g of tetrahydrofuran, and they were reacted in a stream of nitrogen. To the resulting n-dodecyl magnesium chloride solution was added dropwise a solution of 42.3 g (0.15 mole) of mono-n-butyltin trichloride in 200 ml of xylene with stirring at room temperature over the course of 30 minutes. Then, the reaction mixture was reacted for 3 hours at the refluxing temperature, and then subjected to a hydrolysis treatment to obtain 99.8 g of n-butyl tri-n-dodecyltin having a purity of 98.7% as an oily substance.
