PURPOSE: To prepare the titled substance in high concentration, by adding an alcohol and an inert organic solvent dropwise to vanadium oxytrichloride liquid, reacting the components with each other passing an inert gas slowly through the reaction mixture, and after the completion of the reaction, introducing a large amount of the inert gas into the liquid to cause the bumping of the liquid.

CONSTITUTION: A mixture of sufficiently dehydrated alcohol (e.g. ethanol) and sufficiently dehydrated inert organic solvent (e.g. hexane, CCl4, benzene, etc.) is added dropwise to vanadium oxytrichloride liquid, and the components are made to react with each other by passing an inert gas slowly (to an extent to cause the convection of the reaction liquid) through the liquid. After the completion of the reaction, a large amount of the inert gas is introduced into the liquid to cause the bumping of the liquid. The generated hydrochloric acid gas is removed from the system by this method to obtain the objective substance.

EFFECT: Since the necessary amount of the inert organic solvent is as low as 0.5W 1pt.vol per 1pt. of the alcohol, the dehydration can be carried out easily; and since the absolute amount of the residual water is low, the hydrolysis of the product can be suppressed to an extremely low level.

USE: Polymerization catalyst for olefins.