PURPOSE: To effectively obtain the subject compound by a novel process wherein a specific raw compound is reacted with water in the presence of a Lewis acid and a chlorocarbon solvent.

CONSTITUTION: A compound of formula I (wherein L1 and L2 are each a leaving group; and Ar is an aromatic or heteroaromatic group), [preferably a compound having Cl as L1 and L2 such as 2-chloro-6-(trichloromethyl)pyridine or the like] is reacted with water in the presence of a Lewis acid (preferably anhydrous ferric chloride) and a chlorocarbon solvent including at least two chlorine atoms (preferably 1,2-dichloroethane) to obtain the objective compound of formula II. The Lewis acid is preferably employed in a molar ratio thereof to the compound of formula I of 0.1 or less, and the compound of formula I is preferably employed in an equimolar amount to water. This reaction is preferably carried out by mixing the compound of formula I with the Lewis acid in the chlorocarbon solvent under reflux and subsequently adding water for hours to the reaction mixture under reflux.