On the other hand, we reported the C-H oxygenation reaction of methane (CH4) through the light activation of chlorine dioxide radical (ClO2 • ). In these oxidation reactions, the chlorine radical (Cl • ) generated from the ClO2 • gas upon light activation cleaved the C-H bond. The C-H bond dissociation energy of CH4 is 104 kcal mol -1 , which was higher than that of CHCl3 (95.7 kcal mol -1 ). These results prompted us to investigate the generation of COCl2 through the oxygenation of CHCl3 with ClO2 • under visible-light irradiation, because ClO2 • has a strong absorption band in the visible-light region.