To safely purify carbonyl chloride without liquefaction and highly profitably phosgenate by purifying contaminated carbon monoxide by adsorption in a solvent and using the obtained carbonyl chloride solution.

This method of phosgenation comprises purifying chlorine and contaminated carbon monoxide produced from contaminated carbon monoxide by adsorption in a solvent (for example, ortho-dichlorobenzene, dichlorobenzene isomer mixture, monochlorobenzene or toluene) and subsequently using the obtained purified carbonyl chloride solution for the phosgenation. For example, the phosgenation is carried out by purifying fresh contaminated carbonyl chloride by adsorption in a solvent in an adsorption column, using the adsorption column for recovering the carbonyl chloride from an exhaust gas produced by the phosgenation reaction, and subsequently feeding the purified fresh carbonyl chloride solution to the phosgenation reaction.