Abstract: A process is provided for producing oxalyl chloride by first photochemically chlorinating ethylene carbonate to form tetrachloroethylene carbonate and hydrogen chloride and then decomposing the tetrachloroethylene carbonate to oxalyl chloride and phosgene. The chlorination reaction is performed in a reaction vessel having an illuminated side arm conduit of narrow cross-sectional area. Chlorine is introduced at the base of the conduit and together with the hydrogen chloride evolved in the reaction continuously circulates the ethylene carbonate-chlorine reaction mixture through the narrow reaction zone within the conduit. The temperature of the ethylene carbonate-chlorine reaction mixture is controlled in the range of 70.degree. to 100.degree. C., preferably in the range of 79.degree. to 81.degree. C. The tetrachloroethylene carbonate is decomposed by heating same with a catalytic amount of a tertiary amine or amide.