Irradiation at wavelengths above 360 nm of a suspension of Dowex 2-X8 anion exchange resin (Cl¯ form) in
chloroform causes the decomposition of chloroform with formation of COCl2 and HCl. The presence of CCl4 as the most
important secondary product, along with the lack of any photodecomposition in CDCl3, the absence of photodecomposition
when O2 is excluded, and the lack of any secondary products related to CHCl2 radicals rule out a mechanism based on
sensitized C–Cl dissociation, as occurs in the direct UV photolysis of chloroform. A mechanism is proposed in which an
initial photoreaction produces COCl2 and HCl at a slow rate, along with CCl4. A second photoreaction causes Cl dissociation
from CCl4, greatly increasing the net rate of COCl2 and HCl formation after a sufficient concentration of CCl4 is attained.
Keywords: Chloroform, photocatalysis, photodecomposition, Dowex, anion exchange resin, phosgene.
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