The Photochemical Reaction of Pentachlorophenol

A herbicide, sodium pentachlorophenoxide (Na-PCP), used in Japan, is easily decomposed with sunlight after its application in the rice field. The photochemical reaction of Na-PCP in an aqueous solution on exposure to sunlight afforded numerous products which were mainly accompanied with chloranilic acid and a yellow compound (I). The chemical structure of the yellow compound I was established as being 3, 4, 5-trichloro-6-(2′-hydroxy-3′, 4′, 5′, 6′-tetrachlorophenoxy)-o-benzoquinone by chemical and spectroscopic evidences.

Minor decomposition products of sodium pentachlorophenoxide (Na-PCP) in an aqueous solution by sunlight have been isolated. Chemical structures of them are described, and infrared and ultraviolet spectra are presented in support of these stractures. These illustrate a new type of oxidative reaction of phenols.