PHOTOCHEMISTRY AND ENVIRONMENT .4. PHOTOCHEMICAL BEHAVIOR OF MONOCHLOROPHENOLS IN DILUTE AQUEOUS-SOLUTION

The photochemical behavior of chlorophenols is different than that of non-halogenated phenols. In the former, the 1st step is a C-Cl bond scission, which is not influenced by O2. Cl is converted into HCl. For monochlorophenols, the position of the Cl on the ring strongly influences the transformation. In the molecular form, 2-chlorophenol is converted into pyrocatechol. In the anionic form however, it is reduced in a cyclopentadienic acid which dimerizes according to a Diels-Alder reaction. The irradiation of 3-chlorophenol leads to resorcinol whatever the pH. This would appear to suggest a photohydrolysis mechanism. With 4-chlorophenol, the photochemical conversion is not so specific. Hydroquinone is formed (mainly in aerated solution), along with polyphenolic oligomers. A radical mechanism is proposed.