Phototransformation of 4-chloro-2-methylphenoxy acetic acid (MCPA)

MCPA was irradiated in various conditions: in aqueous solution at different wavelengths, on silica in the absence of water, in the presence of TiO2, i n aqueous suspension. In solution a wavelength effect was observed: the for mation of 4-hydroxy-2-methylphenoxyacetic acid is the main pathway at wavel engths shorter than 300 nm, whereas 4-chloro-2-methylphenol is the main pro duct resulting from sunlight irradiation. Direct photolysis on silica and p hotocatalytic transformation mainly lead to the formation of 4-chloro-2-met hylphenol.