Phototransformation of 4-chloro-2-methylphenol in water: influence of humic substances on the reaction

The phototransformation of 4-chloro-2-methylphenol was studied in distilled , natural or humic substances containing waters. Samples were irradiated un der different conditions: in monochromatic Light at 280 nm, in polychromati c light with lamps emitting within the wavelength ranges 290-350 nm and 300 -450nm and in solar-light. When 4-chloro-2-methylphenol is irradiated in pu re water, dechlorination occurs with a good efficiency (Phi = 0.66). Methyl benzoquinone is the main primary photoproduct in oxygenated solution; methy lhydroquinone and methylhydroxybenzoquinone are produced via secondary phot olysis of methylbenzoquinone, especially in polychromatic light. Humic subs tances enhance significantly the rate of photodegradation of 4-chloro-2-met hylphenol at lambda > 300 nm. The photoinduced reaction yields 3-chloro-tra ns-trans- and 3-chloro-cis-trans-1-methyl-1-one 2,4-hexadienoic acids. The opening of the aromatic ring is explained by the abstraction of the phenoli c hydrogen atom by reactive species produced by excitation of the humic sub stances followed by the reaction of the 4-chloro-2-methylphenoxyl radical w ith HO2./O-2(-.). radicals. When 4-chloro-2-methylphenol is dissolved in na tural waters and exposed to solar-light, dechlorinated and ring opening pro ducts are produced. It is deduced that under environmental conditions 4-chl oro-2-methylphenol can be phototransformed by both direct and photoinduced processes. (C) 1998 Elsevier Science S.A. All rights reserved.