PHOTOLYTIC DECHLORINATION OF 4-CHLOROPHENOL USING AN ARF-ASTERISK EXCIMER-LASER

A photochemical study of the dechlorination of 4-chlorophenol (I) in O -2- and N-2-saturated aqueous solutions under 193 nm radiation was car ried out using an ArF excimer laser. Higher (1.07 x 10(-2)M) and lowe r (4.49 x 10(-4)M) initial concentrations were studied. At the higher substrate concentration, the quantum yields for the disappearance of I (phi approximate to 0.30) and for the generation of chloride ions (ph i approximate to 0.25) were independent of the dissolved gas (O-2- or N-2-saturated). It is also of interest that a significant amount of 4- chlorocatechol was generated at this higher substrate concentration. F inding 4-chlorocatechol is a new result for the direct photolysis of I in the absence of added H2O2. For the lower substrate concentration, the average quantum yields for the initial disappearance of I (phi app roximate to 0.55) and for the initial generation of chloride ions (phi approximate to 0.45) were both larger than the quantum yields obtaine d with the higher substrate concentration. It was found beyond the ini tial radiation times (n > 3 x 10(20) photons absorbed by the solutions ), that the dechlorination of I in the O-2-saturated solutions was sli ghtly more efficient than the N-2-saturated solutions, whereas initial ly they were approximately the same for both the O-2- and N-2-saturate d solutions. Different products from the dechlorination of I were obse rved depending on the initial substrate concentration. At the higher i nitial substrate concentration, the major products from the dechlorina tion of I were oligomers. At the lower initial substrate concentration , hydroquinone was the major product in O-2-saturated solutions, but o ligomers were still the major product when these solutions were N-2-sa turated. Explanations for the observations are given and are consisten t with these findings.