No abstract

A photochemical study of the dechlorination of 4-chlorophenol (I) in 2-and N2-saturated aqueous solutions under 193nm radiation was carried out using an ArF* excimer laser. Higher (1.07χ 10~2Μ) and lower (4.49x lO^M) initial concentrations were studied. At the higher substrate concentration, the quantum yields for the disappearance of 1 (Φ « 0.30) and for the generation of chloride ions (Φ « 0.25) were independent of the dissolved gas (O2-or N2-saturated). It is also of interest that a significant amount of 4-chlorocatechol was generated at this higher substrate concentration. Finding 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 (Φ « 0.55) and for the initial generation of chloride ions (Φ « 0.45) were both larger than the quantum yields obtained with the higher substrate concentration. It was found beyond the initial radiation times (n > 3 χ 10 20 photons absorbed by the solutions), that the dechlorination of I in the C^-saturated solutions was slightly more efficient than the N2-saturated solutions, whereas initially they were approximately the same for both the (V and ^-saturated solutions. Different products from the dechlorination of I were observed depending on the initial substrate concentration. At the higher initial substrate concentration, the major products from the dechlorination of I were oligomers. At the lower initial substrate concentration, hydroquinone was the major product in O2-saturated solutions, but oligomers were still the major product when these solutions were No-saturated. Explanations for the observations are given and are consistent with these findings.