DEGRADATION OF MONOCHLOROPHENOLS BY GAMMA-IRRADIATION

The degradation of aqueous 5 x 10(-4) mol dm(-3) 2-, 3- and 4-chloroph enol (2-ClP, 3-ClP, 4-ClP) under reducing and oxidizing conditions has been studied by steady state gamma-radiolysis. The reaction with e(aq )(-) leads to reductive dechlorination which equals the degradation of the chlorophenols. Solely phenol is the major organic compound formed . In N2O saturated solutions the dehalogenation is much less effective . In the case of 4-ClP 40% and in that of 2- and 3-ClP only 20% of the decomposed substrates are resulting in chlorine free organic compound s. From these pyrocatechol for 2-ClP and hydroquinone for 4-ClP could be identified in minor amounts. Main products are the hydroxylated sub strates originating from the primarily formed ortho-and para OH-adduct s. These are for 2-ClP: chlorohydroquinone and 3-chlorocatechol, for 3 -ClP: chlorohydroquinone, 3- and 4-chlorocatechol and for 4-ClP: 4-chl orocatechol. In the presence of oxygen, where the OH-adducts are conve rted into peroxyl radicals, the degradation yield of the substrates co rresponds to that of OH radicals up to doses of 0.5 kGy. The dechlorin ation process in this dose range is 50% for 4-ClP, and 33% for 2- and 3-ClP. The position of chlorine on the aromatic ring strongly influenc es the dehalogenation and degradation process. A pronounced dependency of the dose/yield curves on the oxygen concentration was observed. Th is indicates that For an efficient degradation process of chlorophenol s oxygen supply is necessary during irradiation. (C) 1997 Elsevier Sci ence Ltd. All rights reserved.