Photolytical Degradation Products of Pentachlorophenol in Aqueous Solution and Organic Solvent
Maria Pythias B. Espino
Institute of Chemistry, College of Science
University of the Philippines, Diliman, Quezon City, Philippines
*corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.
ABSTRACT
The photolytical degradation of pentachlorophenol in water, ethyl alcohol, and ethyl acetate was investigated to provide an understanding of its persistence and the nature of its degradation products. The photodegradation of pentachlorophenol in water was found to be most efficient resulting in complete dechlorination and production of acetic acid, oxalic acid, and chloride ion as final products. The chlorinated degradation products of pentachlorophenol in water (2,3,4,6-tetrachlorophenol; 2,3,5,6-tetrachlorophenol; 2,4,5-trichlorophenol; 2,3,6-trichlorophenol; 2,6-dichlorophenol; dichlorobenzenediol), ethyl alcohol (2,4,6-trichlorophenol; 2,3,6-trichlorophenol; 2,5-dichlorophenol; 2,3-dichlorophenol), and ethyl acetate (2,3,6-trichlorophenol; 2,4-dichlorophenol) were identified. A theoretical determination of the degradation products using density functional theory computations of atomic charge distribution that correlated with the experimental findings of this study is proposed.
INTRODUCTION
The use of ultraviolet (UV) radiation alone or in combination with oxidizing agents and catalysts to degrade chlorophenols has been reported in literature. In general, the addition of catalysts or oxidants enhances the photodegradation process. The efficacy of sulphonated phthalocyanine complexes as catalysts and sensitizers to photodegrade chlorophenols was established by Ozoemena et al. (2001). Pandiyan et al. (2002), Rao et al. (2003), and Kim et al. (2007) used titanium dioxide as catalyst in the photooxidation of chlorophenols. Pandiyan et al. (2002) found that in the presence of titanium dioxide, polychlorinated phenols are more difficult to dechlorinate than monochlorinated phenols. Antonaraki et al. (2002) studied the photolysis of chlorophenols using UV and visible light in combination with hydrogen peroxide or a polyoxometallate catalyst, and related the decomposition rate with the position and number of chlorine atoms in the phenolic ring. They found that a chlorine atom in the meta position accelarates the photodecomposition process. The photochemical decomposition of chlorophenols using UV light and various oxidants such as hydrogen peroxide, ozone or Fenton's reagent involves free radical formation (Benitez et al. 2000; Ghaly et al. 2001).
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