Photoproduction of hydroxyl radicals from Fe(III)-hydroxy complex: a quantitative assessment

Photolysis of aqueous solutions of ferric perchlorate in the presence of me thanol, benzene and 2-deoxy-D-ribose at low pH has been investigated using sunlight and UV light in order to quantitatively assess the involvement of hydroxyl radicals ((OH)-O-.) in the photolysis of Fe(III)-hydroxy complexes . Time-dependent formation of formaldehyde, phenol and thiobarbituric acid- reactive substance (TBA-RS) was observed in the presence of methanol, benze ne and 2-deoxy-D-ribose, respectively. The observed quantum yields of forma ldehyde, phenol and TBA-RS are 0.025,0.0098 and 0.0038, respectively, using UV light. A slightly lower quantum yields are obtained with sunlight owing to its lower intensity. The mechanistic aspects of these reactions are pro posed based on the formation of (OH)-O-. from the photo-excited Fe(OH)(2+) complex and their subsequent reactions with methanol, benzene and 2-deoxy-D -ribose. The quantum yield of (OH)-O-. is calculated from the observed quan tum yields of formaldehyde, phenol and TBA-RS based on the reported percent age contribution of (OH)-O-. in the formation of these products using radia tion chemical techniques from the respective reactions. The calculated quan tum yields of (OH)-O-. were in the range 0.018-0.025 and 0.014-0.018 with U V light and sunlight, respectively. The results obtained with the photolyti c studies have been compared with those from radiation chemical studies. (C ) 2001 Elsevier Science B.V. All rights reserved.