A Laboratory Exercise for Photochemistry and Photobiology: Production of Hydrogen Peroxide

Understanding the Facile Photooxidation of Ru(bpy)32+ in Strongly Acidic Aqueous Solution Containing Dissolved Oxygen

“…The facile nature of this process below pH 4.5 ( k = 8.6 × 10 5 M -1 s -1 ) has been reported previously by others . These results strongly suggest that H 2 O 2 is formed in the present study through eq 20 and the pathway of eq 18 is unlikely although such a mechanism has been proposed for H 2 O 2 formation in the riboflavin system . It is noteworthy that the HO 2 • intermediate does not degrade the ruthenium complex to any measurable extent; instead, it stays around long enough until it finds a partner for eq 20.…”

“…33 These results strongly suggest that H 2 O 2 is formed in the present study through eq 20 and the pathway of eq 18 is unlikely although such a mechanism has been proposed for H 2 O 2 formation in the riboflavin system. 34 It is noteworthy that the HO 2 • intermediate does not degrade the ruthenium complex to any measurable extent; 12 instead, it stays around long enough until it finds a partner for eq 20. Disproportionation reactions are a useful means of circumventing multielectron-transfer processes as would otherwise be necessary for H 2 O 2 formation.…”

“…Disproportionation reactions are a useful means of circumventing multielectron-transfer processes as would otherwise be necessary for H 2 O 2 formation. 2f, 34 The remaining question is, what leads to facile formation of HO 2 • in high acid? First, O 2 •must be formed in preference to O 2 ( 1 ∆ g ) whereas calculations of the free energies at pH 7 suggest otherwise.…”

“…It is noteworthy that the HO 2 • intermediate does not degrade the ruthenium complex to any measurable extent; instead, it stays around long enough until it finds a partner for eq 20. Disproportionation reactions are a useful means of circumventing multielectron-transfer processes as would otherwise be necessary for H 2 O 2 formation. 2f, …”