Effect of Electron Scavengers on the Chain Reaction of Sulfo-Group Substitution for Bromine in 1-Bromo-2-hydroxynaphthalene Photosensitized with Tris(2,2′-bipyridyl)ruthenium(II)

Abstract

The effect of electron scavengers (carbon tetrachloride, chloroform, and chloranil) on the chain radical-ion reaction of sulfo-group substitution for bromine in 1-bromo-2-hydroxynaphthalene photosensitized with a tris(2,2′-bipyridyl)ruthenium(II) complex was studied in an aqueous solution of sodium sulfite. It was found that “ sacrificial” electron scavengers enhanced the quantum yield of the photosensitized substitution reaction. Using the flash photolysis technique, it was shown that the electron scavengers reacted with the ruthenium(I) complex formed as a result of dissociation of a radical-ion pair in the initiation step. The rates constants for the reaction of chloroform, carbon tetrachloride, and chloranil with the ruthenium(I) complex are 1.5 × 104, 1.2 × 107, and 1.5 × 109 dm3 mol−1 s−1, respectively. The chain length of the substitution reaction in aqueous solution in the presence of carbon tetrachloride is 220 ± 20.