Sensitized dissociation of peroxides and peresters in the presence of thiopyrylium salts

The photosensitized dissociation of peroxides and peresters in the presence of thiopyrylium salts has been studied. The quenching rate constants of the triplet state of the salts under consideration were (3–5) × 107 l mol−1 s−1 with benzoyl peroxide (BPO) and (3–11) × 107 l mol−1 s−1 with 3,3′,4,4′-tetra(tert-butylperoxycarbonyl)benzophenone (BTTB) in acetonitrile, the thiopyranyl radical is formed in the presence of BTTB. The mechanism of dissociation photosensitization of these peroxides by pyrylium and thiopyrylium salts is discussed and interpreted in terms of an energy transfer through an electron-exchange mechanism in the case of BTTB and classical energy transfer when BPO is used.