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Time-resolved Pulse Radiolysis Studies on the Free Radicals and Hydrated Electrons with Halogenated Phenols

Carbon-centered radicals (reducing and non-reducing) have been shown to react very fast with halogenated phenols, resulting in a transient adduct radical with distinct optical absorptions in the UV. These adduct radicals exist in equilibrium with the initial reaction partners. Earlier studies had failed to provide any evidence for this intermediate. The decay of the transient radical adduct is accelerated by protons and proton donors such as the halogenated phenol itself. Acceleration of the decay also occurs with increasing OH– concentration, leaving an optimal pH window of 6 - 8 for direct observation of the transient. Dehalogenation appears to be prevented whenever the transient adduct is protonated. Proton acceptors, on the other hand, appear to facilitate dehalogenation. With certain radicals, such as a-hydroxyalkyl or •CO2– radicals, chain processes can be initiated.

halogenated phenols; dehalogenation; radicals; hydrated electron; protonation; reduction; rate constants; pulse radiolysis

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