Mechanism of 2-iodophenol photolysis in aqueous solution

Abstract

The photolysis of 2-iodophenol (2-IPhOH) was investigated by means of laser flash photolysis and product studies. Two major heterolytic dehalogenation pathways could be evidenced upon irradiation of anionic 2-IPhO⁻: ring contraction leading to cyclopentadienic acids via a Wolff rearrangement (ϕ_a = 0.11 ± 0.02), and α-ketocarbene formation (ϕ_c = 0.03 ± 0.01) yielding products characteristic for triplet carbene reactivity. In contrast, the irradiation of neutral 2-IPhOH leads mainly to homolytic cleavage of the carbon-halogen bond (ϕ = 0.08 ± 0.01) with subsequent formation of biphenyls in deoxygenated solution. This specific reaction, which is not observed with other halogenated phenols, is explained by the low energy of the C–I bond. The relative efficiencies of the heterolytic pathways in the halogenophenol series are discussed in terms of the multiplicity of the excited states involved and of the internal heavy atom effect.