Magnesium octaethylporphyrin (MgOEP) in foils of polystyrene was oxygenated quantitatively by visible light and oxygen to yield the corresponding formylbilinate. In poly[1‐phenylethyleneco‐1‐(1‐imidazolyl)ethylene] (95:5 or 78:22 mol %) the quantitative formation of MgOEP cation radical was observed. The photooxygenation was fully suppressed in this copolymer. This is explained with a physical quenching of singlet oxygen by imidazole. — Oxidation of MgOEP with benzoyl peroxide in the presence of imidazole yields either octaethyl‐5‐imidazolylporphyrin or 10‐benzoyloxy‐octaethyl‐5,15‐diimidazolylporphyrin and other highly substituted porphyrins. The latter produces only one absorption band (λmax ≈︁ 560 nm) in the visible range and yields isoporphyrins (λmax ≈︁ 900 nm) in a reversible reaction with an excess of benzoyl peroxide. The same reaction with the imidazole‐containing copolymer leads to a covalent binding of MgOEP. The reversible formation of an isoporphyrin is observed with molecular oxygen.
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Fuhrhop et al. (1982) studied this question.
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