Aromatic Ring Opening in the Presence of Oxygen in Irradiated Solutions

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WHEN aqueous solutions of benzene are irradiated in vacuo with α-rays or neutrons which produce oxygen, a dialdehyde, identified as mucondialdehyde, is produced1. The same product was found also when solutions of benzene containing oxygen were irradiated with X-rays2. Thus ring opening appeared to be connected with the presence of oxygen, rather than with high radical concentrations and multiple reactions on the same benzene ring. The identification of the product as mucondialdehyde was confirmed3. Material balance cannot be obtained4 unless the formation of oxidation products other than phenol is assumed. The interesting possibility arises that aromatic ring opening in the presence of oxygen may occur as the result of a single primary radical reaction step and that mucondialdehyde is a primary product, being formed in direct competition with the formation of phenol. Analytical methods were used which enabled us to determine phenol, catechol and quinol1,2 in the presence of hydrogen peroxide5 and of mucondialdehyde, o- and p-quinone. These last three were determined after condensation with p-NO2-phenylhydrazine in 2 N sulphuric acid, extraction into carbon tetrachloride, re-extraction into 2 N sodium hydroxide and spectrophotometric measurement in 0.8 N sodium hydrate at 390 mµ (mucondialdehyde); 510 mµ (max.) and 400 mµ (min.) (o-quinone); and 475 mµ (p-quinone). Details of the analytical methods developed will be published separately.

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LOEFF, I., STEIN, G. Aromatic Ring Opening in the Presence of Oxygen in Irradiated Solutions. Nature 184, 901 (1959) doi:10.1038/184901a0

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