γ-Radiolyse von 4-Nitrophenol in Wässriger HBr-Lösung

Abstract

In the γ-radiolysis of aqueous solutions of 4-nitrophenol, 4-nitropyrocatechol ( G= 2·95) and 4-aminophenol ( G = 1·1) are formed. The addition of HBr in concentrations up to 0·5 mol dm −3 HBr has a protective effect. The G-value for the disappearance of 4-nitrophenol is strongly reduced (Fig. 2). At 0·5 mol dm −3 HBr G(4-nitro-pyrocatechol) is lowered to 0·1, and G(4-aminophenol) to 0·15. This effect is explained by assuming that the OH radicals react with Br − giving Br . atoms which further react to Br 2 −. An explanation of this protective effect is based on the assumption that Br . or Br 2 − may either dehydrogenate the 4-nitrophenol-H atom adduct, or that, alternatively, the 4-nitrophenol-Br atom adduct may react with the H atom adduct resulting in the formation of HBr and two molecules of 4-nitrophenol. With HBr concentrations above 0·5 mol dm −3 the G value for the disappearance of the substrate increases again owing to loss through bromination. In a 9 mol dm −3 HBr solution 2-bromo-4-nitrophenol ( G = 4,9) and 4-aminophenol ( G = 1·37) are formed. Some possible mechanisms of bromination are discussed. A satisfactory material balance was obtained for all HBr concentrations investigated.