SOLVENT-SENSITIVE RADIOCHEMICAL REACTIONS .2. FRIES REARRANGEMENT OF ARYL ESTERS AND ARYL AMIDES

In a series of screening experiments p‐tolyl acetate (1a), phenyl benzoate (1b), p‐tolyl benzoate (1c), acetanilide (1d), and 2‐naphthyl acetate (5) have been subjected to γ‐radiolysis in aromatic and saturated hydrocarbon solutions. Qualitatively, the products formed correspond to those observed also with the respective photo‐FRIES reactions, i.e., hydroxy‐ and amino‐aryl ketones due to rearrangements, and products due to homolytic fission into aryloxy and aniline radicals, respectively, were produced. The relatively high G values of conversion in dilute solutions indicate that energy transfer from the solvent is operative. E.g., 0,1 M p‐tolyl acetate (1a) in benzene has a G value of over 0.3 for ortho‐rearrangement to 2a, and of 0.55 for cresol (4a) formation. Kinetic evidence points to different energy requirements of the ortho‐rearrangement and the phenol formation, and to more than one excited state of benzene acting as energy donor. The ratio of the observed rate constants of the energy transfer to self‐quenching in benzene is about 80 1 · mole−1 for the ortho‐rearrangement to 2a. The over‐all reaction is strongly quenched upon addition of p‐terphenyl. A comparison of the quantitative data obtained in this work with available published data reveals differences between benzene‐sensitized runs with γ radiation and photochemical experiments. Thus, the ratios of ortho vs. para and amphi rearrangement, and of homolytic fission vs. rearrangements are higher in the solvent‐sensitized radiolyses. Copyright © 1968 Verlag GmbH & Co. KGaA, Weinheim