JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 9, zyxwvu 187-190 (1996) DEPROTONATION OF ORGANIC RADICAL CATIONS. CHEMICAL EVIDENCE FOR PROTON TRANSFER BETWEEN AND SUPEROXIDE RADICAL ANIONS 9,lO-DIHYDROANTHRACENCERADICAL CATIONS RYOICHI AKABA," MITSURU IWASAKI, AND TSUYOSHI MATSUMURA zyx Department zyxwvutsr of Chemistry, Gloima College of Technology, Toriha-machi, Maebashi, Gunma 371, Japan MASAKI KAMATA Department of Chemistry, Faculty of Education, Niigata University, Ikarashi, Niigata 950-21, Japan AND HIROKI ITOH Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, Koshirakawa, Yamagata 990, Japan Photoinduced electron-transfer oxygenation of 9,lO-dihydroanthracene was carried out with zyx 2,4,6- triphenylpyrylium tetrafluoroborate (TPP) and 9,lO-dicyanoanthracene (DCA) as sensitizers. The time course of the oxygenation products was studied, and the results showed that anthrone was formed zyx as a primary product in the DCA-sensitized oxygenation whereas in the TPP-sensitized oxygenation anthracene was the primary, major product which under the reaction conditions was converted to anthrone. A mechanism involving proton transfer in the radical ion pair consisting of 9,10-dihydronathracene radical cation and superoxide radical anion, which cannot occur in the TPP-sensitized oxygenation, was proposed to rationalize the difference in the product distribution in the two sensitized oxygenation reactions. 1. INTRODUCTION We have recently shown that 2,4,6-triphenylpyrylium (TPP) salt-sensitized oxygenation of aralkyl hydrocar- bons such as triphenylmethane and diphenylmethane gave the corresponding carbonyl compounds in modest to high yields, and proposed that the photooxygenation proceeded through deprotonation of their radical cations generated by the photoinduced electron transfer (PET). ' Since it is well known that the superoxide radical anions (0, -') cannot be formed under the photooxygenation conditions with TPP,* comparative studies between 9,lO-dicyanoanthracene (DCA)- and TPP-sensitized oxygenation of organic compounds may give an insight into the reactivity of radical ion pairs consisting of the organic radical cations and O2 -.. Although the participa- tion of 02-' has been invoked to explain the products * Author zyxwvutsrqp for correspondence. and their distribution in the DCA-sensitized oxygena- tion, little evidence supporting the direct involvement of 0, -' in the initially formed radical ion pairs has been reported. In many cases, products and their distribution ascribed to the reactions of radical cations with 02-' in the DCA-sensitized oxygenation may also be explained in terms of the reactions of radical cations and/or radical species derived thereof with molecular oxygen. (yp /// CN Formula 1 CCC 0894- 32301961030187 -04 zyxwvuts 0 1996 by John Wiley & Sons, Ltd. Received 23 August I995 Revised 20 October 1995