Oxidative photocyclisation of 2-biphenylol in dilute aqueous solution

Abstract

Formation of 2-hydroxydibenzofuran (2-HODBF) was observed when an air-saturated solution of 2-biphenylol (OPP - o.phenylphenol) was irradiated at 296, 313 or 334 nm (2<pH<11). The isolated product was identified by 300 MHz 1H NMR and MS spectra. The quantum yield of OPP conversion was higher with the anionic form ( Φ=0.06±0.01 at pH=10.5) than with the molecular form ( Φ=0.015±0.005 for 5.5≤pH≤7). On the contrary, chemical yield for 2-HODBF was higher in neutral solution (about 0.15 for conversion extent equal to 0.2–0.7) than in basic solution (0.1 at pH=10.5 at 20% conversion). The intermediate formation of phenylbenzoquinone (PBQ) was pointed out by HPLC analysis. OPP is commonly used for fruit preservation and the biological properties of 2-HODBF should be controlled. ▪ Among the phenolic compounds currently investigated in our Research Group for many years, 2-biphenylol, more commonly named o.phenylphenol (OPP), has interesting fundamental properties like a dual fluorescence emission and prompts ecotoxicological concern.