The Addition Reaction of Acyl Radicals to 9,10-Phenanthrenequinone in the Presence of the Corresponding Aldehydes. A Support for the In-Cage Mechanism of the Photochemical Reaction of 9,10-Phenanthrenequinone with Aldehydes

Abstract

Abstract Regarding the photochemical reaction of 9,10-phenanthrenequinone, 1, with acetaldehyde, 2, two reaction mechanisms have been proposed: the in-cage mechanism (Eq. 1) and the radical chain mechanism involving an acyl radical as the chain carrier (Eq. 2). For the establishment of the true reaction mechanism, the thermal addition reaction of an acyl radical to 9,10-phenanthrenequinone was investigated. The products in the thermal reaction were the dimeric isomers of the aryloxyl radical, 6, i.e., 4 and 5, which were quite different from the product of the photochemical reaction of 9,10-phenanthrenequinone with acetaldehyde, i.e., 9-acetoxy-10-hydroxyphenan-threne, 3. These results, as well as the estimation of the quantum efficiency for the photochemical reaction, exclude the radical chain mechanism (Eq. 2) and strongly support the in-cage mechanism (Eq. 1) for the photochemical reaction of 9,10-phenanthrenequinone with aldehyde.