The electrochemical preparation and kinetic and product studies of acylated quinol and quinol ether imines. In search of the hydrolysis products of the "ultimate" carcinogen of N-Acetyl-2-aminofluorene

Abstract

The N-acetyl and benzoyl derivatives of 4-methoxy-4-phenyl-2,5-cyclohexadienonime ine and the N-benzoyl derivative of 4-hydroxy-4-phenyl-2,5-cyclohexadienoimnei ne (la-c) have been prepared via anodic oxidation of the corresponding amide of 4-aminobiphenyl in either methanol or water/ acetonitrile, respectively. The products and the kinetics of the acidic and basic hydrolyses of these compounds were studied and the results compared with other N-acylquinol imine derivatives, including N-acetyl-4-hydroxy-4-phenyl-2,5-cyclohexadienoinmei ne (Id),g enerated by solvolytic routes. The chemistry of these compounds was dependent upon the pH and the substituents on the quinol imine derivative. The major reaction pathways were hydrolysis of the imine linkage to afford the respective dienone and phenyl migration to afford the amides of 2-hydroxy- or 2-methoxy-5-aminobiphenyl. The reactivity of the quinol imine derivatives follows the order: 4-hydroxyl more reactive than 4-methoxyl compounds and N-acetyl more reactive than N-benzoyl derivatives. The higher reactivity for the former compounds is attributed to the greater electron-donating ability of the 4-hydroxyl versus the 4-methoxyl group. The higher reactivity of the N-acetyl relative to the N-benzoyl derivatives is attributed to the ca. 30-fold increase in basicity of the N-acetyl functionality. The additive effect of the 4-hydroxyl and N-acetyl functionality on the basic quinol imine moiety makes compounds having both of the groups difficult to isolate in aqueous media. This serves as a limitation for the preparation of the quinol imine derivative of N-acetyl-2-aminofluorene via the anodic oxidation methods reported herein.