Photolysis and thermolysis of phenyl azide in acetic acid. Trapping of 1-azacyclohepta-1,2,4,6-tetraene and nucleophilic aromatic substitution

Abstract

Photolysis and thermolysis of phenyl azide in acetic acid yielded ¹H-azepin-2(3H)-one (4), 2-methylbenzoxazole (15), 2- and 4-acetamidophenyl acetates (16) and (12), 2- and 4-acetamidophenols (14) and (13), acetanilide, and azobenzene. Addition of ethanol to the system caused a linear decrease in the yield of (4) and a more remarkable decrease in total yield for the para-products than that for the ortho-products to give 2- and 4-acetamidophenyl ethyl ethers (9) and (8). Photolysis of the azide in ethanol in the presence of phenol afforded 2-phenoxy-3H-azepine (5) and aniline, but no 2- and 4-phenetidines. The yield of compounds (4) and (12)–(16) was independent of the presence of penta-1,3-diene (0.01 M), and somewhat decreased by an addition of bromobenzene. The rate of decomposition of azide in acetic acid was not accelerated as compared with that in 1,4-dioxan, and the activation parameters varied little in the two solvents. The results suggest that 1-azacyclohepta-1,2,4,6-tetraene (1) formed via singles phenylnitrene or via singles excited phenyl azide is trapped by acetic acid or phenol to give (4) or (5), and that a resonance-stabilized ion (3) neighbouring acetate anion is formed by an attack of the singlet nitrene on acetic acid to give aromatic nucleophilic substitution.