A novel rearrangement of substituted phenylhydroxylamines

The rearrangement in different solvents of a number of substituted phenyl hydroxyl amines has been investigated. Kinetically, the N-acyl-N-phenylhydroxyl amines show a great sensitivity to electronic changes in the molecule. Electron withdrawing substituents decrease the rate, and electron donating substituents increase the rate markedly. In all compounds investigated, 0-dichloroacetyl-N-acetyl-N-(4-methylphenyl)hydroxyl amine and 0-di chioroacetyl-N-acetyl-N-phenylhydroxyl amine, two different compounds could be isolated depending on whether or not a base was present. The compound always isolated when no base was present was the kinetically controlled product X or XIII. The second product was the thermodynamically more stable product XI or XIV. The structure of the kinetically controlled product has been shown to be a novel one. Oxygen-18 tracer studies have shown that the rearrangement of O-dichioroacetyl-[raised 18]O-N-acetyl-N-(4-methylphenyl)hydroxyl amine rearranges in neat solution by an ion pair mechanism, whereby the oxygen-18 strategically placed in the di chioroacetyl carbonyl group was mixed exactly half and half with the phenyl hydroxyl amine oxygen. The rearrangement of O-dichioroacetyl-[raised 18]O-N-acetyl-N-phenylhydroxyl amine in chloroform solution occurred by transfer of all the labelled oxygen to the ortho position. This result indicates a change in mechanism from that of the 4-methyl compound. In dichloroacetic acid, O-dichloroacetyl-[raised 18]O-N-acetyl-N-phenylhydroxyl amine rearranged by three different pathways; one intermolecular, one cyclic, and the third by an intramolecular process. Just by changing the ring substituents, two different mechanisms were detected. Also, the change in solvent produced a marked change in mechanism. Therefore, the solvent and electronic effects indicate a very complex and delicate system.