The Photochemistry of Carbon-Nitrogen Multiple Bonds in Aqueous Solution. 1. Aromatic Oximes, Oxime Ethers, and Nitriles

Article abstract of DOI:10.1021/jo00385a030

The photochemistry of typical C=N and C<*>N compounds was investigated in aqueous solution from pH 2 to 12.It was found that both aromatic aldoximes and ketoximes readily undergo photohydrolysis via their lowest singlet states, with Φ values generally in the 0.01 - 0.15 range.Both the neutral oxime and oximate anion undergo photohydrolysis, with the former reaction being acid-catalyzed.For both forms of the oxime, evidence was obtained for oxazirane intermediates.For the neutral form, there is also a less efficient hydrolysis mechanism, which is important at pH 8 - 10 and involves the uncatalyzed addition of water to the C=N bond.A similar uncatalyzed hydrolysis mechanism is found for the oxime ethers at all pH's.The unsubstituted oxime ethers photohydrolyze only by the pH independent route with a photoefficiency (Φ = 0.01-0,025) that is practically identical with that of the parent oximes in the Ph 8 - 10 range.Attempts were made to photohydrolyze analogously substituted benzonitriles under the same conditions, since fluorescence quenching in acid solution had shown that their lowest singlet states exhibit greatly enhanced basicity.Surprisingly all attempts to photohydrolyze the nitriles were unsuccessful.