Sensitized photoreduction of nitrosoazoles on titanium dioxide

The photosensitized reduction of some 4-nitrosopyrazoles and 4-nitrosoimida zoles using titanium dioxide as a photocatalyst has been investigated. The photoreaction produces the corresponding 4-aminoazoles and assumes an initi al electron transfer from the conduction band of the excited titanium dioxi de to the nitroso compound, followed by hydrogen transfer from the solvent. The photoreduction reaction takes also place by irradiating nitrosoazoles in the presence of triethylamine in acetonitrile, pointing out the electron transfer also to occur from a-ground state donor to the excited nitrosoazo le.