Photochemical and photocatalytic reduction of nitrobenzene in the presence of cyclohexene

mIrradiation with light of wavelength higher than 350 nm of deaerated mixtures of nitrobenzene and cyclohexene leads to the reduction of the nitro-compound, with the formation of C6H5N(O)=NC6H5 (32%), C6H5N=NC6H5 (21%), C6H5NH2 (15%), C6H5N(H)C6H9 (32%). The same stable reduction products are obtained when the photochemical experiments are carried out in the presence of powder dispersions of TiO2 or WO3 or CdS. On the other hand, the photocatalytic contribution of these semiconductors plays an important role in the relative product distribution, which is observed to depend on both competitive adsorption-desorption equilibria of the involved reagents and intermediates on the solid surface and the different reducing power of the photoexcited semiconductors. Cyclohexene participates in the photoinduced reduction of nitrobenzene, undergoing oxidation, and producing the required electrons and protons. Experimental evidence for the formation of radical species deriving from the oxidation of this alkene is obtained by ESR spin trapping investigation. We report here for the first time, the photoinduced allylic amination of cyclohexene with nitrobenzene to give the important building block of synthetic interest C6H5N(H)C6H9. (C) 2000 Elsevier Science S.A. All rights reserved.