Photochemical and photocatalytic reduction of nitrobenzene in the presenceof cyclohexene

mIrradiation with light of wavelength higher than 350 nm of deaerated mixtu res of nitrobenzene and cyclohexene leads to the reduction of the nitro-com pound, with the formation of C6H5N(O)=NC6H5 (32%), C6H5N=NC6H5 (21%), C6H5N H2 (15%), C6H5N(H)C6H9 (32%). The same stable reduction products are obtain ed when the photochemical experiments are carried out in the presence of po wder dispersions of TiO2 or WO3 or CdS. On the other hand, the photocatalyt ic contribution of these semiconductors plays an important role in the rela tive 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 n itrobenzene, undergoing oxidation, and producing the required electrons and protons. Experimental evidence for the formation of radical species derivi ng from the oxidation of this alkene is obtained by ESR spin trapping inves tigation. We report here for the first time, the photoinduced allylic amina tion of cyclohexene with nitrobenzene to give the important building block of synthetic interest C6H5N(H)C6H9. (C) 2000 Elsevier Science S.A. All righ ts reserved.