Study On Selectivity Of N = N And C = N By Photochemical / Photocatalytic Path Selectivity

C=N double bond and N=N double bond exists widely in organics, such as pharmaceutical intermediates, dyes, and proteins, etc. These organics are synthesized by traditional thermal catalytic methods, which could cause high energy consumption, need harsh reaction conditions and could cause serious environmental pollution. Owing to mild reaction conditions, high conversion and selectivity, the synthesis pathway of photochemical and photocatalytic have attracted more and more attention. Photochemical reaction is that the reactant molecules is excited after absorbing the photon energy with the transitions of π-π* or n-π*, and the energy of the excited molecule in the singlet state or in triplet state line matches with the HOMO orbital energy of other organic molecule, they can occur the bond formation reactions. However, the photocatalytic process is different from the photochemical reaction process, in which the photocatalyst absorbs the light, then activates the absorbing molecules of the surface and react with each other.Based on these reasons, this thesis is composed of two parts contents. The first part is that the selective reduction of nitrobenzene to azoxybenzene which contain N=N double bond through photo-excitation method; another part is that the photocatalytic selective oxidation benzylamine to imine which contain C=N double bond using modified C3N4 as catalyst. The details are as follows:1) In the photochemical reaction, the effects of temperature and light intensity on the activity of the reduction of nitrobenzene were investigated, suggesting that this reaction is a free radical reaction. With the assistance of various characterizations, such as ultraviolet-visible spectroscopy(UV-Vis), nuclear magnetic resonance(NMR) and electron paramagnetic resonance(EPR), we carefully studied the mechanism of the reaction. After being irradiated by light the nitrobenzene reactant molecules were excited and occurred n-π* transition, which could abstract one hydrogen atom from the solvent to form the azoxybenzene that containing N=N bond with high selectivity. Meanwhile, after losing the hydrogen atom, the propylamine as the providing hydrogen reagents could convert to the corresponding imine containing C=N bond. Thereby, we had achieved the purpose of generating N=N and C=N bonds by ‘one pot’ method.2) We studied the formation process of C=N bond by the photocatalystic selective oxidation of benzylamine to imine using modified C3N4 as catalyst. In this work, C3N4 was prepared by changing the ratio of melamine and melamine, which was further modified by heat treatment in an inert atmosphere. With the assistance of various characterizations, such as X ray diffraction(XRD), infrared spectroscopy(IR), UV-Vis, thermogravimetry(TG) and nitrogen adsorption, we confirmed that the sulfur was doped into C3N4 with the change of its structure and stability, finally affecting the activity of this reaction. The effects of temperature and light intensity on the activity of the oxidation of benzlyamine were investigated. The result showed that the sample of 75S-C3N4-4 h had the better reaction activity, that is, the conversion of benzylamine and the selectivity of imine reached 99 %. Meanwhile, the sample of 75S-C3N4-4 h had better universality for benzylamine derivatives and had wonderful stability.