Study On Synthesis Of N, N′-diphenylurea By Redox Carbonylation Catalyzed By Co(II) Schiff Base Complexes From Salicyladehyde And Diamine

Urea compounds are agricultural pesticides, pharmaceuticals and fine chemicals,in which N,N′-diphenylurea is one kind of very important compounds that can be used as an intermediate to synthesize herbicides and pesticides. The traditional syntheses for ureas compounds include reactions of amines with isocyanates or phosgene. Highly toxic phosgene, corrosive hydrogen chloride and a large amount of contaminative solution were inevitably involved in these processes, which caused serious problems of environmental pollution and equipment corrosion. In recent years, attention has been paid to the most promising non-phosgene process for the synthesis of various ureas, namely, the reductive carbonylation of nitro-compounds or the oxidative carbonylation of amines because the method has high atom economy.Co(II) Schiff base complexes from salicyladehyde and diamine such as Co(II)salen or Co(II)salophen with p-toluenesulphonic acid or benzoic acid was applied for catalyzing the selective oxidative-reduction carbonylation of nitrobenzene and aniline to synthesize N,N′-diphenylurea.Conclusions presented in this thesis were summarized as follows:1. A novel catalytic system [bis(salicyladehyde)– ethylenediimine] Co(II) [Co(II)salen]/ p-toluenesulphonic acid(PTS) for the synthesis of N,N′-diphenylurea(DPU) by oxidative-reductive carbonylation of nitrobenzene and aniline has been developed. The effects of catalytic system, reaction temperature, carbon monoxide pressure, reaction time, the amount of catalyst and co-catalyst and n (PhNH2) / n (PhNO2) on the reaction were investigated. When the reaction was carried out under the conditions of n[Co(II)salen]/n(PhNO2)=1/50, n[Co(II)salen]/n(PTS)=1, n (PhNH2) /n (PhNO2) = 4, T= 150 oC, P (CO) = 3 MPa , and t = 3 h , using toluene as a solvent , the isolated yield of DPU reached 74 % with PhNO2 and PhNH2 conversion of 86.6 % and 91.2 % respectively.2. A novel catalytic system [Bis(salicylaldehyde) o– phenylenediiminato] Co(II)/benzoic acid for the synthesis of N,N′-diphenylurea(DPU) by oxidative-reductive carbonylation of nitrobenzene and aniline has been developed. The effects of reaction temperature, carbon monoxide pressure, reaction time, the amount of catalyst and co-catalyst and n (PhNH2) / n (PhNO2) on the reaction were investigated. When the reaction was carried out under the conditions of n[Co(II)salophen]/n(PhNO2)=1/50, n[Co(II)salophen]/n(benzoic acid)=1, n (PhNH2) /n (PhNO2)= 5,θ=150 oC, p (CO) = 4 MPa, and t = 7 h, using toluene as a solvent, the isolated yield of DPU reached 60 % with PhNO2 and PhNH2 conversion of 67.0 % and 51.0 % respectively.3. The activity of a series of catalysts whose structures are similar with Co(II)salophen or Co(II)salen′s was studied in the carbolynation reaction of nitrobenzene and aniline in order to investigate the effects of structure of catalysts on the carbolynation reaction.4. The plausible reaction mechanism for synthesis of DPU by the Co(II) catalyzed carbolynation of nitrobenzene and aniline was studied.