Synergic catalysis of W and Ni originating from substitution of trivacant phosphotungstate for the selective oxidation of aniline to azoxybenzene

Partial substitution of polyoxometalate(POM)is an efficient route to modulate the catalytic property of maternal POM.In this work,a new Keggin type POM involving{Ni 6}cluster,{[Ni(H_(2)O)_(2)(Dach)_(2)][Ni(Dach)_(2)]_(2)}{[Ni_(6)Cl(μ-OH)_(3)(H_(2)O)(Dach)_(3)(WO_(4))(PW9 O_(3)_(4))][Ni_(6)(μ-OH)_(3)(H_(2)O)_(2)(Dach)_(3)(WO_(4))(PW9 O_(3)_(4))]}Cl·27H_(2)O,(1,Dach=1,2-diaminocyclohexane)was synthesized.Compounds 1 shows excellent catalytic performance in the selective oxidation of aniline to azoxybenzene(AOB)in water.The apparently different results from that with the matrix{PW_(9)O_(34)}({PW9})suggest the successful regulation of the catalytic property of{PW9}by the introduction of the{Ni6}cluster into the skeleton.The experimental results indicate that the highlighted performance of 1 is contributed by the synergy of W and Ni sites,which are respectively responsible for the oxidation and condensation steps in the production of AOB.The good selectivity to AOB is essentially attributed to the effective modulation of the reaction rates of oxidation and condensation steps by W and Ni sites,respectively.

The relationship of morphology and catalytic performance of CeO_(2) catalysts for reducing nitrobenzene to azoxybenzene under the base-free condition

CeO_(2) morphology was proposed to be a crucial factor for reducing nitrobenzene to azoxybenzene under the base-free condition.Herein,the structure-activity relationship of CeO_(2) catalysts was explored to improve the azoxybenzene yield.A series of CeO_(2) catalysts we re synthesized with seven morphologies to obtain different Ce^(3+) proportion and various surface areas.Notably,the catalytic performance of these samples for reducing nitrobenzene to azoxybenzene enhanced with the increasing Ce^(3+) proportio n.With the highest surface Ce^(3+) proportion,the Rod-CeO_(2) catalyst exhibited 100% conversion of nitrobenzene and 89.8% azoxybenzene selectivity in 7 h at 150℃ under 1 MPa CO.Moreover,the preliminary mechanistic analysis indicated that the inhabitation of azoxybenzene to by-product azobenzene resulted in the high selectivity of azoxybenzene.

Selective oxidation of primary substituted aromatic amines to azoxy products using lacunary catalyses

Some of the substituted anilines were selectively converted in to the corresponding azoxy and azobenzenes by oxidation with 30%aqueous hydrogen peroxide.The reactions were catalyzed by various heteropolyoxometalates,at boiling point of the used solvents.An improvement in the product yield and selectivity towards azoxybenzens was also observed.Azobenzenes was obtained as by-product.In the all similar cases,the highest yield of azoxy compounds was observed using K_5PW_(11) ZnO_(39) as catalyst in N,N-dimethyl...

Methoxylation and Direct Hydrogenative Coupling of Chloronitrobenzenes in Continuous Flow

A novel continuous flow method for the methoxylation of chloronitrobenzenes was developed. The reaction went smoothly and high yields were achieved under the optimized conditions. Furthermore, up to 76% yield of azoxybenzenes were obtained from the corresponding nitrobenzenes in the presence of NaOH in continuous flow. Compared to batch conditions, the reaction time was significantly shortened, and the chemical waste was reduced obviously.