N-heterocyclic Palladium Complex As Catalysts For The Synthesis Of Diphenyl Carbonate By Oxidative Carbonylation

Diphenyl carbonate(DPC) is an important intermediate for the synthesis of the general engineering material-polycarbonate(PC).The methods for DPC synthesis include phosgene method, transesterification method and phenol oxidative carbonylation method. Among them, oxidative carbonylation method can effectively avoid the use of toxic phosgene, the reaction process is short and environmentally benign. It has already become the main research direction in the field both at home and abroad.The key technology in oxidative carbonylation reaction is focused on the selection of heterogeneous and homogeneous catalytic system. Compared with heterogeneous system, homogeneous catalytic system can overcome those disadvantages such as poor heat and mass transfer efficiency, high pressure-drops. Meanwhile, the catalytic activity can be improved by molecular design of complex ligand, and the yield of DPC may be increased.In this work, four kinds of catalysts Bis[1,3-bis(diphenyl)imidazole] dichloropalladium(Pd Cl2(dm-Ph)2), Bis[1,3-bis(2,4,6-trimethylphenyl)imidazole] dichloropalladium(Pd Cl2(dm-Mes)2), Bis[(1,3-bis(methyl)imidazole] dichloropalladium(Pd Cl2(dmMe)2), Bis[1,3-bis(tertiarybutyl)inidazole] dichloropalladium(Pd Cl2(dm-t-Bu)2) were synthesized by using Pd Cl2 as active component and N-heterocyclic compound as ligand. The catalysts were characterized by IR, 1HNMR, EA, and TG methods. Meanwhile, the effects of different ligands, different catalytic additives and different reactive conditions on the catalytic activity and selectivity were investigated by oxidative carbonylation of phenol. The conclusions were as follows:(1) Under the same reaction conditions, the catalytic activity order of the different catalysts is Pd Cl2(dm-t-Bu)2>Pd Cl2(dm-Me)2>Pd Cl2(dm-Mes)2>Pd Cl2(dm-Ph)2. It showed that catalytic activity is associated with the stability of the complexes catalyst. The electronic-donating ability of substituent in different ligand is stronger, the electronic feedback ability to the active component Pd is stronger, and the complexe is more stable.(2) The choice of inorganic additives found that the effect of Cu Cl2 is the best. It is found that the reduction potential of Cu Cl2 is between Pd2+/Pd0(0.99 V) and O2/H2O(1.23 V), which could effectively reoxidized Pd0 to Pd2+. Additionly the electron transfer effect in it was enhanced, then promoted the catalytic ability of the obtained catalysts.(3) The results show that when use Pd Cl2(dm-t-Bu)2 as the catalysts, add 30 m L methylene chloride as solvent, 0.75 mmol Cu Cl2 as inorganic promoter, 0.375 mmol benzoquinone as organic promoter, 2.5 g 4A molecular sieves for removal agent and 3.0 g tetrabutyl ammonium bromide as surfactant, at 100 ℃, the total pressure was 5 MPa(oxygen partial pressure was 7%), the reaction time was 3 hours, the yield of DPC was the highest, which the exact yield was 22.8%.