| Amides are important intermediates and raw materials in organic synthesis forengineering plastics, detergents, and lubricants. Hydration of nitriles to amides is themost important method to achieve amides. Besides, nitriles can be converted toamides by oxidation with H2O2 under a basic condition. Organic/aqueous biphasiccatalytic system, which enables an easy recovery of the catalyst by decantation, hasrecently attracted attention. We investigated hydration of nitriles with variouswater-soluble catalysts. It showed these water-soluble catalysts give better resultsthan that of reported catalysts. Furthermore, catalytic oxidation of nitriles to amidewith heteropolyacids in presence of oxygen as a green and economical oxidant wasstudied. The nitriles can be converted to amides with a moderate yield and highselectivity in the process.The complexes of transition metal Cu, Ir, Ru, Zn and monophosphine bearingligand (TPPTS) as well as biphosphine ligands (DPPMS,DPPES,DPPPS,BDPX-S,BDNAS) were used as catalysts for the hydration of nitriles. The resultsshow that central metals and ligands had remarkable effect on the reaction.Complexes formed with [Ir(COD)Cl]2 and TPPTS show highest activity in alliridium complexes. However, activity and selectivity of the complexes generatedwith Cu(acac)2 and biphosphine in situ are much higher than analogous monophosphine complexes. Changing the central metals or phosphine ligands wouldinfluence the combination ability of the complexes and nitriles. The influence of base,co-solvent, temperature, and catalyst loading on the reaction were investigated. Notonly conversion but also selectivity were enhanced with the increased concentrationof the base. The reaction was accelerated greatly by adding methanol or surfactantwhich increase the solubility of substrate into the water and make easy contact ofcatalyst with substrate. Under optimal conditions, benzonitrile were converted intoamide with an excellent selectivity. Two best catalysts Cu(acac)2/DPPMS and[Ir(COD)Cl]2/TPPTS were carried out in hydration of substituted aromatic nitrilesas well as some aliphatic nitriles. The results show the catalyst formed withCu(acac)2 and DPPMS in situ was the best one. Except that ortho-substitutedaromatic nitriles, most aromatic nitriles were converted to amides in high yield andexcellent selectivity in presence of Cu-DPPMS catalyst. Two different metal ionsshow the cooperation effect in hydration of benzonitrile and p-chloro benzonitrileand give better results.Heteropolyacids, as new multifunction catalysts, are widely used in variousorganic reactions. Under basic condition, we firstly investigated the oxidation ofnitriles to amides with Na2WO4 and H3PW12O40, H7[PMo12O42]·xH2O as catalysts andoxygen as oxidant. It showed Keggin type heteropolyacid H7[PMo12O42]·xH2O giveshighest activity among all heterpolyacids. The best results (88% yield, 99%selectivity) were achieved at the condition of PO2=2Mpa, pH=13, catalyst/substrate=1/20, Csurfactant=1×10-3mol/L. |
PDF Full Text Request