Different Ligands And Palladium Complexes Preparation And Catalytic Hydrogenation,

Palladium complexes of a copolymer, poly(4-vinylpyridine-co-acrylic acid) (abbr.as PVPA-Pd), and of the molecular complexes of poly(4-vinylpyridine) with acid, such as HC1, HAc,and polyacrylicacid, (abbr.as P4VPIHC1-Pd, P4VPIHAc-Pd, P4VPIPAA-Pd) were prepared. Their catalytic behaviors for the hydrogenation of different unsaturated organic compounds have been examined. It was found that P4VPJHCI-Pd and P4VP/PAA-Pd showed almost no activity for the hydrogenation of nitrobenzene, but PVPA-Pd and P4VPIHAc-Pd exhibited good catalytic activity. Therefore, hydrogenation of the catalytic behaviors of PVPA-Pd and P4 VP/RAe-Pd for the aromatic nitro compounds were investigated in detail. Some important experimental results are listed as follows: 1. The highest hydrogenation rate was found when the molar content of 4-vinylpyridine in PVPA was 57.5% and Vpy/Pd-6:l for PVPA-Pd, 4-vinylpyridinelHAclO:l and Vpy/d4:l for P4VP/HAc-Pd. 2. The suitable hydrogenation condition for both PVPA-Pd and P4VP/HAc-Pd were found when using ethanol as the hydrogenation media at the temperature of 45 . In addition, in the presence of an inorganic base, especially KOH, PVPA-Pd and P4 VP/RAe-Pd systems exhibited very high catalytic activity. 3. All the catalysts can catalyze the hydrogenation of nitrobenzene, p-nitroaniline, p-methoxynotrobenzene to the corresponding aniline quantitatively. 4. The rate for the PVPA-Pd catalyzed hydrogenation of substituted nitrobenzenes is in the order of -OH >-OCH3 >4-f >-NH2 >-CHO. For the different isomers of a substituted nitrobenzene, the catalytic activity is in the order of para-> meta- > orth-. 5. Both PVPA-Pd and P4VP/HAc-Pd can be dissolved in ethanol forming a homogeneous hydrogenation system. 6. The two catalysts showed good catalytic stability. When turnover numbers of nitrobenzene was reaching up to 2000, the total reaction time was 4.Shr for PVPA-Pd, 6.6hr for P4VP/HAc-Pd. The total time when the turnover numbers ofp-methoxynitrobenzene reaching up to 2000 is 2.3hr for PVPA-Pd. On the bases of the above results and compared with the results that we acquired before, we can find that PVPA-Pd and P4VPIHAc-Pd show higher catalytic activity than poly(4-vinylpyridine-co-N-vinylpyrrolidine)d (abbr.as PVPN-Pd) and P4VP-Pd, which illustrated that the coordination environment of the basic ligand atom with palladium was greatly a~cted by the introduction of an acid unit.