摘要
本文报导了合成并使用半包结的二乙醇胺和三乙醇胺钼络合物,cis-亚氨基二乙氧基二氧化钼(VI)(A)和cis-氮川基三乙氧基二氧化钼(VI)(B)为叔丁基过氧化氢存在下的烯烃环氧化反应催化剂.研究了这两个络合物的催化活性,考察了溶剂、水、催化剂用量和反应温度对环已烯环氧化反应的影响.同时也研究了络合物在烯烃不存在的情况下对叔丁基过氧化氢的分解性能.由于配位体效应而使得两个络合物的催化活性不同,络合物(A)的催化活性高于络合物(B),亦高于文献钼催化剂的水平.文中还对这一体系的反应机理进行了探讨.
Diethanol amine and triethanol amine can form stable half inclusion complexes with many transition metal cations. These complexes are of the structural character that the half coordinate sphere of the central metal is occupied by the chelate ligand, and the other half coordinate sphere is unoccupied or occupied only by monodentate ligands. When they are used as catalysts, the catalytic reaction may take place on the half sphere that is not occupied by the chelate ligand. It may lead to high catalytic activity and/or high selectivity. In the present work, cis-dioxomolybdenum(VI) iminodiethanoxide MoO2 [OCH2CH2]2 NH·CH3OH ( A ) and cis-dioxomolybdenum ( VI ) nitrilotri-ethanoxide H[MoO2 ( OCH2CH2 ) 3N](B), the half-inclusion complexes, have been first used as the catalysts for the epoxidation of cyclohex-ene with tertbutylhydroperoxide ( TBHP ) .
Complex ( A ) and ( B ) were synthesized by the reaction of MoO5 with diethanol amine and triethanol amine respectively, and characterized by C, H and N elemental analyses, 1H-NMR spectra, 13C-NMR spectra and infrared spectra.
The catalytic epoxidation was carried out under an inert atmosphere of nitrogen. Complex ( A ) is a very active catalyst for the epoxidation. In the presence of (A), the conversion of TBHP is 100%, and the selectivity to epoxide is 97% in 150 minutes at 80℃. However, complex ( B ) is less active. The conversion of TBHP in the presence of ( B ) is 64%, and the selectivity is 98% in 150 minutes at 80℃. The presence of water hinders the epoxidation and the conversion of TBHP decreases with the increase of the amount of complex ( A ) . The conversion of TBHP in the epoxidation catalyzed by ( A ) and ( B ) is incr -eased with the increase of reaction temperature, but the selectivity is decreased. The best reaction temperature is found to be 80℃. The reaction can barely take place in butanol.In the absence of cyclohexe-ne, TBHP can decompose in the presence of ( A ) , and barely decompose in the presence of ( B ) .
Complex ( A ) is a methanol solvated complex. In the catalytic epo-xidation, tert-butyl hydroperoxide can easily substitute the alcohol to form a molybdenum (VI) -hydroperoxide complex. This is the rate-determining step of the reaction. However, there is one more intramolecular hydroxyl group coordinating to the central metal in complex ( B). It is very difficult for tert-butyl hydroperoxide to compete with this adjacent hydroxyl group to form the molybdenum (VI)-hydroperoxide complex, thus making complex(B) less active than complex(A) for both epoxidation and decomposition of tert-butyl hydroperoxide.
出处
《分子催化》
EI
CAS
CSCD
1989年第4期276-283,共8页
Journal of Molecular Catalysis(China)
