Study Of Acid-catalytic Activity Of Charge-transfer Salts Based On Keggin-type Polyoxometalates

Using four saturated Keggin-type polyoxometalates (POMs), i.e. tungstosilicic, tungstophosphoric, molybdosilicic and molybdophosphoric acids as the parent acids. In aqueous solutions, H+can be exchanged by other cations, thus the counter cations, i.e. the alkali metal ions, the ammonium ion, nitrogen-containing organic cations, transition metal ions and transition metal-biimidazole cations, charge-transfer salts based on keggin-type polyoxometalates were prepared by means of direct precipitation. And we selected the synthesis of cyclohexanone ethylene ketal as a model reaction, the catalytic activities of these charge-transfer salts were evaluated. The influences of different acid catalysts and counter cations on the catalytic performance were systemically explored. The results show that the acidic ability and solubility of the parent cmpounds can be adjusted through changing cations, thus some highly efficient, reusable, easily separated acid-catalysts based on polyoxoacids can be further obtained. Copper-2,2’-biimidazole complex was introduced into the POM system, the efficient heterogeneous catalyst was prepared. This work laid a solid experimental foundation for further research and development of these catalysts, and has an important practical significance.1. When the parent acids are the same, the catalytic activities and laws of the POMs using Na+, K+, NH4+, Bu4N+, nitrogen-containing organic cations (e.g. protonated imidazole, 2,2’-biimidazole,2,2’-bipyridine,4,4’-bipyridine, etc.), Cu2+, Co2+, Mn2+, Zn2+, Ni2+, Fe3+, [Cu(H2biim)2]2+, [Co(H2biim)2]2+, [Mn(H2biim)2]2+, [Zn(H2biim)2]2+, [Ni(H2biim)2]2+and [Fe(H2biim)2]3+as counter cations were evalued for the synthesis of cyclohexanone ethylene ketal.2. When the counter cations are the same, the catalytic activities and laws of these POMs containing different polyoxoanions, such as tungstosilicic acid, tungstophosphoric, molybdosilicic and molybdophosphoric acids were evalued for the synthesis of cyclohexanone ethylene ketal.3.Using H4SiWi2O40, (H4biim)H2SiWi2O40, [Cu(H2biim)2]H2SiWi2O40 as catalysts, respectively, the effects of the amounto of the catalyst to cyclohexanone, the molar ratio of the starting material, the reaction time, as well as the frequency of recycles on cyclohexanone ethylene ketal yield were researched.