Polyphosphazene-Functionalized Microspheres as Efficient Catalysts for the Knoevenagel Reaction under Mild Conditions

Inspired by the formation of microspheres by hexachlorocyclotriphosphazene and 4, 4'-sulfonyldiphenol, polyphosphazene-functionalized microspheres were developed. Benefits from the supported supper basic phosphazene, the yield exceeded 99 % at room temperature in the manner of second-order reaction kinetics toward Knoevenagel reaction and was still maintained at 99 % after 16 runs. In the experimental temperature from 0 °C to 90 °C, the yield increased from 92 % to 99 %, reflecting that the catalyst had strong applicability under mild conditions. This behavior was conducive to energy conservation. Meanwhile, simple separation and recovery further enhanced this advantage. In addition, the catalyst was also found to be insensitive to aqueous solution or organic solvents such as toluene, THF, EtOH and CH₃ CN. This property gave the Knoevenagel reaction a vast choice. All these features exhibit that this novel catalyst is an attractive and applicable alternative in organic synthesis.