Synthesis Of Thermoregulated Phase-separable Catalyst And Application For Intermolecular STETTER Reaction

Ionic liquids for liquid/liquid two-phase catalysis provides a new approach of resolving the catalyst separation and recovery. Based on the concept of thermoregulated phase-separable catalysis (TPSC), a series thiazolium and triazolium thermoregulated ionic liquid catalysts with different polyether-substituted chain (n=11,16,42) and different anion (Cl, Br-, I, BF4-, PF6-) were designed and synthesized. The structures of new compounds were characterized by NMR and IR. The solubility of catalysts in different temperatures and organic solvents were studied. The results showed that the catalysts possessed a critical solution temperature (CST) in toluene/n-heptane mixed solvent and exhibited the properties of "homogeneous reaction in high temperature and two-phase separation in low temperature".The thermoregulated ionic liquid catalysts were used in Stetter reaction of ethyl acrylate with furfural and n-butanal. The effects of anion and ethoxy chain on reactions were investigated. The catalyst with bromine anion and ethoxy chain length n=16 showed good catalysis and recycle. The reaction conditions were also optimized.In the stetter reaction of ethyl acrylate with n-butanal catalyzed by the thiazolium ionic liquid catalyst with Br- and n=16, the optimum reaction conditions were as follow:t=12 h, T=60℃, and the quantity of catalyst of 15 mol%. Under the optimum reaction conditions, the conversion of n-butanal and yield were 99.0% and 37.2%, respectively. After 6 recycles of the catalyst, the conversion and yield still could reach up to 96.0% and 34.0%, respectively. In the Stetter reaction of ethyl acrylate with furfural catalyzed by the thiazolium ionic liquid catalyst with Br-and n=16, the optimum reaction conditions were as follow:t=12 h, T=60℃, and the quantity of catalyst of 15 mol%. Under the optimum reaction conditions, the conversion of furfural and yield were 99.0% and 42.3%, respectively. After 8 recycles of the catalyst, the conversion and yield still were higher than 95.0% and 35.0%, respectively.In the Stetter reaction of ethyl acrylate with n-butanal catalyzed by the triazolium ionic liquid catalyst with Br-and n=16, the optimum reaction conditions were as follow:t=16 h, T=70℃, and the quantity of catalyst of 15 mol%. Under the optimum reaction conditions, the conversion of n-butanal and yield were 99.0% and 37.4%, respectively. After 5 recycles of the catalyst, the conversion and yield still could reach up to 95.0% and 34.0%, respectively. In the Stetter reaction of ethyl acrylate with furfural catalyzed by the triazolium ionic liquid catalyst with Br- and n=16, the optimum reaction conditions were as follow:t=16 h, T=70℃, and the quantity of catalyst of 20 mol%. Under the optimum reaction conditions, the conversion of furfural and yield were 99.0% and 41.8%, respectively. After 6 recycles of the catalyst, the conversion and yield still were higher than 95.0% and 36.0%, respectively. The loss of the catalyst was about 4%-5% after 6 recycles. The byproducts of Stetter reactions were determined by GC-MS, and the reaction mechanism was discussed.The thiazolium and triazolium thermoregulated phase-separable catalysis with the characteristic of "homogeneous reaction in high temperature, two-phase separation in low temperature" can achieve the integration of reaction-separation. It not only provides a new idea of green catalysis in Stetter reaction but also makes a very effectively way for liquid/liquid two-phase catalysis in other organic reactions.