Preperation And Catalytic Properties Of Immobilized SnCl₄ For Prins Condensation Reaction

3-methylbut-3-en-l-ol (MBOH) is an important chemical intermediate for producing organic compounds such as water reducer, pesticides and citral aldehyde. MBOH is available to be produced by Prins condensation reaction of isobutene with formaldehyde under anhydrous conditions in the presence of SnCl4, ZnCl2, or SiCl4 as catalyst. However, these homogeneous catalysts pose considerable problems such as equipment corrosion, disposal problems due to large amount of acidic effluents, and difficulties in product isolation. Thus, many efforts have been concentrated on solid acid catalysts for its environmentally friendly manufacture.In this paper, MBOH was synthesized over immobilized SnCl4 catalyst via Prins condensation reaction of isobutene with paraformaldehyde. The effects of support types, preparation conditions of the catalyst and reaction conditions on the physico-chemical properties and catalytic performance of the immobilized SnCl4 catalyst were investigated. The main results are as follows:(1) The support types influence the chloride loadings, the coordination environment of tin species, surface acidity, and the catalytic activity of the immobilized SnCl4 catalyst. Three supports of silica gel, silica-alumina and alumina were used to prepare the immobilized SnCl4 catalysts. The results of ICP-OES and 119Sn Mossbauer spectra indicated that SnClx-SiO2 has the lowest electron density of tin nucleus, because more-SnO2Cl2 was found over the SiO2 support. The result of Py-FTIR indicated that Bronsted acid sites and Lewis acid sites existed in the three catalysts, and Lewis acid sites are the predominant acid species. And the acidity strength of above three catalysts decreases with the trend of:SnClx-SiO2> SnClx-SiO2-Al2O3> SnClx-Al2O3. The high catalytic activity and selectivity obtained over SnClx-SiO2 might be ascribed to its strong Lewis acidity and low electron density of tin nucleus.(2) Preparation conditions of immobilized SnCl4 catalyst greatly affected the loadings of the chloride and the activity of the catalyst. With the increase of grafting temperature, the chloride loading increases and the value of Cl/Sn atomic ratio decreases. When grafting temperature is 250℃, SnClx-SiO2 catalyst possesses the best selectivity to MBOH. The similar catalytic activityies can be obtained over two SnClx-SiO2 catalysts, which were prepared by impregnation method and two-step method, respectively.(3) Effect of reaction conditions on Prins condensation reaction was investigated. The results demonstrated that catalyst dosage, reaction temperature and solvent types can obviously influence the yield and selectivity of MBOH. The optimal reaction condition is SnClx/SiO2 as the catalyst containing 0.12 mmol SnClx, isobutene/paraformaldehyde molar ratio of 4:1, dioxane as the solvent, reaction pressure of 2.2 MPa, reaction temperature of 120℃.