Silica‐immobilized acid ionic liquid: An efficient catalyst for pentanal self‐condensation

Abstract

BACKGROUND: Pentanal self-condensation to 2-propyl-2-heptenal is an important process of carbon chain extension for the industrial manufacture of 2-propylheptanol, which is an important plasticizer alcohol. The existing industrial processes all use liquid alkali catalysts, so they suffer from problems such as difficult recovery and high costs for treatment of alkalicontaining wastewater. In the present work, three immobilized acid ionic liquids were prepared separately with SiO 2 , MCM-41, and SBA-15 as support for pentanal self-condensation. RESULTS: The structures of the as-prepared immobilized acid ionic liquids were confirmed with the help of FT-IR, TG, SEM-EDS, and N 2 adsorption-desorption techniques. The characterization and activity evaluation results indicate that there are positive correlations among the number of hydroxyl groups on the support surface, ionic liquid loading, and the catalytic activity. Among the three immobilized acid ionic liquids, silica-immobilized acid ionic liquids (SiO 2-IL-SO 3 H) showed an extraordinary catalytic performance for pentanal self-condensation because of its higher ionic liquid loading. The yield and selectivity of 2-propyl-2-heptenal could respectively reach 73.9% and 91.5% under suitable reaction conditions and a high turnover number (TON) of 179.1 was obtained. CONCLUSION: Pyridine adsorption infrared spectroscopy and density functional theory (DFT) simulation were employed to investigate the structure and acidity of SiO 2-IL-SO 3 H. The optimized structures were obtained, and the calculation results indicate that the acidity of SiO 2-IL-SO 3 H is higher than the corresponding homogeneous ionic liquid system, which may be the main reason for its excellent catalytic performance and catalytic efficiency.

Preparation of ZrO2via a microwave-assisted hydrothermal method and its catalytic performance for n-pentanal self-condensation

“…Although a satisfactory target product yield is achieved, the shortcomings of the liquid alkali catalyst are also obvious, which is not in line with the concept of sustainable development. To overcome the drawbacks of the liquid alkali catalyst, several catalyst systems of solid acid (TiO 2 , MIF-100 (Fe) and Amberlyst-15), [20][21][22] solid base (supported alkali metal nitrate and aminopropyl functionalized chitosan), 23,24 and ionic liquid (silica-immobilized acid ionic liquid and [PEmim]Cl-0.5(CH 3 COO) 2 Zn) 25,26 were investigated for self-condensation of n-pentanal. TiO 2 showed the best catalytic performance among these catalysts: the yield and selectivity of 2-PHEA were respectively 93.7% and 99.1% under the suitable reaction conditions of a catalyst dosage of 15 wt%, a reaction temperature of 190 1C, and a reaction time of 8 h. The most important advantage is that TiO 2 does not suffer from the problem of hydration with the by-product water which causes catalyst deactivation.…”