| Acetone condensation for production of mesityl oxid (MO), diacetone alcohol (DAA), isophorone (IP) and other fine chemicals is an important chemical process, and to research and develop the recyclable and catalysts for acetone condensation are of great theoretical and practical significances. The preparation, structure and catalytic properties of polymer immobilized L-proline catalysts for acetone condensation reaction have been studied by using various physico-chemical methods in this paper. The results obtained in this work have provided important reference informations for the deep investigation of relationship among the composition, structure and catalytic properties of polymer immobilized L-proline catalysts, and for the development of heterogeneous catalysts with both excellent catalytic properties and recyclability. The main results are summarized as follows.1. The catalytic evluation results for condensation reaction of acetone catalyzed by different amino acids have shown that L-proline catalyst has the best catalytic activity. Under the optimum reaction conditions (L-proline 5 mol%, reaction temperature 90℃ and reaction time 4 h), acetone conversion was 26.5 mol% with the selectivities of 78.4 mol% MO,6.1 mol% DAA and 1.5 mol% IP, respectively. The density functional theory (DFT) calculation results suggested that enamine intermediates formed by reaction of acetone with L-proline was more stable and easier to form hydrogen bond with another acetone molecule, which may be the main reason for the excellent catalytic activity of L-proline. However, the L-proline catalyst was easier to decompose, its recovery was as low as 70.0%.2. It has been found that piperidine exerts great promotional effects on the L-proline catalyst for acetone condensation reaction. For the acetone condensation reaction catalyzed by L-proline/piperidine (2.3 mol%) under the above reaction conditions, the acetone conversion was 37.9 mol% with the selectivities of 78.0 mol% MO,5.7 mol% DAA and 3.5 mol% IP. The apparent activation energy (Ea) measurement results have shown that apparent activation energy of L-proline and L-proline/piperidine are Ea=218.5 kJ/mol and 88.3kJ/mol, respectively.3. The novel polymer immobilized L-proline catalyst (PNL①) and polymer immobilized L-proline and piperidine catalyst (PNLD) have been prepared by copolymerization method using N-isopropylacrylamide (N), O-acryloyl-trans-4-hydroxy-L-proline hydrochloride (L) and O-acryloyl-4-methylol-piperidine hydrochloride (D) as raw materials. The PNL① and PNLD catalysts show higher recovery and higher recyclablity than L-proline/piperidine catalyst.4. It has been revealed that acetone condensation reaction catalyzed by L-proline can not be coupled with hydrogen-transfering reaction of MO-IP A catalyzed by Pt/C because of two catalysts poisoning probably due to N-Pt coordination. The Pt/C catalysts have high activity, selectivity and recyclablity for hydrogen-transfering reaction of MO-IPA to MIBK. |
