Synthesis Of Polyacrylic Acid Grafted Silica Supported DMAP Catalyst And Studies On Its Catalytic Properties

Polymer catalysts are referring to all of the polymer materials with catalytic activities in chemical reactions,which is an important branch of functional polymer materials. By the inspiration of Merrifield solid phase synthesis,the organic polymers (polystyrene sulfuric acid) loading ([Pt (NH3)4 ]2+) complex catalyst finally came out . This research work immediately sparked widespread concern and interest of catalytic scientists around the world, since then Polymer-supported catalytic complex catalysis has become an independent field of cross-disciplinary research. In the subsequent 30 years people have designed and synthesized a large number of Polymer-supported catalysts with different structures and different uses, and due to the polymer effect among the various functional groups in the polymer chain, such as synergy, some have special optically active structures, and their catalytic activity in selective catalysis were much higher than the corresponding homogeneous small molecules catalyst.In a large number of small-molecule catalysts ,4-N, N dimethylamino-pyridine (DMAP), due to its strong nucleophilicity is often used as a catalyst for a number of important reactions, such as acylation, silylation, triphenyl methylation, and ester rearrangement, Darkin-West reaction, Baylis-Hillman reaction. However, because of its belonging to small organic molecules, DMAP does not facilitate the recovery and utilization, resulting in wasted costs. In order to change this situation many researchers have grafted it to low-cost commercial materials, such as organic polymer resins, inorganic materials (silica gel and molecular sieve), and micro-capsules. We found that either the soluble homogeneous catalysts or the insoluble heterogeneous catalysts had more or less deficiencies when they were recycled. By comparing a variety of supported DMAP catalysts in the literature, we designed to combine the single soluble homogeneous catalysts and the insoluble heterogeneous catalysts, based on such considerations we have chosen silica gel grafted polyacrylic acid, which is a combination of silica gel and polyacrylic acid, as the carrier to immobilize DMAP. This carrier will set the advantages of organic polymer and silica gel in one: the linear long chain polyacrylic acid polymer is soluble in a variety of solvents, and can extend freely in the reaction solvent system, so the catalyst can be fully utilized. While the silica is insoluble, so the silica supported catalyst can be filtered directly when the reaction is completed, and can be facilitate recycled. We use the coupling agentγ-amino propyltriethoxysilane to graft silica gel and polyacrylic acid polymer in our design. This design combines the advantages of both while cleverly avoiding its shortcomings.In this paper, we designed to use pyridine as the raw materials. First we got nitropyridine N-oxide 2 through the oxidation and nitration, after reduction we got 4-aminopyridine 3, which then reacted with two molecules of methyl acrylate through the Michael addition to generate compound 4. 1-pyridyl-4-piperidine-one was synthesized via Claisen ester condensation and decarboxylation from 4, and then reacted with hydroxylamine hydrochloride in 50% ethanol solution to generate oxime 5. Compound 6 was obtained by hydrogenation in methanol using Raney nickel as the catalyst, which reacted with Boc-protected 6-aminocaproic acid to generate compound 7, the amino-terminal with DMAP analogue 8 was obtained by deprotection. S-PAA-DMAP was finally synthesized by connecting the DMAP analogue 8 and silica gel grafting polyacrylic acid.To study the catalytic performance of S-PAA-DMAP catalyst, we chose Fries rearrangement and the acetylation ofα-phenylethanol as our model reaction in the catalytic part of our experiment. In Fries rearrangement we used 30% mol catalyst for reaction 6~8h to make raw materials completely transformed. Inα-Phenylethanol acetylation we used 10% mol both of S-PAA-DMAP and DMAP to achieve similar results. The catalyst was reused three times, to get a result respectively, 91%, 86% and 84% in yield. S-PAA-DMAP has a good stability as a catalyst, which put forward a new mode of thinking for the future work of the immobilized catalyst.