Synthesis method of alicyclic epoxy resin

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1. Epoxidation method of organic peroxyacids and their derivatives In 1909, Nilolaus Prilezhaev discovered that peracetic acid can epoxidize various double bonds, whether they are chain end double bonds or mid-chain double bonds, and can epoxidize double bonds on aliphatic rings. Subsequent studies have shown that organic peroxyacid is a very effective epoxidant, and the cyclic chlorination process between it and olefins is an electrostatic addition. The olefin structure, peroxyacid structure, reaction medium and temperature affect the rate of epoxidation reaction, and the catalyst has no effect on the reaction. Among them, alkenes with electron-withdrawing groups, such as hydroxyl groups, will reduce the reaction rate. ； On the contrary, those with donating groups, such as hydrocarbon groups, will accelerate the reaction. Peracetic acid is widely used because of its simple structure, easy preparation, and low price. Depending on whether the incompletely reacted organic peroxyacid is separated during the preparation of alicyclic epoxy resin, the preparation methods can be divided into two types: in-situ epoxidation method and separated epoxidation method. 1. In-situ epoxidation method In-situ epoxidation method means that the epoxidation reaction of synthesizing organic peroxyacid and olefin is carried out in the same system. The organic peroxyacid thus generated reacts with the olefin immediately, and there is no peroxyacid enrichment process. For example, acetic acid is first mixed with a compound containing an olefinic chain, and then hydrogen peroxide is added to the system. Acetic acid and hydrogen peroxide react to form peracetic acid, which is immediately epoxidized with a substrate containing an olefinic bond to obtain the product. This method is characterized by simple process, low equipment investment, and no safety hazards caused by peroxide enrichment. 2. Separation epoxidation method The separation epoxidation method is different from the in-situ epoxidation method. It refers to the separation of the synthesis of organic peroxyacid and the epoxidation process. This method is characterized by the separation of the two processes, which is conducive to separate detection and control of the two processes, and is therefore suitable for industrial large-scale production. The U.S. UCC Company and Shanghai Petrochemical General Plant both use this method to produce epoxy resin. 2. Epoxidation method of halohydrins and their derivatives. The most common halohydrin is hypochlorous acid H0-C1+. Its epoxidation mechanism is shown in Reaction Equation 2. The reaction mechanism can be extended to bromine and iodine. First, the electrophilic halogen ion attacks the olefinic bond to form a halide ion, and then the nucleophilic group attacks the halide cation from behind. This nucleophilic group may be 0H- or H20. Then under the action of a base, the oxygen anion attacks the carbon atom connected to the halogen from behind, and the halide anion leaves to form an epoxy group. The nucleophilic group in the reaction may also be a halide anion, which will form a by-product bihalogen molecule. It can be seen from the above mechanism that the reaction has two behind-the-scenes stereochemical processes, so that the product can maintain the stereoconfiguration of the raw material. This is the reason why some organic synthesizers are interested in this epoxidation method. At present, the hypochlorous acid method is mainly used to produce propylene oxide in China. In the 1980s, metalloporphyrin compounds appeared to catalyze the epoxidation reaction using sodium hypochlorite as the epoxidant. Its characteristic is that the reaction process is reduced from the original two steps to one step, and the metalloporphyrin compounds have high catalytic activity, and the reaction system is simple and can be used at room temperature. 3. Hydrogen peroxide method This synthesis method uses hydrogen peroxide as the oxidant and is mainly used to epoxidize some alicyclic olefins with hydroxyl groups. The key to the reaction is the need for a highly active catalyst. In the 1950s and 1960s, tungsten trioxide once occupied a certain position as a catalyst for this reaction. at present. Many new types of catalysts have emerged, usually containing metal ions. Such as Ti4+, V4+, Cr3+. Among them, the better one is Ti/Si02 accelerator, which can catalytically oxidize molecules with smaller molecular weight at low temperatures. 4. Inorganic oxidant method Common oxidants include oxygen, ozone, chromic acid, potassium permanganate, etc. Oxygen, as the cheapest oxidant, has always been a favored raw material in redox reactions. But so far it cannot be used as an ordinary direct epoxidizing agent. It only appears in some special epoxidation reactions, such as the cyclization reaction of α-pinene containing conjugated double bonds with oxygen, and then rearrangement to obtain diepoxy compounds (Equation 3). The rearrangement process is the backbone of this reaction. It can be a spontaneous thermodynamic rearrangement under reheating, a light-induced rearrangement, or a cobalt-catalyzed rearrangement. Also, the silver-catalyzed oxygen epoxidation method is only used to synthesize ethylene oxide. It is not effective for long-chain olefins (propylene oxide is not produced by this method), and it cannot epoxidize alicyclic olefins. Chromic acid and potassium permanganate are traditional oxidants. If the reaction conditions are well controlled, they can also be used in epoxidation reactions. 5. Biomimetic porphyrin iron, as an active substance in blood cells, has very high activity on oxygen. Therefore, people were inspired to use gold leaf lin to catalyze epoxidation reactions. In 1979, Groves was the first to use metalloporphyrins to imitate biological systems to catalyze the epoxidation of alkenes. However, metalloporphyrins are homogeneous catalysts and cannot be recycled and reused. In addition, metalloporphyrins are relatively expensive. Therefore, recently people have used various methods to load metalloporphyrins, such as simply adsorbing manganese porphyrins on silica gel or combining them with polymer monomers and then polymerizing them into functional polymers.