| Turpentine is not only the important renewable resource, but aslo precious industrial chemicals. α-Pinene and β-pinene are the main components of turpentine, and the special chemical structure makes their chemical properties active enough to take part in many reactions, such as isomerization, hydrogenation and oxidation reaction. One of the epoxidation reaction product of a-pinene is 2,3-epoxy pinane, which is a kind of important fine chemicals and pharmaceutical intermediates, and can be used to prepare the trans-sobrerol by the hydration reaction. The trans-sobrerol is a kind of mucolytic drug, which has the expectorant antiasthmatic effect and mainly used for the treatment of diseases such as bronchitis and asthma. Another one of the epoxidation reaction product of α-pinene is verbenone, which is also a kind of important spice and pharmaceutical intermediates, and is usually used to prepare the repellent for dendroctonus valens leconte. Ionic liquids have so many advantages such as high degree of thermal stability, no corrosion to equipments, easily renewable, reusable that they are a kind of green industrial solvent which are friendly to the environment and have great application prospects.The ionic liquid [bmim]BF4 was prepared by ion exchange method in this paper. Besides, the Salen-Mn complexes were prepared as catalyst to catalyze α-pinene epoxidation reaction in ionic liquid solvents. This catalyst system has good catalysis and could be easily separated from epoxidation products. The whole research was divided into four parts which were as follows:(1) The investigation of ionic liquid and kinds of catalystsThe catalytic performance of the ionic liquid had been investigated, which came to a conclusion that the catalytic activity of ionic liquid was very low without other catalysts. The epoxidation of α-pinene by Salen-Mn complex in ionic liquid was investigated, which showed that the catalytic activity of the catalyst system was significantly improved. By contrast, it turned out that the Salen-Mn complex which synthesized by ethylenediamine and salicylaldehyde had the best catalytic performance than other catalysts in the epoxidation reaction of α-pinene.(2) The investigation of the epoxidation conditionThe optimal conditions of α-pinene epoxidation were obtained by single factor and orthogonal experiments and were shown as follows:reaction temperature 0℃, When using H2O2 as oxidant, the mole ratio of catalyst, a-pinene, H2O2, [bmim]BF4 and CH2Cl20.05:1:6:7:15, reaction time 6h. The conversion of a-pinene attained to 99.82% and the selectivity of trans-Sobrerol up to 40.81%. When using TBHP as oxidant, the mole ratio of catalyst, a-pinene, TBHP, [bmim]BF4 and CH2Cl2 0.04:1:6:7:15, reaction time 7h. The conversion of a-pinene attained to 100% and the selectivity of verbenone up to 53.52%.(3) The characterization of the ionic liquid and the catalystsThe structures of ionic liquid and Salen-Mn complexes were characterized by infrared method and ultraviolet method. Besides, Salen ligand and part of Salen-Mn complexes was also characterized by thermogravimetry. The results showed that the ionic liquid and Salen-Mn complexes were consistent with theliterature values.(4) The preliminary discussion of mechanismThe mechanism of a-pinene epoxidation was discussed preliminarily and was proved by UV analysis. It was considered that, during the reaction, Salen-Mn was first oxidized into a peroxygen metal intermediate containing active oxygen, and then the reactive oxygen atom was transferred to the double bond of the a-pinene, which was oxidized to the epoxy bond. At the same time, the intermediate was reduced into Salen-Mn complex to react with oxygen sources until the end of the reaction. |
PDF Full Text Request