Preparation Of Rhodium - Phosphine Complex And Its Application In Asymmetric Hydrogenation Of A - Pinene

Turpentine is not only a kind of important renewable nautral sources but aslo a sort of valuable industrial chemicals. Our country is abundant in gum turpentine, and gmain components are α-pinene and β-pinene. Because of their special chemical structure, α-pinene and β-pinene are very active for many reactions, such as hydrogenation, oxidation and isomerization reaction. The pinane which is an major industrial material for the perfume and pharmaceutical industry can be prepared through the catalytic hydrogenation of pinene, and it is an important intermediate for the synthesis of linalool, citronellol, rose oxide, dihydromyrcenol and so many valuable fragrance compounds. Depending on reaction conditions, hydrogen attachment to the double bond can result in the formation of two cis- and trans-pinane isomers. The activity of cis-pinane is considerably higher than that of trans-pinane, so the cis-pinane is primarily demand for industrial manufacture. As we known, noble metal catalysts have the higher catalytic activity.and the more milder reaction conditions than the non -noble metal, especially the transitionmetal ions or complexes in homogeneous solution have proved to be effective catalysts for the asymmetric hydrogenation. However, it is not easy to separate the products and the catalysts which are difficult to recycle. The ionic liquids have so many advantages such as high degree of thermal and chemical stability, non-volatile, immobilized organometallic compounds. The use of ionic liquids in two-phase catalytic reactions can make a high catalytic activity as the homogeneous reactions and the products can be separated easily with the catalysts as the heterogeneous reaction. Thus the ionic liquids are a kind of "ideal green and efficient" solvent and a special "catalyst support" which provide a new way for the separation and recycle of the transition metal catalyst in homogeneous reactions.The complexe RhCl(PPh3)3 was prepared in this paper to catalyze a-pinene hydrogenation reaction in ionic liquid solvents. This catalyst system has good catalysis and could be easily separated from hydrogenation products to recycle.The whole research was divided into four parts which were as follows:(1) The investigation of medium of hydrogenation reactionsThe effect of medium on hydrogenation reactions of α-pinene catalyzed with RhCl(PPh3)3 had been investigated.There is a relatively well catalytic activity of non- solvent,however the products and catalysts are partially miscible led to a difficult separation.A goog catalytic activity was obtained with RhCl(PPh3)3 dissolved the ionic liquids and the catalytic system can be separated easily from hydrogenation products to recycle.(2)The investigation of the preparation condition of catalystThe RhCl(PPh3)3 was prepared with the [BMIM]PF6 and [BMIM]BF4 as medium of hydrogenation, and the effects of various preparation factors including the molar ratio of PPh3 and RhCl3·3H2O, reflux temperature and reflux time on the hydrogenation of α-pinene had been investigated.The optimum conditions were as follows:the molar ratio of PPh3 and RhCl3·3H2O was N2, reflux temperature was T3 and reflux time was t2 with the [BMIM]PF6 as medium of hydrogenation;the molar ratio of PPh3 and RhCl3·3H2O was N’1, reflux temperature was T’1 and reflux time was t’2 with the [BMIM]BF4 as medium of hydrogenation.The structures of RhCl(PPh3)3 complexes were characterized by infrared method and elemental analysis.The results showed that RhCl(PPh3)3 complexes were consistent with the literature values.(3)The investigation of the hydrogenation conditionThe optimal conditions of a-pinene hydrogenation were obtained by single factor and orthogonal experiments with the ionic liquid [BMIM]PF6 as medium of hydrogenation and were shown as follows:reaction temperature E2, reaction pressure Pi,the catalyst dosage M3, the ionic liquid [BMIM]PF6 dosage L3, reaction time J2.The conversion of a-pinene attained to 99.49% and the enantioselectivity of cis-pinane up to 96.73%.The optimal conditions of α- pinene hydrogenation were obtained by single factor experiments with the ionic liquid [BMIM]BF4 as medium of hydrogenation and were shown as follows:reaction temperature I5, reaction pressure P2,the catalyst dosage m3,the ionic liquid [BMIM]PF6 dosage Q1, reaction time G3.The conversion of a-pinene attained to 99.31% and the enantioselectivity of cis-pinane up to 98.38%.