Study On The Isomerization And Addition Reaction Of α-PINENE Catalyzed By Phosphomolybdic Acid

There has been extensive concern in recent years for phosphomolybdic acid (PMA) with Keggin structure as an efficient heteropoly acid catalyst due to its special catalytic performance. In this dissertation, PMA has been used as a homogeneous catalyst, and immobilized PMA on activated carbon (PMA/C) has also been prepared as a solid acid heterogeneous catalyst. Both catalysts have been applied for isomerization ofα-pinene, the addition reaction betweenα-pinene and methanol as well as the Diels-Alder reaction betweenα-pinene and maleic anhydride.Since homogeneous reaction meets several problems e.g. inconvenient separation process and difficulty of recovery for catalyst after reaction, a series of PMA/C solid catalysts with different loading have been prepared via impregnation with activated carbon as support. Structure, surface morphology and the acidity of the prepared PMA/C catalysts were investigated by FT-IR, XRD, BET, TG and NH3-TPD. The results clearly revealed that PMA highly dispersed on the surface of carbon still kept its Keggin structure. Meanwhile, the thermal stability of the immobilized PMA has been strengthened significantly. The acidic amount increased with the increase of loading amount of PMA, which contributes to the enhancement of catalytic activity.The isomerization ofα-pinene is one of the fundamental reactions for deep processing of pine oil. The isomerization ofα-pinene catalyzed by PMA demonstrated high activity and special selectivity. The isomerization ofα-pinene catalyzed both homogeneously and heterogeneously by PMA and PMA/C has been studied respectively. It has been found that the reaction activity and selectivity depend on the polarity of solvents. The effects of catalyst amount, reaction temperature and time on the homogeneous and heterogeneous catalytic isomerization were explored subsequently, and the optimum reaction conditions were eventually determined.Dienophile maleic anhydride andα-terpinene can take the Diels-Alder reaction, the later is one of the main products ofα-pinene isomerization. Theα-terpinene and maleic anhydride adduct (TMA) can be produced by adding maleic anhydride into theα-pinene isomerization system directly. For the homogeneous system, the yield of TMA can reach 93%, while the yield of 80% can be attained with PMA/C as the heterogeneous catalyst.The addition reaction betweenα-terpinene and methanol, or methoxylation, can also take place betweenα-pinene and methanol under the catalysis of acid. The main product isα-terpinyl methyl ether (TME). The highest yield for TME can attain 37% with homogeneous catalysis of PMA. While catalyzed by PMA/C, 33% of the yield could be achieved for TME. The yield value was higher than most of the previous reports, which revealed the high catalytic activity of PMA.Compared with the homogeneous catalytic reactions, the results for the heterogeneous catalysis reactions were inferior obviously, which indicated the PMA/C catalyst has lower catalytic activity. However, the stability and reusability of the PMA/C catalyst have been strengthened, which allowed wider application of PMA catalyst.Besides, the possible reaction mechanisms were proposed for the three reactions catalyzed by PMA and PMA/C catalysts based on our investigation and the previous reports. It is anticipated to provide certain help for future related research.