Cyclopropanation Of Alkenes On Heterogeneous Catalysts

Compared to homogeneous catalysis, heterogeneous catalysis has several advantages such as easier catalyst-product separation, easier catalyst recycle and continuous production. Heterogeneous catalysis is especially important to catalytic cyclopropanation, which is an explosive process in an autoclave reactor because of the fast release of nitrogen after its induction period. However, the fixed-bed reactor can alleviate this problem with reactants continuously flowing through the heterogeneous catalyst. For above reasons, it is very interesting and necessary to study the heterogeneous catalytic cyclopropanation. First, we prepared a series of supported catalysts and tried to select some highly active and selective catalysts. Then we modified these catalysts with chiral molecules in order to achieve some enantio-selectivity. Besides above work, we also tried other methods to prepare heterogeneous chiral catalysts. The main results are summarized as follows: (1) Several transition metals were supported on Si02 or A1203 and the cylopropanation reaction of styrene with EDA (ethyl diazoacetate) is chosen to evaluate the performance of the different catalysts. We found that supported copper oxide has high activity for the cyclopropanation reaction, so copper oxide was supported on varied supports with different loadings. This study shows that the loading has great influence on the catalytic performance of the catalyst. The optimum loading on a support is corresponding to the monolayer dispersion volume of copper w oxide on this support. For different supports, the catalytic activity is much different. The highest selectivity is obtained for the catalyst using Ti02 as the support. Because the specific surface area of T102 support is very small (47.5 m2Ig), Ti02-A1203 was Abstract prepared as the support in which Ti02 is highly dispersed on A1203 (210 m2Ig). The catalyst CuO/Ti02-A1203 (12%) can give a yield of 93.5% cyclopropanes under mild reaction conditions. This is comparable to the best results of cyclopropanation in homogeneous catalyst systems. Furthermore, the catalysts and the reaction were characterized by ESR, UV-Vis, TPR, XRD, GC-MS and the reaction mechanism and the effect of the supports were discussed. (2) Above catalysts were used to catalyze cyclopropanation of 2,5-dimethyl-2,4-hexdiene, which was an important industrial substrate. 94% yield of cyclopropanes was obtained. This proves the prospect of this catalyst to be used in the industry. (3) We have tried to modify the supported copper oxide catalyst with chiral molecules, such as cinchonidine and tartaric acid, and also tended to develop other methods to prepare other heterogeneous chiral catalysts. However, so far we are not yet successful to realize the asymmetric cyclopropanation with heterogeneous catalysts for this thesis work.