Neue heterogenkatalysierte Duftstoffsynthesen durch Aldolreaktion

摘要

The aldol condensation is often used regarding the synthesis of different fine chemicals like fragrances and their precursors. In the petrochemical industry, the aldol condensation is also used to produce more valuable chemicals. In the course of this thesis, several heterogeneous catalysts, mainly based on rare earth oxides, were used to accelerate this reaction. Synthesis of 4-(4-Hydroxyphenyl)-3-buten-2-on. The main focus of this thesis was the synthesis of 4-(4-Hydroxyphenyl)-3-buten-2-on out of 4-HBA and acetone. As catalysts, rare earth oxides were used, as full catalysts as well as impregnated on different carrier materials. It could be shown that the very slow reaction can be highly accelerated by adding the mentioned catalysts. The most active catalyst, which was tested during this thesis was1 wt% La2O3/TiO2. This catalyst showed extraordinary high performance and yields of over 97% could be reached with an almost 100% selectivity. However in a continiuous flow experiment the catalyst showed a deactivation within several days due to the accumulation of organic material. After a recalcination of the catalyst, the activity could be fully restored. Synthesis of pseudoionone. The synthesis of pseudoionone was investigated in a similar way. Again the rare earth metal oxides were tested and the 3 wt% La2O3/TiO2 catalyst was found as most active catalyst with a selectivity of 87% at complete conversion. The catalytic perpormance of 1 wt% La2O3/TiO2 was also tested in several different aldol condensations: Synthesis of cinnamon aldehyde. The synthesis of cinnamon aldehylde from benzaldehye and acetaldehyde was investigated. Due to the high reactivity of acetaldehyde compared to acetone, autocondensation products like crotone aldehyde were found. Therefore the amount of acetaldehyde was limited (5:1 ratio of benzaldehyde to acetaldehyde). With these reaction parameters, conversion of 15% benzaldehyde with a selectivity of 86% to cinnamon aldehyde could be achieved. Synthesis of vanillidine acetone. The synthesis of vanillidine acetone is very simmilar to the synthesis of 4-(4-Hydroxyphenyl)-3-buten-2-on. Therefore the same reaction parameters were chosen and with the same catalyst a complete conversion with 98% selectivity to vanillidine acetone could be achieved. Synthesis of pulegone. Quite different to the other tested condensations, the synthesis of pulegone from acetone and 3-MCHN could be achieved. The product spectrum showed a high amount of various products which are mainly formed by the autocondensation of acetone like diacetone alcohol, mesityle oxide or isomesityle oxide. The desired product however could only be found in traces. The reason for this poor results was the inversion of the methylene component and the carbonyl component. Synthesis of 4-(2-Furyl)-3-buten-2-on. The synthesis of 4-(2-Furyl)-3-buten-2-on out of furfural and acetone was also investigated. It could be shown, that the starting materials are much more active than the materials in the previously described reactions and the reaction parameters had to be adjusted. The conversion had to be limited too, because of the formation of consecutive products.