104870-56-6Relevant articles and documents
Diiodosamarium, a unique catalyst precursor for ene reactions of unsaturated carbonyl compounds
Sarkar, Tarun K.,Nandy, Sandip K.
, p. 5195 - 5198 (1996)
SmI2 presents catalytic activity for ene cyclizations of a series of unsaturated carbonyl compounds, some of which are prone to rearrangement or polymerization under standard conditions.
TiO2(SiO2)x and ZrO2(SiO 2)x cryogels as catalysts for the citronellal cyclization to isopulegol
Jimeno, Ciril,Miras, Jonathan,Esquena, Jordi
, p. 616 - 623 (2013)
TiO2(SiO2)x and ZrO2(SiO 2)x mixed oxides prepared by a simple sol-gel procedure plus freeze-drying achieve very high surface areas. Such cryogels are shown to catalyze the cyclization of citronellal to isopulegol. The dispersion of the active metal has been optimized, as it is shown that high specific surface areas are the key for the catalytic activity of the cogels. Nevertheless zirconia-silica cryogels depict much higher catalytic activity, with only 5 mol% Zr being required, than the corresponding titania-silica mixed oxides.
Comparison of acidic site quantification methods for a series of nanoscopic aluminum hydroxide fluorides
Hemmann, Felix,Jaeger, Christian,Kemnitz, Erhard
, p. 56900 - 56909 (2014)
Quantitative determination of acidic surface sites is highly important for the characterization of solid acids because the activity of a catalyst is often related to the concentration of these sites. A recently developed method using 15N Nuclear Magnetic Resonance spectroscopy (NMR) for the quantification of acidic Lewis and Bronsted sites has been tested for a series of nanoscopic aluminum hydroxide fluorides. Comparison with other methods for the quantitative determination of acidic sites shows that this 15N NMR quantification method is a promising technique for the comprehensive investigation of acidic sites. Three different acidic sites, one Bronsted and two Lewis sites, can be distinguished by their 15N chemical shifts of pyridine and simultaneously quantified under conditions corresponding to catalytic reaction conditions. Determination of the individual concentrations of acidic sites allows further insight into the catalytic process. It was found that the concentration of Bronsted sites correlates with catalyzed conversion of citronellal to isopulegol in the investigated series of catalysts. Additionally, investigations indicate that one of the Lewis sites become blocked during the reaction of citronellal.
Citronellal cyclisation over heteropoly acid supported on modified montmorillonite catalyst: effects of acidity and pore structure on catalytic activity
Shah, Abdul Karim,Park, Sungsoo,Khan, Hassnain Abbas,Bhatti, Umair Hassan,Kumar, Praveen,Bhutto, Abdul Waheed,Park, Yeung Ho
, p. 2405 - 2423 (2018)
Citronellal cyclisation to isopulegol is an important intermediate step in the production of menthol. Several heteropoly acids (PTA) supported on modified montmorillonite (MM) catalysts were synthesized and then tested in cyclisation reactions. The prepared samples were characterized by XRD, ICP-OES, FTIR, N2 sorption, NH3-TPD, pyridine adsorption, amine titration and FE-SEM techniques. Effects of post-treatment were studied on montmorillonite pore structure, acidity and catalytic activity. The catalytic activity and isopulegol selectivity improved with acid-treatment and PTA loading. The amount of Lewis acidity of montmorillonite was enhanced with acid-treatment and PTA impregnation. In cyclisation, highest catalytic activity (31.87?mmol?cat?g?1?min?1) was achieved with 96% isopulegol yield in the use of 20% PTA-MM catalyst. The highest catalytic activity and selectivity were obtained in the presence of higher acidity and strong Lewis acidic sites, whereas effects of pore structure blockage seemed minor. The catalytic activity further decreased with the loss of active acidic sites (L and B) due to PTA decomposition with calcination at a higher temperature.
Metal Nanoparticles Supported on Perfluorinated Superacid Polymers: A Family of Bifunctional Catalysts for the Selective, One-Pot Conversion of Vegetable Substrates in Water
Moreno-Marrodan, Carmen,Liguori, Francesca,Barbaro, Pierluigi,Caporali, Stefano,Merlo, Luca,Oldani, Claudio
, p. 4256 - 4267 (2017)
We describe the rational design of a new versatile family of bifunctional catalytic materials based on the combination of supported metal nanoparticles (Pd, Rh, Ru) and the superacid, perfluorinated Aquivion PFSA polymer. The heterogeneous catalysts were tested in the multi-step valorisation of representative plant derivatives to high-added-value chemicals. Particularly, the conversion of (+)-citronellal to (-)-menthol and levulinic acid to γ-valerolactone was achieved in one pot and in one stage in the water phase and shows full selectivity at a high conversion level under mild reaction conditions. The results are discussed in terms of the catalyst micro-structure.
Insights into the Complexity of Heterogeneous Liquid-Phase Catalysis: Case Study on the Cyclization of Citronellal
Müller, Philipp,Wolf, Patrick,Hermans, Ive
, p. 2760 - 2769 (2016)
Heterogeneously catalyzed liquid-phase reactions are highly complex chemical systems. As the local molecular composition close to the active site is often unknown, sophisticated spectroscopic tools are needed to gain insights on a molecular level. One solution to these challenges is the use of modulation excitation spectroscopy with attenuated total reflection infrared spectroscopy. We use this highly sensitive and selective technique to study the Lewis acid-catalyzed cyclization of citronellal over mesoporous Sn-SBA-15 and microporous Sn-Beta. We find that the reaction mechanism is generally similar for the two materials. However, the confined space at the active site within the zeolite stabilizes the coordination of citronellal to the SnIV site and prevents byproduct formation, as well as the reverse reaction due to size-exclusion of the product isopulegol. The use of the Lewis base acetonitrile as solvent reduces the catalytic performance with Sn-SBA-15 drastically, while Sn-Beta remains highly active. Infrared spectra reveal a simultaneous coordination of citronellal and acetonitrile to the tin site in Sn-Beta, whereas in Sn-SBA-15, the more-accessible SnIV site leads to much stronger and hence detrimental competitive adsorption. The results obtained in this study indicate that the substrate-catalyst-solvent combination needs to be optimized in order to maximize the performance of solid-liquid reactions.
Cyclization of citronellal over zeolites and mesoporous materials for production of isopulegol
Maeki-Arvela, Paeivi,Kumar, Narendra,Nieminen, Ville,Sjoeholm, Rainer,Salmi, Tapio,Murzin, Dmitry Yu.
, p. 155 - 169 (2004)
Cyclization of (+)-citronellal was investigated over zeolites and mesoporous materials as well as on silica under a nitrogen atmosphere in cyclohexane as a solvent. The highest cyclization rates were observed over mesoporous materials and 12-membered ring zeolites with high Bronsted acid concentration, while very low cyclization rates were achieved over silica with low or no Bronsted acidity, respectively. At the same a time low cyclization rate was observed over 10-membered ring pore H-ZSM-5 with a high Bronsted acid site concentration, which is due to diffusional limitation of the product in the narrow pores. The selectivity to cyclization products was very high over all the catalysts, being independent of the conversion of citronellal. Neither concentration of the Bronsted nor Lewis acid sites influenced the stereoselectivity to isopulegol. The support structure had only a minor effect on the stereoselectivity. Quantum mechanical calculations were carried out to explain the experimental results. The calculated stabilities of the carbocationic reaction intermediates correlated well with the observed stereoselectivity. The stereoselectivities were analogous when starting from racemic citronellal mixture or enantiopure (+)-citronellal; the former one gave 8 different pulegols, whereas only 4 pulegols were formed from (+)-citronellal.
Directed hydrogenation of acyclic homoallylic alcohols: Enantioselective syntheses of (+)- and (-)-laurenditerpenol
Chittiboyina, Amar G.,Peddikotla, Prabhakar,Avery, Mitchell A.,Khan, Ikhlas A.
, p. 9223 - 9232 (2013)
Laurenditerpenol is the first marine natural product shown to inhibit hypoxia-inducible factor 1 (HIF-1) activation. Preclinical studies support that the inhibition of HIF-1 is one of the molecular targets for antitumor drug discovery. The synthetically c
Highly selective menthol synthesis by one-pot transformation of citronellal using Ru/H-BEA catalysts
Pl?sser, Jutta,Lucas, Martin,Claus, Peter
, p. 189 - 197 (2014)
The one-pot transformation of citronellal to menthol requires a combined cyclization-hydrogenation step for which Ru/H-BEA catalysts were identified as highly active and selective catalysts. After identifying zeolite H-BEA as the most promising heterogeneous catalyst for the cyclization of citronellal to the intermediate isopulegol, bifunctional metal/H-BEA catalysts were investigated in the one-pot transformation of citronellal to menthols. Using Pd undesired defunctionalization prevailed, while using Pt and Ru, the formation of menthols predominated. Finally, for Ru/H-BEA catalysts, the effect of catalyst composition (Si:Al ratio, Ru content) and reaction conditions (temperature, hydrogen pressure, and solvent) was investigated to diminish citronellal hydrogenation, dimerization, and defunctionalization. Accordingly, with a 1%Ru/H-BEA-25 catalyst (Ru particle size = 1 nm) in dioxane at 15 bar hydrogen pressure and 373 K, a very high selectivity to menthols of 93% at nearly full conversion was obtained. The catalyst is also highly diastereoselective producing 79% of the desired (±)-menthol.
Nb-doped variants of high surface aluminium fluoride: A very strong bi-acidic solid catalyst
Marshall, Clara Patricia,Scholz, Gudrun,Braun, Thomas,Kemnitz, Erhard
, p. 6834 - 6845 (2019)
A niobium doped high surface aluminium fluoride (HS-AlF3) catalyst was prepared, using an approach in which niobium doped aluminium hydroxide fluoride obtained via reaction of aqueous HF with the respective metal alkoxides in isopropanol is further fluorinated under flow of CHClF2 at 200 °C. A comparable procedure was used to synthesize a Nb-free variant for comparison. Both catalysts exhibit very strong Lewis acidic surface sites which are capable to activate strong carbon-halogen bonds at room temperature, just as the classical high-surface AlF3 (HS-AlF3), obtained by reacting aluminium isopropoxide with anhydrous HF, does. The catalysts were characterized by elemental analysis, P-XRD, MAS NMR spectroscopy, N2 adsorption, NH3-TPD, and pyridine photoacoustic FT-IR spectroscopy. In contrast to previously reported niobium doped HS-AlF3, which was prepared using anhydrous HF, the doped catalyst obtained via this aqueous HF-route shows excellent performance both in the isomerization of 1,2-dibromohexafluoropropane, a reaction that occurs only in the presence of the strongest Lewis acids, and in the cyclization of citronellal to isopulegol, a reaction which requires both, Lewis and Br?nsted acid sites.
