Eliška Vyskočilová

Characterization and use of MoO3 modified alumosilicates in Prins cyclization of isoprenol and isovaleraldehyde

MoO3 modified alumosilicates were prepared by impregnation method and used in Prins cyclization of isoprenol and isovaleraldehyde forming 2-isobutyl-4-methyltetrahydro-2H-pyran-4-ol (important compound for fragrant industry). Alumosilicates of Siral type were chosen as supports and compared with pure silica and alumina. Prepared catalysts were characterized by available methods: XRD, XRF, solid UV–Vis, TGA, TPD of pyridine, nitrogen adsorption and SEM. It was found that impregnation of Siral by MoO3 gave homogeneous distribution of Mo species on the support. On the other side using pure silica as a support the crystallic structure of MoO3 was detected in the resulting material. Impregnation of pure alumina by MoO3 resulted in the formation of aluminum molybdate. All prepared materials were used in above mentioned reaction. With increasing amount of silica in alumosilicate the increase of reaction rate and selectivity was observed up to 40% of silica in the material. Comparable results (selectivity to substituted tetrahydropyranol up to 50%) were obtained using Siral 40 and silica as supports for MoO3. These materials may be also used repeatedly without loss of activity and selectivity.

Preparation of 2-isobutyl-4-methyltetrahydro-2H-pyran-4-ol via Prins cyclization using Fe-modified silica

Prins cyclization of isoprenol and isovaleraldehyde producing 2-isobutyl-4-methyltetrahydro-2H-pyran-4-ol was chosen as a model reaction in iron-modified silica catalysts testing. Two sources of iron were used—iron nitrate and iron chloride. Catalysts were prepared by different procedures and characterized using available methods (XRD, UV/Vis, TPD of pyridine, TGA and XRF). In both types of catalyst, the interaction between the oxygen atoms of silica and the iron atoms of the modifier was confirmed. The iron nitrate-modified catalyst possessed very low acidity enabling only the formation of hemiacetal of isoprenol and isovaleraldehyde or diacetal. The iron chloride modification was performed either by wet impregnation or by impregnation under solvent-free conditions. Both types of such prepared catalysts were active in Prins cyclization, producing the desired substituted tetrahydropyranol. The positive influence of water on the selectivity for the desired compound was confirmed. Siral-type alumosilicates used as support negatively influenced the selectivity. Silica modified by iron chloride may be used as an alternative catalyst in the preparation of substituted tetrahydropyranols; the achieved selectivity was up to 70%.

The capacity and effectiveness of diosmectite and charcoal in trapping the compounds causing the most frequent intoxications in acute medicine: A comparative study

The aim of the study was to compare the adsorption ability of two adsorbent materials, namely diosmectite and activated charcoal towards selected model compounds that are most commonly involved in acute intoxication. Eleven model compounds were selected: acetylsalicylic acid, α-amanitin, amlodipine, digoxin, phenobarbital, ibuprofen, imipramine, carbamazepine, oxazepam, promethazine, and theophylline. Of the tested compounds, promethazine and imipramine were the most effectively adsorbed to diosmectite. Their adsorption to diosmectite (0.356±0.029mg promethazine/mg diosmectite and 0.354±0.019mg imipramine/mg diosmectite, respectively) was significantly higher than their adsorption to activated charcoal. The effect of temperature and pH on the adsorption efficiencies was also evaluated. In the case of experiments with mixture of both adsorbents, they mostly behaved in a solution independently or in a slightly antagonistic way. Using various methods such as N2 adsorption and thermogravimetric analysis, the structure and texture of diosmectite and activated charcoal were attained.

Hyper-Cross-Linked Polyacetylene-Type Microporous Networks Decorated with Terminal Ethynyl Groups as Heterogeneous Acid Catalysts for Acetalization and Esterification Reactions

Heterogeneous catalysts based on materials with permanent porosity are of great interest owing to their high specific surface area, easy separation, recovery, and recycling ability. Additionally, porous polymer catalysts (PPCs) allow us to tune catalytic activity by introducing various functional centres. This study reports the preparation of PPCs with a permanent micro/mesoporous texture and a specific surface area SBET of up to 1000 m2  g-1 active in acid-catalyzed reactions, namely aldehyde and ketone acetalization and carboxylic acid esterification. These PPC-type conjugated hyper-cross-linked polyarylacetylene networks were prepared by chain-growth homopolymerization of 1,4-diethynylbenzene, 1,3,5-triethynylbenzene and tetrakis(4-ethynylphenyl)methane. However, only some ethynyl groups of the monomers (from 58 to 80 %) were polymerized into the polyacetylene network segments while the other ethynyl groups remained unreacted. Depending on the number of ethynyl groups per monomer molecule and the covalent structure of the monomer, PPCs were decorated with unreacted ethynyl groups from 3.2 to 6.7 mmol g-1 . The hydrogen atoms of the unreacted ethynyl groups served as acid catalytic centres of the aforementioned organic reactions. To the best of our knowledge, this is first study describing the high activity of hydrogen atoms of ethynyl groups in acid-catalyzed reactions.

A synthetic route to 4-alkyl-α-methylhydrocinnamylaldehydes

The 4-Alkyl-α-methylhydrocinnamylaldehydes (alkyl-isopropyl, isobutyl, methyl) are frequently used fragrances with desired floral (lilac, cyclamen, lily-of-the-valley) scent. These substances are valued for their good stability in basic solution and, therefore, are frequently used in soaps, detergents, or shampoos. These substances are synthesized by a two-step synthesis involving base catalyzed aldol condensation of 4-alkylbenzaldehyde with propanal followed by selective hydrogenation of the C=C bond. In aldol condensation, selectivity is decreased by formation of undesired products of propanal autocondensation 2-methylpent-2-enal. In this work the reaction conditions for homogenous catalyzed aldol condensation of 4-isobutylbenzadehyde with propanal were tested (catalyst type and amount, molar ratio of reactants, solvent type). Reaction conditions giving the best results (92% conversion, 79% selectivity) were adapted to other 4-alkyl-α-methylcinnamylaldehydes preparation with similar results. In the second step—hydrogenation of aldol product different types of catalyst (nickel, cobalt, palladium or Adkins catalyst), and also different solvents, were tested. Hydrogenation conditions leading to the highest yield (72% selectivity at 95% conversion) were adapted to other 4-alkylhydrocinnamyladehydes with similar results.