Catalyst For Condensation Research Articles

Synthesis of ionic liquid intercalated layered double hydroxides of magnesium and aluminum: A greener catalyst of Knoevenagel condensation

Due to their structural merits that arise from their stability and high surface area, the layered double hydroxide (LDH) materials have caused strong attention. These characteristics provided intriguing possibilities with improved efficiency for catalytic applications. In this work, the preparation of 1-butyl-3-methylimidazolium hydroxide ([BMIM]+OH−) intercalated by a facile approach in a layered double hydroxide (LDH) matrix is reported and its implementation as a greener catalyst is shown. Different physico-chemical techniques such as XRD, FTIR, TGA, and N2-physisorption, HRTEM, and CO2 adsorption are implemented to characterize the structure of the fabricated catalysts. The [BMIM]+OH−/LDH exhibit outstanding catalytic performance in Knoevenagel condensation, resulting from the high LDH surface area and synergistic effects between both the intercalated ionic liquid and LDHs matrix. Knoevenagel’s fabricated catalysts can be exploited to catalyze different condensations and can be reused well. This work therefore generates good opportunities in the field of catalysis for the preparing and implementation of LDH-based catalysts.

Synthesis and characterization of functionalized NaP Zeolite@CoFe2O4 hybrid materials: a micro–meso-structure catalyst for aldol condensation

In this work, magnetic nanocomposite of NaP Zeolite and CoFe2O4 as magnetic nanoparticles (MNP’s) with different ratios were prepared and in the second step functionalized with 2-aminopyridine as a basic group. All samples were characterized by FT-IR, XRD, VSM, FESEM, EDX, TEM, and BET and thermal analyses. The results show that CoFe2O4 MNP’s was dispersed on NaP Zeolite without any significant aggregation with particle size about 30–50 nm. The BET and TEM confirmed the presence of mesoporous phase in the surface of NaP Zeolite/CoFe2O4 and preparation a micro–meso-structure. The NaP Zeolite/CoFe2O4 and NaP Zeolite/CoFe2O4/Am-Py were used as acid–base catalysts for aldol condensation of cyclohexanone with benzaldehyde, and furfural with acetone which produce curcumin and biofuel intermediates, respectively, in solvent-free condition. The effect of different factors such as the percent of CoFe2O4 MNP’s, catalyst amount, solvent, time and temperature was investigated. The catalyst was easily separated with an external magnet and reused four times without significant change in the yield. These catalysts have various advantages including high loading capacity, low leaching for CoFe2O4 MNP’s and simple and efficient recovery procedure which can be used under mild and ecofriendly condition.

An Efficient and Green Microwave-Assisted Synthesis of Quinoline DerivativesviaKnoevengal Condensation

:We have developed an efficient and green synthesis of quinoline derivatives using L-proline under Knoevenagel condensation. L-proline was found to be an efficient catalyst for the Knoevenagel condensation of substituted 2-aminoaryl ketones 1 with the active methylene compounds 2, affording quinolone derivatives 3. The reaction has been done under conventional as well as under microwave conditions. The latter procedure has been found to be much more efficient in terms of time and yield.

Preparation of a Pickering emulsion by modification of an amine-functionalized graphene oxide surface with organosilane: efficient catalyst for the Knoevenagel condensation of malononitrile with aldehydes at mild temperature

In this study, a series of Pickering emulsions for catalysis of Knoevenagel condensations of malononitrile with aldehydes were prepared by surface modification of amine-functionalized graphene oxide (GO-NH2) with trimethoxymethylsilane (MTMS).

An in situ approach to functionalize metal-organic frameworks with tertiary aliphatic amino groups.

Metal-catalyzed reductive amination of formyl-containing linkers with N,N-dialkylformamide solvents is concomitant with the solvothermal coordination assembly, leading to novel MOFs functionalized with tertiary aliphatic amino groups. This illustrates a novel one-pot strategy to functionalize MOFs through in situ organic transformation. The UiO-66 MOFs partially functionalized with the amino groups are highly active heterogeneous catalysts for Knoevenagel condensation.

Catalysts for vapor phase condensation of С1-С4 alcohols with carbon chain elongation

Catalysts for vapor phase condensation of С1-С4 alcohols with carbon chain elongation

Deep eutectic solvent: An efficient and green catalyst for the three-component condensation of indoles, aromatic aldehydes, and activated methylene compounds

The deep eutectic solvent-catalyzed multicomponent reaction of aldehydes, indoles, and activated methylene compounds under sonication has been developed. The method proceeded well for a wide scope of substrates under mild condition to afford 3-substituted indoles in moderate to good yields. Interestingly, no additives or solvents are used for the protocol. Moreover, the deep eutectic solvent (zinc chloride and choline chloride) is an inexpensive and recyclable catalyst making the protocol more efficient, facile, and cost-effective.

Solvent-free synthesis of jet fuel by aldol condensation and hydroprocessing of cyclopentanone as biomass-derivates

The conversion of biomass to jet fuel by thermochemical methods has become attractive to achieve the disposal of wastes and the production of highly valued fuels and chemicals. Aldol condensation of cyclopentanone from biomass catalytic fast pyrolysis and hydroprocessing of condensates were performed over Mg–Al–O and Ni/γ-Al2O3 to produce jet fuel under solvent-free conditions. The analysis of the carbon flow revealed that 37 carbon mole (CM) C10 alkane and 28 CM C15 alkane can ultimately be obtained from 100 CM cyclopentanone. Condensation catalyst with the Mg/Al mole ratio of 3:1 performed best due to its higher strength of weak and medium basic sites. Aldol condensation of cyclopentanone was confirmed to be a consecutive reaction that was obviously promoted at higher temperature. With regard to hydroprocessing, the yield of alkanes was greatly increased to 83.79% at 260 °C. Hydroprocessing of dimers and trimers followed very different pathways, and dimeric alcohols and trimeric alkenes played the role of important intermediates respectively. This study advances the development of jet fuel production from sustainable and green sources, providing a theoretical foundation for technology optimization and catalysts design.

Facile ultrasound-assisted grafting of silica gel by aminopropyltriethoxysilane for aldol condensation of furfural and acetone.

This work focuses on the development of a simple method to prepare heterogeneous catalysts with tunable basicity and stability for aldol condensation of furfural and acetone. Silica gel was grafted by aminopropyltriethoxysilane (APTES) with 20, 30, 40 and 50 wt. % of APTES using probe-type ultrasonicator with a power of 130 W and a frequency of 20 kHz. The grafted samples were studied by XRD, SEM, N2 sorption, FTIR, XPS, CHN and TG analysis, and CO2-TPD. The sonication facilitated the bond formation between APTES and the silica gel with less pore blocking than the conventional grafting method. The basicity of the samples was tunable with the quantity of APTES loading. The grafted samples were active catalysts for aldol condensation between furfural and acetone at 60 °C. The catalyst with 30 wt. % APTES grafting (30APS-U) provided a nearly complete furfural conversion and high furfurylbutenone selectivity. The conversion and selectivity increased with time and reached the highest values at 24 h. Thus, the catalysts with tunable basicity prepared by ultrasound-assisted grafting of silica with various APTES amounts were effective in furfural valorization.

Optimization of the process conditions for minimizing the deactivation in the furfural-cyclopentanone aldol condensation in a continuous reactor

This work demonstrates the key role of salts (both anions and alkaline cations) in the activity and stability of Mg-Zr mixed oxide as catalyst for the furfural-cyclopentanone aldol condensation in a continuous fixed bed reactor. Reactants oligomers are shown to cause active sites blockage, controlling the reaction conditions being required to maximize the selectivity for the first condensation adduct.The best results were obtained at pH = 8, using KHCO3 for fixing this pH. At these conditions, 75 % and 14 % of C10 and C15 yields were observed at 8 h on stream, whereas experiments performed at the other conditions show almost total deactivation. This good performance (performance and stability) is explained by a synergistic effect of two phenomena: a good buffering activity of the anion, and the ion exchange involving Na and K, which leads to the stabilization of the basic sites.

Boosting Enantioselectivity of Chiral Organocatalysts with Ultrathin Two-Dimensional Metal-Organic Framework Nanosheets.

The development of methodologies for inducing and tailoring enantioselectivities of catalysts is an important issue in asymmetric catalysis. In this work, we demonstrate for the first time that chiral molecular catalysts can be boosted from completely nonselective to highly enantioselective when installed in nanostructured metal-organic frameworks (MOFs). Exfoliation of layered crystals is one of the most direct synthetic routes to unltrathin nanosheets, but its use in MOFs is limited by the availability of layered MOFs. We illustrate that layered MOFs can be designed using ligand-capped metal clusters and angular organic linkers. This leads to the synthesis of two three-dimensional (3D) layered porous MOFs from Zn4-p-tert-butylsulfonyl calix[4]arene and chiral angular 1,1'-binaphthol/-biphenol dicarboxylic acids, which can be ultrasonic exfoliated into one- and two-layer nanosheets. The obtained MOF materials are efficient catalysts for asymmetric cascade condensation and cyclization of 2-aminobenzamide and aldehydes to produce 2,3-dihyroquinazolinones. While both binaphthol and biphenol display no enantioselectivity, restriction of their freedom in the MOFs leads to 56-90% and 46-72% ee, respectively, which are increased to 72-94% and 64-82% ee after exposure to external surfaces of the flexible nanosheets. Moreover, the MOF crystals and nanosheets exhibit highly sensitive fluorescent enhancement in the presence of chiral amino alcohols with enantioselectivity factors being, respectively, increased up to 1.4 and 2.3 times of the values of the diols, allowing them to be utilized in chiral sensing. Therefore, the observed enantioselectivities increase in the order organocatalyst < MOF crystals < MOF nanosheets in both catalysis and sensing. This work not only provides a strategy to make 3D layered MOFs and their untrathin nanosheets but also paves the way to utilize nanostructured MOFs to manipulate enantioselectivities of molecular catalysts.

Toward Continuous‐Flow Synthesis of Biologically Interesting Pyrazole Derivatives

AbstractA two‐step continuous‐flow synthesis of substituted pyrazole derivatives has been developed via the formation of vinylidene keto esters as key intermediates. Heterogeneous Ni2+‐montmorillonite was found to be an efficient catalyst for orthoester condensation of 1,3‐dicarbonyls under flow conditions. The intermediate reacted with methylhydrazine to afford pyrazole derivatives, for which suitable selection of a solvent played a key role in achieving high yields and excellent regioselectivities of the desired products. An application of this protocol has been demonstrated by the synthesis of a key intermediate for biologically active pyrazoles such as Bixafen.magnified image

Cu-metal-organic framework supported on chitosan for efficient condensation of aromatic aldehydes and malononitrile

In this study, a novel copper-based metal-organic framework (Cu-MOF)-immobilized modified chitosan (CS-CA), CS-CA/Cu-MOF, has been constructed easily and applied as an extremely efficient and economic mesoporous catalyst for the Knoevenagel condensation between aromatic aldehydes with malononitrile under mild reaction conditions. The resultant catalyst is characterized via various techniques including FTIR, XRD, FE-SEM, EDX, TEM, BET and STA analyses. The CS-CA/Cu-MOF was reused eight times without a noteworthy decrease in the catalytic activity. The use of CS-CA/Cu-MOF results in outstanding catalytic activity, high recyclability, very short reaction time at 25 °C, and an easy work-up process for the Knoevenagel condensation.

Sodium Tungstate Supported on a Three‐dimensional and Networked SBA‐15 for Knoevenagel Reaction

AbstractSodium tungstate (ST) supported on a three‐dimensional and networked SBA‐15 (3D‐SBA‐15) was utilized as a novel efficient catalyst for the Knoevenagel condensation of aldehydes with active methylene compounds such as malononitrile and ethyl cyanoacetate to afford substituted olefins through the conventional magnetic stirring or under ultrasound irradiation. ST/3D‐SBA‐15 catalyst was prepared using an incipient wetness impregnation method and confirmed by series of characterizations such as Fourier‐transform infrared spectra (FT‐IR), scanning electron microscope (SEM), X‐ray diffraction (XRD), N2 adsorption‐desorption and inductively coupled plasma‐optical emission spectroscopy. The reaction proceeded smoothly under the both stirring and ultrasound‐assisted conditions at room temperature. The 30ST/3D‐SBA‐15 catalyst with 30 wt% loading of Na2WO4 showed the highest catalytic performance with excellent yield within short time, and improvements were observed by carrying out the reactions under ultrasound irradiation. In addition, the solvent effect was significant in this work, and the optimum solvent was ethanol and water with volume ratio of 1 : 1.

Magnesium modified calcium hydroxyapatite: An efficient and recyclable catalyst for the one-pot Biginelli condensation

Magnesium modified calcium hydroxyapatite Ca(10-x)Mgx(PO4)6(OH)2, 0 ≤ x ≤ 3, have been synthesised using double decomposition method. The resulting materials have been fully characterised by X-ray powder diffraction, chemical analysis and infrared spectroscopy. X-ray diffraction analysis shows that the obtained materials consist of a single phase having an apatitic structure. The catalytic activity of the synthesised compounds was tested on the one pot Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2-(1H)-one. The substitution of calcium by magnesium ions has a positive effect on the efficiency of the catalyst. Moreover, increasing the magnesium ion concentration in the apatite leads to better yields in Biginelli product and a faster rate of the reaction. The catalyst is easily recyclable can be used at least five times without significant change in activity.

Magnetically separable catalyst for condensation of renewable aldehydes and 2-methylfuran to saturated cyclic oxygenates

The saturated cyclic ethers produced from biomass derived aldehydes and 2-methylfuran are the potential diesel fuel candidates. The synthesis of saturated cyclic ethers is a two step process which involves acid catalyzed condensation of aldehydes with 2-methylfuran and the subsequent selective furan ring hydrogenation of the condensation products. Here, we designed a novel recyclable magnetic solid acid catalyst such as [Fe3O4@SiO2-Pr-Py-H][2HSO42−] and employed for the condensation of 2-methylfuran with formaldehyde as model substrates and reaction parameters were optimized. Under the set reaction conditions, condensation of 2-methylfuran with several other aldehydes were also successfully achieved with very good yields. Further, several supported noble metal catalysts were screened in order to find suitable catalyst system for selective furan ring hydrogenation of condensation products. Among those, 5% Pd/C was found to be very active and selective for furan ring hydrogenation without formation of ring opened products under very low hydrogen pressure at room temperature. Prepared catalysts were thoroughly characterized with sophisticated techniques.

Waste Seashells as a Highly Active Catalyst for Cyclopentanone Self-Aldol Condensation

For the first time, waste-seashell-derived CaO catalysts were used as high-performance solid base catalysts for cyclopentanone self-condensation, which is an important reaction in bio-jet fuel or perfume precursor synthesis. Among the investigated seashell-derived catalysts, Scapharca Broughtonii-derived CaO catalyst (S-shell-750) exhibited the highest dimer yield (92.1%), which was comparable with commercial CaO (88.2%). The activity sequence of different catalysts was consistent with the CaO purity sequence and contact angle sequence. X-ray diffraction (XRD) results showed that CaCO3 in waste shell were completely converted to CaO after calcination at 750 °C or above for 4 h. CO2 temperature-programmed desorption (CO2-TPD) results indicate that both the amount and strength of base sites increase significantly when the calcination temperature climbs to 750 °C. Therefore, we can attribute the excellent performance of S-shell-750/850/950 catalysts to the higher CaO content, relatively low hydrophilicity, and stronger acidity and basicity of this catalyst. This study developed a new route for waste shell utilization in bio-derived ketone aldol condensation.

Metal- and halogen-free synthesis of ordered mesoporous carbon materials

Abstract Mesoporous carbon materials are of great interest as catalyst supports. However, the presence of impurities such as the metal or halide ions which are often used to catalyse the polymerisation and condensation reactions in their preparation can be poisonous to the final catalyst product. For this reason, in this work, metal- and halogen-free mesoporous polymer and carbon materials (OMCs) were synthesised using a modified two phase method employing alternative polymerisation and condensation catalysts. The OMC materials synthesised exhibit a highly ordered two dimensional hexagonal arrangement of cylindrical mesopores, as revealed by small angle XRD, gas physisorption and TEM analysis, and have typical specific surface areas of ca. 600 m2/g, pore size of ca. 7.0 nm, and pore volume of approximately 0.60 cm3/g. Their physical evolution with increasing calcination temperature is examined as are the effects of varying synthesis parameters on the nature of the final mesostructure.

Effect of metal modification of titania and hydrogen co-feeding on the reaction pathways and catalytic stability in the acetone aldol condensation

A stable performance of TiO2 catalysts for gas-phase acetone aldol condensation was observed when reduced metals were added (Pt or Ni, 1.5 wt%) and the reactions were conducted in presence of hydrogen. In both cases, the resulting metal-loaded catalysts are stable for 10 h, whereas continuous deactivation is observed for the parent TiO2 catalyst (573 K). Both the activation of the H2 molecule by metal nanoparticles and the change of the catalytic surface by metal insertion (in the case of Ni-loaded catalyst) enable suppressing oligomerization (by hindering enolates formation) and the strong adsorption of intermediates (by decreasing the concentration of high-strength acid-basic active sites), respectively.More interestingly, these metals allow to tune the selectivity of the reaction. Indeed, the Ni-loaded titania catalyst is highly selective for the synthesis of α,β-unsaturated ketones (selectivity to unsaturated C6 and C9 species >98%, at ∼12% acetone conversion), whereas the Pt-loaded one is highly selective to the formation of saturated C6 and C9 ketones (MIBK and DIBK, with selectivities >95% at ∼42% acetone conversion).The catalytic activity and stability of the two materials (Ni/TiO2 and Pt/TiO2) in both absence and presence of H2 are compared between them and with those of the parent TiO2. The results obtained by the reaction gas-phase analysis are supplemented through different solid characterization techniques (i.e., CO2-TPD and NH3-TPD, HRTEM, XPS, TPO, and DRIFTS).

Highly efficient Nb2O5 catalyst for aldol condensation of biomass-derived carbonyl molecules to fuel precursors

Aldol condensation is of significant importance for the production of fuel precursors from biomass-derived chemicals and has received increasing attention. Here we report a Nb2O5 catalyst with excellent activity and stability in the aldol condensation of biomass-derived carbonyl molecules. It is found that in the aldol condensation of furfural with 4-heptanone, Nb2O5 has obviously superior activity, which is not only better than that of other common solid acid catalysts (ZrO2 and Al2O3), more importantly, but also better than that of solid base catalysts (MgO, CaO, and magnesium-aluminum hydrotalcite). The detailed characterizations by N2 sorption/desorption, NH3-TPD, Py-FTIR and DRIFTS study of acetone adsorption reveal that Nb2O5 has a strong ability to activate the C=O bond in carbonyl molecules, which helps to generate a metal enolate intermediate and undergo the nucleophilic addition to form a new C–C bond. Furthermore, the applicability of Nb2O5 to aldol condensation is extended to other biomass-derived carbonyl molecules and high yields of target fuel precursors are obtained. Finally, a multifunctional Pd/Nb2O5 catalyst is prepared and successfully used in the one-pot synthesis of liquid alkanes from biomass-derived carbonyl molecules by combining the aldol condensation with the sequential hydrodeoxygenation.