Catalyzed Aldol Condensation Research Articles

Oxidative coupling of furfural with alcohols to 2-alkyl-3-(2-furyl) acroleins using Li-ion battery waste based LiNiaMnbCocOd/graphite catalyst

Carbon number upgrading of bio-furans by coupling with other renewable feedstocks is an attractive approach for producing renewable fuel and polymer feedstocks. In this work, used Li-ion battery waste based low cost catalyst was shown as an alternative to expensive noble metal catalysts for coupling furfural with alcohols to give 2-alkyl-3-(2-furyl) acroleins. The catalyst was prepared by pyrolyzing the black electrode coating from 18650 Li-ion cells in a used laptop battery at 600 °C in air. Highest furfural conversions of 72.6, 83.6, 100.0 and 95.4 % were observed for 1-propanol, 1-butanol, 1-pentanol and 1-hexanol respectively, using 0.6 mmol LiOH/mmol of furfural and using 25 mg/mmol of furfural catalyst loading, 0.345 MPa O2, 110 °C for 4.0 h. However, recycling of LiNiaMnbCocOd/graphite catalyst showed significant loss in catalytic activity in four cycles of reuse. A reaction scheme involving oxidation of alcohols to aldehydes followed by base catalyzed aldol condensation was proposed to explain the coupling to give 2-alkyl-3-(2-furyl) acroleins.

Synthesis, Characterization and Thermal Study of Some new Copolyesters from mono-carbonyl analogues of Curcumin and Thymol blue dye

A series of copolyesters were prepared from a dicarboxylic acid, curcumin analogues (monocarbonyl) and thymol blue dye in the mole ratio of 2:1:1 by direct polycondensation using triethylamine (Et3N) as the condensation agent. The dicarboxylic used is 2,6-Pyridine dicarbonyl dichloride acid. The curcumin analogues were prepared by acid catalyzed Aldol condensation reaction. These copolyesters were characterized by FT-IR. The fluorescence of the synthesized copolyesters was also investigated. Furthermore, Thermo gravimetric analysis (TGA) was used to investigate the thermal stability of these copolymers

Catalytic Aldol Condensation of 5‐Hydroxymethylfurfural and its Synthesis from Concentrated Feed of Carbohydrates

Abstract1‐(5‐(Hydroxymethyl)furan‐2‐yl)‐5‐methylhex‐1‐en‐3‐one was prepared from cellulose or glucose by a sequence of depolymerization/dehydration/aldol condensation reactions. The synthesis of HMF was first performed starting from a highly concentrated feed of glucose and cellulose (31 wt.%) using choline chloride in MIBK/water biphasic media via the formation of a glucoside intermediate. Next, the aldol condensation of HMF with MIBK was investigated over alkaline metal oxides. Among the catalysts used, commercial BaO was highly efficient with a yield of aldol product above 90 %. Under air, BaO instantaneously transformed into Ba(OH)2, H2O and BaO2 which are regarded as active phases for the reaction. The catalyst basicity and solvent were key parameters to govern the selectivity of the reaction by limiting secondary reactions.

Comprehensive screening strategy coupled with structure-guided engineering of l-threonine aldolase from Pseudomonas putida for enhanced catalytic efficiency towards l-threo-4-methylsulfonylphenylserine.

l-Threonine aldolases (TAs) can catalyze aldol condensation reactions to form β-hydroxy-α-amino acids, but afford unsatisfactory conversion and poor stereoselectivity at the Cβ position. In this study, a directed evolution coupling high-throughput screening method was developed to screen more efficient l-TA mutants based on their aldol condensation activity. A mutant library with over 4000l-TA mutants from Pseudomonas putida were obtained by random mutagenesis. About 10% of mutants retained activity toward 4-methylsulfonylbenzaldehyde, with five site mutations (A9L, Y13K, H133N, E147D, and Y312E) showing higher activity. Iterative combinatorial mutant A9V/Y13K/Y312R catalyzed l-threo-4-methylsulfonylphenylserine with a 72% conversion and 86% diastereoselectivity, representing 2.3-fold and 5.1-fold improvements relative to the wild-type. Molecular dynamics simulations illustrated that additional hydrogen bonds, water bridge force, hydrophobic interactions, and π-cation interactions were present in the A9V/Y13K/Y312R mutant compared with the wild-type to reshape the substrate-binding pocket, resulting in a higher conversion and Cβ stereoselectivity. This study provides a useful strategy for engineering TAs to resolve the low Cβ stereoselectivity problem and contributes to the industrial application of TAs.

Selective Synthesis of Renewable Bio-Jet Fuel Precursors from Furfural and 2-Butanone via Heterogeneously Catalyzed Aldol Condensation

This study aims to synthesize α,β-unsaturated carbonyl compounds with branched structures via aldol condensation of furfural and 2-butanone using magnesium–aluminum (MgAl) mixed oxides as heterogeneous acid–base catalysts. Regarding the molecular structure of 2-butanone, there are two possible enolate ions generated by subtracting the α-hydrogen atoms at the methyl or methylene groups of 2-butanone. The branched-chain C9 products, derived from the methylene enolate ion, can be applied as bio-jet fuel precursors. The most suitable catalyst, contributing the highest furfural conversion (63%) and selectivity of the branched-chain C9 products (77%), is LDO3, the mixed oxides with 3:1 Mg:Al atomic ratio, with a high surface area and a large number of medium basic sites. The suitable reaction conditions to produce the branched-chain C9 ketones are 1:5 furfural:2-butanone molar ratio, 5 wt.% catalyst loading, 120 °C reaction temperature, and 8 h reaction time. Additionally, this study investigates the adsorption of 2-butanone onto a mixed oxide using in situ Fourier transform infrared spectroscopy; the results of which suggest that the methylene enolate of 2-butanone is the likely dominant surface intermediate at elevated temperatures. Accordingly, the calculation, based on density functional theory, indicates that the methylene enolate ion of 2-butanone is the kinetically favorable intermediate on an MgO(100) as a model oxide surface.

Acid catalyzed one-pot approach towards the synthesis of curcuminoid systems: unsymmetrical diarylidene cycloalkanones, exploration of their single crystals, optical and nonlinear optical properties.

In the present study crystalline unsymmetrical diarylidene ketone derivatives BNTP and BDBC have been prepared by two sequential acid catalyzed aldol condensation reactions in a one pot manner. The crystal structures of both compounds were confirmed by single crystal X-ray diffraction analysis which revealed the presence of H-bonding interactions of type C-H⋯O, along with weak C-H⋯π and weak π⋯π stacking interactions that are involved in the crystal stabilization of both organic compounds. Hirshfeld surface analysis is carried out for the broad investigation of the intermolecular interactions in both compounds. The quantum chemical investigation was performed on the optimized molecular geometries of BNTP and BDBC to calculate optical and nonlinear optical (NLO) properties. The density functional theory (DFT) study showed that the third-order NLO polarizabilities of compounds BNTP and BDBC are found to be 226.45 × 10-36 esu and 238.72 × 10-36 esu, respectively, which indicates noticeable good NLO response properties. Additionally, the BNTP and BDBC molecules also showed the HOMO-LUMO orbital gaps of 5.96 eV and 6.06 eV, respectively. Furthermore, the computation of UV-visible spectra of the titled compounds indicated a limited and/or no absorption above the 400 nm region, directing a good transparency and NLO property trade-off for both synthesized compounds that may play a significant contribution in the future for optoelectronic technologies.

Synthesis of high-grade Jet fuel blending precursors by aldol condensation of lignocellulosic ketones using HfTPA/MCM-41 with strong acids and enhanced stability

Upgrading lignocellulosic ketones to Jet fuel precursors by aldol condensation is the key step for the synthesis of high-grade bio-Jet fuels. State-of-art works are confined in pure feedstock used, catalysis sites leaching and coking. Therefore, we synthesized a strong solid acid HfTPA/MCM-41 and used it to catalyze aldol condensation of lignocellulosic ketone mixture to bio-jet fuel blending precursors, where 80 %Hf1.5TPA/MCM-41 shows better activity than 80 %HPW/MCM-41 and commercial zeolites with 66.8 % yield of products obtained. The good performance of the catalyst is ascribed to good acid properties, large surface area and especially new strong L acids and good stability based on anti-coking and water tolerance by Hf doping, which changes the electronic structure of the catalyst surface to efficiently activate CO bond of ketones to form a metal enolate intermediate and anchoring HPW from leaching. This work demonstrates an efficient way to synthesize high-performance acid catalyst applied in bio-jet fuel synthesis.

Formation of the CaSnO3 crystalline phase during catalytic aldol condensation of acetone under supercritical conditions

Formation of the CaSnO3 crystalline phase during catalytic aldol condensation of acetone under supercritical conditions

Catalytic aldol condensation of bio-derived furanic aldehydes and acetone: Challenges and opportunities

Bio-derived furfural and 5-hydroxymethylfurfural can be combined with acetone to yield aldol condensation products that may serve as biofuel and polymer precursors. We have explored different catalytic systems to obtain and purify each product in the most efficient way. The results of the catalytic tests of the cross-condensations and of the self-condensation of acetone allowed the comparison of the different reactivity of the two aldehydes. Online and in situ/operando ATR-IR was used to monitor the reaction over time and to study the interaction of the reaction species with the solid catalyst, especially the formation of deactivating organic matter that covers the surface, which is a major issue in heterogeneous condensation processes. In situ NMR was used to study the ongoing reaction, assessing its stereoselectivity, and to study the behavior of deuterated species in the catalytic system. Finally, the preparation of C14, a hetero-double-condensation product, was also explored.

Synthesis and Characterization of Some New Copolyester from Curcumin Mono-Carbonyl Analogues

Nine copolyesters were prepared from a dicarboxylic acid, curcumin analogues (monocarbonyl) and phenophthalene dye in the mole ratio of 2:1:1 by direct polycondensation using triethylamine (Et3N) as the condensation agent. The dicarboxylic used is 2,6-Pyridine dicarbonyl dichloride acid. The curcumin analogues were prepared by acid catalyzed Aldol condensation reaction. These copolyesters were characterized by FT-IR. The fluorescence of the synthesized copolyesters was also investigated. Furthermore, Thermo gravimetric analysis (TGA) was used to investigate the thermal stability of these copolymers.

Sustainable production of biofuel precursors by aldol condensation with biomass-derived 5-methylfurfural

Renewable 5-methylfurfural was subjected to a ‘green’ base- catalyzed aldol condensation with a variety of ketones to afford the corresponding furan-containing α,β-unsaturated carbonyl compounds with high yields and selectivities. The products obtained can serve as precursors for the long- chained fuel-grade liquid bio-alkanes.

Recent advances in amine catalyzed aldol condensations

ABSTRACT During the past two decades, new insights have driven the development and optimization of aminated materials as aldol condensation catalysts. Amines, either primary or secondary, facilitate the reaction via an enamine mechanism. If the spatial placement with respect to the amine allows it, weak acid sites such as silanols or hydroxyls, can cooperate as hydrogen bond donors and aid in proton transfer steps. Furthermore, the reaction environment, i.e., support and solvent and their mutual interactions, is also a key determining factor. In particular, co-feeding small amounts of water suppresses the formation of inhibiting and site-blocking species. However, silica-based materials are susceptible to hydrolysis. This led to the development of water tolerant (bio)polymer supported amine catalysts which also exhibit selective component enrichment properties, opening up opportunities for further catalyst development.

Nontraditional Aldol Condensation Performance of Highly Efficient and Reusable Cs+ Single Sites in β-Zeolite Channels.

Aldol reactions (self- and cross-aldol condensations) for conjugated enone synthesis were efficiently performed on large-sized Cs+ single sites (1 wt %) confined in β-zeolite channels in toluene, which showed the highest level of catalytic aldol condensation activity among reported zeolite catalysts. In general, aldol condensation reactions for C-C bond synthesis can proceed by acids (e.g., H+), bases (e.g., OH-), enolate species, and acidic or basic solid catalysts. However, the Cs+ single site/β sample without significant acid-base property showed unprecedented, efficient, and reusable catalysis for self-aldol and cross-aldol condensations. Intrinsically inactive Cs+ single sites due to the noble-gas electronic structure were transformed to active Cs+ single sites in β-zeolite channels. Cs+/β has many advantages such as broad substrate scope, eco-friendliness, high product selectivity and yield, and simple work-up procedure. Thus, the Cs+ single site/β provides an attractive and useful methodology for practical C-C bond synthesis. On the basis of the Cs+/β characterization by X-ray photoelectron spectroscopy (XPS), in situ X-ray absorption fine structure (XAFS) (X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS)), and temperature-programmed desorption (TPD), density functional theory (DFT) calculations of the self- and cross-aldol condensation reaction pathways involving the transition states on the Cs+ single site in β-zeolite channel revealed nontraditional concerted interligand bond rearrangement mechanisms.

Rosaphen synthesis: homogeneously catalyzed aldol condensation of cinnamaldehyde or hydrocinnamaldehyde with propanal followed by hydrogenation over ruthenium and nickel supported catalysts

Rosaphen synthesis: homogeneously catalyzed aldol condensation of cinnamaldehyde or hydrocinnamaldehyde with propanal followed by hydrogenation over ruthenium and nickel supported catalysts

Combination of spray drying encapsulation and steaming transformation toward robust hierarchical zeolite microspheres: Synthesis, formation mechanism and acid catalysis

Binder-free zeolite microspheres with hierarchical porosities are prepared by combining spray-drying encapsulation and steaming transformation. Amorphous aluminosilicate microspheres encapsulating tetrapropylammonium hydroxide (TPAOH) are first synthesized by spray drying. Then, they are successfully transformed into robust zeolite microspheres by using a steam-assisted crystallization (SAC) process. The drying temperature plays a decisive role in encapsulation and preservation of TPAOH guiding zeolite crystallization, as well as the morphology and sizes of the obtained zeolites. The morphology, structure and crystallinity of the resulted zeolites can also be controlled by adjusting the water/gel mass ratio and SAC time. The detailed structure and crystallization evolution over the SAC transformation process is studied and discussed. The typical obtained zeolite microspheres possess surface buckled morphologies, uniform large particle sizes, hierarchical porosities, good mechanic strength and intrinsic strong acid sites. They demonstrate enhanced catalytic activity and stability in acid catalytic aldol condensation.

Oxide-catalyzed self- and cross-condensation of cycloketones. Kinetically relevant steps that determine product distribution

Metal oxides with acid-base properties can be used to catalyze aldol condensation and potentially obtain valuable chemicals from biomass-derived oxygenates. Understanding the reaction mechanisms could enable the development of effective catalysts with controllable selectivity. Here, we investigate the reaction parameters that affect the kinetics and product distribution of self- and cross-aldol condensation of cyclopentanone (CPO) and cyclohexanone (CHO) over CeO2 and ZrO2 catalysts by combining detailed analysis of experiments and DFT calculations. It is well-known that either the deprotonation of an α-C–H that generates an enolate or the C–C coupling that produces the dimers can be rate-limiting step. Indeed, the detailed kinetics analysis shows that the observed data can be fitted by unimolecular or bimolecular Langmuir-Hinshelwood models. Specifically, on the ZrO2 catalyst, the unimolecular α-C–H activation is the rate limiting step for the CPO self-condensation, while the bimolecular C–C coupling limits the CHO self-condensation. By contrast, on CeO2, the bimolecular C–C coupling step seems to be rate-limiting for both CPO and CHO self-condensation reactions. The adsorption parameters derived from kinetics fitting indicate that when the two reactants are co-fed, the surface is preferentially covered by CHO. So, the condensation rate of [CPO]-activated products ([CPO]CPO + [CPO]CHO) decreases in the presence of CHO, due to the competitive adsorption. However, despite a higher surface coverage, CHO is not an effective electrophile because it imposes stronger steric constraints to the formation of the C–C bond than CPO. Therefore, for a given enolate, the product distribution shows that [CPO]CPO > [CPO]CHO and, similarly [CHO]CPO > [CHO]CHO. Likewise, the yields of [CPO]- and [CHO]-activated products in mixed CPO/CHO feeds are similar because the higher surface coverage and stability of the [CHO] enolate is counterbalanced by the inhibition of C–C coupling by steric constraints when CHO is involved. In summary, the overall rank of products observed experimentally can be explained in terms of a combination of the following effects: relative surface coverage of the reactants, steric constraints for the C–C coupling, stability of the enolate, and effectiveness of the electrophile to accept an electron.

Mesoporous Zeolitic Materials (MZMs) Derived From Zeolite Y Using a Microwave Method for Catalysis.

Mesostructured zeolitic materials (MZMs) with relatively high acidity in comparison with the mesoporous siliceous MCM-41 were prepared via an efficient, mild, and simple post-synthetic treatment of Y zeolite facilitated by microwave irradiation, i.e., microwave-assisted chelation (MWAC). The disordered mesoporous aluminosilicates materials (DMASs) of MZM were created from Y zeolite in the absence of using mesoscale templates. The prepared DMASs showed the good mesoporous features with the mesopore area and volume of ~260 m2 g−1 and ~0.37 cm3 g−1, respectively, and with the mesopore sizes distributed in a range of 2–10 nm. MZMs possess a total acidity of about 0.6 mmol g−1 and exhibited comparatively superior catalytic activity to the parent Y zeolite and MCM-41 in the vapor phase catalytic dealkylation of 1,3,5-triisopropylbenzene (TiPBz) and liquid phase catalytic aldol condensation of benzaldehyde with 1-heptanal. Although the yield loss was inevitable for preparing MZMs using the MWAC method, the preliminary economic analysis of the preparation cost of MZMs showed the promise. Additionally, a comprehensive comparison of the state-of-the-art mesoporous materials concerning their sustainable aspects was made, showing that MZMs are promising mesoporous materials for further development and functionalization for catalysis.

Support effects of Cs/Al2O3 catalyzed aldol condensation of methyl acetate with formaldehyde

In this work, the support effects on vapor-phase aldol condensation of methyl acetate (MeOAc) with formaldehyde (HCHO) over cesium catalysts are understood by the employment of Al2O3 with different morphologies and crystal phases. The structural and electronic properties of these supported Cs catalysts are characterized by multiple techniques, such as XRD, HAADF-STEM, EDS-mapping, XPS, NH3-TPD and CO2-TPD. The Cs species are found to be highly dispersed on the Al2O3 surfaces, and their compositions vary with the identity of Al2O3. A combined catalyst characterization and testing results indicates a balance between acidic and basic sites, i.e., an acid-base synergy, for the production of MA: the excess acidic sites lead to the lower MA selectivity due to the promoted further condensation, while the excess basic sites with the lower MeOAc conversion due to the insufficient activated HCHO species. These insights could be valuable for the design and optimization of catalysts for this reaction.

Cu2+/Zeolite catalyzed aldol condensation: Greener synthesis of 4′-piperidinophenyl enones

A series containing twelve substituted 4′-piperidinophenyl chalcones were synthesized from crossed-aldol condensation between 4-piperidionphenyl methyl ketone and substituted benzaldehydes using solid Cu 2+ /Zeolite catalyzed microwave assisted method. This condensation gave more than 85% yield. The structures of chalcones were analyzed by physico-chemical properties and spectroscopic data. The influence of the catalyst was investigated by observed quantity of yields.

Efficient Synthesis of Functionalized 6‐(2‐Oxoindolin‐3‐yl)‐5‐azaspiro[2.4]heptanes

AbstractThe base catalyzed aldol condensation of various N‐benzylisatins with 1‐acetyl‐N‐arylcyclopropanecarboxamides resulted in functionalized 3‐hydroxyoxindolin‐2‐ones in high yields, which were in turn successfully transferred to functionalized 6‐(2‐oxoindolin‐3‐yl)‐5‐azaspiro[2.4]heptanes in acetic acid in the presence of the concentrated hydrochloric acid by sequential acid catalyzed dehydration and aza‐Michael addition process. The 1H NMR spectra and the single crystal structure indicated that the obtained functionalized 6‐(2‐oxoindolin‐3‐yl)‐5‐azaspiro[2.4]heptanes have a S,S‐configuration.