Catalyst For Aldol Condensation Reactions Research Articles

The role of primary amines in modified chitosan to enhance the aldol condensation of biomass-derived carbonyl compounds

Aldol condensation is a key step for converting the lignocellulosic platform compounds to fuel. The catalyst used in the aldol condensation requires the avoidance of the overactivation of aldehyde groups while fully activating ketone carbonyl groups. Herein, the modified chitosan (NaOH/CT-0.6) was applied for the efficient syntheses of single condensation product from biomass-derived furfural (FFR) and methyl isobutyl ketone (MIBK), achieving an 87.01% yield of C11 at 60 °C and 3 h. Catalyst characterization revealed that the exposure of –NH2 groups in chitosan after modification led to the formation of the imine with the CO groups of FFR. It was confirmed that the imine formation avoided the overactivation of aldehyde groups and improved cross-condensation product yield. Furthermore, the theoretical feasibility of the imine catalytic path was elucidated through DFT simulation and in situ DRIFTS analysis. Finally, the obtained condensation products were subjected to hydrodeoxygenation (HDO) over the 2 wt% Pd/Nb2O5, obtaining the hydrocarbon components suitable for bio-jet fuels. This work contributes significantly to the design of novel catalysts for aldol condensation reactions and the efficient conversion of biomass.

A Novel Magnetic Immobilized Para-Aminobenzoic Acid-Cu(II) Complex: A Green, Efficient and Reusable Catalyst for Aldol Condensation Reactions in Green Media

In this the study a novel, efficient and recoverable heterogeneous nanocatalyst with regards to green chemistry purpose was approached. The structure of the newly synthesized heterogeneous magnetic nanocatalyst with enhanced and improved catalytic efficiency were determined by various instrumental techniques, including SEM, VSM, TGA, XRD, UV–VIS FT-IR and EDXA. The results, showed that the synthesized nanoparticles are superparamagnetic with a size range of 10–20 nm. Then the catalytic activity and efficient performance of Fe3O4@PABA-Cu(II) MNPs were analyzed toward the synthesis of novel 5-arylidenthiazolidine-2,4-diones and 5-arylidene-2-imidazolidine-2,4-dione derivatives via aldol condensation reactions between a variety of (hetero) aromatic aldehydes and hydantoin or thiazolidine-2,4-dione multifunctional privileged scaffolds under reflux condensations in ethanol as a benign solvent. Nontoxic nature and environment-friendly properties of the catalyst, simple workup, short time of reaction, easy separation of the catalyst from products, efficiency, and excellent yields are beneficial aspects of this method. It is the first report of aldol synthesis of new 5-arylidenthiazolidine-2,4-dione, and 5-arylidene-imidazolidine-2,4-dione derivatives using a reusable copper-PABA complex supported on Fe3O4 MNPs (Fe3O4@PABA-Cu(II)) catalyst in Green media.

Functionalized cellulose nanofibril aerogels as cooperative acid–base organocatalysts for liquid flow reactions

Cellulose nanomaterial aerogels are macroscopic porous solids with relatively high surface areas and are thus an interesting basis for renewable catalyst materials. Cross-linked acid–base bifunctional catalyst aerogels are produced here from TEMPO-oxidized cellulose nanofibrils (TOCNF) and demonstrated in both batch and flow catalysis. Recently established acid–base modification for catalysis is expanded upon for chemical or physical cross-linking with small molecules and polymers. Low density and relatively high surface area (up to 74 m2 g−1) aerogel catalysts are produced with a variety of processing approaches and then freeze-dried from water or tert-butyl alcohol/water mixtures. Finer pore structure and increased surface area are achieved with tert-butyl alcohol as co-solvent. Chemical cross-linking improved aerogel stability to solvents. Homogeneous and aerogel TOCNF catalysts are shown to be effective acid–base cooperative catalysts for aldol condensation reactions in batch reactions. Continuous flow reactions are performed with glass column reactors packed with aerogel catalysts that showed improved rates relative to batch experiments, while also demonstrating physical stability. Catalyst deactivation in flow reactions is observed and observations of deactivation support previously reported mechanisms of site poisoning by competitive chemisorption of reactants in analogous acid–base catalysts. This report is a key demonstration of cellulose nanofibril aerogels for catalysis in continuous liquid flow reactions.

Activity and stability of mesoporous CeO2 and ZrO2 catalysts for the self-condensation of cyclopentanone

Metal oxides containing acid-base pairs are widely used as catalysts for aldol condensation reactions, but they are often prone to secondary condensation and fast deactivation. In this contribution, high-surface area mesoporous CeO2 and ZrO2 have been synthesized and tested as catalysts for the self-condensation of cyclopentanone, an attractive molecular building block for several biomass upgrading strategies. The catalytic activity, stability, and overall kinetics behavior of these two catalysts have been compared in the liquid phase. A detailed kinetics analysis shows that on both oxides, the reaction is controlled by the initial unimolecular α-H abstraction step, in which cyclopentanone forms the crucial enolate intermediate. Subsequently, the enolate couples with another cyclopentanone molecule in a bimolecular C-C coupling step. CO2-TPD analysis and site titration with probe molecules indicate that initially the most active catalyst is the mesoporous ZrO2 sample with strong base character. However, this catalyst exhibits a very rapid deactivation. By contrast, the mesoporous CeO2 prepared in this study has lower basicity strength, which results in lower initial activity, but enhanced stability.

Boehmite-An Efficient and Recyclable Acid-Base Bifunctional Catalyst for Aldol Condensation Reaction.

In this work boehmite was used as an acid-base bifunctional catalyst for aldol condensation reactions of aromatic aldehydes and ketones. The catalyst was prepared by simple sol-gel method using Al(NO3)3·9H2O and NH4OH as precursors. The catalyst has been characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), UV-visible spectroscopy (DRS), BET surface area analyses. Boehmite is successfully applied as catalyst for the condensation reaction between 4-nitrobenzaldehyde and acetone as a model substrate giving α, β-unsaturated ketones without any side product. The scope of the reaction is extended for various substituted aldehydes. A probable mechanism has been suggested to explain the cooperative behavior of the acidic and basic sites. The catalyst is environmentally friendly and easily recovered from the reaction mixture. Also the catalyst is reusable up to 3 catalytic cycles.

A new catalyst for aldol condensation reactions

Abstract A new manganese complex was synthesised incorporating 1,2-diaminobenzene linked ketopinic acid scaffold, and successfully utilised as catalyst in the aldol condensation reactions of benzaldehyde with various aliphatic ketones to obtain products with excellent yield of >99 %.

Alanine-supported protic ionic liquids as efficient catalysts for aldol condensation reactions

Abstract A series of novel protic ionic liquids were immobilized on alanine, a cheap readily available amino acid. These short aliphatic chain ionic liquids have a low cost of preparation, a low toxicity, and need simple synthesis/purification processes. Their catalytic activity was tested for citral–acetone and benzaldehyde–acetone condensations, two reactions with an interest for pharmacological as well as flavor and fragrance industry. Good results were obtained in terms of conversion and selectivity; moreover, the catalysts can be recycled and reused for several consecutive cycles without significant loss of activity.

Aldol Reactions of the trans-o-Hydroxybenzylidenepyruvate Hydratase-Aldolase (tHBP-HA) from Pseudomonas fluorescens N3

In this paper, a recombinant trans-o-hydroxybenzylidenepyruvate hydratase-aldolase (tHBP-HA) of Pseudomonas fluorescens N3 was used as a new catalyst for aldol condensation reactions. The reaction of some aldehydes with a different electronic activation catalyzed by tHBP-HA is presented and discussed together with some hints on the product structure. The enzyme is strictly pyruvate-dependent but uses different aldehydes as acceptors. The structure of the products is highly dependent on the electronic characteristics of the aldehyde. The results are interesting for both their synthetic importance and the mechanism of the formation of the products. Not only the products obtained and the recognition power are reported, but also some characteristics of its mechanism are analyzed. The results clearly show that the enzyme is efficiently prepared, purified, and stored, that it recognizes many different substrates, and that the products depend on the substrate electronic nature.

1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) an efficient homogeneous catalyst for aldol condensation reactions. Study of the catalyst recovery and reusability using CO2

In this work it was shown that TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene), a cheap and commercially available guanidine base, efficiently catalyzes aldol condensation reactions yielding interesting products for pharmacological and fragrance industries. This methodology works under solvent-less conditions and affords with very good conversions the corresponding products. Moreover, a simple and effective separation protocol using the CO2 fixation was employed. The catalyst could be recovered and re-used for three consecutive runs without significant loss of activity.

The DBU-H2O complex as a new catalyst for aldol condensation reactions

Abstract Finding new Bronsted-type basic catalysts that can perform condensation reactions of interest to fine chemistry with good activities and selectivities is a constant challenge. In this communication we report the activity of the DBU-H2O system as a basic catalyst for aldol condensation reactions. Diazabicyclo [5.4.0] undec-7-ene (DBU) is a non-nucleophilic, strong tertiary amine base that is widely used in organic synthesis. We demonstrate that DBU, which has Lewis basic properties is inactive for aldol condensation reactions. However when it reacts with equimolar amounts of water it transforms towards a second resonance structure with Bronsted basic properties and therefore, high activity for these reactions. Besides, the DBU-H2O complex is found to be very efficient with reusability for several times.

Aldol Condensations Over Reconstructed Mg–Al Hydrotalcites: Structure–Activity Relationships Related to the Rehydration Method

Two different rehydration procedures in the liquid or gas phase have been applied to reconstruct mixed oxides derived from calcined hydrotalcite-like materials to be used as catalysts for aldol condensation reactions. The as-synthesized hydrotalcite, its decomposition product, as well as the reconstructed solids upon rehydration were characterized by XRD, N(2) adsorption, He pycnometry, FTIR, SEM, TEM, (27)Al MAS-NMR and CO(2)-TPD (TPD=temperature-programmed desorption). Compared to the Mg-Al mixed oxide rehydrated in the gas phase (HT-rg), that rehydrated in the liquid phase (HT-rl) exhibits a superior catalytic performance with respect to the aldol condensation of citral with ketones to yield pseudoionones and in the self-aldolization of acetone. The textural properties of HT-rl and HT-rg differ strongly and determine the catalytic behavior. A memory effect led to a higher degree of reconstruction of the lamellar structure when the mixed oxide was rehydrated in the gas phase rather than in the liquid phase, although liquid-phase rehydration under fast stirring produced a surface area that was 26 times greater. This contrasts to typical statements in the literature claiming a higher degree of reconstruction in the presence of large amounts of water in the medium. CO(2)-TPD shows that the number of OH(-) groups and their nature are very similar in HT-rg and HT-rl, and cannot explain the markedly different catalytic behavior. Accordingly, only a small fraction of the available basic sites in the rehydrated samples is active in liquid-phase aldol condensations. Our results support the model in which only basic sites near the edges of the hydrotalcite platelets are partaking in aldol reactions. Based on this, reconstructed materials with small crystallites (produced by exfoliation during mechanical stirring), that is, possessing a high external surface area, are beneficial in the reactions compared to larger crystals with a high degree of intraplatelet porosity.

Supported Choline Hydroxide (Ionic Liquid) as Heterogeneous Catalyst for Aldol Condensation Reactions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Supported choline hydroxide (ionic liquid) as heterogeneous catalyst for aldol condensation reactions.

Choline hydroxide was used as a basic catalyst for aldol condensation reactions to produce new C-C bonds between several ketones and aldehydes. Choline supported on MgO exhibits higher TOF values than other well known basic catalysts in these reactions.

Activation of Mg–Al Hydrotalcite Catalysts for Aldol Condensation Reactions

The condensation of benzaldehyde and acetone to aldol has been investigated in the liquid phase at 273 K on hydrotalcites transformed into basic solids by activation following different procedures. No activity was observed on the pure hydrotalcite (carbonated) or on the solid just decarbonated at 723 K. The activity went through a maximum after calcination at 723 K, followed by rehydration by water vapor at room temperature. The calorimetric determination of the adsorption of carbon dioxide demonstrated a lower basicity on the rehydrated surface, compared to the mixed oxide. Traces of chlorine retained in the synthesis were detrimental for catalytic properties. An aldol yield higher than 85 mol% was obtained after optimum activation. The higher activity of the rehydrated sample suggests that aldolisation in the heterogeneous phase is specifically catalyzed by hydroxide ions.