Research progress of catalysts for aldol condensation of biomass based compounds

A new recyclable basic ionic liquid was introduced as an efficient catalyst for aldol condensation and transesterification reactions under environmentally friendly conditions. The catalyst was prepared based on methyl imidazolium moieties bearing hydroxide counter anions via the Hofmann elimination on a 1,3,5‐triazine framework. The ionic liquid with two functionalities including anion stabilizer and high basicity, was used as an efficient catalyst for aldol condensation as well as transesterification reaction of a variety of alkyl benzoates. All reactions were performed in the absence of any external reagent, co‐catalyst, or solvent, in line with environmental protection. The kinetics isotope effect (KIE) was conducted for the transesterification reaction to elucidate the mechanism and rate determining step (RDS). It worth noted that, the homogeneous catalyst could be recycled from the reaction mixture and reused for several consecutive runs with insignificant drop of basicity and conversion.

A new organic ligand, 5-(carboxyformamido)isophthalic acid (5-CFIA), was prepared and employed for the synthesis of two compounds [M3(C10H4O7N1)2(8H2O)]·H2O (M = Cd, Mn). The compounds have three-dimensionally extended structures. Both the compounds were found to be luminescent at room temperature. The luminescence nature was exploited for the detection of Hg2+ ions in an aqueous medium with good selectivity. The interactions between Hg2+ ions and the compounds quench the luminescence intensity and act as a turn-off sensor. Both the compounds exhibited low limits for the detection of Hg2+ ions and in the range mandated by the WHO. The interactions between Hg2+ ions and the compound involve the -NH group, which was probed using Raman and IR spectroscopic techniques. These studies provide important pointers toward the mechanism of this turn-off luminescence behavior. The compounds were explored for base-catalyzed aldol condensation and Lewis acid-promoted β-enaminoester formation reactions. The aldol condensation reaction uses the -NH functionality as a base. The studies indicate that the electron-withdrawing group produces products with higher yields. The β-enaminoester reaction uses the Lewis acid centers, and the studies reveal that the electron-withdrawing groups produce lesser yields of the products. The catalytic nature of the reaction and recyclability of the catalysts were also established. The catalytic reactions employ ethanol (aldol condensation) and no solvent (β-enaminoester), which suggests that the reactions are green and environmentally friendly. The Mn compound was observed to be anti-ferromagnetic.

Objectives: Removing organic solvents in chemical synthesis is important in the drive towards benign chemical technologies. Organic solvents are high on the list of toxic compounds due to the problems in containing volatile compounds and the sheer large volume of them used in industry. Some advantages of utilizing solventless reactions are that the compounds are often sufficiently pure to avoid extensive purification using chromatography, the reactions can be rapid, and often reaching substantial completion in several minutes compared to hours in organic solvents, and the energy usage can be much lower. Among organic reactions, aldol condensations are important and excellent tools in organic synthesis, providing a good way to form carbon–carbon bonds. The main objectives of this paper are to carryout crossed - aldol condensation reactions with dicyclohexylketones with different aromatics aldehydes in the presence of silica sulphuric acid [SiO2.OSO3H] as an ionic liquid catalyst under solvent free condition to afford the corresponding α, β - unsaturated crossed - aldol products in excellent yields and to recover and reuse the catalyst for subsequent use. Study design: Green chemical reaction using silica-sulphuric acid as a catalyst under solventless condition.

The boundary lubrication mode is usually implemented in conditions of low sliding speeds and high loads. The formation of strong boundary lubricating films under this friction mode determines the operability and durability of the friction units. It is believed that the formation of surface boundary films during friction includes the stages of the lubricant oxidation, and the aldol condensation reaction of oxidized molecules. As a result, high-molecular substances called “friction polymers” are formed. The paper studies the formation of surface films in the presence of substances with different reactivity in the aldol condensation and Claisen condensation reactions. Sunflower oil, bis (2-ethylhexyl) sebacate (DEHS), triisodecyl benzene-1,2,4-tricarboxylate (TC) were used as lubricants. It is shown by ATR IR-spectroscopy of that the common thing for the studied oils is that the C=O and C-O groups participate in the formation of boundary films in these oils. The addition of substances, active in aldol condensation reactions, into lubricants does not accelerate the formation of boundary films. Additives that can chemically interact with iron contribute to the dissolution of the surface oxide film and accelerate the formation of boundary layers. The formation of “friction polymers” occurs when the lubricant molecules interact with the metal surface.

In this study, a series of long‐chain dicarboxylic acid ester precursors were synthesized via aldol condensation reactions catalyzed by protic ionic liquids (PILs). When 2,5‐diformylfuran (DFF) and methyl levulinate (MLA) were employed as substrates, the yield of long‐chain dicarboxylic acid ester precursors reached 91.0% in the presence of pyrrolidine lactate. This preparation process eliminated the need for additional acids and bases, thereby minimizing the generation of waste salts, which was a common issue in base‐catalyzed systems and biosynthesis methods. Nuclear magnetic resonance (NMR) characterization revealed that a strong interaction between the hydroxyl group of the catalyst and the carbonyl group of MLA facilitated the activation of the substrate for the aldol condensation reaction. Notably, the yield of dicarboxylic acid ester precursors remained stable even after five catalytic cycles, demonstrating the excellent reusability of the catalyst. Furthermore, pyrrolidine lactate exhibited broad applicability in both aldol condensation and Knoevenagel condensation reactions. This work presented a novel and sustainable strategy for the synthesis of long‐chain dicarboxylic acid ester precursors.

One of the most important indicators of the suitability of new types of fibrous materials for processing in products with specified properties is the degree of grinding. A detailed analysis of the influence of various factors on the quality of grinding of fibrous materials was carried out. The information is necessary for predicting the properties of new types of materials and controlling the technological process for obtaining fibrous materials with improved and controlled characteristics. The advantages of a modern method for analyzing the properties of fibers in the process of obtaining new types of materials are shown, which makes it possible to evaluate the active fiber surface and its fractional composition.

Characterization of l-2-keto-3-deoxyfuconate aldolases in a nonphosphorylating l-fucose metabolism pathway in anaerobic bacteria

Herein, we synthesized guanidine functionalized graphene oxide nanocomposites referred to GO‐GN NCs using hummer's method. GO‐GN NCs was characterized using Fourier‐Transform Infrared Spectroscopy, Powder X‐ray Diffraction, Thermogravimetric Analysis, Raman Spectroscopy, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, Brunauer‐Emmett‐Teller (BET) surface area analysis to confirm successful formation of GO‐GN NCs catalysts. The catalytic performance for GO‐GN NCs was evaluated for Knoevenagel and Aldol condensation reaction in aqueous medium at ambient condition and result shows that it could be used as a highly efficient, stable, and durable catalyst. In addition, it has another feature such as easy workup procedure, large substrate tolerance, high reaction yield, good recyclability, and environmental friendliness.

Isophorone is a relatively small molecule with several neighboring reacting sites, making it susceptible to various competing reactions with aldehydes, including aldol, Baylis-Hillman (BH), aldol condensation, and Michael addition reactions. In the present work, we have designed a switchable 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-catalyzed procedure, where the reaction of isophorone with aldehydes is guided chemoselectively toward either aldol, BH, or aldol condensation reactions, depending on the use of water and/or heat. This controllable divergency likely stems from the ability to tune the dual nucleophilicity/basicity characters of the DBU/H2O medium. In other words, the nucleophilicity of DBU plays a crucial role in directing the process toward the formation of the BH adducts in the absence of water. At the same time, the aldol pathway dominates when water is present. The conditions were amenable for tandem processes, as demonstrated for an aldol condensation/Diels-Alder sequence.

In recent years ionic liquids have emerged as an important class of compounds for the synthesis of metal nanoparticles. The significant advantage of using ionic liquids is their dual role of reaction solvent and nanoparticle stabilizer. The variability of ionic liquids enables their chemical properties to be tuned by the rational introduction of functional moieties. Metal nanoparticles and ionic liquids appear to be ideal complementary components for the construction of multifunctional catalytic systems. The development of multifunctional systems based on the combination of catalytically active nanoparticles and functionalized ionic liquids allows the integration of complex multi-step catalytic reactions in a one-pot process. The design of efficient metal nanoparticle ? functionalized ionic liquid catalysts is currently attracting much attention. The thesis is centered on the design, synthesis, characterisation and the catalytic applications of novel metal nanoparticle ? ionic liquid based catalytic systems. In the first chapter a general introduction to the field of metal nanoparticles immobilized in ionic liquids is presented, and the recent evolution of metal nanoparticle ? acidic ionic liquid multifunctional catalysts is reviewed. The second chapter covers the studies on chlorometallate ionic liquids. Lewis acidity of various chlorometallate systems was evaluated with respect to the speciation present in these systems. The speciation in chlorozincate ionic liquids was determined by different techniques. The obtained scale of Lewis acidity of the chlorometallate ionic liquids and the understanding of the speciation in these systems allowed accurate selection of the appropriate system for catalytic applications. The third and the fourth chapters describe the studies concerning the ability of the chlorometallate ionic liquids to function in a cooperative manner with rhodium nanoparticles in hydrogenation reactions. A novel bifunctional catalyst, consisting of rhodium nanoparticles dispersed in a Lewis acidic ionic liquid medium, was developed. In the third chapter the rhodium nanoparticle component of the catalyst is characterized. Subsequently, the combined bifunctional catalytic system was used to catalyse the hydrogenation of aromatic compounds and was found to exhibit excellent activity under mild conditions. In the fourth chapter, the high activity of the rhodium nanoparticle ? Lewis acidic ionic liquid catalyst the direct hydrogenation of challenging heteroarene substrates is demonstrated. Chlorozincate(II), chloroaluminate(III) and chlorogallate(III) ionic liquids were found to be effective as a second active component of the catalytic system. The chemoselective reduction of different quinolines, pyridines, benzofurans was performed at mild conditions ? 30 bar and 80-120°C and the corresponding heterocycles were obtained in high yields. The high selectivity of the catalyst and its tolerance to different functional groups was demonstrated on a broad range of substrates. The recyclability of the rhodium nanoparticle ? Lewis acidic ionic liquid catalyst was evaluated. The final chapter presents two reduced graphene oxide supported rhodium nanoparticle catalysts obtained in ionic liquid media via microwave-assisted and conventional thermal heating methods. The rhodium nanoparticle-reduced graphene oxide composites were characterized by different techniques. The catalytic performance of the rhodium nanoparticle-reduced graphene oxide composites was evaluated in the hydrogenation of quinoline compounds under mild conditions, i.e. 10 bar and 80°C. The advantages of the microwave-assisted ionic liquid synthesis for the production of highly efficient catalysts were demonstrated. The long-term stability of the catalyst obtained by microwave-assisted method was studied and the catalyst could be recycled several times without significant loss in activity and selectivity.

Upgrading of biomass-derived furanic compounds into high-quality fuels involving aldol condensation strategy

Liquid fuel intermediates can be produced via aldol condensation reactions through furan aldehydes and ketones driven from biomass. It was found that cerous phosphate (CP) with two different crystal structures (hexagonal and monoclinic structure), which was tailored by different hydrothermal temperature (120 °C for the hexagonal structure and 180 °C for the monoclinic structure) and calcination temperature (900 °C for the monoclinic structure) as a solid acid catalyst, exhibit high catalytic performance in aldol condensation between furfural and acetone. The CP with hexagonal structure gave 89.1% conversion of furfural with 42% yield of 4-(2-furyl)-3-buten-2-one (FAc) and 17.5% of yield of 1,5-di-2-furanyl-1,4-pentadien-3-one (F2Ac), much higher than CP with monoclinic structure. However, both furfural conversion and aldol product yield increased from 82.3% to 96% and from 50.5% to 68.4%, respectively, for CP with the monoclinic structure after calcination owing to the higher amount of acid of catalyst after calcination but decreased continuously for CP with hexagonal structure after calcination because of its rapidly reduced BET surface area and total pore volume. The results indicated that calcination affects significantly the physical–chemical properties of CP catalysts, which influence subsequently the catalytic performance in the aldol condensation reaction. Recycling experiments showed that the catalytic performance after five number runs for CP with monoclinic structure after calcination was acceptable but was not ideal for CP with hexagonal structure owing to its poor hydrothermal stability.

An innovative cascade deoxygenation concept coupling the thermal pyrolysis of lignocellulose with two consecutive (acidic and basic) catalytic beds in a single reactor has been developed. Thereby, thermal pyrolysis vapors produced by pyrolysis of acid-washed wheat straw have been upgraded by combining an acidic ZrO2-supported ZSM-5 zeolite and a basic K-grafted USY zeolite, both being prepared in technical form by extrusion with attapulgite binder. Investigation of the different coupling alternatives has shown that the most efficient strategy relies on passing the pyrolysis vapors first by the acid catalyst followed by the basic one in a fixed-bed reactor arrangement. In this way, an enhanced degree of bio-oil deoxygenation is achieved since the K/USY catalyst promotes the occurrence of both aldol condensation and ketonization reactions, thus leading to further bio-oil upgrading by removal of oxygen in the form of CO2 and H2O while affording the formation of C–C bonds. Moreover, this second basic catalyst promotes the further conversion of the oligomers still present in the bio-oil. Accordingly, the sequential integration of the two catalytic systems leads to a clear synergetic effect, improving the efficiency of the bio-oil deoxygenation process and affording the production of liquid organic fractions with oxygen content as low as 12 wt % and energy yield of 32% regarding the raw lignocellulosic biomass.

Retroreflective materials for traffic control devices are designed to return light from a vehicle’s headlamps back to the driver. Recent advances in material technology have created prismatic retroreflective sheeting. This type of material does not have the predictability in its retroreflective performance of the older, glass-bead material. The ASTM recently recognized three new types of prismatic material for traffic control devices. The on-road performance of these new material types was examined through the use of computer simulation of sign luminance. Inputs to the computer model included vehicle dimensions, headlamp illumination data, material retroreflectivity data, sign placement, and roadway geometry. A variety of sign positions and roadway types was included to illustrate the similarities and differences among the three new types of material. The ranking of the three materials in terms of sign-luminance performance depends on the roadway configuration and the viewing distance. ASTM Type VII is shown to be comparable to Type VIII at long distances with small entrance angles but superior to Type VIII and IX in large entrance-angle situations. ASTM Type IX is shown to have higher luminance at shorter distances associated with sign-legibility distance ranges. Engineers and specifiers are encouraged to evaluate on-road sign performance at night before making material choices.

Furanic jet fuels – Water-free aldol condensation of furfural and cyclopentanone