Acid-catalyzed Dehydration Reaction Research Articles

Production of drop-in biodiesel blendstocks via competitive acid-catalyzed dehydration reactions using ethanol oligomerization products

Ethanol can be catalytically upgraded to drop-in diesel fuel.

Influence of the synthesis method of Cu/Y zeolite catalysts for the gas phase oxidative carbonylation of methanol to dimethyl carbonate

Dimethyl carbonate is an environmentally friendly molecule with increasing applications as reactant, solvent, and fuel additive. Oxidative carbonylation of methanol, with reactants in the gas phase and catalyzed by copper-exchanged Y zeolites, is a promising alternative route for dimethyl carbonate production. This work is focused on the improvement of the catalyst formulation and preparation methods. Catalysts were prepared using two methodologies: solid-state ion exchange and liquid-ethanol ion exchange. Five different copper salts were used as precursors and the NH4+ and Na+ forms of the Y zeolite as supports. The Na+ form of the Y zeolite removed the Brønsted acidity of the support and, therefore, the reaction rate of acid-catalyzed undesired dehydration and decomposition reactions was reduced. The use of copper chloride salts as precursors was crucial to obtain suitable catalysts for dimethyl carbonate formation. Among all the tested catalysts, those prepared using CuCl2 precursor and the Na-Y zeolite by the liquid-ethanol ion exchange method showed the best performance (0.72 molDMC/molCu h). This catalyst exhibited the highest surface chloride content and Lewis acidity.

An integral design and synthesis approach to heterogeneous catalysts: Tailoring the surface characteristics and mass and heat transport properties

A novel integrated approach to designing and synthesizing heterogeneous catalysts with customized surface characteristics and improved heat and mass transport properties is studied. This unique approach utilizes hydrothermal reactions of aluminum (Al) metal substrates with controlled interfacial chemistry, manipulating the kinetics of aluminum hydroxide crystal growth to develop Al@Al2O3 core–shell metal-ceramic composite micro-architectures. The shapes, spatial orientation, and surface-exposed crystal facets of the porous γ-Al2O3 crystallites of the Al@Al2O3 core–shell are effectively tailored via modulation of the specific charge interaction of the boehmite crystallites with heteroatom ions in the solution. The reaction chemistry and formation mechanism of the Al@Al2O3 core–shell micro-composites with morphologically modulated γ-Al2O3 crystallites are studied in detail, along with their physicochemical and catalytic properties. For the acid-catalyzed ethanol dehydration reaction, the Al@Al2O3 catalysts with tailored morphologies and exposed γ-Al2O3 crystal facets demonstrate the high effectiveness of the integrated design and synthesis approach to heterogeneous catalysts, modulating the intrinsic catalytic activities with enhanced mass and heat transport properties at the same time.

Protic Brønsted acidic ionic liquids with variable acidity for efficient conversion of xylose and hemicellulose to furfural

Furfural (FF) is an important platform molecule originated from biomass, but it’s synthesis through the traditional acid-catalyzed dehydration reaction of xylose and hemicellulose remains problematic due to the poor activity and equipment corrosion. Therefore, a series of [HSO4]-based protic Brønsted acidic ionic liquids (BAILs) are employed as green catalysts to achieve efficient and sustainable preparation of FF from xylose or hemicellulose in this work. Furfural yields of 75.4% or 80.4% were achieved under optimal operating conditions with [Hpy][HSO4] as catalyst, hemicellulose or xylose as substrates, higher than those catalysed with most ionic liquids reported so far. The chemical structures of BAILs were confirmed by NMR and FT-IR spectroscopy, and the Hammett acidity (H0) were determined using UV–vis spectroscopy with 4-nitroaniline as probe. The acidity of BAILs were tuned through methyl substitution on the pyridinium ring, and its effect on the catalysis performance was investigated. In addition, the reaction constants and the corresponding activation energies of BAILs for dehydration of xylose to FF were calculated by kinetic equations. Overall, the highly efficient catalysis performance, good recyclability and low cost enables [Hpy][HSO4] to be potentially applied for large-scale preparation of FF.

Universal and Stable Slippery Coatings: Chemical Combination Induced Adhesive-Lubricant Cooperation.

Liquid lubricant of low affinity makes slippery coatings widely used in lubricating, anti-biofouling, anti-icing, fluid guiding, and drag reduction. Two critical challenges, however, remain in the practical application of slippery coatings consisting of liquid lubricants: (1) universality regardless of roughness and chemical composition of substrates, (2) stability of surface lubricity against evaporation. Herein, a chemical method is reported to create a universal and stable slippery lubricant-adhesive cooperated coating (SLACC) through acid catalyzed dehydration reaction between the phenolic hydroxyl of polydopamine (PDA), with universal (for challenge-1) and strong (for challenge-2) adhesion properties, and liquid-like polydimethylsiloxane (PDMS), with lubricant properties. Through overlying PDMS on PDA, a spatial gradient interpenetration of chemical combined PDA and PDMS leaving lubricant PDMS at the outermost of coating is achieved. This structure contributes to the following performances of SLACC: nearly universality suitable for 100 different abiotic or biotic substrates and stability sustainable for long-term usages, UV radiating, refrigerating, hot air drying, freeze drying, knife scratch and abrasion. This proposed strategy is envisioned anti-fouling from plane to tube and exhibits drag reduction in confined space.

Non-Faradaic Electrochemical Promotion of Brønsted Acid-Catalyzed Dehydration Reactions over Molybdenum Oxide

Non-Faradaic Electrochemical Promotion of Brønsted Acid-Catalyzed Dehydration Reactions over Molybdenum Oxide

Highly fluorescent aryl-cyclopentadienyl ligands and their tetra-nuclear mixed metallic potassium-dysprosium clusters.

Two alkyl substituted triaryl-cyclopentadienyl ligands [4,4′-(4-phenylcyclopenta-1,3-diene-1,2-diyl)bis(methylbenzene) (1) and 4,4′,4′′-(cyclopenta-1,3-diene-1,2,4-triyl)tris(methylbenzene) (2)] have been synthesized via cross-aldol condensation followed by Zn-dust mediated cyclization and acid catalyzed dehydration reactions. The fluorescence properties of 1 and 2 have been studied in solution and solid state. The ligands exhibited aggregation-induced emission enhancement (AIEE) in THF/water solution. 1 and 2 have been found to be significantly more fluorescent in the solid state than in their respective solutions. This phenomenon can be attributed to the strong intermolecular CH⋯π interactions present in 1 and 2 which leads to the tight packing of molecules in their solid-state. Both 1, 2 and their corresponding anions have been studied by theoretical calculations. Ligands 1 and 2 have been shown to react with anhydrous DyCl3 in the presence of potassium metal at high temperature to afford two fluorescent chloride-bridged tetra-nuclear mixed potassium–dysprosium metallocenes [(Me2Cp)4Dy2IIICl4K2]·3.5(C7H8) (5) and [(Me3Cp)4Dy2IIICl4K2]·3(C7H8) (6), respectively in good yields.

Ag- and Cu-Promoted Mesoporous Ta-SiO2 Catalysts Prepared by Non-Hydrolytic Sol-Gel for the Conversion of Ethanol to Butadiene

The direct catalytic conversion of bioethanol to butadiene, also known as the Lebedev process, is one of the most promising solution to replace the petro-based production of this important bulk chemical. Considering the intricate reaction mechanism—where a combination of acid-catalyzed dehydration reactions and metal-catalyzed dehydrogenation have to take place simultaneously—tailor-made bifunctional catalysts are required. We propose to use non-hydrolytic sol-gel (NHSG) chemistry to prepare mesoporous Ta-SiO2 materials which are further promoted by Ag via impregnation. An acetamide elimination route is presented, starting from silicon tetraacetate and pentakis(dimethylamido)tantalum(V), in the presence of a Pluronic surfactant. The catalysts display advantageous texture, with specific surface area in the 600–1000 m² g−1 range, large pore volume (0.6–1.0 mL g−1), an average pore diameter of 4 nm and only a small contribution from micropores. Using an array of characterization techniques, we show that NHSG allows achieving a high degree of dispersion of tantalum, mainly incorporated as single sites in the silica matrix. The presence of these monomeric TaOx active sites is responsible for the much higher dehydration ability, as compared to the corresponding catalyst prepared by impregnation of Ta onto a pristine silica support. We attempt to optimize the butadiene yield by changing the relative proportion of Ta and Ag and by tuning the space velocity. We also demonstrate that Ag or Cu can be introduced directly in one step, during the NHSG process. Copper doping is shown to be much more efficient than silver doping to guide the reaction towards the production of butadiene.

The Dark Side of Biomass Valorization: A Laboratory Experiment To Understand Humin Formation, Catalysis, and Green Chemistry

This laboratory experiment introduces students to an important reaction in biomass valorization and allows them to gain a practical understanding of green chemistry. Acid-catalyzed dehydration reactions of fructose to 5-hydroxymethylfurfural and thus humins were performed both with and without aqueous solvent, along with two different catalysts (Amberlyst-15 and alumina). Students were able to compare and analyze the effects of these different conditions using thin-layer chromatography, while grasping concepts of catalysis and circular economy. By observing the formation of humins under some of the reactions tested, the students could evidence systems thinking in humin valorization.

Effects of pyridine and pyrrole moieties on supercapacitive properties of imine-rich nitrogen-doped graphene

In this study, a series of imine-rich nitrogen-doped graphenes (IR-NGs), where pyridine and pyrrole functionalities were selectively incorporated in the near vicinity of imine groups, were synthesized, and used as electrode materials for supercapacitors. The facile acid-catalyzed dehydration reactions of graphene oxide (GO) with 6-aminoquinoline and 5-aminoindole could produce specific pyridine- and pyrrole-modified IR-NGs, respectively, denoted as PD-NG and PR-NG, respectively. In addition, aniline was reacted with GO to obtain the reference AN-NG, which only contains imine groups. The compositional and structural features of these three IR-NG compounds were confirmed using various spectroscopic and microscopic measurements. The specific capacitances of these IR-NGs in 6 M aqueous KOH solution as an electrolyte gradually increased as follows: PD-NG < AN-NG < PR-NG. The highest capacitance of 174 F g−1 was obtained from PR-NG at the current density of 1.0 A g−1, whereas the capacitances of PD-NG and AN-NG were limited to 125 and 138 F g−1, respectively, under the same conditions. These results indicated that the contributions of the pyridine and pyrrole moieties on the supercapacitive properties of IR-NGs were significant.

Effects of chloride ions in acid-catalyzed biomass dehydration reactions in polar aprotic solvents

The use of polar aprotic solvents in acid-catalyzed biomass conversion reactions can lead to improved reaction rates and selectivities. We show that further increases in catalyst performance in polar aprotic solvents can be achieved through the addition of inorganic salts, specifically chlorides. Reaction kinetics studies of the Brønsted acid-catalyzed dehydration of fructose to hydroxymethylfurfural (HMF) show that the use of catalytic concentrations of chloride salts leads to a 10-fold increase in reactivity. Furthermore, increased HMF yields can be achieved using polar aprotic solvents mixed with chlorides. Ab initio molecular dynamics simulations (AIMD) show that highly localized negative charge on Cl− allows the chloride anion to more readily approach and stabilize the oxocarbenium ion that forms and the deprotonation transition state. High concentrations of polar aprotic solvents form local hydrophilic environments near the reactive hydroxyl group which stabilize both the proton and chloride anions and promote the dehydration of fructose.

Terpyridine-Containing Imine-Rich Graphene for the Oxygen Reduction Reaction

We report a facile synthetic method for the preparation of a terpyridine-containing imine-rich graphene (IrGO-Tpy) using an acid-catalyzed dehydration reaction between graphene oxide (GO) and 4′-(aminophenyl)-2,2′:6′2″-terpyridine. Owing to the presence of terpyridine ligands, cobalt ions (Co2+) were readily incorporated into the IrGO-Tpy structures, affording a metal complex, denoted IrGo-Tpy-Co. Cyclic voltammetry and linear sweep voltammetry measurements confirm the noticeable oxygen reduction reaction (ORR) activities of the IrGo-Tpy and IrGo-Tpy-Co electroacatalysts in alkaline electrolytes, along with the additional merits of high selectivity, excellent long-term durability, and good resistance to methanol crossover. In addition, a remarkable improvement in the ORR performance was observed for IrGO-Tpy-Co compared with that of IrGo-Tpy, arising from the significant contribution of the cobalt-terpyridine complex in facilitating the ORR process.

Facile synthesis of nitrogen-doped graphene containing azobenzene moieties for the oxygen reduction reaction

ABSTRACTNitrogen-doped graphene containing azobenzene (NG-AB) was synthesized via a simple wet, acid-catalyzed dehydration reaction between graphene oxide (GO) and 4-aminoazobenzene. The structural features of NG-AB were confirmed by elemental analysis, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Owing to the efficient incorporation of nitrogen and the restoration of the graphitic structure that occurred during the reaction, NG-AB shows significant electrocatalytic activity for the oxygen reduction reaction (ORR) with excellent selectivity, durability, and a high tolerance to methanol crossover.

A facile approach to tailoring electrocatalytic activities of imine-rich nitrogen-doped graphene for oxygen reduction reaction

We report efficient modulation of the electrocatalytic activity of imine-rich nitrogen-doped graphene nanosheets (IRnGs) in the oxygen reduction reaction (ORR) by chemical functionalization. IRnGs are prepared by a simple acid-catalyzed dehydration reaction between graphene oxide and aniline derivatives. Various electron-donating and electron-withdrawing substituents are introduced in the para-position of aniline to afford diverse IRnG electrocatalysts. Cyclic voltammetry and rotating ring disk electrode measurements show that the electrocatalytic activity of IRnGs for ORR is highly sensitive to the electronic characteristics of functionalities present in their chemical structures. Thus, the above ORR activities are significantly improved by increasing the electron-withdrawing capability of substituents, since this promotes the beneficial polarization of electrocatalytically active imine bond (CN) in IRnGs. In addition, metal-free IRnGs electrocatalysts offer additional advantages of high selectivity, good long-term stability and excellent tolerance to methanol crossover for ORR in alkaline solution.

Simple solution-based synthesis of pyridinic-rich nitrogen-doped graphene nanoplatelets for supercapacitors

Pyridinic–rich nitrogen-doped graphene nanoplatelets (PRGOs) were synthesized using an acid–catalyzed dehydration reaction between GO and 3,4-diaminopyridine. Specific pyridinic nitrogen configurations can be efficiently introduced to graphitic network through newly formed imine and pyrizaine linkages. The structure of PRGOs was confirmed by various microscopic and spectroscopic analyses. In addition, the nitrogen content in PRGOs can be readily controlled over a wide range (1.9–9.1wt.%) by simple change in the feed ratios of reactants. Owing to the simultaneous structural restoration and nitrogen doping onto graphitic structure, PRGOs show high performance of supercapacitors, including enhanced specific capacitance and long-term stability. Furthermore, the effect of nitrogen contents on specific capacitance has also been investigated to optimize doping levels of nitrogen atoms in PRGOs. The highest specific capacitance of 214Fg−1 at current density of 0.1Ag−1 has been achieved from PRGO-5 with a moderate nitrogen content of 5.3wt.%, due to its balanced electric double layer capacitance and pseudocapacitance.

Synthesis of 1,1-Diphenylethylene (DPE): The Marriage of a Grignard Reaction and a Column Chromatography Experiment

The synthesis of 1,1-diphenylethylene (DPE) via a Grignard reaction, followed by an acid-catalyzed dehydration reaction, yields a mixture of compounds. DPE is a high boiling liquid that cannot be purified using simple distillation. However, it is easily separated from the more polar starting material and intermediate alcohol using both thin layer and column chromatography. Second-semester organic chemistry laboratory students learn the techniques of running reactions under anhydrous conditions and of column chromatography. In addition, the experiment demonstrates clearly the relationship between thin layer and column chromatography.

Understanding the Importance of Carbenium Ions in the Conversion of Biomass-Derived Alcohols with First-Principles Calculations

Dehydration reactions play a key role in the conversion of biomass derivatives to valuable chemicals, such as alcohols to alkenes. Both Lewis and Brønsted acid-catalyzed dehydration reactions of biomass-derived alcohols involve transition states with carbenium ion characteristics. In this work, we employed high-level ab initio theoretical methods to investigate the effect of molecular structure on the physicochemical properties of a set of alcohols that appear to control dehydration chemistry. Specifically, we calculated the carbenium ion stability (CIS, alkene-binding H+) and proton affinity (PA, alcohol-binding H+) of various C2–C8 alcohols to show the effect of alcohol size and degree of primary heteroatom substitution on the properties of the reactive species. Our results show a strong linear correlation between CIS and PA, following the substitution order of the reacting alcohols (i.e., primary < secondary < tertiary). Additionally, the calculated binding free energy (BE) of water on the formed carbenium ions was found to be exothermic and to decrease in magnitude with increasing alcohol substitution level. We demonstrate that the CIS and/or the PA are excellent structural descriptors for the alcohols and, most importantly, they can serve as reactivity descriptors to screen a large number of alcohols in the conversion of biomass-based alcohols involving the formation of carbenium ions. We demonstrate this concept in both Lewis and Brønsted acid-catalyzed dehydration reactions.

Recent progress in catalytic selective dehydration of sorbitol

Recently, the use of renewable biomasses has attracted much attention from academics and industry. Sorbitol is a useful biomass- derived chemical that can be converted to high-added-value products; it can be conveniently obtained from cellulose via glucose. Isosorbide and 1,4-anhydrosorbitol, which can be produced by dehydration of sorbitol, are potentially important bio-based industrial chemicals. Sorbitol can be transformed into 1,4-anhydrosorbitol and isosorbide through acid-catalyzed selective dehydration. The catalyst acidity is the most important factor in acid-catalyzed dehydration reactions. It has been observed that strong acidity is favorable for producing isosorbide. Various homogeneous and heterogeneous catalysts have been developed for sorbitol dehydration, depending on the desired products. Mineral acids such as sulfuric acid and hydrochloric acid, and metal halides such as SnCl4 and AlCl3 are efficient catalysts for sorbitol dehydration. However, processes using homogeneous acids have drawbacks from environmental and safety perspectives. Moreover, homogenous catalyst separation from the reaction mixture is cumbersome, which may add extra costs to commercial synthesis. Various solid catalysts such as zeolites, metal(IV) phosphates, layered niobium- molybdate, tungstophosphoric acids supported on various metal oxides, metal oxides modified with phosphoric acid, a superhydrophobic mesoporous polymer-based acid catalyst, and resins (amberlyst-15) have recently been tested in the selective dehydration of sorbitol. In addition, high-temperature liquid water has attracted much attention as a promising reaction medium for sorbitol dehydration. Future prospects for catalytic dehydration of sorbitol are summarized.

Graphene/Multi-Walled Carbon Nanotubes Hybrid Materials for Supercapacitors

We have developed a versatile method for the preparation of chemically linked graphene/multi-walled carbon nanotubes (MWNTs) hybrid materials via simple acid-catalyzed dehydration reaction between graphene oxide (GO) and amine- functionalized MWNTs (af-MWNTs). In this condition, ketone (-C=O) groups in GO and primary amine (-NH2) moieties in af-MWNTs readily react to form imine (-C=N-) linkage. The chemical structures of graphene/MWNTs hybrid materials have been investigated using various microscopic and spectroscopic measurements. As a result of the synergetic effects of hybrid materials such as improved surface area and the superior structural restoration of graphitic networks, the hybrid materials demon- strate improved capacitance with excellent long-term stability. Furthermore, controlled experiments were conducted to optimize the weight ratio of graphene/MWNTs in hybrid materials. The highest capacitance of 132.4 F/g was obtained from the GM7.5 material, in which the weight ratio between graphene and MWNTs was adjusted to 7.5/1, in 1M KOH electrolyte at a scan rate of 100 mV/s.

ChemInform Abstract: Rhenium‐Catalyzed Dehydration and Deoxydehydration of Alcohols and Polyols: Opportunities for the Formation of Olefins from Biomass

AbstractReview: 96 refs.