Amphoteric Catalyst Research Articles

Post-Synthetic Generation of Amino-Acid-Functionalized UiO-66-NH2 Metal–Organic Framework Nanostructures as an Amphoteric Catalyst for Organic Reactions

Post-Synthetic Generation of Amino-Acid-Functionalized UiO-66-NH₂ Metal–Organic Framework Nanostructures as an Amphoteric Catalyst for Organic Reactions

Research progress of catalysts for aldol condensation of biomass based compounds.

Research progress of catalysts of the aldol condensation reaction of biomass based compounds is summarized for the synthesis of liquid fuel precursors and chemicals. In summary, an acidic catalyst, alkaline catalyst, acid-base amphoteric catalyst, ionic liquid and other catalysts can catalyze the aldol condensation reaction. The aldol condensation reaction catalyzed by an acid catalyst has the problems of low conversion and low yield. The basic catalyst catalyzes the aldol condensation reaction with high conversion and yield, but the existence of liquid alkali is difficult to separate from the product. The reaction temperature needed for oxide and hydrotalcite alkali is relatively high. The basic resin has good catalytic activity and at a low reaction temperature, and is easy to separate from the target product. Acid-base amphoteric catalysts have received extensive attention from researchers for their excellent activity and selectivity. Ionic liquid is a new type of material, which can also be used for the aldol condensation reaction. In the future application of aldol condensation, the development of strong alkaline resin is a good research direction.

Acid catalyzed synthesis of dimethyl isosorbide via dimethyl carbonate chemistry

Dimethyl isosorbide (DMI) is a bio-based solvent that can be used as green alternative for conventional dipolar media (dimethyl sulfoxide, dimethylformamide, and dimethylacetamide). The main synthetic procedures to DMI reported in the literature are based on the methylation of isosorbide employing different alkylating agents including toxic halogen compounds such as alkyl halides. A more sustainable alternative would be to employ dimethyl carbonate (DMC), a well-known green reagent and solvent, considered one of the most promising methylating agents for its good biodegradability and low toxicity. Indeed, in recent years, DMC-promoted methylation of isosorbide has been extensively exploited although mostly in the presence of a base or an amphoteric catalyst. In this work, we report for the first time a comprehensive investigation on the synthesis of DMI via DMC chemistry promoted by heterogeneous acid catalyst (Amberlyst-36 and Purolite CT275DR). Reaction conditions were optimized and then applied for the methylation of isosorbide and its epimers, isoidide and isomannide. Considerations on the related reaction mechanism were reported highlighting the difference in the preferred reaction pathways among this new synthetic approach and the previously reported base-catalyzed procedures.

Combined experimental and computational study of Al2O3 catalyzed transamidation of secondary amides with amines.

Amides are the most extensively used substances in both synthetic organic and bioorganic chemistry. Unfortunately, the traditional synthesis of amides suffers from some important drawbacks, including low atom efficiency, high catalyst loading, separation of products from the reaction mixture and production of byproducts. Al2O3 is an amphoteric catalyst that activates the carbonyl carbon of the secondary amide group and helps the C–N cleavage of the reactant amide group by attacking the N–H hydrogen. By using the concepts of amphoteric properties of Al2O3, amides were synthesized from secondary amides and amines in the presence of triethylamine solvent. Several aliphatic and aromatic amines were used for the transamidation of N-methylbenzamide in the presence of the Al2O3 catalyst. Moreover, using the Gaussian09 software at the DFT level, HUMO, LUMO and the intrinsic reaction coordinates (IRCs) have also been calculated to find out the transition state of the reaction and energy. In this study, five successful compounds were synthesized by the transamidation of secondary amides with amines using a reusable Al2O3 catalyst. The catalyst was reused several times with no significant loss in its catalytic activity. The products were purified by recrystallization and column chromatography techniques. This catalytic method is effective for the simultaneous activation of the carbonyl group and N–H bond by using the Al2O3 catalyst.

Ordered mesoporous γ-Al2O3 as highly efficient and recyclable catalyst for the Knoevenagel reaction at room temperature

Coumarins are important class of organic compounds and intensively used in agricultural and pharmaceutical industries. We have developed a strategy for the synthesis of coumarin derivatives quantitatively via Knoevenagel condensation reaction of an ortho-hydroxyaryl aldehyde and an activated methylene compounds in the presence of ordered mesoporous γ-Al2O3 as a heterogeneous catalyst. The catalyst has been thoroughly characterized through powder X-ray diffraction, N2 sorption analysis, FTIR spectroscopy, TG/DTA, NH3-TPD and CO2-TPD (temperature programmed desorption) analysis. The material possesses periodicity in mesopores and both surface acidic and basic sites having strengths of 1.47 and 1.11 mmol g−1, respectively, which is highly favorable for carrying out the Knoevenagel condensation reaction for the synthesis of a wide range of condensation product (yields ∼98%) under very mild conditions. This amphoteric catalyst exhibits good surface Lewis acidity/basicity and high recyclability up to sixth reaction cycles without any significant loss in the product yield.

ChemInform Abstract: Regioselective One‐Pot Three‐Component Synthesis of Quinoline Based 1,2,4‐Triazolo[1,5‐a]quinoline Derivatives.

A one-pot three-component approach for the synthesis of 2-(piperidin-1-yl) quinoline based 1,2,4-triazolo[1,5-a]quinoline derivatives (4a–l) has been described by the reaction of aldehyde (1a–f), methyl 2-cyanoacetate (2) and enaminones (3a–b). Different regioselectivities of the reaction are attained with different catalysts and the highest regioselectivity is achieved by L-proline. This new procedure provides an efficient method to construct fused tricyclic heterocycles containing 1,2,4-triazole analogues. In this regard, we have used the least amount of amphoteric catalyst, like L-proline, ammonium acetate and a mixture of pyrolidine with acetic acid, to obtain the 1,4-dihydroquinoline derivative 5a as a by-product. The salient features of this protocol are the mild reaction conditions, high yield (75–85%) and higher regioselectivity toward the desired products 4a–l. The structures of the title compounds were confirmed by FT-IR, 1H NMR, 13C NMR and mass spectrometry.

The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonate

– The reactions of isosorbide and its epimers, isomannide and isoidide, with dimethyl carbonate have been herein investigated as easy access to bio-based products by a free-halogen chemistry approach. Isosorbide and its epimers show a different reactivity in bimolecular nucleophilic substitution with DMC. Carboxymethylation reaction was carried out in the presence of DMC and a weak base resulting in the high-yielding synthesis of dicarboxymethyl derivatives. Isomannide was the most reactive anydro sugars due to the less sterically hindered exo position of the OH groups. On the other hand, methylation of isosorbide and its epimers, conducted in the presence of a strong base and DMC, showed the higher reactivity of the endo hydroxyl group, isoidide being the most reactive epimer. This result has been ascribed to the neighbouring effect due to the combination of the oxygen in β-position and the intramolecular hydrogen bond within the anhydro sugar structure. Methylation reactions were also conducted in autoclave at high temperature with the amphoteric catalyst hydrotalcite using DMC as reagent and solvent. In this case, the reactivity of the epimers resulted quite different with isosorbide being the most reactive reagent possibly as a result of the structure of hydrotalcite comprising of both acidic and basic sites. The neighbouring effect was observed with good evidence in these methylation reactions.

The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonate

– The reactions of isosorbide and its epimers, isomannide and isoidide, with dimethyl carbonate have been herein investigated as easy access to bio-based products by a free-halogen chemistry approach. Isosorbide and its epimers show a different reactivity in bimolecular nucleophilic substitution with DMC. Carboxymethylation reaction was carried out in the presence of DMC and a weak base resulting in the high-yielding synthesis of dicarboxymethyl derivatives. Isomannide was the most reactive anydro sugars due to the less sterically hindered exo position of the OH groups. On the other hand, methylation of isosorbide and its epimers, conducted in the presence of a strong base and DMC, showed the higher reactivity of the endo hydroxyl group, isoidide being the most reactive epimer. This result has been ascribed to the neighbouring effect due to the combination of the oxygen in β-position and the intramolecular hydrogen bond within the anhydro sugar structure. Methylation reactions were also conducted in autoclave at high temperature with the amphoteric catalyst hydrotalcite using DMC as reagent and solvent. In this case, the reactivity of the epimers resulted quite different with isosorbide being the most reactive reagent possibly as a result of the structure of hydrotalcite comprising of both acidic and basic sites. The neighbouring effect was observed with good evidence in these methylation reactions.

The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonate

ABSTRACT – The reactions of isosorbide and its epimers, isomannide and isoidide, with dimethyl carbonate have been herein investigated as easy access to bio-based products by a free-halogen chemistry approach. Isosorbide and its epimers show a different reactivity in bimolecular nucleophilic substitution with DMC. Carboxymethylation reaction was carried out in the presence of DMC and a weak base resulting in the high-yielding synthesis of dicarboxymethyl derivatives. Isomannide was the most reactive anydro sugars due to the less sterically hindered exo position of the OH groups. On the other hand, methylation of isosorbide and its epimers, conducted in the presence of a strong base and DMC, showed the higher reactivity of the endo hydroxyl group, isoidide being the most reactive epimer. This result has been ascribed to the neighbouring effect due to the combination of the oxygen in β-position and the intramolecular hydrogen bond within the anhydro sugar structure. Methylation reactions were also conducted in autoclave at high temperature with the amphoteric catalyst hydrotalcite using DMC as reagent and solvent. In this case, the reactivity of the epimers resulted quite different with isosorbide being the most reactive reagent possibly as a result of the structure of hydrotalcite comprising of both acidic and basic sites. The neighbouring effect was observed with good evidence in these methylation reactions.

The neighbouring effect of isosorbide and its epimers in their reactions with dimethyl carbonate

Abstract The reactions of isosorbide and its epimers, isomannide and isoidide, with dimethyl carbonate have been herein investigated as easy access to bio-based products by a free-halogen chemistry approach. Isosorbide and its epimers show a different reactivity in bimolecular nucleophilic substitution with dimethyl carbonate (DMC). Carboxymethylation reaction was carried out in the presence of DMC and a weak base resulting in the high-yielding synthesis of dicarboxymethyl derivatives. Isomannide was the most reactive anhydro sugar due to the less sterically hindered exo position of the OH groups. On the other hand, methylation of isosorbide and its epimers, conducted in the presence of a strong base and DMC, showed the higher reactivity of the endo hydroxyl group, isoidide being the most reactive epimer. This result has been ascribed to the neighboring effect due to the combination of the oxygen in β-position and the intramolecular hydrogen bond within the anhydro sugar structure. Methylation reactions were also conducted in autoclave at high temperature with the amphoteric catalyst hydrotalcite using DMC as reagent and solvent. In this case, the reactivity of the epimers resulted quite differently with isosorbide being the most reactive reagent possibly as a result of the structure of hydrotalcite comprising of both acidic and basic sites. The neighboring effect was observed with good evidence in these methylation reactions.

Niobium-Containing Hydroxyapatites as Amphoteric Catalysts: Synthesis, Properties, and Activity

We present here a new class of Nb-containing catalysts offering both acid and base functionalities thanks to the hydroxyapatite (HAP) structure, which acts as a host matrix for guest niobium species. Incorporation of Nb has led to samples with strengthened amphoteric properties with a prevalence of acid or basic sites depending on the synthesis procedure. Nb-containing HAP samples (12–14 wt % of Nb) have been synthesized by coprecipitation in water and in alcoholic solutions and by impregnation starting from different precursors. The intrinsic and effective acid and base properties have been measured, and a series of mass and surface characterizations have been performed to determine the Nb content, its oxidation state as well as its morphologic, structural, and electronic properties. The performances of the samples have been studied in several reactions of liquid–solid heterogeneous catalysis in batch or fixed tubular reactors working in the recirculation mode on the basis of the known catalytic features...

Design of amphoteric mixed oxides of zinc and Group 3 elements (Al, Ga, In): migration effects on basic features

The design of new amphoteric catalysts is of great interest for several industrial processes, especially those covering dehydration and dehydrogenation phenomena. Adsorption microcalorimetry was used to monitor the design of mixed oxides of zinc with Group 3 elements (aluminium, gallium, indium) with amphoteric character and enhanced specific surface area. Acid-base features were found to evolve non-linearly with the relative amounts of metal, and the strengths of the created acidic or basic sites were measured by adsorption microcalorimetry. A panel of bifunctional catalysts of various acid-base (amounts, strengths) and redox character was obtained. Besides, special interest was given to In-Zn mixed oxides for their enhanced basicity: this series of catalysts displays important basic features of high strength (q(diff) (SO₂ ads.) > 200 kJ mol(SO₂)⁻¹ in substantial amounts (1 - 2 μmol m(catalyst)⁻²), whose impact on efficiency or selectivity in catalytic dehydration/dehydrogenation can be valuable.

Chemoselective and regioselective reduction of citral (3,7-dimethyl-2,6-octadienal) by gas-phase hydrogen transfer over acid–basic catalysts

The selective reduction of citral (3,7-dimethyl-2,6-octadienal) by gas-phase hydrogen transfer over various acid–base catalysts (MgO, ZrO 2, MgO/B 2O 3 and AlPO 4/SiO 2), using different alcohols as hydrogen donors, was studied. Chemical and surface properties of the solids were characterized by thermal programmed desorption–mass spectrometry (TPD–MS), using pyridine, dimethylpyridine and CO 2 to titrate total acidity, Brönsted acidity and total basicity, respectively. Acid (AlPO 4/SiO 2) and amphoteric catalysts (ZrO 2) led to the reduction of the alkene double bonds with 100% selectivity and produced citronellal (ca. 85%) and, to a lesser extent, dihydrocitronellal (15%). On the other hand, basic catalysts such as MgO led to the preferential reduction of the carbonyl group and to geraniol and nerol as end-products. The introduction of B 2O 3 in the reaction medium (as the MgO/B 2O 3 catalyst) substantially increased the selectivity for geraniol and nerol, so much so that, under optimal conditions, a selectivity of ca. 31% was readily achieved at a conversion of 15%.

Kinetics of the esterification of phthalic anhydride with 2-ethylhexanol: Part IV: Non-catalytic process. Final kinetic comparison of the catalysts

The kinetics of the non-catalytic esterification of mono-2-ethylhexyl phthalate has been investigated in an isothermal semibatch reactor. The reaction appears to be second order with respect only to mono-2-ethylhexyl phthalate and the reaction rate does not depend on the concentration of 2-ethylhexanol. The kinetic parameters have been determined. Final comparison of the esterification process in the presence of acid catalysts, amphoteric catalyst and for the non-catalytic reaction has been carried out.

Study of the Meerwein—Pondorff—Verley reaction between ethanol and acetone on various metal oxides

The Meerwein—Pondorff—Verley (MPV) reaction between ethanol and acetone was investigated on various metal oxides having different acid-base properties. It is shown that the reaction occurred on Lewis acid or base catalysts. From results of specific poisoning and FTIR studies of ethanol and acetone or acetone ( d 6) adsorption, two different schemes are proposed for the MPV reaction, according to the metal oxide's presented surface basicity (MgO, ZrO 2) or Lewis acidity (Al 2O 37z.sbnd;Cl). On amphoteric catalysts (Al 2O 3) both schemes were possible. Secondary reactions, which mainly occurred on acidic catalysts as condensation of acetone and/or acetaldehyde and alcohol dehydration, are also discussed.

Methylbutynol: a new and simple diagnostic tool for acidic and basic sites of solids

In order to characterize acid-base properties of a material surface under gas-phase reaction conditions, a new test reaction has been investigated. We have shown that 2-methyl-3-butyn-2-oĺundergoes dehydration over solid acid materials and gives acetone and acetylene over solid basic materials. These reactions are very sensitive to the usual modifications that can occur during catalyst preparation. Production of 3-hydroxy-3-methyl-2-butanone seems to be characteristic of amphoteric catalysts possessing acid-base ion pairs.