Direct Hydroxymethylation of Furaldehydes with Aqueous Formaldehyde over a Reusable Sulfuric Functionalized Resin Catalyst.

Transformation of C5 furaldehydes to the corresponding C6 furaldehydes over a heterogeneous catalyst is a versatile but demanding reaction process. This report describes our discovery that Amberlyst-15, a conventional sulfuric functionalized resin, affords a 43.1% yield for 5-hydroxymethyl-2-furaldehyde (HMF) production with 57.5% selectivity via direct hydroxymethylation of 2-furaldehyde (furfural) with an aqueous formaldehyde reagent. This report is the first to describe an important achievement on the heterogeneous acid catalyst-assisted HMF production from furfural via direct hydroxymethylation in a batch reactor system. The Amberlyst-15 was also reusable and applicable for C5 furaldehyde upgrading of various types: furfuryl alcohol, furfurylamine, and furoic acid toward the corresponding C6 furaldehydes. Results show that a liquid flow system becomes an advanced tool for the continuous production of upgrading furaldehydes through a fixed Amberlyst-15 catalyst bed. Accordingly, the sulfuric functionalized resin-catalyzed direct hydroxymethylation of furaldehydes with aqueous formaldehyde in both batch and flow reactor systems is worthwhile and opens up new avenues for biomass transformations in particles, an important area of inedible biomass utilization.

Effect of SiO2 amount on heterogeneous base catalysis of SiO2@Mg-Al layered double hydroxide.

The effects of SiO2 amount on the base catalysis of highly active finely crystallized Mg-Al type layered double hydroxides prepared by the co-precipitation method with coexistence of SiO2 spheres, denoted as SiO2@LDHs, were investigated. With the Si/(Mg + Al) atomic ratios of 0-0.50, the highest activity for the Knoevenagel condensation was observed in the case of Si/(Mg + Al) = 0.17, as the reaction rate of 171.1 mmol g(cat)-1 h-1. The base activity increased concomitantly with decreasing LDH crystallite size up to Si/(Mg + Al) atomic ratio of 0.17. However, above the Si/(Mg + Al) atomic ratio of 0.17, the reaction rate and TOFbase were decreased although the total base amount was increased. Results of TEM-EDS and 29Si CP-MAS NMR suggest that the co-existing SiO2 causes advantages for dispersion and reduction of the LDH crystallite to improve the base catalysis of SiO2@Mg-Al LDH, whereas the excess SiO2 species unfortunately poisons the highly active sites on the finely crystallized LDH crystals above a Si/(Mg + Al) atomic ratio of 0.17. According to these results, we inferred that the amount of spherical SiO2 seeds in the co-precipitation method is an important factor to increase the base catalysis of SiO2@LDHs; i.e. the control of Si/(Mg + Al) atomic ratio is necessary to avoid the poisoning of highly active base sites on the LDH crystal.

Gold Nanoparticles Supported on Alumina as a Catalyst for Surface Plasmon-Enhanced Selective Reductions of Nitrobenzene.

Au nanoparticles supported on alumina (Au/Al2O3) with average particle size of 3.9 ± 0.7 nm and surface plasmon band centerned at 516.5 nm were prepared by deposition-precipitation method, and their photocatalytic activities for the reduction of nitrobenzene using either formic acid in acetonitrile (method A) or KOH in 2-propanol (method B) were investigated. Even at room temperature, the Au/Al2O3 was found to be highly active and selective for conversion of nitrobenzene to aniline when used with formic acid in acetonitrile or to azobenzene when performed with KOH in 2-propanol under irradiation with green light-emitting diode (517 nm).

Selective Oxidation of 1,6-Hexanediol to 6-Hydroxycaproic Acid over Reusable Hydrotalcite-Supported Au-Pd Bimetallic Catalysts.

Selective oxidation of 1,6-hexanediol into 6-hydroxycaproic acid was achieved over hydrotalcite-supported Au-Pd bimetallic nanoparticles as heterogeneous catalyst using aqueous H2 O2 . N,N-dimethyldodecylamine N-oxide (DDAO) was used as an efficient capping agent. Spectroscopic analyses by UV/Vis, TEM, XPS, and X-ray absorption spectroscopy suggested that interactions between gold and palladium atoms are responsible for the high activity of the reusable Au40 Pd60 -DDAO/HT catalyst.

One-pot conversions of raffinose into furfural derivatives and sugar alcohols by using heterogeneous catalysts.

Inedible and/or waste biomass reserves are being strongly focused upon as a suitable new energy and chemical source. Raffinose, which is an indigestible trisaccharide composed of glucose, galactose, and fructose, is found abundantly in beet molasses, sugar cane, and seeds of many leguminous plants. Herein, we demonstrate the one-pot synthesis of furan derivatives and sugar alcohols from raffinose by using heterogeneous acid, base, and/or metal-supported catalysts. The combination of Amberlyst-15 and hydrotalcite (HT) showed a high activity (37% yield) for 5-hydroxymethyl-2-furaldehyde (HMF) through continuous hydrolysis, isomerization, and dehydration reactions. In addition, the use of a hydrotalcite-supported ruthenium catalyst (Ru/HT) successfully afforded 2,5-diformylfuran (DFF, 27% yield) from HMF produced by raffinose, directly. Moreover, the hydrogenation of hexoses obtained by raffinose hydrolysis into sugar alcohols (galactitol, mannitol, sorbitol) was also achieved in a high yield (91%) with Amberlyst-15 and Ru/HT catalysts. Thus, we suggest that raffinose has great potential for the synthesis of important industrial intermediates under mild reaction conditions.

Direct synthesis of 1,6-hexanediol from HMF over a heterogeneous Pd/ZrP catalyst using formic acid as hydrogen source.

A new approach is developed for hydrogenolytic ring opening of biobased 5-hydroxymethylfurfural (HMF), dehydration product of hexoses, towards 1,6-hexanediol (HDO) under atmospheric pressure. The highest yield of HDO, 43%, is achieved over reusable Pd/zirconium phosphate (ZrP) catalyst at 413 K in the presence of formic acid as hydrogen source. In comparison with various Brønsted and/or Lewis acidic supports, the specific Brønsted acidity on ZrP support effectively accelerated the cleavage of C-O bond in a furan ring.

Synthesis of α-amino acids from glucosamine-HCl and its derivatives by aerobic oxidation in water catalyzed by Au nanoparticles on basic supports.

The golden wonder: Various α-amino acids such as glucosaminic acid, galactosaminic acid, or N-acetyl-glucosaminic acid can be obtained from the corresponding glucosamine derivatives (amino sugars). This is achieved through an aqueous oxidation that catalyzed by Au nanoparticles dispersed on basic support under mild reaction conditions in water.

Role of base in the formation of silver nanoparticles synthesized using sodium acrylate as a dual reducing and encapsulating agent.

The formation mechanism of Ag nanoparticles (NPs) synthesized with a wet-chemical reduction method using sodium acrylate as a dual reducing and capping agent was investigated with various analytical techniques. The time course of the state of the reaction solution was investigated using UV-vis and XAFS spectroscopies which showed that the NP formation rate increased with increasing concentration of sodium hydroxide (NaOH). The detailed kinetic analyses reveal that both the reduction rate of Ag ions and the nucleation rate of Ag NPs are dramatically increased with increasing NaOH concentration. XANES analyses imply that another reaction pathway via alternative Ag(+) species, such as Ag(OH)(x), was developed in the presence of NaOH. Consequently, NaOH is found to play an important role not only in creating specific intermediates in the reduction of Ag(+) to Ag(0), but also in accelerating the reduction and nucleation rates by enhancing the oxidation of sodium acrylate, thereby increasing the rate of formation of the Ag NPs.

Selective oxidation of glycerol by using a hydrotalcite-supported platinum catalyst under atmospheric oxygen pressure in water.

A hydrotalcite-supported platinum (Pt/HT) catalyst was found to be a highly active and selective heterogeneous catalyst for glycerol oxidation in pure water under atmospheric oxygen pressure in a high glycerol/metal molar ratio up to 3125. High selectivity toward glyceric acid (78 %) was obtained even at room temperature under air atmosphere. The Pt/HT catalyst selectively oxidized the primary hydroxyl group of 1,2-propandiol to give the corresponding carboxylic acid (lactic acid) as well as glycerol. The activity of the catalyst was greatly influenced by the Mg/Al ratio of hydrotalcite. Glycerol conversion increased with increasing the Mg/Al ratio of hydrotalcite (from trace to 56 %). X-ray absorption fine structure (XAFS) measurements indicated that the catalytic oxidation activity was proportional to the metallic platinum concentration, and more than 35 % of metallic platinum was necessary for this reaction. TEM measurements and titration analysis by using benzoic acid suggested that the solid basicity of hydrotalcite plays important roles in the precise control of platinum size and metal concentration as well as the initial promotion of alcohol oxidation.

In situ time-resolved XAFS study on the formation mechanism of Cu nanoparticles using poly(N-vinyl-2-pyrrolidone) as a capping agent.

The formation mechanism of copper nanoparticles (NPs) using poly(N-vinyl-2-pyrrolidone) (PVP) as a capping agent was investigated by measurements of X-ray diffraction (XRD), transmission electron microscopy (TEM), in situ time-resolved X-ray adsorption fine structure (XAFS) analysis, in situ UV-vis spectroscopy, and an indicator method. XAFS analyses, in combination with TEM observations and the indicator method, revealed that the stable intermediates such as Cu(OH)(2) and Cu(+)-PVP intermediate were formed during an induction period of nucleation of Cu NPs, which play a critical role in the Cu NP formation. Our results suggest that the PVP capping agent is important not only to protect NPs from overgrowth and aggregation but also to control the reaction kinetics of NP formation.

A one-pot reaction for biorefinery: combination of solid acid and base catalysts for direct production of 5-hydroxymethylfurfural from saccharides.

5-Hydroxymethylfurfural (HMF), one of the most important intermediates derived from biomass, was directly produced from monosaccharides (fructose and glucose) and disaccharides (sucrose and cellobiose) by a simple one-pot reaction including hydrolysis, isomerization and dehydration using solid acid and base catalysts under mild conditions.

Nucleophilic substitution reactions of alcohols with use of montmorillonite catalysts as solid Brønsted acids.

We have developed an environmentally benign synthetic approach to nucleophilic substitution reactions of alcohols that minimizes or eliminates the formation of byproducts, resulting in a highly atom-efficient chemical process. Proton- and metal-exchanged montmorillonites (H- and Mn+-mont) were prepared easily by treating Na+-mont with an aqueous solution of hydrogen chloride or metal salt, respectively. The H-mont possessed outstanding catalytic activity for nucleophilic substitution reactions of a variety of alcohols with anilines, because the unique acidity of the H-mont catalyst effectively prevents the neutralization by the basic anilines. In addition, amides, indoles, 1,3-dicarbonyl compounds, and allylsilane act as nucleophiles for the H-mont-catalyzed substitutions of alcohols, which allowed efficient formation of various C-N and C-C bonds. The solid H-mont was reusable without any appreciable loss in its catalytic activity and selectivity. Especially, an Al3+-mont showed high catalytic activity for the alpha-benzylation of 1,3-dicarbonyl compounds with primary alcohols due to cooperative catalysis between a protonic acid site and a Lewis acidic Al3+ species in its interlayer spaces.

Highly efficient C-C bond-forming reactions in aqueous media catalyzed by monomeric vanadate species in an apatite framework.

A calcium vanadate apatite (VAp), in which PO4(3-) of hydroxyapatite (HAP), Ca10(PO4)6(OH)2, is completely substituted by VO4(3-) in the apatite framework, was synthesized. Physicochemical analysis of the VAp reveals the presence of isolated VO4 tetrahedron units with a pentavalent oxidation state. The VAp acts as a high-performance heterogeneous base catalyst for various carbon-carbon bond-forming reactions such as Michael and aldol reactions in aqueous media and the H-D exchange reactions using deuterium oxide. For example, a 200-mmol-scale Michael reaction under triphasic conditions proceeded rapidly, with an extremely high turnover number of up to 260 400 and an excellent turnover frequency of 48 s(-1). No vanadium leaching was detected during the above reactions, and the catalyst was readily recycled with no loss of activity.

Efficient C-N bond formations catalyzed by a proton-exchanged montmorillonite as a heterogeneous Brønsted acid.

Nucleophilic addition of sulfonamides and carboxamides to simple alkenes proceeded smoothly using a proton-exchanged montmorillonite catalyst. The spent catalyst was recovered easily from the reaction mixture and was reusable at least five times without any loss of activity. The unique acidity of the proton-exchanged montmorillonite (H-mont) catalyst was found to be applicable to additional reactions: substitution of hydroxyl groups of alcohols with amides and anilines.

Environmentally friendly one-pot synthesis of alpha-alkylated nitriles using hydrotalcite-supported metal species as multifunctional solid catalysts.

A ruthenium-grafted hydrotalcite (Ru/HT) and hydrotalcite-supported palladium nanoparticles (Pd(nano)/HT) are easily prepared by treating basic layered double hydroxide, hydrotalcite (HT, Mg(6)Al(2)(OH)(16)CO(3)) with aqueous RuCl(3)n H(2)O and K(2)[PdCl(4)] solutions, respectively, using surface impregnation methods. Analysis by means of X-ray diffraction, and energy-dispersive X-ray, electron paramagnetic resonance, and X-ray absorption fine structure spectroscopies proves that a monomeric Ru(IV) species is grafted onto the surface of the HT. Meanwhile, after reduction of a surface-isolated Pd(II) species, highly dispersed Pd nanoclusters with a mean diameter of about 70 A is observed on the Pd(nano)/HT surface by transmission electron microscopy analysis. These hydrotalcite-supported metal catalysts can effectively promote alpha-alkylation reactions of various nitriles with primary alcohols or carbonyl compounds through tandem reactions consisting of metal-catalyzed oxidation and reduction, and an aldol reaction promoted by the base sites of the HT. In these catalytic alpha-alkylations, homogeneous bases are unnecessary and the only by-product is water. Additionally, these catalyst systems are applicable to one-pot syntheses of glutaronitrile derivatives.

Reconstructed hydrotalcite as a highly active heterogeneous base catalyst for carbon-carbon bond formations in the presence of water.

The aldol reaction of carbonyl compounds is efficiently catalyzed by reconstructed hydrotalcites, obtained by treating the Mg-Al mixed oxide with water, as solid base catalysts in the presence of water. The catalysis of the reconstructed hydrotalcites is attributable to the surface base sites, created during the organization of the layered structure, with uniformly distributed strength. Furthermore, the reconstructed hydrotalcites provide a unique acid-base bifunctional surface capable of promoting the Knoevenagel and Michael reactions of nitriles with carbonyl compounds.