Hidefumi Hirai

Preparation of Colloidal Transition Metals in Polymers by Reduction with Alcohols or Ethers

Abstract Colloidal dispersions of rhodium, palladium, osmium, iridium, and platinum are prepared by refluxing the methanol-water solutions of rhodium(III) chloride, palladium(II) chloride, osmium(VIII) oxide, sodium chloroiridate, and chloroplatinic acid, respectively, in the presence of poly(vinyl alcohol) as a protective colloid. The preparations of colloidal dispersions of rhodium are successful in the presence of vinyl polymer with polar group such as poly(vinyl alcohol), polyvinylpyrrolidone, or poly(methyl vinyl ether). Polyethyleneimine, gelatin, polyethylene glycol), and dextran are ineffective as the protective colloid. Water-soluble primary alcohols such as methanol and ethanol, water-soluble secondary alcohols such as 2-propanol, and water-soluble diethers such as 1,4-dioxane are available as reductants for preparation of the colloidal dispersion of rhodium. The average diameters of metal particles in the colloidal dispersions of palladium, rhodium, platinum, iridium, and osmium in poly(vinyl a...

Formation and Catalytic Functionality of Synthetic Polymer-Noble Metal Colloid

Abstract Colloidal dispersions of noble metals in synthetic polymers are prepared by reduction with alcohol. Reflux of a solution of rhodium(III) chloride and poly(vinyl alcohol) (PVA) in a methanol-water mixed solvent under argon or air for 4 hr gives a homogeneous solution of colloidal dispersion of rhodium (Rh-PVA-MeOH/H2O). The particle size of metallic rhodium is distributed n a narrow range of 30-70 A, and the average diameter is 40 A. The formation of colloidal rhodium proceeds through three steps: coordination of poly(vinyl alcohol) to rhodium(III) ion, reduction with methanol to form small particles (8 A in diameter), and growth of the small particle to large particle (40 A in diameter). Polyvinylpyrrolidone (PVP) and poly(methyl vinyl ether) (PMVE) can be used in place of poly(vinyl alcohol) and result in colloidal dispersions, respectively, similar to Rh-PVA-MeOH/H2O. Colloidal dispersions in nonaqueous solvent can be prepared by using ethanol instead of methanol-water (Rh-PVP-EtOH) and by usin...

Preparation of Colloidal Rhodium in Poly(vinyl Alcohol) by Reduction with Methanol

Abstract Refluxing of a solution of poly(vinyl alcohol) and rhodium(III) chloride in methanol-water gives a colloidal dispersion of rhodium which is an effective catalyst for hydrogenation of cyclohexene in methanol at 30°C under atmospheric hydrogen pressure. Formaldehyde is produced quantitatively with the reduction of rhodium(III) chloride to metallic rhodium. The rhodium particles in the colloidal dispersion are found to consist of two kinds of particles, about 8 and 40 A in diameter by electron microscopy. The sizes of the small (8 A) and large (40 A) particles are almost constant during the course of refluxing. The number of small particles, which is the great majority of particles at the early stage of refluxing, gradually decreases; concurrently the number of large particle increases on prolonged refluxing. An absorption peak appears at 260 nm at the early stage of refluxing. The presence of the 260 nm peak, which indicates the coordination of poly(vinyl alcohol) to rhodium(III) ion, is indispensa...

Polymerized Micelle-Protected Platinum Clusters. Preparation and Application to Catalyst for Visible Light-Induced Hydrogen Generation

Abstract Platinum clusters protected by polymerized micelles were prepared by radical polymerization of unsaturated surfactants which were involved in micelle-protected platinum clusters. The micelle-protected platinum clusters were successfully prepared by photoreduction of hexachloroplatinic acid in water in the presence of unsaturated surfactants. The platinum clusters thus obtained were characterized by electron microscopy and IR and 1H-NMR spectroscopies. The average diameter of the platinum particles was about 1 nm by electron microscopy, and the polymerization was confirmed by IR and 1H-NMR spectra. The platinum clusters thus obtained proved to be highly active catalysts for visible light-induced hydrogen generation in the system of EDTA/Ru(bpy)3 2+/MV2+. The polymerized micelle-protected platinum clusters showed higher catalytic activity than the linear polymer-protected one. The catalytic activity was affected by the electric charge of the surfactants in the polymerized micelle-protected platinum...

Oligomers from Hydroxymethylfurancarboxylic Acid

Abstract Polycondensation of 5-hydroxymethyl-2-furancarboxylic acid (1) was studied. Oligoesters of 1 were prepared by using 2-chloro-l-methylpyridinium iodide (2) as a polycondensation agent. The solution polycondensation in pyridine at a 2 / 1 molar ratio more than 1.2 at 60°C gave selectively the macrocyclic oligoesters at a total yield more than 91 % : cyclic trimer (>33%), tetramer (>35%), pentamer (>13%) and higher oligomers (> 9%). The polycondensation in n-hexane in place of pyridine with tri-n-butylamine as a scavenger of hydrogen halide produced selectively the linear oligoesters from trimer to hexamer. That in toluene instead of n-hexane yielded the polyester, the cyclic and linear oligoesters. A mechanism is proposed for the formation of the cyclic oligoesters.

Colloidal palladium protected with poly(N-vinyl-2-pyrrolidone) for selective hydrogenation of cyclopentadiene

Colloidal dispersions of palladium were prepared by refluxing solutions of palladium(II) chloride and poly(N-vinyl-2-pyrrolidone) in alcohols. The average diameter of the palladium particles was controlled in the range 18–56 A by using appropriate species of alcohols and additives. The colloidal palladium exhibited high activity and selectivity as a catalyst for hydrogenation of cyclopentadiene to cyclopentene in methanol at 30°C under 1 atm of hydrogen. Effects of particle size of the colloidal palladium and the polymer used as a protective colloid upon the selectivity of monoene formation and the kinetics of the reaction were studied. The high selectivity of the colloidal palladium for monoene formation is discussed in terms of selective adsorption of the diene on the catalytic site. poly(N-vinyl-2-pyrrolidone) plays an important role in stabilizing the colloidal dispersion as a protective colloid and in increasing the hydrogenation selectivity through the interaction with the palladium particles.

Selective syntheses using cyclodextrins as catalysts: Part 3. Improvements by immobilization of selective catalysts for the synthesis of 4-hydroxybenzoic acid [1]

Abstract Improvements of β-cyclodextrin (β-CyD) as a catalyst for selective syntheses of 4-hydroxybenzoic acids have been achieved by its immobilization. Three types of immobilized β-CyD catalysts I , II , and III (with molar ratios 5.7, 3.3 and 1.2, respectively, of β-CyD residue to 2-hydroxypropyl residue) were prepared by the reaction of β-CyD with epichlorohydrin. All the immobilized catalysts exhibit 100% selectivity and high (larger than 80 mol%) yield for the syntheses of 4-hydroxybenzoic acids from the corresponding phenols and carbon tetrachloride in alkaline aqueous solutions. In the absence of the immobilized catalysts, however, the yields and the selectivities are much lower: 15 mol% and 56% for 4-hydroxybenzoic acid. The selectivities (100%) exhibited by the immobilized catalysts are considerably larger than the values (92–99%) obtained with free β-CyD catalyst. The immobilized β-CyD catalysts are easily recovered from the reaction mixtures either by centrifugation or by filtration, and are successfully re-used without any measurable loss in the catalytic activity. The enhancement of the selective catalysis of β-CyD by immobilization has been attributed to a specific reaction field effect produced by many alkoxide ions of β-CyD residues in the immobilized catalysts.

Selective synthesis of 2,6-naphthalenedicarboxylic acid by use of cyclodextrin as catalyst

Abstract The selective synthesis of 2,6-naphthalenedicarboxylic acid from 2-naphthalenecarboxylic acid with carbon tetrachloride, copper powder, and aqueous alkali was achieved by using of β-cyclodextrin (β-CyD) as a catalyst at 60°C under nitrogen, producing 2,6-naphthalenedicarboxylic acid in 67 mol% yield with 84% selectivity. The one-pot preparation of 2,6-naphthalenedicarboxylic acid from naphthalene was attained at 84°C by using of β-CyD, producing 2,6-naphthalenedicarboxylic acid in 65 mol% yield with 79% selectivity. When α-CyD or γ-CyD was used instead of β-CyD on the carboxylation of 2-naphthalenecarboxylic acid and naphthalene, respectively, the reaction hardly proceeded. The conformation of β-CyD–2-naphthalenecarboxylate inclusion complex in aqueous alkaline solution was determined by the nuclear magnetic resonance spectroscopy using 1 H homonuclear Overhauser enhancement on the rotating frame. The 2-naphthalenecarboxylate anion was axially included in the cavity of β-CyD with an orientation which directed the 5-, 6-, and 7-positions of 2-naphthalenecarboxylate anion to the secondary hydroxyl side of β-CyD. It was concluded that the high selectivity of the carboxylation of 2-naphthalenecarboxylic acid was ascribed to the conformation of the β-CyD–2-naphthalenecarboxylate inclusion complex. The selective carboxylation of naphthalene was attributed to the formations of the β-CyD–naphthalene and β-CyD–2-naphthalenecarboxylate inclusion complexes.

13C-NMR investigations of synthetic branched polysaccharides

Abstract 13C-NMR spectra of glucose-branched polysaccharides synthesized by the reaction of 3,4,6tri-O-acetyl-(1,2-O-ethylortho-acetyl)-α- d -glucopyranose with curdlan or cellulose acetate followed by deacetylation were measured and assigned. Although most of the branches are β-(1 → 6) linked, a small amount of α-(1 → 6)linked branches were found.

Hydrosilylation of carbon dioxide catalysed by ruthenium complexes

Carbon dioxide was found to be catalytically fixed into silyl esters of formic acid by the reaction with hydrosilanes in the presence of some ruthenium phosphine complexes.