Yusuke Izumi

Catalysis by heterogeneous supported heteropoly acid

Abstract Catalytic performance and availability of supported heteropoly acid under vapor-phase conditions were studied through alkylation of benzene with ethylene, esterification of acetic acid with ethanol, and dehydration of 2-propanol as model reactions. These reactions differ from each other in terms of the affinity of reaction substrate for heteropoly acid. Heteropolytungstic acid exhibited high catalytic activity and selectivity when it was loaded on silica gel or on activated carbon. In every reaction, there was observed a ceiling of catalytic activity at a certain content of heteropoly acid (ca. 15–25 wt%). The results of XRD and TPD measurements on supported heteropoly acid suggest that the reactions which are operated at more than 150 °C proceed principally on the surface, or at most in the surface layers, of the heteropoly acid crystallites dispersed on support. Supported heteropoly acid appears to excel silica-alumina, supported phosphoric acid, and acidic zeolites in the catalytic capability particularly for those reactions which are carried out at relatively low temperatures (less than 200 °C) or involve water as a reactant or a product.

Efficient homogeneous acid catalysis of heteropoly acid and its characterization through ether cleavage reactions

Summary A Keggin-type heteropoly acid has revealed high catalytic activities for the cleavage reactions of epoxides, tetrahydrofuran, dibutyl ether and butyl methyl ether with acetic acid, acetic anhydride and butyl acetate in the non-aqueous homogeneous liquid phase at 30–118 °C. The catalytic activities of the heteropoly acid were much higher than those of conventional acid catalysts such as sulfuric acid, p-toluensulfonic acid and boron trifluoride etherate, at the same catalysts concentrations or the same proton concentrations. On the basis of comparative measurements of electrical conductivity, acidity, and softness of anion for the solutions of acid catalysts, the eficcient acid catalysis by heteropoly acid was suggested to be due to the specific properties of the heteropoly anion, which can be characterized by very weak basicity and great softness, togerther with the large size of the polyhedral structure.

Alkali metal salts and ammonium salts of Keggin-type heteropolyacids as solid acid catalysts for liquid-phase Friedel-Crafts reactions

Abstract The possibility of using a heteropolyacid salt as solid acid catalyst for liquid-phase Friedel-Crafts reactions was investigated through extensive examinations on various kinds of the salt prepared from different combinations of Keggin anions and their counter cations including ammonium ion. The catalytic behavior of the salt was discussed in relation to acidity, surface area, porosity, and thermal stability. Of the different kinds of insoluble acidic salt, K, Rb, Cs, and ammonium salts were mesoporous materials with large surface area (50–170 m 2 g −1 ), strong acidity (H 0 −1 ). Particularly, K 2.5 H 0.5 PW 12 O 40 , Rb 2.5 H 0.5 PW 12 O 40 , Cs 2.5 H 0.5 PW 12 O 40 , Cs 2.5 H 0.5 PMo 12 O 40 , K 2 H 2 SiW 12 O 40 , Cs 2 H 2 SiW 12 O 40 , and (NH 4 ) 2 HPW 12 O 40 worked as efficient solid acid catalysts for liquid-phase Friedel-Crafts alkylation of benzene with benzyl chloride, and some of them could also be effectively applied to the acylation of p -xylene with benzoyl chloride or benzoic anhydride. The salt catalysts were much more active than HY, LaY, Nafion-H and Zn-promoted montmorillonite.

Vapor-phase beckmann rearrangement over alumina-supported boria catalyst prepared by vapor decomposition method

Abstract The present work introduced a new method of catalyst preparation which involved the vapor decomposition of B(OEt) 3 onto silica gel to produce a silica-supported boria ( B 2 O 3 SiO 2 ). A B 2 O 3 SiO 2 catalyst prepared by this method (B 2 O 3 content 34 wt%) showed high catalytic efficiency for the vapor-phase Beckmann rearrangement of cyclohexanone oxime (oxime conversion: 98%, e-caprolactam selectivity: 96 mol%, at 250 °C). The vapor decomposition B 2 O 3 SiO 2 was more active and selective at any B 2 O 3 content than the B 2 O 3 SiO 2 obtained by the ordinary impregnation method using H 3 BO 3 . The amounts of the acid sites whose acid strengths exceeded 80 kJ/mol in terms of the differential heat of adsorption of ammonia (DHA) were 0.7 and 0.4 mmol/g for the most active vapor decomposition B 2 O 3 SiO 2 and the most active impregnation B 2 O 3 SiO 2 , respectively. The vapor decomposition effected uniform deposition of B 2 O 3 on SiO 2 , and produced a solid acid with relatively uniform distribution of acid strength. It is suggested that the acid strength ( H 0 ) of an effective catalyst pertinent to the vapor-phase Beckmann rearrangement should be less than −5.6 which approximately corresponds to a DHA value of more than 80 kJ/mol.

Silica-included heteropoly compounds as solid acid catalysts

12-Tungstophosphoric acid (H3PW12O40) and its acidic cesium salt (Cs2.5H0.5PW12O40), which readily dissolve or disperse as a colloid in water or in highly polar organic media, could be immobilized into a silica matrix by means of a sol-gel technique. This involves the hydrolysis of ethyl orthosilicate to afford insoluble and easily separable solid acid catalysts. The silica-included heteropoly compounds thus obtained were porous materials with mesopores and large surface areas, and were thermally more stable than the acidic ion-exchange resin Amberlyst-15. They effectively catalyzed the hydrolysis of ethyl acetate in the liquid phase owing to their strong acidity. Their turnover frequencies were larger than those of Amberlyst-15 and H-ZSM-5. H3PW12O40, when included in a silica matrix, showed higher catalytic activity than as an aqueous solution.

Vapor-phase Beckmann rearrangement over silica-supported boria catalyst prepared by vapor decomposition method

Abstract The present work introduced a new method of catalyst preparation which involved the vapor decomposition of B(OEt) 3 onto silica gel to produce a silica-supported boria ( B 2 O 3 SiO 2 ). A B 2 O 3 SiO 2 catalyst prepared by this method (B 2 O 3 content 34 wt%) showed high catalytic efficiency for the vapor-phase Beckmann rearrangement of cyclohexanone oxime (oxime conversion: 98%, e-caprolactam selectivity: 96 mol%, at 250 °C). The vapor decomposition B 2 O 3 SiO 2 was more active and selective at any B 2 O 3 content than the B 2 O 3 SiO 2 obtained by the ordinary impregnation method using H 3 BO 3 . The amounts of the acid sites whose acid strengths exceeded 80 kJ/mol in terms of the differential heat of adsorption of ammonia (DHA) were 0.7 and 0.4 mmol/g for the most active vapor decomposition B 2 O 3 SiO 2 and the most active impregnation B 2 O 3 SiO 2 , respectively. The vapor decomposition effected uniform deposition of B 2 O 3 on SiO 2 , and produced a solid acid with relatively uniform distribution of acid strength. It is suggested that the acid strength ( H 0 ) of an effective catalyst pertinent to the vapor-phase Beckmann rearrangement should be less than −5.6 which approximately corresponds to a DHA value of more than 80 kJ/mol.

The first example of aldol reactions between trimethylsilyl enol ethers and aldehydes by the aid of rhodium complex

Abstract Crossed aldol reaction of trimethylsilyl enol ether with aldehyde is successfully performed with the aid of catalytic amount of rhodium complex, [(COD)Rh(DPPB)] + X − (X = PF 6 and ClO 4 ) or Rh 4 (CO) 12 , under neutral conditions.

Reductive carbonylation of nitrobenzene catalyzed by heteropolyanion-modified palladium

Abstract The Keggin-type heteropolyanion containing Mo or V as addenda atoms shows an appreciable promoting effect on the catalysis of PdCl 2 in the reductive carbonylation of nitrobenzene to form methyl N -phenylcarbamate in the presence of methanol in a moderately polar solvent such as 1,2-dimethoxyethane at 130–170°C under an initial CO pressure of 11–41 atm. The catalyst was recovered and reused to give a total Pd turnover of 168. Partially reduced heteropolyanion was effective for modifying Pd(II), presumably as a basic macroligand.

Organic Syntheses Using Aluminosilicates

Publisher Summary This chapter discusses the usage of organic synthesis. Surfaces of porous inorganic solids have long been employed as “reaction fields” in organic reactions to produce bulk chemicals. Organic syntheses on porous solids have also been recognized as a useful synthetic method to produce fine chemicals with various functional groups. In many cases, the presence of inorganic materials enabled better yields and higher selectivities under much milder reaction conditions as compared with conventional reaction systems conducted in homogeneous solutions. Making good use of porous solids, such as silica and alumina in liquid phase, organic reactions provides various advantages, such as inclusion of a reaction substrate and a reagent into a small pore with nanometer dimensions, in the case of a bimolecular reaction, brings the two molecules into proximity, thus lowering the activation entropy of the reaction. The chapter describes liquid–phase organic reactions carried out below 100°C on zeolite and clay, comparing them with reactions carried out by existent synthetic methods from the standpoint of synthetic organic chemistry.

Clay-mediated meso-tetraarylporphyrin synthesis

Abstract meso -Tetraalporphyrin syntheses from aromatic aldehydes and pyrrole in clay nanospaces were investigated. The clay-promoted porphyrin synthesis was also contrasted with the Lindsey BF 3 -catalyzed system.