Masayuki Shirai

Heck reactions of iodobenzene and methyl acrylate with conventional supported palladium catalysts in the presence of organic and/or inorganic bases without ligands

The vinylation of iodobenzene with methyl acrylate has been studied with several supported palladium catalysts in N-methylpyrrolidone in the presence of triethylamine and/or sodium carbonate. The reaction can be performed in air without any solubilizing or activating ligands. It was found that significant amounts of palladium leach out into the solvent and these dissolved Pd species essentially catalyze the reaction. It is interesting, however, that almost all the palladium species in the solution can redeposit onto the surface of the supports after the reaction has been completed (at 100% conversion of iodobenzene). Thus, the catalysts were recyclable without loss of activity. The use of both inorganic and organic bases is very effective in the promotion of the palladium redeposition as well as in the enhancement of the reaction rate. For Heck reactions with bromobenzene and chlorobenzene it was found that the use of triethylamine and sodium carbonate increases the selectivity of the Heck coupling product (benzene is also produced for these two substrates), but the mixed bases do not affect the overall rate of reaction as much.

Gold nanoparticles stabilized on nanocrystalline magnesium oxide as an active catalyst for reduction of nitroarenes in aqueous medium at room temperature

Gold nanoparticles deposited on nanocrystalline magnesium oxide is a very efficient catalyst for the reduction of nitroarenes in aqueous medium at room temperature. Sodium borohydride is used as the source of hydrogen for the reduction of nitro groups. This catalytic system selectively reduces the nitro group even in the presence of other sensitive functional groups under very mild conditions in good to excellent yields without the requirement of any promoters. The reaction kinetics of reduction of 4-nitrophenol to 4-aminophenol has been studied by UV-visible spectrophotometry, and its apparent rate constant has been determined and compared with those of other supported gold catalysts. The spent heterogeneous catalyst is recovered by simple centrifugation, and reused for multiple cycles.

The leaching and re-deposition of metal species from and onto conventional supported palladium catalysts in the Heck reaction of iodobenzene and methyl acrylate in N-methylpyrrolidone

When supported palladium catalysts are used for Heck vinylation of iodobenzene with methyl acrylate in N-methylpyrrolidone (NMP) in the presence of triethylamine and sodium carbonate bases, the reaction proceeds homogeneously with dissolved active palladium species that are formed through coordination of NMP and triethylamine with palladium. These active species easily react with iodobenzene (oxidative addition), beginning the catalytic cycle of Heck coupling. The last step of catalyst regeneration takes place with the action of sodium carbonate. The active palladium species are not stable and deposit the metal to support when they cannot find iodobenzene to react in the reaction mixture after this substrate is completely consumed. The re-deposition of palladium occurs on the surfaces of bare support and/or palladium particles remaining on it, depending on the nature of support surface and the number and size of residual metal particles. The growth of palladium particles has been observed after the reuse of catalyst in some case. However, the supported catalysts are recyclable without loss of activity.

CATALYTIC GASIFICATION OF WOOD BIOMASS IN SUBCRITICAL AND SUPERCRITICAL WATER

ABSTRACT Research in biomass gasification with subcritical and supercritical water is reviewed. Catalytic conversion of biomass in sub- and supercritical water is a low-temperature gasification technique that can be carried out from 473 to 973 K. Research is categorized according to temperature and water density, since reaction mechanisms greatly depend on these variables.

Sorbitol dehydration in high temperature liquid water

Sorbitol dehydration in high temperature liquid water proceeded at 523–573 K without adding any acid catalysts. Anhydrosorbitols (1,4-anhydrosorbitol (1,4-AHSO), 2,5-anhydrosorbitol (2,5-AHSO) and 1,5-anhydrosorbitol (1,5-AHSO)) were produced by the monomolecular dehydration of sorbitol, and isosorbide was produced by the stepwise dehydration of 1,4-AHSO. The formation rates of 1,4-AHSO and 2,5-AHSO (five-membered cyclic ethers) from sorbitol dehydration were much larger than that of 1,5-AHSO (six-membered cyclic ether), and 1,4-AHSO was the main product of the monomolecular dehydration of sorbitol. The dehydration rate of sorbitol to 1,4-AHSO was faster than that of 1,4-AHSO to isosorbide; therefore, 1,4-AHSO could be obtained as an intermediate product. A kinetic analysis of sorbitol dehydration in high temperature liquid water showed that the maximum yield of 1,4-AHSO from the dehydration of sorbitol increased with decreasing reaction temperature (for example, 80% at 500 K) and that the maximum yield of isosorbide was 57% at 590 K for 1 h. 1,4-AHSO and isosorbide could be produced selectively from sorbitol dehydration in high temperature liquid water by controlling both the reaction temperature and reaction time.

Palladium-catalyzed homogeneous and heterogeneous Heck reactions in NMP and water-mixed solvents using organic, inorganic and mixed bases

The use of mixed solvent of N-methylpyrrolidone (NMP) and water and of mixed base of triethylamine and sodium carbonate was effective for promoting the rate of homogeneous Heck reaction of iodobenzene and methyl acrylate with palladium acetate as catalyst in the absence of any ligands. It was observed that palladium precipitated and formed colloidal particles during the reaction and this was promoted by the presence of water. However, the reaction proceeded with palladium species dissolved in the solvent, which were more active than those in pure NMP solvent. When the same Heck reaction was conducted with an activated carbon-supported palladium catalyst, the presence of water was also effective for promoting the rate of reaction. It was observed that palladium was leached out from the support and the dissolved palladium species were also active species for this heterogeneous reaction. The presence of water seemed to suppress the leaching of palladium into the solvent and/or enhance the formation of colloidal palladium particles. The concentration of active palladium species was smaller in the mixed solvent than in pure NMP solvent. However, these were more active, resulting in the larger rate of reaction in the presence of water.

Chemical fixation of carbon dioxide to propylene carbonate using smectite catalysts with high activity and selectivity

The reaction of propylene oxide and carbon dioxide to propylene carbonate was carried out using Mg-, Ni- and Mg-Ni-containing smectite catalysts which contain different amounts of alkali atoms such as sodium, potassium and lithium. These catalysts are highly active and selective for this reaction. The catalytic activity strongly depends on the elemental composition of the catalyst used. Particularly the amount of alkali atoms incorporated in the catalyst is the most important factor governing the catalytic performance. The most active catalyst among those prepared in the present study shows a turnover number of 105 mmol/g for the propylene carbonate formation, which is the highest turnover number compared with those reported so far (10 mmol/g) for the title reaction.

Gas-phase hydrogenation of nitriles by nickel on various supports

Abstract Gas-phase hydrogenation of benzonitrile and acetonitrile was investigated using 5% nickel on various supports at normal pressure and in a temperature range of 170–230°C. The only products obtained were the corresponding primary amines; however, the catalytic activity was strongly influenced by the support used, being in the order of alumina>titania>silica-alumina>silica. The activity was higher for the catalyst having a smaller degree of nickel dispersion measured by temperature programmed desorption of hydrogen.

Heck reactions in a non-aqueous ionic liquid using silica supported palladium complex catalysts

Abstract The Heck reaction of iodobenzene and 4-methyl-iodobenzene with olefins using silica-supported palladium complex catalysts was conducted in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF 6 ), exhibiting higher activities than in DMF in addition to easy product isolation and catalyst recycling.

Concurrent Synthesis of Dimethyl Carbonate and Ethylene Glycol via Transesterification of Ethylene Carbonate and Methanol Using Smectite Catalysts Containing Mg and/or Ni

Smectites containing magnesium and/or nickel in the lattice were found to be excellent heterogeneous catalysts for the concurrent synthesis of dimethyl carbonate and ethylene glycol by transesterification of ethylene carbonate with methanol. The catalytic activity strongly depends on the elemental composition of the catalysts and is correlated with the number of moderately basic sites present on the catalyst.