Toshiyasu Sakakura

Selective and high yield synthesis of dimethyl carbonate directly from carbon dioxide and methanol

Supercritical carbon dioxide is efficiently converted to dimethyl carbonate (DMC) via the reaction with methanol in the presence of a catalytic amount of dialkyltin oxide or its derivatives. The removal of water is the key to accomplishing the high conversion by shifting the equilibrium to dimethyl carbonate. Dehydration is successfully carried out by circulating the reaction mixture through a dehydrating tube packed with molecular sieve 3A. Under the effective dehydration conditions, the DMC yield is almost linearly dependent on the reaction time, catalyst amount, methanol concentration, and CO2 pressure.

Synthesis of dimethyl carbonate from carbon dioxide: catalysis and mechanism

Abstract The turnover number of the catalytic production of dimethyl carbonate from CO2 and methanol is restricted by thermodynamics as well as catalyst decomposition. The catalytic efficiency is remarkably improved using an acetal as the starting material in methanol. The catalytic activity and selectivity also depend strongly on the CO2 pressure. A possible catalytic cycle involving transformation of CO2 to dimethyl carbonate is postulated based on mechanistic studies at a molecular level.

New procedure for recycling homogeneous catalyst: propylene carbonate synthesis under supercritical CO2 conditions

Polyfluoroalkyl phosphonium iodides, Rf3RPI (Rf = C4F9C2H4, C6F13C2H4, C8F17C2H4; R = Me, Rf), catalyzed propylene carbonate synthesis from propylene oxide and carbon dioxide under supercritical CO2 conditions, where propylene carbonate was spontaneously separated out of the supercritical CO2 phase. The Rf3RPI catalyst could be recycled with maintaining a high CO2 pressure and temperature by separating the propylene carbonate from the bottom of the reactor followed by supplying propylene oxide and CO2 to the upper supercritical CO2 phase in which the Rf3RPI remained.

Catalytic fixation of CO2 to cyclic carbonates by phosphonium chlorides immobilized on fluorous polymer

Phosphonium chloride covalently bound to the fluorous polymer is proved to be an efficient and recyclable homogeneous CO2-soluble catalyst for organic solvent-free synthesis of cyclic carbonates from epoxides and CO2 under supercritical CO2 conditions. The catalyst can be easily recovered by simple filtration after reaction and reused with retention of high activity and selectivity. In addition, the effects of various reaction variables on the catalytic performance are also discussed in detail. The process represents a simpler access to preparing cyclic carbonates with the ease of homogeneous catalyst recycling.

Synergistic hybrid catalyst for cyclic carbonate synthesis: Remarkable acceleration caused by immobilization of homogeneous catalyst on silica

The catalytic activity of phosphonium salts towards cyclic carbonate synthesis from propylene oxide and CO2 has been enormously enhanced by their immobilization onto silica that itself has no catalytic activity.

Lanthanoid-catalysed Tishchenko reaction of mono- or di-aldehydes

Abstract Lanthanoid complexes are found to be very active catalysts for the Tishchenko reaction of aldehydes. In the presence of Cp∗2LnCH(SiMe3)2 (Ln = Nd, La), esters are obtained from corresponding monoaldehydes in high yields. This method is applicable to dialdehydes. The reaction of o-phthalaldehyde proceeds intramolecularly to give phthalide quantitatively. Terephthalaldehyde and di(4-formylphenyl) ether are cleanly converted into the poly[p-(carboxymethylene)phenylene] (II) and poly[p-(carboxymethylene)(p-phenylenoxy)phenylene] (III), respectively. On the other hand, isophthalaldehyde polymerizes first and then the polymer is transformed into a macrocyclic lactone 1,5,11-trioxo-2,4;8,10;14,16-tribenzo-6,12,18-trioxacyclooctadecane (I-a) in high yields. The 18-membered macrocyclic structure of I-a was determined by the X-ray analysis. Stoichiometric reactions of the La complex with benzaldehyde indicated the intermediacy of alkoxo complexes in the catalysis.

Hydrosilation of dienes catalyzed by Cp*2NdCH(SiMe3)2

Abstract Cp*2NdCH(SiMe3)2 efficiently catalyzes hydrosilation of 1,3-, 1,5-, and 1,6-dienes under mild conditions with unusual selectivities as compared with later transition metal-catalyzed reactions; hydrosilation of isoprene affords mainly (E)-, not (Z)-, allylsilane. On the other hand, hydrosilation of 1,5- and 1,6-dienes proceeds through intramolecular CC bond formation to give (silylmethyl)-cyclopentanes.

Selective synthesis of N-aryl hydroxylamines by the hydrogenation of nitroaromatics using supported platinum catalysts

Various substituted nitroaromatics were successfully hydrogenated to the corresponding N-aryl hydroxylamines in excellent yields (up to 99%) using supported platinum catalysts such as Pt/SiO2 under a hydrogen atmosphere (1 bar) at room temperature. The key to the fast and highly selective formation of hydroxylamines is the addition of small amounts of amines such as triethylamine and dimethyl sulfoxide; amines promote the conversion of nitroaromatics, while dimethyl sulfoxide inhibits further hydrogenation of hydroxylamines to anilines. The promotive effect depends on which type of amine and primary amine was most effective. The hydrogenation efficiently proceeded in common organic solvents, including isopropanol, diethyl ether, and acetone. This methodology should extend the application range of conventional solid catalysts to fine chemicals synthesis.

Iron-catalysed green synthesis of carboxylic esters by the intermolecular addition of carboxylic acids to alkenes

Iron triflate, in situ-formed from FeCl3 and triflic acid, or FeCl3 and silver triflate efficiently catalyse the intermolecular addition of carboxylic acids to various alkenes to yield carboxylic esters; the reaction is applicable to the synthesis of unstable esters, such as acrylates.

Synthesis of ketimines via palladium complex-catalyzed cross-coupling of imidoyl chlorides with organotin compounds

Abstract Imidoyl chlorides were successfully transformed into ketimines when treated with organotin compounds in the presence of palladium complex catalysts.