Yasumasa Takenaka

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.

Synthesis of Cyclic Sulfites from Epoxides and Sulfur Dioxide with Silica‐Immobilized Homogeneous Catalysts

Quaternary ammonium- and amino-functionalized silica catalysts have been prepared for the selective synthesis of cyclic sulfites from epoxides and sulfur dioxide, demonstrating the effects of immobilizing the homogeneous catalysts on silica. The cycloaddition of sulfur dioxide to various epoxides was conducted under solvent-free conditions at 100 °C. The quaternary ammonium- and amino-functionalized silica catalysts produced cyclic sulfites in high yields (79-96 %) that are comparable to those produced by the homogeneous catalysts. The functionalized silica catalysts could be separated from the product solution by filtration, thereby avoiding the catalytic decomposition of the cyclic sulfite products upon distillation of the product solution. Heterogenization of a homogeneous catalyst by immobilization can, therefore, improve the efficiency of the purification of crude reaction products. Despite a decrease in catalytic activity after each recycling step, the heterogeneous pyridine-functionalized silica catalyst provided high yields after as many as five recycling processes.

Synthesis of linear and branched polyketones from the Rh complex catalyzed living alternating copolymerization of (4-alkylphenyl)allene with CO

Copolymerization of (4-hexylphenyl)allene and of (4-dodecylphenyl)allene with carbon monoxide (1 atm) catalyzed by Rh[η3-CH(Ar′)C{C(CHAr′)CH2C (CHAr′)CH2CH2CHCHAr′}CH2](PPh3)2 (A; Ar′ = C6H4OMe-p) gives the corresponding polyketones: I-[—CO—C(CHAr)—CH2—]n [1: Ar = C6H4C6H13-p, 2 : Ar = C6H4C12H25-p; I = CH2C(CHAr′)C(CHAr′)CH2C(CHAr′)CH2CH2CHCHAr′]. Molecular weights of the polyketone prepared from (4-hexylphenyl)allene and CO are similar to the calculated from the monomer to initiator ratios until the molecular weight reaches to 45,000, indicating the living polymerization. Melting points of the polyketones I-[—CO—C(CHC6H4R-p)—CH2—]n (n = ca. 100) increase in the order R = C12H25 < C6H13 < C4H9 < CH3 < H. Block and random copolymerization of phenylallene and (4-alkylphenyl)allene with carbon monoxide gives the new copoly- ketones. The polymerization of a mixture of (4-methylphenyl)allene and smaller amounts of bis(allenyl)benzene under CO afforded the polyketone with a crosslinked structure.