The relationship between the association constants of phenol with ethers and those of tricholoroacetic acid with ethers : Estimation of association constants of trichloroacetic acid with oxirane

The association constants, K_p, of phenol with ethers (tetrahydrofuran, tetrahydropyran dibutyl ether, dipropyl ether, 1,4-dioxane) and those , K_T, of trichloroacetic acid with ethers were measured in CCl₄ over a temparature range 20°–40° using near IR spectra. A linear relationship between K_p and K_T was found. On the basis of this realtionship the association constants of trichloroacetic acid with propylene oxide were estimated from those of phenol with propylene oxide.     

Effect of the electrostatic interaction on the redox reaction of positively charged cytochrome C adsorbed on the negatively charged surfaces of acid-terminated alkanethiol monolayers on a Au(111) electrode

The electrochemical properties of cytochrome c (cyt c) adsorbed on mixed self-assembled monolayers (SAMs) of 2-mercaptoethanesulfonate (MES)/2-mercaptoethanol (MEL) are compared with those on single-component SAMs of MES, MEL, and mercaptopropionic acid (MPA), using cyclic voltammetry and potential-modulated UV-vis reflectance spectroscopy. The rate constant of electron transfer (ET), k(et), of cyt c adsorbed on the SAM of MPA decreases from 1450 +/- 210 s(-1) at pH 7 to 890 +/- 100 s(-1) at pH 9. In contrast, the value of k(et) of cyt c on the SAM of MES is pH-independent at 100 +/- 15 s(-1). Those facts suggest that a large negative charge density on the SAM surface slows down the ET between cyt c and the electrode. The surface charge density of the SAM affects also the amount of electroactive cyt c, Gamma(e), which decreases from 10.0 +/- 1.0 to 5.3 +/- 1.1 pmol cm(-2) with increasing pH from 7 to 9 on the SAM of MPA. Similarly, the k(et) of cyt c adsorbed on the mixed SAMs of MES/MEL sharply decreases from 900 +/- 300 s(-1) to 110 s(-1) as the surface mole fraction of MES increases beyond 0.5, suggesting the presence of a negative surface charge threshold beyond which the rate of ET of cyt c is dramatically lowered. The decrease in the k(et) on the SAMs at high negative charge densities probably results from the confinement of adsorbed cyt c by the strong electrostatic force to an orientation that is not optimal for the ET reaction.     

Novel protecting groups. III. A study of the reaction of 2-picolyl 1-oxide derivatives with acetic anhydride

2-Picolyl 1-oxides (I-VIII) were prepared and the reaction of I-VII with acetic anhydride was followed by the gas chromatography. In this reaction, the increasing order of the rate of disappearance of the 2-pieolyl 1-oxide derivatives was found to be IV>III>VII>I>VI>II>V. Under comparable conditions, a half-life of VIII is midway between that of I and VI. The 2-picolyl 1-oxide group was found to be potentially useful for the blocking of hydroxyl functions of phosphates (viz., VIII), although ca. 4% of the organic phosphate remained unblocked after the deblocking procedure (acetic anhydride treatment and subsequent hydrolysis).     

Fischer-Tropsch synthesis over Ru/Al2O3 catalysts

Fischer-Tropsch syntheses (FTS) were carried out in a slurry phase over Ru/Al₂O₃ catalysts using hexadecane as a solvent. The outcome of the FTS was dependent on the oxide support, calcination temperature, synthesis gas composition and sulfur content. The addition of Mn/Na to Ru/Al₂O₃ was effective in raising the initial activity and C5+ selectivity, but after 20 hours, the performance of the modified catalyst was similar to that of the unmodified catalyst. An additional investigation involving the use of fresh vs used catalysts demonstrated that an agglomeration of the metallic Ru, at least in part, does occur during the reaction.     

Evolution of carbonylation catalysis: no need for carbon monoxide

Progress in organometallic catalysis began with the discovery of the Roelen reaction (hydroformylation with carbon monoxide and hydrogen) in 1938 and the Reppe reaction (hydrocarboxylation with carbon monoxide and water) in 1939. Since then, carbonylation chemistry by using carbon monoxide has occupied a central position in organometallic chemistry, as it relates to organic synthesis. There is, however, the problem of using gaseous carbon monoxide (a toxic greenhouse gas) in this chemistry. Recently, some strategies that address this issue have appeared. This minireview describes carbonylation reactions that can be conducted without the direct use of carbon monoxide. These carbonylation reactions provide reliable and accessible tools for synthetic organic chemists.     

Ru3(CO)12-catalyzed C-H/CO/olefin coupling of N-pyridylindolines. Direct carbonylation at a C-H bond delta to the pyridine nitrogen

The reaction of N-pyridylindolines with CO and ethylene in the presence of Ru3(CO)12 results in direct carbonylation at a C-H bond delta to the pyridine sp2 nitrogen, which represents a new type of C-H/CO/olefin coupling. The presence of a pyridine ring as a directing group on the substrates is essential for the reaction to proceed. The choice of N,N-dimethylacetamide (DMA) as the solvent is crucial for the reaction to proceed efficiently.     

Catalytic asymmetric Pauson-Khand-type reactions of enynes with formaldehyde in aqueous media

The first example of an aqueous, asymmetric, and CO gas-free Pauson-Khand-type reaction is described. Using formaldehyde as a commercially available substitute for carbon monoxide, combined use of a hydrophilic phosphine (TPPTS) and a hydrophobic, chiral phosphine (tolBINAP) enable the reaction to proceed smoothly in aqueous media, even in the absence of carbon monoxide, and stereoselectively.     

The geometry of surfaces in 4-space from a contact viewpoint

We study the geometry of the surfaces embedded in ⁴ through their generic contacts with hyperplanes. The inflection points on them are shown to be the umbilic points of their families of height functions. As a consequence we prove that any generic convexly embedded 2-sphere in ⁴ has inflection points.The research of the second author was partially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil.The research of the third author was partially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil.     

Enantioselective Friedel–Crafts reactions of ethenetricarboxylates and substituted pyrroles and furans and intramolecular reaction of benzene derivatives

Compared to enantioselective Friedel–Crafts reactions of indoles, reactions of alkylidene malonates with monocyclic aromatic compounds generally proceed with low enantioselectivity. The Friedel–Crafts reactions of ethenetricarboxylates 1 and monocyclic heteroaromatic compounds, such as substituted pyrroles and furans were investigated. The reaction of 1 with 2,4-dimethylpyrrole in the presence of a chiral bisoxazoline–copper(II) complex (10 mol %) in tetrahydrofuran at room temperature gave alkylated products in up to 72% ee. The reaction of 1 with 2-substituted furans gave alkylated products in 46–62% ee. The absolute stereochemistry of the furan Friedel–Crafts product 7e was determined by transformation to the known 2,3-dimethylbutyric acid. The intramolecular reaction of benzene derivatives gave cyclized products up to 56% ee.