Supported ruthenium catalyst as an effective catalyst for selective oxidation of toluene

The investigation comprised an evaluation of the use of the catalyst 1%Ru/TiO₂ in the liquid-phase conversion of toluene to benzyl alcohol and benzaldehyde. Transmission electron microscopy (TEM) and N₂ adsorption-desorption isotherms were deployed to delineate the properties of the supported catalysts. The findings indicated a good catalytic performance by 1%Ru/TiO₂ under green reaction conditions. This performance was deemed a consequence of the spread and loading of Ru on the TiO₂. The reaction conditions such as temperature, reaction time, type of support, catalyst preparation method, and activating quantity) were optimized to achieve superior reaction parameters. Catalyst produced via sol-immobilization has higher activity than the one prepared with the wet-impregnation method, which lead to a transformation rate of up to 9.5%, with the selectivity for benzyl alcohol at 92%.     

Electron-deficient benzotriazoles for the selective N-acetylation of nucleosides

The use of an acetylated benzotriazole for the selective protection of the amino groups of cytidine and 2′-deoxycytidine is reported. The use of the acetyl group is of considerable interest industrially in this role, and a single-step protection strategy advantageous in bulk production. 1-Acetyl-4-nitrobenzotriazole was found to readily acetylate the amine of cytidine preferentially over the exposed alcohol functionalities. With adaptation of the protocol, 2′-deoxycytidine was protected using the same reagent. A similar approach was attempted for the benzoylation of adenosine but was found to be unsuitable.     

Alumina as an versatile catalyst for the selective acetalization of aldehydes

Alumina was found to be an effective and convenient catalyst for acetalization of aldehydes to the corresponding 1,3-dioxoranes and 1,3-dioxanes. It can be used for selective protection of only formyl group of ketoaldehydes.     

Facile redbrick clay as splendid catalyst for selective dehydration of alcohols

Research on Chemical Intermediates - Excellent catalytic activity of activated redbrick clay (ARB) for dehydration and highly selective conversion of cyclohexanol to cyclohexene and 1-phenylethanol...     

Solid-phase reagents for selective monophosphorylation of carbohydrates and nucleosides

Two classes of aminomethyl polystyrene resin-bound linkers of p-acetoxybenzyl alcohol were subjected to reactions with 2-cyanoethyl N,N-diisopropylchlorophosphoramidite to produce the corresponding polymer-bound phosphitylating reagents. These were reacted with a number of unprotected nucleosides and carbohydrates in the presence of 1H-tetrazole. Oxidation with tert-butyl hydroperoxide followed by removal of the cyanoethoxy group with 1,8-diazabicyclo[5.4.0]undec-7-ene afforded the corresponding polymer-bound phosphate diesters. Acidic cleavage of the p-acetoxybenzyl alcohol linker yielded monophosphorylated products with high regioselectivity and trapped linkers on the resins that can be reused.     

Resonant laser ablation as a selective metal ion source for gas-phase ion molecule reactions

Resonant laser ablation (RLA) is used as a source to selectively generate multiple metal ion species from the same sample. The capability of rapidly changing metal ions for gas-phase ion chemistry studies is a significant advantage in ion-molecule chemistry. The simple experimental arrangement uses relatively modest laser pulse energies (≤ 25 µJ/pulse) from a tunable dye laser to desorb and selectively ionize different metal atoms from a multicomponent sample. In turn, this allows the chemistry of several components to be investigated without breaking vacuum or altering the experimental geometry. This work demonstrates the use of RLA as a selective source of several reagent metal ions for gas-phase ion chemistry investigations. In particular, the reactivity of acetone with Cr⁺, Fe⁺, Ni⁺, and Cu⁺ was examined for metal ions selectively created by RLA from a standard steel sample.     

Ferrocene/ferrocenium ion as a catalyst for the photodecomposition of chloroform

Irradiation (λ > 320 nm) of ferrocene in chloroform causes decomposition of chloroform and the accumulation of HCl, CCl₃OOH, and C₂Cl₆. This appears to occur initially through a cycle in which (a) ferrocene is oxidized to ferrocenium and tetrachloroferrate ions, (b) FeCl₄ ⁻ undergoes photodissociation, and (c) ferrocenium reoxidizes the chloroferrate(II) species. On extended photolysis, the concentrations of CCl₃OOH and FeCl₄ ⁻ build up and a competing cycle in which FeCl₄ ⁻ is restored through oxidation of the chloroferrate(II) species by CCl₃OOH accelerates the decomposition rate.     

Cyclic aromatic oligoamides as highly selective receptors for the guanidinium ion

A class of six-residue, shape-persistent aromatic oligoamide macrocycles bind the guanidinium ion with very high selectivity.     

Platinum-containing hyper-cross-linked polystyrene as a modifier-free selective catalyst for L-sorbose oxidation.

Impregnation of hyper-cross-linked polystyrene (HPS) with tetrahydrofuran (THF) or methanol (ML) solutions containing platinic acid results in the formation of Pt(II) complexes within the nanocavities of HPS. Subsequent reduction of the complexes by H2 yields stable Pt nanoparticles with a mean diameter of 1.3 nm in THF and 1.4 nm in ML. The highest selectivity (98% at 100% conversion) measured during the catalytic oxidation of L-sorbose in water is obtained with the HPS-Pt-THF complex prior to H2 reduction. During an induction period of about 100 min, L-sorbose conversion is negligible while catalytic species develop in situ. The structure of the catalyst isolated after the induction period is analyzed by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electron micrographs reveal a broad distribution of Pt nanoparticles, 71% of which measure less than or equal to 2.0 nm in diameter. These nanoparticles are most likely responsible for the high catalytic activity and selectivity observed. The formation of nanoparticles measuring up to 5.9 nm in diameter is attributed to the facilitated intercavity transport and aggregation of smaller nanoparticles in swollen HPS. The catalytic properties of these novel Pt nanoparticles are highly robust, remaining stable even after 15 repeated uses.     

Metal ion coordination to azole nucleosides

To evaluate the possibility of introducing azole nucleosides as building blocks for metal-mediated base pairs in artificial oligonucleotides, imidazole nucleoside, 1,2,4-triazole nucleoside and tetrazole nucleoside have been synthesized and characterized. The X-ray crystal structures of p-toluoyl-protected 1,2,4-triazole and tetrazole nucleosides are reported. Contrary to the situation primarily found for deoxyribonucleosides, the sugar moieties adopt C3'-endo conformations. The acidity of the beta nucleosides increases with increasing number of nitrogen ring atoms, giving pKa values of 6.01 +/- 0.05, 1.32+/-0.05 and <-3, respectively. This decrease in basicity results in a decreasing ability to form 2:1 complexes with linearly coordinating metal ions such as Ag+ and Hg2+. In all cases, the Ag+ complexes are of higher stability than the corresponding Hg2+ complexes. Whereas imidazole nucleoside forms highly stable 2:1 complexes with both metal ions (estimated log beta2 values of >10), only Ag+ is able to reach this coordination pattern in the case of triazole nucleoside (log beta2 = 4.3 +/- 0.1). Tetrazole nucleoside does not form 2:1 complexes at all under the experimental conditions used. These data suggest that imidazole nucleoside, and to a lesser extent 1,2,4-triazole nucleoside, are likely candidates for successful incorporation as ligands in oligonucleotides based on metal-mediated base pairs. DFT calculations further corroborate this idea, providing model complexes for such base pairs with glycosidic bond distances (10.8-11.0 Angstroms) resembling those in idealized B-DNA (10.85 Angstroms).     

Peptide-cleaving catalyst selective for peptide deformylase

A peptide-cleaving catalyst selective for peptide deformylase (PDF) was obtained from a library containing about 15 000 catalyst candidates. The catalyst cleaved the polypeptide backbone of PDF at Gln(152)-Arg(153). Docking simulations suggested multiple modes of interactions in the complex formed between the catalyst and PDF.     

Protein-cleaving catalyst selective for protein substrate

A protein-cleaving catalyst specific for a disease-related protein can be used as a catalytic drug. As the first protein-cleaving catalyst selective for a protein substrate, a catalyst for myoglobin was designed by attaching Cu(II) or Co(III) complex of cyclen to a binding site searched by a combinatorial method using peptide nucleic acid monomers as building units. [reaction: see text]     

Trimethylsilyl trichloroacetate: a new reagent for salt-free silylations

Trimethylsilyl trichloroacetate ($\text{1}$) is a convenient reagent for the silylation of phenols, carboxylic acids, mercaptans, amides, acetylenes, and β-keto esters, while the reaction of $\text{1}$ with aldehydes and ketones affords silylated trichloromethyl carbinols ($\text{5}$).     

Nitrate ion association with Sm3+ ion

A solvent extraction method withTBP as an extractant was used for the determination of the stability constantsK ₁ ^o for the SmNO ₃ ²⁺ complex, for different least approach distanceså of ions. It was established thatå=6.5 Å for SmNO ₃ ²⁺ .

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Zur Assoziation von Nitrat-Ion mit Sm³⁺

Zusammenfassung Die StabilitätskonstantenK ₁ ^o für den SmNO ₃ ²⁺ -Komplex bei verschiedenen Mindestannäherungsdistanzenå der Ionen wurden mittels einer Lösungsmittelextraktionsmethode mitTBP ermittelt. Der beste Wert fürå war 6.5 Å.

     

An efficient and selective conversion of sorbitol in ionic liquids: Use of ion exchange resin as a solid acid catalyst

Sorbitol was readily converted by heating in hydrophobic ionic liquids by the presence of ion exchange resins. Chemoseletivity of the dehydration depended on the choice of ion exchange resin; Nafion selectively produced isosorbide while Amberlite gave 1,5-anhydrosorbitol along with unreacted sorbitol. Ionic liquids used in the reaction were readily recovered by simple extraction procedure. With these procedures, we succeeded to prepare isosorbide in pure form, not contaminated with either ionic liquids or acid catalyst, by simple experimental procedure.     

Phosphorylated mesoporous carbon as effective catalyst for the selective fructose dehydration to HMF

Phosphorylated mesoporous carbons (PMCs) were investigated as catalysts in the dehydration of fructose to hydroxymethylfurfural (HMF). The acidic PMCs show better selectivity to HMF compared to sulfonated carbon catalyst (SC) despite lower activity. The concentration of P-O groups on the PMC was correlated with the activity/selectivity of the catalysts; the higher the P-O concentration, the higher the activity. However, the higher the P-O content, the lower the selectivity to HMF. Indeed, a lower concentration of the P-O groups minimized the degradation of HMF to levulinic acid and the formation of by-products, such as humines. Stability tests showed that these systems deactivate due to the formation of humines and water insoluble by-products derived from the dehydration of fructose which blocked the catalytically active sites.