Comparison of Various Options for Designing the Direct Oxidation of Methane to Methanol

Russian Journal of Applied Chemistry - Various options for designing the direct oxidation of natural gas to methanol are considered: flow-through, with a distributed supply of the oxidizer along...     

Production of Ethylene,CO, and Hydrogen by Oxidative Cracking of Oil Refinery Gas Components

Flowsheets based on the results of experimental studies and detailed kinetic modeling were suggested for oxidative cracking of oil refinery gas components to obtain ethylene, CO, and hydrogen. The calculations show that oxidative cracking alone does not allow production of ethylene and СО in ratios required for the further catalytic carbonylation and hydroformylation of ethylene. Matrix conversion of a part of oxy-cracking products is suggested as an additional step for producing CO and hydrogen.

     

Ethyl 2-(α-hydroxyhexafluoroisopropyl)acrylate as a potential precursor of fluorine- and sulfur-containing CH-acids

The reactivity of ethyl 2-(α-hydroxyhexafluoroisopropyl)acrylate (1) was studied. The addition of thioacetic acid to compound1 occurs at 20°C, while reactions with thiols proceed only at 120°C and are accelerated in the presence of an acid catalyst. Dealkylation of acrylate1 with iodotrimethylsiliane affords 4,4,4-trifluoro-3-hydroxy-2-iodomethyl-3-trifluoromethylbutyric acid, which served as the starting compound for the synthesis of 3-chloro-4,4,4-trifluoro-2-iodomethyl-3-trifluoromethylbutyroyl chloride, a potential precursor of alicyclic fluorine- and sulfur-containing CH-acids.     

Three-dimensional structure of the Arg32His mutant of the human tumor necrosis factor determined at 2.5 Å resolution from X-ray data for a twin crystal

The three-dimensional structure of the Arg32His mutant of the human tumor necrosis factor (TNF-α) was established at 2.5 Å resolution by the molecular replacement method. The crystals of the mutant belong to sp. gr. R3. The specimen has a hemihedral twinning fraction of approximately one half with the twin law corresponding to an additional twofold axis along the a-or b-axis of the crystal lattice. The model analysis of interactions between functionally important loop 29–36 of the mutant and the receptors p55 and p75 was performed.     

Ruthenium-catalyzed azide-alkyne cycloaddition: scope and mechanism

The catalytic activity of a series of ruthenium(II) complexes in azide-alkyne cycloadditions has been evaluated. The [Cp*RuCl] complexes, such as Cp*RuCl(PPh 3) 2, Cp*RuCl(COD), and Cp*RuCl(NBD), were among the most effective catalysts. In the presence of catalytic Cp*RuCl(PPh 3) 2 or Cp*RuCl(COD), primary and secondary azides react with a broad range of terminal alkynes containing a range of functionalities selectively producing 1,5-disubstituted 1,2,3-triazoles; tertiary azides were significantly less reactive. Both complexes also promote the cycloaddition reactions of organic azides with internal alkynes, providing access to fully-substituted 1,2,3-triazoles. The ruthenium-catalyzed azide-alkyne cycloaddition (RuAAC) appears to proceed via oxidative coupling of the azide and alkyne reactants to give a six-membered ruthenacycle intermediate, in which the first new carbon-nitrogen bond is formed between the more electronegative carbon of the alkyne and the terminal, electrophilic nitrogen of the azide. This step is followed by reductive elimination, which forms the triazole product. DFT calculations support this mechanistic proposal and indicate that the reductive elimination step is rate-determining.     

Stereo sensitivity of exchange interactions in Ni<Superscript>II</Superscript> and Cu<Superscript>II</Superscript> heterospin complexes with 5-formylpyrrolyl-substituted nitroxides

5-Formylpyrrolyl-substituted nitronyl and imino nitroxide radicals HL¹ and HL² were synthesized. Their solid phases are formed by packing pairs of the molecules. In the {HL¹...HL¹} pairs, the dominant interaction is the ferromagnetic exchange with J/kB = 8.8 K (Hamiltonian \(H = 2J\left( {\overrightarrow {{s_1}} \overrightarrow {{s_2}} } \right)\)). The ferromagnetic exchange occurs also in the heterospin molecules [Ni(L¹)₂], [Cu(L¹)₂], and [Ni(L²)₂(MeOH)₂]. In the complexes [Ni(L¹)₂] and [Cu(L¹)₂], a small change in the mutual orientation of the coordinated ligands has a considerable effect on the value and the sign of the energy of exchange interactions between the unpaired electrons of the metal ion and paramagnetic ligands.     

Ruthenium-catalyzed cycloaddition of aryl azides and alkynes

The formation of 1,5-disubstituted 1,2,3-triazoles from aryl azides and alkynes was readily accomplished using [Cp*RuCl]4 catalyst in dimethylformamide. It was also demonstrated that the reaction provided higher yields, cleaner product, and shorter reaction times when carried out under microwave irradiation.     

Ligand-accelerated Cu-catalyzed azide-alkyne cycloaddition: a mechanistic report

The experimental rate law for the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction was found to vary in complex ways with concentration, the presence of chloride ion, and the presence of accelerating ligands. Several examples of discontinuous ("threshold behavior") kinetics were observed, along with a decidedly nonlinear correlation of electronic substituent parameter with the rate of CuAAC reaction with p-substituted arylazides. The previously observed tendency of the CuAAC reaction to provide ditriazoles from a conformationally constrained 1,3-diazide was found to be affected by a class of polybenzimidazole ligands introduced in the accompanying article. Various lines of evidence suggest that the standard tris(triazolylmethyl)amine ligand binds less strongly to Cu(I) than its benzimidazole analogues. On the basis of these observations, it is proposed that (a) a central nitrogen donor provides electron density at Cu(I) that assists the cycloaddition reaction, (b) the three-armed motif bearing relatively weakly coordinating heterocyclic ligands serves to bind the metal with sufficient strength while providing access to necessary coordination site(s), (c) at least two active catalysts or mechanisms are operative under the conditions studied, and (d) pendant acid or ester arms in the proper position can assist the reaction by speeding the protiolysis step that cleaves the Cu-C bond of a Cu.triazolyl intermediate.