Crystal structures and theoretical calculations of trans-2,4,4-trimethyl-4-silathiane 1-oxide and 4,4-dimethyl-4-silathiane 1,1-dioxide

The crystal and molecular structures of trans-2,4,4-trimethyl-4-silathiane 1-oxide 1 and 4,4-dimethyl-4-silathiane 1,1-dioxide 2 were determined by single crystal X-ray diffraction. Both compounds have the chair conformation with the 2-Me and the S=O group in compound 1 occupying the equatorial positions. The DFT (B3LYP/6-311G(d,p)) and MP2 (MP2/6-311G(d,p)) theoretical calculations nicely reproduce the X-ray experimental geometry. The obtained results are discussed in connection with the electronic and structural properties of the compounds.

Si-disubstituted diallylsilanes in homolytic thiylation and electrophilic fragmentation reactions

Approaches to Si-disubstituted 1-thia-5-silacyclooctanes based on homolytic addition of hydrogen sulfide to diallylsilanes R₂Si(CH₂CH=CH₂)₂ and on intramolecular cyclization of Si-disubstituted (allyl)(γ-sulfanylpropyl)silanes have been studied. In the former case the reactivity of the silanes decreases in the order R = MeO > F > Me > Ph, whereas in the latter case the reactivity order is slightly different: Me > MeO ≈ F ? Ph. The reactions of diphenyl-and dimethyldiallylsilanes with the complex BF₃·2AcOH occur in a different manner: The former involves rearrangement to form fluoro(2-methylpent-4-enyl)diphenylsilane, while the latter, elimination of the two allyl groups to fluorodimethylsilane and propene.     

Effect of cobalt weight content on the structure and catalytic properties of Co/CNT catalysts in the fischer–tropsch synthesis

Cobalt-based Fischer–Tropsch synthesis (FTS) catalysts containing 1 to 40 wt % cobalt supported on multi-walled carbon nanotubes (CNTs) have been investigated. The CNTs have been characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray photoelectron spectroscopy. All catalysts have been prepared by impregnating, with an ethanolic solution of cobalt nitrate, the CNTs preoxidized with concentrated nitric acid and have been tested in the FTS at 220°C and atmospheric pressure. Correlations have been established between the cobalt weight content of the catalyst and the Co particle size determined by transmission electron microscopy and X-ray diffraction. The Co content and particle size have an effect on the activity and selectivity of the catalyst and on the target fraction (C₅₊) yield in the FTS. The highest CO conversion is observed for the catalyst containing 20 wt % Co; the highest selectivity and activity, for the catalyst containing 5 wt % Co; the highest C₅₊ yield, for the catalyst containing 10 wt % Co.     

Effect of supercritical CO2 on extremophile cells

The kinetics of inactivation of E. coli and D. radiodurance bacteria and Candida albicans imperfect fungi in compressed gaseous and supercritical carbon dioxide was studied. The possibility of decreasing the concentration of survived cells by 5 to 7 orders of magnitude was demonstrated.     

Inactivation of <Emphasis Type="Italic">Escherichia coli</Emphasis> Cells by Sub- and Supercritical Gases

The kinetics of inactivation of Escherichia coli under the action of pressurized gases (CO₂, O₂ and N₂) is studied. It is demonstrated that the concentration of surviving cells decreases by seven orders of magnitude in the case of CO₂ and less than by one order in the case of O₂ and N₂. An assumption about how bacterial cells are inactivated in the presence of CO₂ is proposed.     

On the Existence of Hypersonic Electrostatic Solitons (Estimation of Limiting Mach Numbers of Ion-Sound Solitons in a Warm Plasma)

Journal of Experimental and Theoretical Physics - We develop a nonlinear theory of ion-sound waves in a collisionless warm electron–ion plasma. The theory is based on analysis of the Sagdeev...     

Reactions of Nitro and Halonitro Derivatives of Aluminum(III) and Copper(II) Phthalocyanines with Concentrated Sulfuric Acid

Transformations of the complexes CuPc(4-NO₂)₄, CuPc(4-Br)₄(5-NO₂)₄, (OH)AlRs(4-NO₂)₄, and (OH)AlPc(4-Cl)₄(5-NO₂)₄ in concentrated sulfuric acid were studied by spectrophotometry. One protonated form of CuPc(4-Br)₄(5-NO₂)₄ and (OH)AlPc(4-NO₂)₄ and two protonated forms of CuPc(4-NO₂)₄ and (OH)AlPc(4-Cl)₄(5-NO₂)₄ were detected experimentally and also by ZINDO1 calculations. Step protonation constants of CuPc(4-NO₂)₄ and (OH)AlPc(4-Cl)₄(5-NO₂)₄ were determined by quantum-chemical calculations and acid-base titration; these complexes can be regarded as weak bases with respect to H₂SO₄. The kinetics of dissociation of the complexes at the MÄN bonds were studied. The rate of dissociation of the Cu(II) complexes and (OH)AlPc(4-NO₂)₄ is proportional to [MPc(R) _n ] and [H₃O⁺]². The rate of dissociation of (OH)AlPc(4-Cl)₄(5-NO₂)₄ showed a weak extremal dependence on the composition of the medium, which was explained by change of its structure in 17.0 M H₂SO₄. The electronic effect of substituents on the reaction center was considered with account taken of a complex mechanism of activation and fine details of the molecular structure of macrocyclic complexes.     

Lithiation-methylation of thiasilinane 1-oxides

Lithiation-methylation of 3,3-dimethyl-1λ⁴,3-thiasilinane 1-oxide and 4,4-dimethyl-1λ⁴,4-thiasilinane 1-oxide under the action of butyllithium or lithium diisopropylamide and methyl iodide was studied. In both cases, monomethylation proceeds selectively α to the sulfoxide group to form 2,3,3-trimethyl-1λ⁴,3-thiasilinane 1-oxide and 2,4,4-trimethyl-1λ⁴,4-thiasilinane 1-oxide, respectively. Subsequently, 2,3,3-trimethyl-1λ⁴,3-thiasilinane 1-oxide undergoes monomethylation into the same α position to give 2,2,3,3-tetramethyl-1λ⁴,3-thiasilinane 1-oxide, while 4,4-dimethyl-1λ⁴,4-thiasilinane 1-oxide is dimethylated into the neighboring α’ position to form two stereoisomers of 2,4,4,6-tetramethyl-1λ⁴,4-thiasilinane 1-oxide with axial-equatorial or equatorial-equatorial methyl groups in the 2 and 6 positions.