The kinetics study of the S + S2 → S3 reaction by the chaperone mechanism

The recombination of S atoms has been found to be stepwise from the smallest unit, the elemental S atom, to the most abundant molecule S(8). The reaction between S + S(2) → S(3) has not been reported either experimentally or by theory, but may be a key intermediate step in the formation of sulfur aerosols in low-O(2) atmospheres. In this work, the kinetics of this reaction is reported with Ar gas used as the chaperone molecule in the production of S(3) via two complex intermediates: SAr + S(2) and S(2)Ar + S. Quasi-classical and classical trajectory methods are used. The rate constant of the S + S(2) + Ar → S(3) + Ar reaction is determined to be 2.66 × 10(-33) cm(6) mol(-1)?s(-1) at 298.15 K. The temperature dependence of the reaction is found to be 2.67 × 10(-33) exp[143.56(1∕T-1∕298.15)]. The second-order rate constant of S + S(2) → S(3) is 6.47 × 10(-14) cm(3)?molecule(-1)?s(-1) at 298.15 K and the Arrhenius-type rate constant is calculated to be 6.25 × 10(-14) exp[450.15(1∕T-1∕298.15)] cm(3)?molecule(-1)?s(-1). This work provides a rate coefficient for a key intermediate species in studies of sulfur formation in the modern Venus atmosphere and the primitive Earth atmosphere, for which assumed model rate coefficients have spanned nearly 4 orders of magnitude. Although a symmetry-induced mass-independent isotope effect is not expected for a chaperone mechanism, the present work is an important step toward evaluating whether mass-independence is expected for thiozone formation as is observed for ozone formation.     

Kinetics of H2S destruction in the radiolysis of CH4−H2S gas mixtures

The kinetics of H₂S destruction in the radiolysis of CH₄–H₂S and CH₄–H₂S–O₂ mixtures has been studied. It has been shown that G(–H₂S) depends on amounts of hydrogen sulfide and the presence of oxygen in the starting mixture and is within the range of 5–13 mol/100 eV. G(H₂) decreases with the increases of O₂ content and amounts to the constant value of 2.     

Pseudoliving radical polymerization of methyl methacrylate in the presence of S,S′-bis(methyl-2-isobutyrate) trithiocarbonate

The polymerization of MMA mediated by symmetric trithiocarbonate as a reversible addition-fragmentation chain-transfer agent is studied. It is shown that the process proceeds according to the two-stage pseudoliving radical mechanism. The polymeric reversible addition-fragmentation chain-transfer agent is more efficient than its low-molecular-mass analog. The use of the polymeric reversible addition-fragmentation chain-transfer agent makes it possible to synthesize narrowly dispersed homopolymers of MMA and related copolymers with a controllable molecular mass. Both chain-transfer agents have practically no effect on the initial rate of copolymerization but allow weakening or even suppression of the gel effect at high conversions.     

Theoretical Studies of the Reaction Mechanisms of CH3S＋NO2

The potential energy surface for the CH3S NO2 reaction has been studied using the ab initio G3(MP2) method. A variety of possible complexes and saddle points along the minimum energy reaction paths have been characterized at UMP2 (full)/6-31G(d) level. The calculations reveal dominating reaction mechanisms of the title reaction: CH3S NO2 firstly produce intermediate CH3SONO,then break up into CH3SO NO. The results are valuable to understand the atmospheric sulfur compounds oxidation mechanism.     

Enantioselective synthesis of (2S,2′R)-erythro-methylphenidate

A new approach towards the enantioselective synthesis of (2S,2′R)-erythro-methylphenidate (1) is described. The key step in the synthesis utilizes Evans' 4-substituted-2-oxazolidinone chiral auxiliary to control the diastereofacial selectivity in the hydrogenation of enamine intermediate 6, yielding the hydrogenated product 7 with excellent diastereoselectivity. Methanolysis of 7 afforded 1 with excellent enantiopurity.     

Synthesis of α-Oxoketene CyclicO,S and S,S Acetals

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Influence of NaI Additions on the Electrical,Dielectric, and Transport Properties in the GeS2–Ga2S3–NaI Glass System

Russian Journal of Electrochemistry - The vitreous system GeS2–Ga2S3 can incorporate a large amount of alkali salts, for example NaI, and such materials have a potential to be used as solid...     

Synthesis of (2R,3S)-isobutyl phenylisoserinate,the Taxol® side chain,from ethyl benzoylacetate

Reduction of ethyl 2-chloro-3-phenyl-3-oxopropionate with borohydride affords predominately the syn-chlorohydrin. Resolution of this ester with the lipase MAP-10 gives (2S,3R)-2-chloro-3-hydroxypropionic acid which after esterification with MeOH/HCl is converted to the cis-epoxide with potassium carbonate and DMF. Aminolysis of the epoxide with aqueous ammonia results in ring opening and amide formation. The amide is converted to an ester upon treatment with isobutyl alcohol and HCl(g) at 100°C. Neutralization then affords the Taxol^® side chain as the free amine.     

Why are the Elemental Nonmetals (F2, Cl2, Br2, I2, S8, P4) of so Many Hues or of Any Hues and Where is the Chromophore? Insight into Intera-X–X Bonds

A unique approach is used to relate the HOMO-LUMO energy difference to the difference between the ionization potential (IP) and electron affinity (EA) to assist in deducing not only the colors, but also chromophores in elemental nonmetals. Our analysis focuses on compounds with lone pair electrons and σ electrons, namely X₂ (X = F, Cl, Br, I), S₈ and P₄. For the dihalogens, the [IP – EA] energies are found to be: F₂ (12.58 eV), Cl₂ (8.98 eV), Br₂ (7.90 eV), I₂ (6.78 eV). We suggest that the interahalogen X–X bond itself is the chromophore for these dihalogens, in which the light absorbed by the F₂, Cl₂, Br₂, I₂ leads to longer wavelengths in the visible by a π → σ* transition. Trace impurities are a likely case of cyclic S₈ which contains amounts of selenium leading to a yellow color, where the [IP – EA] energy of S₈ is found to be 7.02 eV. Elemental P₄ with an [IP – EA] energy of 9.09 eV contains a tetrahedral and σ aromatic structure. In future work, refinement of the analysis will be required for compounds with π electrons and σ electrons, such as polycyclic aromatic hydrocarbons (PAHs).     

Asymmetric synthesis of N,O-diprotected (2S,3S)-N-methyl-δ-hydroxyisoleucine,noncoded amino acid of halipeptin A

The first enantioselective synthesis of N,O-diprotected (2S,3S)-N-methyl-δ-hydroxyisoleucine 4, starting from readily available (tert-butyldimethylsilyl)-2-butyn-1-ol 5, is described. The key steps of this stereochemical flexible synthetic route involve a silyl-assisted [3,3]-sigmatropic rearrangement, for the establishment of the correct stereoisomeric pattern, and a triethylsilane–TFA induced reduction of an oxazolidinone intermediate, to yield the requested N-methylation.     

Synthetic Studies of Didemnaketals Analogue-Construction of the Intermediate (3S,5S,6R)-3,7-Dimethyl-5,6,7-trihydroxy-octanal

TheDidemnaketalsAandBhavebeenreportedtobesignificantinhibitorstoHlV-protease'.Inconnectionwiththetotalsynthesisofthiskindofcompounds,ourrecentresearchinterestisfocusedontheirsyntheticstudiesaswellassynthesisofananaloguel,whichincorPoratedthekeyspiroketalmoietyofthedidemnaketalsAandB.Basedontheretrosyntheticconsideration(Schemcl),thelinearintermediate2wouIdbeconstructedfrom3and4.Furthermore,4wouldbesynthesizedfrom( )-PuIegone5.Wehereinreportedastereoselectivesyntheticprocedureforthe(3S,5S…     

Chemoenzymatic synthesis of Fmoc-protected (2S,3S)-2-hydroxy-3-amino acids and their application in the synthesis of an α-hydroxylated β-hexapeptide

A chemoenzymatic and stereoselective synthesis of Fmoc-protected (2S,3S)-2-hydroxy-3-amino acids from 2-furaldehyde is described as well as their application, without prior hydroxyl protection, in the solid-phase synthesis of a novel completely α-hydroxylated β-hexapeptide.     

Synthesis and structural characterization of camphanates of (−)-(2S3S,3S) and (+)-(2S,3R)-4-Phenyl-3-bromo-2-butanol diastereoisomers

The X-ray crystal structures of (–)-syn-4-phenyl-3-bromo-2-butyl camphanate (I) and (+-anti-4-phenyl-3-bromo-2-butyl camphanate (II) have been determined. Thesyn diastereoisomer of bromohydrin has the (2S,3S) absolute configuration whereas theanti diastereoisomer has the (2S,3R) absolute configuration. The crystallized derivatives I and II have been obtained by the reaction of each stereoisomer of bromohydrin, synthesized by reduction with baker's yeast, with (1S)-camphanic chloride. Crystal data: (I) C₂₀H₂₅BrO₄:M _w: 409.32; orthorhombic,P2₁2₁2₁;a=11.245(3),b=12.086(1),c=14.512(4) å; Z=4; finalR=0.053 for 1819 observed reflections. (II) C₂₀H₂₅BrO₄;M _w=409.32; monoclinic, P2₁;a=11.352(1),b=6.378(1),c=14.255(2) å,=110.38(1);Z=2; finalR=0.045 for 1672 observed reflections.     

Study of C60·2S8 by the methods of induced electron emission

It was shown by the methods of induced electron emission that a transfer of the electron density from C₆₀ molecules to the eight-membered ring of sulfur is characteristic of C₆₀·2S₈. The value of the (+)-plasmon energy for C₆₀·2S₈ is approximately 1 eV less than that for pure C₆₀. In a high vacuum, the C₆₀·2₈ surface is depleted in sulfur.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2149–2152, December, 1994.     

Kinetics of decomposition of the liquid phase of the ternary system LiOH-H2O2-H2O in the presence of the solid phase of Li2O2 · H2O

The kinetics of decomposition of hydrogen peroxide in the liquid phase of the ternary system LiOH-H₂O₂-H₂O was studied in the presence the solid phase of Li₂O₂·H₂O and without it. The main kinetic parameters of the processes studied were determined.     

Biomonitoring of the atmospheric pollution using lichens in the metropolitan area of São Paulo city,Brazil

The atmospheric pollution of São Paulo city is a serious problem due to the expansion of industrial area, increasing number of vehicles and population density. This work presents results obtained in the analysis of lichens collected in different sites of São Paulo city and in non-polluted areas of Atlantic Forest. Concentrations of twenty elements were determined in Canoparmelia texana species and comparisons were made between the results obtained in lichens from different sites. High concentrations of the elements As, Ba, Cd, Co, Cr, Fe, La, Mn, Sb and Zn were found for samples collected in sites located near industries and petrochemical plant. Br and Sb concentrations were also high in lichens from sites affected by vehicular emissions.     

Reactions of the bis(dialkylphosphino)methane complexes Pd2X2(μ-R2PCH2PR2)2 (X = halogen, R = Me or Et) with H2S, S8, COS, and CS2; detection of reaction intermediates

The Pd(2)X(2)(dmpm)(2) complexes [X = Cl (1a), Br (1b), I (1c); dmpm = bis(dimethylphosphino)methane. In all the dipalladium complexes mentioned in this paper, the dmpm, depm, and dppm ligands (unless stated otherwise) are bridging, but for convenience the μ-symbol is omitted.] react with H(2)S to yield H(2) and the bridged-sulfido complexes Pd(2)X(2)(μ-S)(dmpm)(2) (2a-c), of which 2a and 2b are structurally characterized. With 1a, two rapid reversible equilibria are observed by NMR spectroscopy below -30 °C, and two reaction intermediates are detected; both are likely hydrido(mercapto) species. Reaction of 1a with 1 equiv of elemental sulfur also yields 2a. The reaction of 1a with COS results in the initial formation of Pd(2)Cl(2)(μ-COS)(dmpm)(2) (3) that undergoes decarbonylation to yield 2a and Pd(2)Cl(2)(μ-CO)(dmpm)(2) (4), which is also formed via reversible insertion of the CO into the Pd-Pd bond of 1a. The solid-state molecular structure of the previously reported complex Pd(2)Cl(2)(μ-CS(2))(dmpm)(2) (5), together with solution NMR data for 3 and 5, reveal that the bridging heterocumulene ligands coordinate in an η(2)-C,S fashion. Analogous findings were made for the corresponding Pd(2)X(2)(depm)(2) complexes [X = Cl (1a'), Br (1b'), I (1c'); depm = bis(diethylphosphino)methane], although no μ-COS species was detected. The Pd(2)X(2)(μ-S)(depm)(2) complex was structurally characterized. Differences in the chemistry of the previously studied, corresponding dppm systems (dppm = bis(diphenylphosphino)methane) are discussed.