Direct study of the catalytic decomposition of chlorine and chloromethanes over carbon films

The decompositions of chlorine and chloromethanes over pyrolytic carbon surfaces have been studied by modulated beam mass spectrometry in a low-pressure flow reactor between 850–1280 K. Whereas CH₃Cl is thoroughly stable, molecular chlorine readily dissociates by a first-order process with an activation energy about a half of its bond energy. The decompositions of CH₂Cl₂ and CCl₄ over clean silica surfaces initially display marked autoacceleration associated with the formation of soot on reactor walls and reach limiting rates which are much faster than those predicted for their homogeneous pyrolysis under the same conditions.     

New Method of Halogenation of Organophosphorus Compounds

Abstract

N-Chloroalkylamines react usually with tervalent phosphorus compounds to afford products, containing the phosphorus-nitrogen bond. We found that the sterical hindrances favour to the nucleophilic attack of the tervalent phosphorus atom on the “positive” halogen atom with the formation of phosphorus halogenated products. Sterical hindered N-halogenoalkylamines I (Hlg[dbnd]Cl,Br) possess active halogenating properties to react with tervalent phosphorus compounds similarly to methane tetrahalides. Reaction proceeds via the formation of halogenophosphonium intermediates 2, containing an anion R₂N, which reacts with alcohols to afford alkoxyphosphonium salts, transforms into halogenophosphonium salts or P-halogenoylids. Advantages of N-halogenoalkylamines 1 over methane tetrahalides are more high chemical selectivity. Moreover the inclusion of chiral substituents R into N-halogenoalkylamines gives enantioselective halogenating reagents.     

A density functional theory study of copper-catalyzed aziridination of olefins

Density functional theory calculations are reported for the reaction mechanism of selected XCuNHX(X = Cl, Br, I) with olefins to form three-membered ring products. The copper reagents react with olefins via an asynchronous attack on one CH₂ group of ethylene with a relatively low barrier (<78 kJ/mol). These computational results are in good agreement with experimental results, and this suggests that the nitrene transfer process is favored. The BrCuNHBr is found to be the most reactive reagent in the XCuNHX (X = Cl, Br, I) series of reagents. These results are qualitatively consistent with the agreement between copper-catalyzed species character and experimental conditions needed for efficient reaction.     

Reaction of organolithium reagents with α-chlorovinyltrimethylsilanes

The reaction of (CH₃)₃SiC(Cl)=CRR′ (R = R′ = H; R = H, R′ = CH₃; R = R′ = CH₃; R = R′ = C₆H₅) with organolithium, reagents was examined. Alkenylsilanes of structure (CH₃)₃SiCHCH-alkyl were obtained from (CH₃)₃SiC(Cl)CH₂ and alkyllithium reagents. Substrates with R or R′ ≠ H inhibited addition of the organolithium species to the double bond and led to products derived from chlorinelithium exchange (R = R′ = C₆H₅) or proton abstraction from an allylic methyl site (R = H, R′ = CH₃; R = R′ = CH₃).     

Comparative study of 8-hydroxyquinoline derivatives as chelating reagents for flow-injection preconcentration of cobalt in a knotted reactor

8-Hydroxyquinoline (HQ), 2-methyl-8-hydroxyquinoline (CH₃-HQ), 5,7-dichloro-2-methyl-8-hydroxyquinoline (Cl₂-CH₃-HQ), 5,7-dibromo-8-hydroxyquinoline (Br₂-HQ), 5-sulfo-7-iodo-8-hydroxyquinoline (ferron) and 5-sulfo-8-hydroxyquinoline (SO₃H-HQ) were compared as chelating reagents for on-line sorption preconcentration of cobalt in a knotted reactor (KR) precoated with the reagent. The results obtained with the different HQ derivatives reveal those properties of the chelating reagent responsible for the processes taking place in the KR. The influence of hydrophobicity, acidity, stability of the cobalt chelate and type of substituents in the HQ ring system on the separate steps of the flow injection (FI) preconcentration procedure are discussed. According to the performance characteristics of the different HQ derivatives, the most important parameters for on-line preconcentration in a KR are the hydrophobicity of the reagent and the stability of the chelate complex with the analyte.     

Author Index to Volume 62

The gaseous reaction of oxygen atoms with dimethylamine was studied in a cross-jet reactor and found to proceed by electrophilic addition to form an energy-rich N-oxide which rearranges to an hydroxylamine and then decomposes via three routes: (CH₃)₂ N + OH, CH₃NCH₂ + H₂O and CH₃NHO + CH₃.     

The reaction of hexafluoropropene oxide with grignard reagents

The reactions of hexafluoropropene oxide and equimolar amounts of Grignard reagents lead to the formation of 2-halotetrafluoropropanoyl fluorides which were converted to the methyl or ethyl ester for isolation purposes. Treatment of hexafluoropropene oxide with excess Grignard reagent formed an unsaturated ketone of the type R₂CCFCOR (RCH₃ or CH₂CH₃; a route by which this product is formed is postulated.     

Synthetic studies of organodi-π-cyclopentadienyl- titanium (III) derivatives

Two synthetic routes to compounds of the type π-Cp₂Ti^IIIR (R=CH₃, CH₂Si(CH₃)₃, C₆F₅) have been investigated: (a) chemical reduction of π-Cp₂Ti^IV(R)Cl by zinc or aluminum metal in tetrahydrofuran, and (b) conventional organometallic syntheses using organo-lithium or -magnesium reagents and [π-Cp₂Ti^IIICl]₂. The preferred route is via an organolithium reagent, since chemical reduction gives a mixture of products. Green, monomeric complexes (R = CH₂Si(CH₃)₃, C₆F₅) were isolated and characterised. From the reaction of π-Cp₂Ti^IVCl₂ and trimethylsilylmethyllithium in a 1/1 ratio, π-CpTi^IV [CH₂Si(CH₃)₃]₃ was obtained. Unlike π-Cp₂Ti^IIIC₆F₅, π-Cp₂Ti^IIICH₂Si(CH₃)₃ does not form a blue complex with molecular nitrogen.     

The role of modifiers in electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of B,La and U

The role of modifiers in electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of refractory elements such as La or U and carbide forming elements such as B has been studied. Solutions of NH₄F, NH₄Cl, NH₄Br, NaCl, NaF, NH₄HSO₄, (NH₄)₂HPO₄, the gaseous halogenated hydrocarbons CHF₃ and CCl₂F₂ and HCl have been used as modifiers.The mechanism of the modifier effect and the influence of modifiers on sensitivity enhancement have been investigated. The sensitivity enhancements are great enough to achieve absolute detection limits of 2–6 pg for boron and 10 fg for La and U. The signal reproducibility is 0.5–3.0% for a concentration of 1 μg 1⁻¹ La and U, and 20 μg 1⁻¹ boron. Therefore, by adding modifiers, the use of ETV-ICP-MS can be extended to trace element determination of refractory and carbide forming elements in μl amounts of sample.     

Hohe aldehydselektivität bei carbonylolefinierungen mit titan- und chrom-reagenzien

The easily available reagents GCH₂TiCl₃ (G = (CH₃)₃Si, (CH₃)₃Ge) and (CH₃)₃SiCH₂CrCl₂ cause carbonylolefination of aldehydes, but not of ketones. In case of the chromium reagent acidic hydrolysis of the products is necessary.     

Transposition eventuelle lors de l'action de bromures β-ethyleniques CH2CHCH(R)CH2Br (R = CHCH2, C2H5, C6H5) sur le magnesium

Reaction betweenβ-ethylenic bromides CH₂CHCH(R)CH₂2Br and magnesium in ether has been studied. With R = CHCH₂, it gives rise both to normal and rearranged Grignard reagents. With R = C₂H₅ and C₆H₅, only the normal Grignard reagent is formed.     

The methylenation of enolizable ketones and esters using organotitanium chemistry

The titanium methylidene fragment, Cp₂TiCH₂, resulting from Tebbe's reagent, Cp₂TiCH₂·AlMe₂Cl or the β,β-disubstituted metallacycle, CP₂TiCH₂C(Me)(n-Pr)CH₂, methylenates enolizable acidic ketones and converts α,α-disubstituted ketones into titanium enolates. The reagent reacts selectively with ketones over esters.     

The use of chloroalkyldichloroarsines in hybrid ligand synthesis. The preparation of but-3-enylbis(3-dimethylarsinopropyl)arsine and 3-dimethylarsinopropylbis(but-3-enyl)arsine,and their reaction with nickel(II) salts to form pentacoordinate complexes. Novel nickel(II)—olefin bonds

Routes have been developed to the hitherto unobtainable arsine-olefin ligands (CH₂CHCH₂CH₂)_nAs(CH₂CH₂CH₂AsMe₂)_3-n (n = 1, tasol, but-3-enylbis(3-dimethylarsinopropyl)arsine; n = 2, dasdol, 3-dimethylarsinopropylbis(but-3-enyl)arsine) by making use of the difference in reactivity between the ClC and AsCl bonds in the precursor Cl(CH₂)_mAsCl₂ (m = 2,3) molecules. Thus, the triarsine obtained by reaction of 2-chloroethyldichloroarsine with the Grignard reagent of 3-chloropropyldimethylarsine yields 2-chloroethylbis(3-dimethylarsinopropyl)arsine, from which tasol is obtainable by subsequent reaction with either the Grignard reagent of vinyl bromide or, preferably, with vinyllithium. Similarly, 3-chloropropyldichloroarsine reacts with the Grignard reagent of 4-chlorobut-1-ene to form 3-chloropropylbis(but-3-enyl)arsine which, on reaction with sodium dimethylarsenide yields dasdol. The tasol ligand reacts with nickel(II) salts to form [NiX(tasol)]⁺ (X = Cl, Br) and [NiI₂(tasol)], the former are trigonal bipyramidal and contain a nickel(II)—olefin bond, and the latter are square pyramidal containing a [NiI₂As₃] coordination sphere. In addition, tasol forms a number of polynuclear complexes with nickel(II). The dasdol ligand acts as a bidentate arsine to form only [NiX(dasdol)₂)]⁺ The formation of novel nickel(II)—olefin bonds in the [NiX(tasol)]⁺ cations is discussed.     

Reduction of nitronate adducts from RMgX and 1-hethoxy-4-nitronaphthalene to oximes or amines by trivalent phosphorus reagents

The reduction of nitronate adducts from 1-methoxy-4-nitronaphthalene and Grignard reagents (CH₃ MgX, PhCH₂CH₂HgX, i-C₃H₇ MgX, c-C₆H₁₁MgX and t-C₄H₉MgX) with hexamethyl phosphorous triamide and phosphorous trichlorlde is reported. With the former reagent the reaction is chemio and stereoselective and only the E-oxime is recovered being the E-2-alkyl-4-methoxy-1(2H)naphthalenone oximes and the E-2-alkyl-2,3-dihydro-1,4-naphthoquinone-1-oximes obtained after quenching with NH₄Cl and HCl respectively. Oxime stereochemistry is assigned by LIS values caused by Eu(dpm)₃ on ¹³C signals of 2-methyl-4-methoxy-1-(2H)naphthalenone oxime and 2-methyl-2,3-dihydro-1,4-naphthoquinone-1-oxime. Complete reduction to amines is obtained with phosphorous trichloride.     

Surface effects on the diagnostic of carbon/nitrogen low‐pressure plasmas studied by differentially pumped mass spectrometry

In this work, the characterization of the species produced in reactive plasmas by differentially pumped mass spectrometry is addressed. A H₂/CH₄/N₂ mixture (90 : 5 : 5) was fed into a direct current glow discharge and analysed by conventional and cryo‐trap assisted mass spectrometry. The gaseous mixture was chosen because of its particular relevance in the inhibition of tritium‐rich carbon film deposition in fusion plasmas (scavenger technique) and in the deposition of amorphous hydrogenated carbon films by plasma‐assisted chemical vapour deposition. Important changes in the composition of the detected species upon surface modification of the reactor walls (stainless steel or covered by an amorphous hydrogenated carbon layer) or in the way they are sampled (length and spatial configuration of the stainless steel duct) were detected. They are analysed in terms of radical formation and recombination on the reactor walls or into the sampling duct, thus providing some insight into the underlying chemistry. In general, when the reactor walls are covered by an amorphous hydrogenated carbon layer, more hydrocarbons are produced, but the radical production is lower and seem to be less reactive than in stainless steel. Also, two sources of oxygen contamination in the plasma have been identified, from the native oxide layer in stainless steel and from unintended water contamination in the chamber, which modify considerably the detected species. Copyright © 2014 John Wiley & Sons, Ltd.     

Methylene chloride chemical ionization of fumaric and maleic acids and their esters

The chemical ionization (CI) mass spectrometry of fumaric and maleic acids and their esters with methylene chloride as reagent gas is described. The introduction of methylene chloride to the CI(CH₄) plasma led to the formation of new characteristic ions in addition to the protonation and the subsequent fragmentation, revealing diagnostic information on the configuration of geometrical isomers. The new characteristic ions have been found to arise from the addition of the reactant ion of methylene chloride, [CH₂Cl]⁺, to the substrates and, for higher dialkyl esters, from the further McLafferty rearrangement of the adduct ion [M + CH₂Cl]⁺.     

Validation of methane measurement using headspace‐GC–MS and quantification by a stable isotope‐labeled internal standard generated in situ

A previous study has shown the possibility to identify methane (CH₄) using headspace‐GC–MS and quantify it with a stable isotope as internal standard. The main drawback of the GC–MS methods discussed in literature for CH₄ measurement is the absence of a specific internal standard necessary to perform quantification. However, it becomes essential to develop a safer method to limit the manipulation of gaseous CH₄ and to precisely control the injected amount of gas for spiking and calibration by comparison with external calibration. To avoid the manipulation of a stable isotope‐labeled gas, we have chosen to generate a labeled gas as an internal standard in a vial on the basis of the formation of CH₄ by the reaction of Grignard reagent methylmagnesium chloride with deuterated water. This method allows precise measurement of CH₄ concentrations in gaseous sample as well as in a solid or a liquid sample after a thermodesorption step in a headspace vial. A full accuracy profile validation of this method is then presented.     

Doped Sol-Gel Materials as Heterogeneous Reagents for Organic Synthesis

We advance the use of reactive doped sol-gel materials as heterogeneous reagents for organic-chemistry synthesis. Three approaches were demonstrated with SiO₂-based materials: Direct physical entrapment of the organic reagent; in-situ generation of an inorganic reagent within the matrix; and covalent attachment of the reagent to the matrix. With the first, entrapped p-toluenesulfonic acid facilitated the 100% yield esterification of benzoic acid with 1-pentanol, and the 100% dehydration of 1-tetralol to 1,2-dihydronaphthalene; with the second approach, a sol-gel oxidant, SiO₂/MnO₂ was used to convert benzyl alcohol to benzaldehyde and 1-tetralol to 1-tetralone; and with the third, anchored propylamine facilitated dehydrobromination reactions resulting in double-bond formation. Several other reactions with these reagents are described, and their reactivities analyzed.     

Synthesis of o-carboranesiloxanes and study of their reactivity

The coupling of dilithio-o-carborane with , -dichlorooligodimethylsiloxanes of type ClSi(CH₃)₂O[Si(CH₃)₂O]_nSi(CH₃)₂Cl with n from 1 to 3 has been performed. At a molar ratio of the reagent of 11, the products of the reaction are a five-membered ring compound, 1, 3-o-carboranetetramethyldisiloxane and a cyclodimethylsiloxane, and at a ratio of the reagents of 12, a seven-membered ring compound, 1, 5-o-carboranehexamethyltrisiloxane, and a cyclodimethylsiloxane. Attempts to open the seven-membered o-carboranesiloxane ring thermally or with the aid of acidic catalysts were unsuccessful. Under the influence of nucleophilic reagents, cleavage of the C-Si bond takes place with the splitting away of a silicon atom from the o-carborane nucleus and the formation of an o-carbonate and a cyclodimethylsiloxane.     

Effets electroniques en stereochimie—III : Réduction asymétrique de phénylalkylcétones diversement substituées par des organomagnésiens aromatiques chiraux

The asymmetric reduction of phenylalkylketones p-X-C₆H₄COR (X = H, R = C₂H₅, ¹C₃H₇, ¹C₄H₉ and R = C₂H₅, X = CH₃, OCH₃, Cl, CF₃) with chiral aromatic Grignard reagents p-YC₆H₄-CH(C₂H₅) CH₂MgCl (Y = H, OCH₃, CF₃) give optically active phenylalkylcarbinols. The absolute configuration and the enantiomeric excess depends on electronic effects of substituents carried by the organomagnesium reagent and/or ketone.