Presence Of Tetrachloromethane Research Articles

Sequencing of Lys-containing peptides through phosphonylation modification and electrospray ionization mass spectrometry

Lys-containing peptides were phosphonylated at their N-termini by reacting with ethoxyphenylphosphinate (EPP-H) in the presence of tetrachloromethane and triethylamine, and picomolar amount of the modified phosphonamidate peptides were determined by electrospray ionization mass spectrometry, together with tandem mass spectral technique, the intensive b n -type ions relative to other type ions were observed, which clearly provided sequences of the original peptides.

A Picomole-Scale Method for Rapid Peptide Sequencing Through Convenient and Efficient N-Terminal Phosphorylation and Electrospray Ionization Mass Spectrometry

Free or resin-bound peptides were phosphorylated at their N-termini by reacting with dimethyl phosphite in the presence of tetrachloromethane and triethylamine, and some of them were labeled using partial deuterium-labeled dimethyl phosphites (molar ratio of m + 6 and m = 1:1 or m + 6, m + 3 and m = 1:2:1) as the phosphorylating agents. The monophosphorylation of the lysine-containing peptides selectively occurred on the amino group of the N-terminus, not the side-chain of lysine residue. The resin-bound phosphoramidate peptides were cleaved by TFA before ESI-MS. The modified peptides were determined by electrospray ionization mass spectrometry, the protonated molecules of the unlabeled phosphoramidate peptides showed the singlet peaks, and those of the labeled phosphoramidate peptides displayed the doublet and/or triplet peaks. Tandem mass spectra (MS/MS) of the chosen protonated molecules gave sequential loss of the amino acid residues from the C-termini of the peptides, providing a convenient and rapid method for peptide sequencing.

Analysis of peptide mixtures through convenient isotopic labeling and electrospray ionization-mass spectrometry

We have developed a labeling method for sequencing of mixed peptides through modification of peptides and multistage electrospray ionization-mass spectrometry (ESI-MS). Mixed peptides were selectively phosphonylated on amino group through reaction of 2-bromoethyl phenylphosphinate (BEPP-H) or methyl/methyl-d 3 (1:1) phenylphosphinate (MPP-X) with peptides in the presence of tetrachloromethane and triethylamine under mild conditions to provide the labeled phosphonamidate peptides, and their primary ESI mass spectra showed doublet and triplet peaks. The triplet and doublet peaks were corresponding to the protonated molecules of the modified peptides having and having no one lysine residue, respectively, and the singlet peaks were from the non-peptides. Further, tandem mass spectra (MS/MS) of the readily identified protonated molecules unambiguously gave sequence of each member in mixed peptides.

Brominated–chlorinated diphenyl ethers formed by thermolysis of polybrominated diphenyl ethers at low temperatures

Polybrominated diphenyl ethers (PBDEs) are a group of brominated flame retardants (BFRs) used mainly as additives in different kinds of plastic material. Various PBDEs are found in all environmental compartments as well as in tissue and blood serum of animals and humans due to their persistence and tendency to bioaccumulate. Emission of PBDEs into the environment can occur during recycling of PBDE-containing plastic material or during their uncontrolled or insufficient combustion as e.g. in accidental fires or landfill fires. Under these circumstances, PBDEs can also function as precursor molecules for the formation of polybrominated dibenzodioxins (PBDDs) and dibenzofurans (PBDFs). In this study, we qualitatively investigated the reaction of two PBDE congeners, 2,2′,4,4′-tetrabromo diphenyl ether (BDE 47) and 2,2′,4,4′,5,5′-hexabromo diphenyl ether (BDE 153), as well as hexabromobenzene (HBB), a flame retardant used in the past, when exposed to temperatures between 250 °C and 500 °C. The formed reaction products were analysed by high resolution gas chromatography–low resolution mass spectrometry (HRGC-LRMS). Among others brominated–chlorinated diphenyl ethers were formed by chlorodebromination of the PBDEs. In addition, thermolysis of BDE 47 and BDE 153 in the presence of tetrachloromethane as model substance for an organic chlorine source was studied. Thermal treatment of HBB resulted in the formation of brominated–chlorinated benzenes.

Carbon–mineral adsorbents prepared by pyrolysis of waste materials in the presence of tetrachloromethane

Natural bentonite spent in the process of plant oil bleaching was used as an initial material for preparation of carbon–mineral adsorbents. The spent bleaching earth was treated using four procedures: T (thermal treatment); H (hydrothermal treatment); C (thermal treatment with addition of CCl 4 vapor); M (modification of porous structure). Raw bentonite, RB (raw bleaching earth), and carbon materials prepared using plant oil were compared. The physicochemical characteristics of the adsorbents were determined using different methods: nitrogen adsorption/desorption, XRD, TEM, and MS-TPD. Carbon–mineral adsorbents contain from 5.23 to 19.92% C (w/w) and carbon adsorbents include from 84.2 to 91.18% C (w/w). Parallel processes of organic substance carbonization, porous structure modification, sublimation or evaporation of metal chlorides, and removal of hydrogen chloride take place during pyrolysis of waste mineral materials in the CCl 4 atmosphere.

Oxidative Dehydrogenation of Propane on Magnesium Vanadates in the Presence of Tetrachloromethane

Abstract The oxidative dehydrogenation of propane to propene on active catalysts such as magnesium vanadates (MgV2O6, Mg2V2O7, and Mg3V2O8) has been investigated in the presence and absence of tetrachloromethane (TCM) at 723 K. The introduction of a small amount of TCM into the feedstream did not influence the selectivity to propene while the conversion of propane was improved on those catalysts. The conversion was enhanced by approximately twice on Mg2V2O7 upon addition of TCM. It has been shown that the effects of TCM on lattice oxygen in those catalysts mainly control the enhancement. The formation of an excess amount of the chlorinated species on the surface of the catalysts resulted in a decrease of the conversion.

Effect of tetrachloromethane on redox behaviors of copper(II) oxide in the oxidative dehydrogenation of propane

The oxidative dehydrogenation of propane on CuO has been investigated at 723 K in the presence and absence of tetrachloromethane (TCM). Under oxygen-limiting conditions, the conversion of propane and the selectivity to propylene were enhanced by the introduction of TCM. The catalyst converted to metallic Cu during the oxidation in the absence of TCM while no conversion of CuO was observed in the sample used in the presence of TCM. In contrast, the conversion of propane dramatically decreased upon addition of TCM into the feedstream for the oxidation of propane under the oxygen-excess conditions. The catalyst used under the oxygen-excess conditions was not reduced to metallic Cu, regardless of the addition of TCM. It is suggested that an abstraction of lattice oxygen from the catalyst is strongly influenced by the concentration of oxygen in the feed, resulting in the different effect of TCM on the oxidative dehydrogenation of propane.

Effect of the phase transition of iron (III) oxide on the oxidative dehydrogenation of propane in the presence and absence of tetrachloromethane

The oxidative dehydrogenation of propane on α-Fe 2O 3 (hematite) was examined in the presence and absence of tetrachloromethane (TCM) at 723 K. The conversion of propane and the selectivity to propylene were evidently improved upon addition of TCM into the feedstream under oxygen limited conditions. It has been described that the suppression of the phase transition of hematite to maghemite (γ-Fe 2O 3) and a formation of chlorinated species on the catalyst together with gaseous chlorinated species contributes to the activities in the presence of TCM.

Effects of gas- and solid-phase additives on oxidative dehydrogenation of propane on strontium and barium hydroxyapatites

Effects of the introduction of tetrachloromethane (TCM) into the feedstream for the oxidative dehydrogenation of propane have been investigated on strontium and barium hydroxyapatites (SrHAp and BaHAp) with and without treatment with Cu 2+ and Pb 2+. Activities on SrHAp were greater than those on BaHAp in the absence of TCM. Upon adding TCM into the feedstream for propane oxidation on both SrHAp and BaHAp, the conversion of propane decreased while the selectivity to propylene increased with increasing time-on-stream, as observed in the oxidation of other alkanes on hydroxyapatites. While the treatment of both hydroxyapatites with lead resulted in the decrease of the yield of propylene regardless of the addition of TCM, activities on those catalysts doped with copper were improved in the presence of TCM. Particularly SrHAp treated with Cu 2+ afforded approximately 80% selectivity to propylene at 16% conversion of propane at 0.5 h on-stream with TCM and this activity was kept for 6 h on-stream. A direct contribution of TCM to control of the reduction of Cu 2+ in the catalyst leads to the improvement of the catalytic performance.

Nitrous oxide as oxidant for the oxidation of methane on barium hydroxyapatites in the presence and absence of tetrachloromethane

The oxidation of methane with nitrous oxide on PO 4-deficient barium hydroxyapatite (BaHAp) has been investigated in the presence and absence of tetrachloromethane (TCM) and compared to that with oxygen in order to obtain possible activities for the partial oxidation of methane using hydroxyapatite catalysts. In the absence of an external oxidant, the addition of TCM suppressed the formation of oxidation products with the essential elimination of CO and CO 2, in favor of an increased selectivity to C 2H 6 while that to C 2H 4 changed relatively little, indicating that TCM directly contributes to an activation of structural oxygen of the catalyst. In the absence of TCM and with nitrous oxide as the oxidant, the maximum selectivity to the coupling products reached approximately 80% at a conversion of methane of 4.5% at 0.5 h on-stream although calcium hydroxyapatites mainly afforded CO x under the corresponding conditions. However, carbon oxides, primarily CO 2, were the predominant products with oxygen. With nitrous oxide and in the presence of TCM with increasing time-on-stream carbon monoxide became the only significant product. The formation of barium chlorapatite is demonstrated and the relative effects of nitrous oxide and TCM are compared.

Effects of non-stoichiometry of calcium and strontium hydroxyapatites on the oxidation of ethane in the presence of tetrachloromethane

The effects of the introduction of tetrachloromethane (TCM) into the feedstream for the oxidative dehydrogenation of ethane have been investigated on stoichiometric and non-stoichiometric calcium and strontium hydroxyapatites (CaHAp and SrHAp, respectively) at 773 K. The conversion and selectivities in the presence of TCM were found to depend on the reaction conditions, as well as the stoichiometry and structural instability of the catalysts.

Effects of the Thermal Stability and the Fine Structure Changes of Strontium Hydroxyapatites Ion-Exchanged with Lead on Methane Oxidation in the Presence and Absence of Tetrachloromethane

The oxidation of methane has been investigated in the presence and absence of tetrachloromethane (TCM) on strontium hydroxyapatite with (SrPbHAp) and without (SrHAp) ion-exchanged lead. In the absence of TCM at 873 K, the introduction of lead to strontium hydroxyapatite resulted in a substantial increase in the selectivity to C2hydrocarbons and an increase in the conversion of methane and specific activities. In the presence of TCM, the conversion of methane and the selectivity to C2compounds decreased with increasing time-on-stream while that to carbon monoxide increased. However, the change in the specific activities with time-on-stream is dependent upon the composition of the catalysts. Some SrPbHAp catalysts showed evidence of transformation from apatites to the corresponding phosphates at temperatures greater than 873 K. At 773 K, at which temperature the aforementioned hydroxyapatites are relatively stable, no formation of C2compounds was observed in the absence of TCM, and the conversion of methane and the specific activities (with the exception of SrPb26HAp at 0.5 h on-stream) increased with the lead content of the catalysts. On introduction of TCM, the selectivities to CH3Cl and CO2increased and decreased, respectively, on both SrHAp and SrPbHAp catalysts. The results of extended X-ray absorption fine structure (EXAFS) spectroscopic measurements suggest that the catalytic properties of SrPbHAp at 773 K in the absence of TCM are related to the nearest-neighbor distances of the Pb–O bond rather than those of the Sr–O bond.

The oxidation of ethane in the presence and absence of tetrachloromethane on calcium hydroxyapatites with incorporated lead

The oxidative dehydrogenation of ethane has been investigated on various lead-added calcium hydroxyapatites and the effect of the addition of tetrachloromethane (TCM) into the feedstream has been examined. The catalysts are stable up to 873 K but are converted to the corresponding phosphates at approximately 973 K. The conversions of ethane and the selectivities to C 1 and C 2 compounds were found to be dependent on the lead contents of the catalysts, both the pretreatment and reaction temperatures, the presence of TCM and the times-on-stream as well as the structural forms of the catalysts. In the absence of TCM the conversion of ethane and the various selectivities show a dependence on the lead content of the catalysts which is similar at 773 and 873 K, but dissimilar at 973 K due, at least in part to the formation of the phosphates at the latter temperature. With TCM in the process feedstream the influence of the chlorapatites which are formed overrides that of the added lead.

Effect of the introduction of tetrachloromethane into the feedstream for methane oxidation with oxygen and nitrous oxide on thermally stable strontium hydroxyapatites

Thermally stable strontium hydroxyapatite (SrHAp) was prepared with a variety of stoichiometries and employed as catalysts for the oxidation of methane with oxygen and nitrous oxide in the presence and absence of tetrachloromethane (TCM) as a gas‐phase additive. In contrast to the oxidation of methane on thermally unstable SrHAp, non‐selective oxidation to CO and CO2 at 873 K proceeded with oxygen while the selectivity to CO increased with increasing time‐on‐stream in the presence of TCM and was higher than 90% at 6 h on‐stream, regardless of the Sr/P ratios in the catalysts. However, with nitrous oxide the selectivity to CO in the presence of TCM was strongly influenced by the Sr/P ratio with smaller values producing higher CO selectivity. In the presence of TCM, the catalyst consists of a complex mixture of the hydroxyapatite, the corresponding chlorapatite, phosphate, chloride and oxychloride, each of which contributes dissimilarly to the catalytic process.

Enhancement of the Catalytic Activities in the Oxidative Dehydrogenation of Propane on Cerium Oxide in the Presence of Tetrachloromethane.

The oxidative dehydrogenation of propane to propylene has been investigated on rare earth oxides such as La2O3, CeO2, Pr6O11 and Sm2O3 at 723K. The conversion of propane and selectivity to propylene were evidently enhanced by the introduction of small partial pressure of CCl4 into the feedstream on CeO2, but little on the remaining three catalysts.

Surface and Bulk Properties of Stoichiometric and Nonstoichiometric Strontium Hydroxyapatite and the Oxidation of Methane

The oxidation of methane on near-stoichiometric strontium hydroxyapatites pretreated at 873, 1048 and 1123 K in O2has been examined in the presence and absence of tetrachloromethane (TCM) as a gas-phase additive at 973 K. Under these conditions, strontium hydroxyapatite, regardless of its stoichiometry, is converted, at least in part, to Sr3(PO4)2. On introduction of TCM to the feedstream, the selectivities to carbon monoxide, ethane, and ethylene are increased while the conversion of methane is decreased. Qualitatively similar effects of TCM on the oxidation were observed on Sr3(PO4)2prepared by an independent procedure. Strontium chlorapatite, formed from the apatites and phosphate during the oxidation in the presence of TCM, as shown from XRD, contributes to the increased selectivity to CO and decreased conversion of methane.

Pretreatment effect in the oxidative dehydrogenation of ethane on magnesia in the presence and absence of tetrachloromethane

The effects of a small addition of tetrachloromethane (TCM) into the feedstream for the oxidative dehydrogenation of ethane have been investigated over magnesia at reaction temperatures between 723 and 1098 K. Both the conversion of ethane and the selectivity to ethylene at reaction temperatures of 723–823 K were markedly increased on addition of TCM, while at temperatures between 998 and 1098 K little or no changes in these quantities were observed. Pretreatment experiments in which MgO was exposed to TCM + O 2 or TCM + O 2 + H 2O prior to introduction of the reactant stream showed that the chlorided surface which formed during the pretreatment contributed to the aforementioned improvement. The concentration of surface chloride, in whatever form, produced during the pretreatment was influenced by the introduction of water but showed no dependence on the temperature, the partial pressure of TCM in the pretreatment gas or the duration of exposure. Excess chlorination of the surface tended to reduce the beneficial effect especially in the presence of TCM in the feedstream.

Partial oxidation of ethane on silica-supported 12-molybdophosphoric acid in the presence of tetrachloromethane

The introduction of small quantities of tetrachloromethane (TCM) into the feedstream in the oxidation of ethane with nitrous oxide on 12-molybdophosphoric acid (HPMo) supported on silica increases the conversion but has little effect on the selectivities. In the presence of TCM the primary products appear to be ethylene, acetaldehyde and ethyl chloride. Studies of the effects of loading, time-on-stream, contact time and reaction temperature provide evidence for the importance of a loading corresponding approximately to a monolayer of HPMo, the HPMo anion in the production of acetaldehyde and TCM in both the production of ethyl radicals and the selectivity to acetaldehyde.

Synthesis and Reactivity of Silicon Transition Metal Complexes, 34. Pentachlordisilanyl‐ und Disilanyl‐Komplexe von Molybdän und Wolfram: Darstellung, Struktur und spektroskopische Charakterisierung

Synthesis and Reactivity of Silicon Transition Metal Complexes, 34[*]. — Pentachlorodisilanyl and Disilanyl Complexes of Molybdenum and Tungsten: Synthesis, Structure, and Spectroscopic CharacterizationReaction of the lithium metallates Li[M(PMe3)(CO)2C5R5] [M = Mo, W; R = H (1a, b), Me (1c, d)] with Si2Cl6 (2) leads to the formation of the pentachloro(metallo)disilanes 5R5(OC)2(Me3P)M—SiCl2—SiCl3 (3a—d), which are transformed into the metallo disilanes C5R5(OC)2(Me3P)M—SiH2—SiH3 (4a—d) on treatment with LiAlH4. The disilanes 4a—d are reconverted into 3a—d in the presence of tetrachloromethane. Extensive spectroscopic investigations (NMR, Raman, and IR spectroscopy) were performed to establish the transition‐metal effect especially with respect to the H5Si2 ligand. The molecular structure of C5Me5(OC)2(Me3P)W—SiCl2—SiCl3 (3d) was determined by single‐crystal X‐ray diffraction.

Coimpregnated, Sequential, and Reverse Sequential Li/Sr/SiO2 Catalysts for the Oxidative Coupling of Methane in the Absence and Presence of Tetrachloromethane: Active, Selective, and Stable Catalysts

Binary lithium and strontium catalysts supported on silica are prepared by coimpregnation, sequential, and reverse sequential methods and are compared in the oxidative coupling of methane to ethane and ethylene for various loadings of strontium and lithium and in the absence and presence of tetrachloromethane (TCM) in the feedstream. The 10% Li/10% Sr/SiO 2 catalyst produces C 2+ yields up to 29% and is stable for times on-stream up to at least 600 h. The high yield and stability are attributed to the formation of strontium and lithium silicates which are resistant to high temperatures and destructive gaseous environments.