Conversion Of Halides Research Articles

AGA8 supported Cu(I) nanoclusters as in situ generated catalysts for room temperature C‐S coupling reactions in water

A sustainable and green catalytic strategy for C‐S coupling reactions is developed by combining micelle and transition metal. The synergistic AGA8@Cu(I) catalyst forms by spontaneous anchoring of the in situ generated Cu(I) nanoclusters onto the AGA8 micelles and has been fully characterized by FT‐IR, XPS, SEM, TEM, EDS, and ICP‐OES. The catalyst is recyclable and highly effective in mediating the conversion of halides to disulfides in water at room temperature with a broad substrate scope.

Steering single-site metallaphotocatalytic pathway by accumulated electron on carbon nitride support

Organic halide transformation is of high importance for fine chemical synthesis and environmental remediation. Integrated photocatalytic platforms open up distinctive reaction pathway for carbon-halogen bond activation/reconstruction. Herein we reveal carbon nitride (CN)-ligated single atom nickel (Ni1/CN), with accumulated electron on the CN, paves Ni-mediated electron-proton transfer, enabling hydrodehalogenation, along with the catalytic carbon–oxygen (C–O) coupling. The preference for hydrodehalogenation positively correlates with density of electron on CN. EPR measurements suggest photo-generated NiI interacts with aryl halides, followed by electron transfer or reductive elimination to give different products. Further kinetic studies on hydrodehalogenation/C–O coupling show the reaction orders of 0.1/0.5 in aryl halide and 1.5/0.03 in (CN) electron, unveiling rate-determining step as oxidative addition to NiI and (CN) electron transfer for the two conversions. Our work advances in modulating aryl halide conversion by carrier accumulation on the photoactive support and guides metallaphotocatalytic platform design/operation toward target transformations.

Reversible Cl/Cl- redox in a spinel Mn3O4 electrode.

A unique prospect of using halides as charge carriers is the possibility of the halides undergoing anodic redox behaviors when serving as charge carriers for the charge-neutrality compensation of electrodes. However, the anodic conversion of halides to neutral halogen species has often been irreversible at room temperature due to the emergence of diatomic halogen gaseous products. Here, we report that chloride ions can be reversibly converted to near-neutral atomic chlorine species in the Mn3O4 electrode at room temperature in a highly concentrated chloride-based aqueous electrolyte. Notably, the Zn2+ cations inserted in the first discharge and trapped in the Mn3O4 structure create an environment to stabilize the converted chlorine atoms within the structure. Characterization results suggest that the Cl/Cl- redox is responsible for the observed large capacity, as the oxidation state of Mn barely changes upon charging. Computation results corroborate that the converted chlorine species exist as polychloride monoanions, e.g., [Cl3]- and [Cl5]-, inside the Zn2+-trapped Mn3O4, and the presence of polychloride species is confirmed experimentally. Our results point to the halogen plating inside electrode lattices as a new charge-storage mechanism.

Mizoroki-Heck carbon-carbon cross-coupling reactions by water-soluble palladium (II) complexes in neat water

Water-soluble palladium complexes were synthesized, characterized, tested as (pre)catalyst for Mizoroki-Heck carbon-carbon cross-coupling reactions in water. Cross-coupling of aryl iodides and bromides with methyl and ethyl acrylates was achieved at 140 °C. When styrene was employed as the substrate excellent conversion to trans-stilbene was observed using 5 mol% catalyst loading in the presence of TBAB. The catalysts are versatile and can couple various substrates in a non-toxic and benign solvent. After extraction of the organic product the catalyst containing aqueous layer could be recycled twice with a significant drop in the aryl halide conversion after the third recycle. No catalyst poisoning was observed in the mercury poisoning experiments with both catalysts and this proves that both catalytic systems function as molecular homogeneous catalysts.

Observation of Enhanced Hole Extraction in Br Concentration Gradient Perovskite Materials.

Enhancing hole extraction inside the perovskite layer is the key factor for boosting photovoltaic performance. Realization of halide concentration gradient perovskite materials has been expected to exhibit rapid hole extraction due to the precise bandgap tuning. Moreover, a formation of Br-rich region on the tri-iodide perovskite layer is expected to enhance moisture stability without a loss of current density. However, conventional synthetic techniques of perovskite materials such as the solution process have not achieved the realization of halide concentration gradient perovskite materials. In this report, we demonstrate the fabrication of Br concentration gradient mixed halide perovskite materials using a novel and facile halide conversion method based on vaporized hydrobromic acid. Accelerated hole extraction and enhanced lifetime due to Br gradient was verified by observing photoluminescence properties. Through the combination of secondary ion mass spectroscopy and transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis, the diffusion behavior of Br ions in perovskite materials was investigated. The Br-gradient was found to be eventually converted into a homogeneous mixed halide layer after undergoing an intermixing process. Br-substituted perovskite solar cells exhibited a power conversion efficiency of 18.94% due to an increase in open circuit voltage from 1.08 to 1.11 V and an advance in fill-factor from 0.71 to 0.74. Long-term stability was also dramatically enhanced after the conversion process, i.e., the power conversion efficiency of the post-treated device has remained over 97% of the initial value under high humid conditions (40-90%) without any encapsulation for 4 weeks.

Post-synthetic halide conversion and selective halogen capture in hybrid perovskites.

Reaction with halogen vapor allows us to post-synthetically exchange halides in both three- (3D) and two-dimensional (2D) organic-inorganic metal-halide perovskites. Films of 3D Pb-I perovskites cleanly convert to films of Pb-Br or Pb-Cl perovskites upon exposure to Br2 or Cl2 gas, respectively. This gas-solid reaction provides a simple method to produce the high-quality Pb-Br or Pb-Cl perovskite films required for optoelectronic applications. Reactivity with halogens can be extended to the organic layers in 2D metal-halide perovskites. Here, terminal alkene groups placed between the inorganic layers can capture Br2 gas through chemisorption to form dibromoalkanes. This reaction's selectivity for Br2 over I2 allows us to scrub Br2 to obtain high-purity I2 gas streams. We also observe unusual halogen transfer between the inorganic and organic layers within a single perovskite structure. Remarkably, the perovskite's crystallinity is retained during these massive structural rearrangements.

Kinetic investigations into the synthesis of disulphides via tetrathiomolybdate as a sulphur-transfer reagent

Kinetic and mechanistic aspects of the conversion of halides to disulphides using benzyl triethyl ammonium tetrathiomolybdate as sulphur-transfer reagent were investigated. The reaction follows a 1:1 stoichiometry with overall second-order kinetics and involves the formation of monosulphides in addition to disulphides. In the light of our observations, we propose a nucleophilic substitution: carbon–metal–carbon (SN-CMC) reaction mechanism. The proposed mechanism, besides accounting for all of our experimental observations, also explains many aspects of such reactions that have been reported earlier by various groups.

Extraction of Rare Earth Metals from Nd-based Scrap by Electrolysis from Molten Salts

The possibilities of recovery of rare earth metals and alloys from Nd-based scrap by electrolysis from high temperature molten salts were investigated. The realization of such a process will eliminate the oxide or halide conversion steps, leading to a more effective and environmental process, as many hydrometallurgical steps are avoided. The NdFeB compound (which could be scrap from the magnet production or demagnetized spent magnet) is placed in the anode compartment from where the rare earth elements present in the material (Nd, Dy, Pr) will be anodically dissolved in the form of ions, which will be discharged at the cathode as metals and/or magnetic alloys. Different electrolyte compositions and temperatures are tested and the feasibility, kinetics, and efficiency of the process are evaluated.

ChemInform Abstract: Halide Removal from Coal‐Derived Syngas: Review and Thermodynamic Considerations

Halide species are one of the most abundant and damaging impurities in syngas derived from coal. Aside from environmental concerns, halides can cause irreversible damage to downstream processes such as particulate filters, catalysts, gas separation membranes, fuel cells and turbines. The current trend towards high-temperature, dry gas cleaning is making solid sorbents increasingly favourable, and sorbent development must take into consideration the chemical, physical, efficiency and economic aspects of sorbent performance. This article reviews the origins of halides in coals, cleaning requirements and efforts to develop solid sorbents for halide removal for gasification processes. Most research effort to date has concerned (1) the performance and optimization of basic sorbents such as calcium and sodium carbonate and (2) determining the tolerances of catalysts, filters, fuel cells and other plant components to halide impurities. In addition, thermodynamic calculations have been used to compare the performance of a large number of potential sorbents examined using criteria such as conversion, speciation, volatility and regenerability. This exercise confirms alkali and alkaline earth carbonates exhibit the greatest halide conversion at the temperatures demanded by various downstream processes, but these species are not regenerable at high temperatures in the same manner as desulfurization sorbents. Although not previously investigated, scope exists for the investigation of barium carbonate for halide sorption. Halide removal is best performed preceding sulfur removal due to the irreversible inhibition of regenerable desulfurization sorbents by halide species. Copyright © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Methyl Halide to Olefins and Gasoline over Zeolites and SAPO Catalysts: A New Route of MTO and MTG

Rational and efficient conversion of methane to more useful higher hydrocarbons is one of the most important topics of natural gas utilization. Although methane activation and its conversion to valuable compounds attract an increasing attention, methane conversion is often made in indirect way through the very energy-consuming step for syngas production from steam reforming of methane. Some promising results appeared to be of significance for the development of an alternative and potential route for the production of high value-added products from methane. Efficient conversion of methane to higher hydrocarbons could be realized via methyl halide as the intermediate. After the production of halomethane, they could be transformed to gasoline and light olefins over modified zeolites and SAPO molecular sieves. High conversion efficiency and selectivity indicated the feasibility of industrial application. The research gained recently growing interest from the point of view in both fundamental research and industrial application. The study on the reaction mechanism shed light on the possible route of C–C bond construction from methyl halide, which is the very important issue of the C1-reactant conversion to higher hydrocarbons. Hydrogen halide generation during methyl halide conversion did not exert apparent impact on the reaction mechanism and the structure stability of the catalysts. This review deals with the evolution of the field and comments the advantages to be explored and the drawbacks to be prevented for the development of new and sustainable methane-to-olefins (MTO) and methane-to-gasoline (MTG) routes via methyl halides.

Halide removal from coal‐derived syngas: review and thermodynamic considerations

ABSTRACTHalide species are one of the most abundant and damaging impurities in syngas derived from coal. Aside from environmental concerns, halides can cause irreversible damage to downstream processes such as particulate filters, catalysts, gas separation membranes, fuel cells and turbines. The current trend towards high‐temperature, dry gas cleaning is making solid sorbents increasingly favourable, and sorbent development must take into consideration the chemical, physical, efficiency and economic aspects of sorbent performance. This article reviews the origins of halides in coals, cleaning requirements and efforts to develop solid sorbents for halide removal for gasification processes. Most research effort to date has concerned (1) the performance and optimization of basic sorbents such as calcium and sodium carbonate and (2) determining the tolerances of catalysts, filters, fuel cells and other plant components to halide impurities. In addition, thermodynamic calculations have been used to compare the performance of a large number of potential sorbents examined using criteria such as conversion, speciation, volatility and regenerability. This exercise confirms alkali and alkaline earth carbonates exhibit the greatest halide conversion at the temperatures demanded by various downstream processes, but these species are not regenerable at high temperatures in the same manner as desulfurization sorbents. Although not previously investigated, scope exists for the investigation of barium carbonate for halide sorption. Halide removal is best performed preceding sulfur removal due to the irreversible inhibition of regenerable desulfurization sorbents by halide species. Copyright © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

ChemInform Abstract: A Facile Conversion of Halides, Alcohols, and Olefins to Esters Using Iron(III) Perchlorate.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The methyl halide to hydrocarbon reaction over H-SAPO-34

Methyl chloride (MeCl) and methyl bromide (MeBr) were converted to hydrocarbons over a H-SAPO-34 catalyst in a fixed-bed reactor at atmospheric total pressure. The feed rate (WHSV, equivalent to the mass of methanol) was in the range of 0.8–7.7 h −1, and the reaction temperature was varied from 300 to 450 °C. Comparative experiments were performed using methanol (MeOH). An induction period was observed for all reactants. The induction period may be overcome by adding a small amount of propene to the reactor before admission of the methyl halide feed. MeCl and MeBr were converted to the same extent under identical reaction conditions, whereas the methanol conversion was more than one order of magnitude greater than the methyl halide conversion. Product selectivities were similar for all reactants. Partial pressure variations of MeCl (0.1 vs. 1.0 bar pressure) indicated a first-order reaction rate in MeCl at 350–450 °C. Rapid catalyst deactivation was observed for all reactants at and above 350 °C. Repeated reaction–regeneration cycles using 1 bar of MeCl at 450 °C led to a loss of initial activity only, whereas the subsequent activity and product distribution with time on stream were identical for cycles 2–5. No structural changes in the catalyst were observed by X-ray diffraction after the regeneration tests.

Silver Halide Recrystalization: I. Qualitative Kinetics for the Conversion of AgCl to AgClBr

The reaction rates for the conversion of AgCl to AgClBr were studied qualitatively using a reflection spectrophotometric technique. The conversion rate was found to be dependent upon many factors, including the source of bromide and the presence and concentration of ripeners and restrainers. Soluble bromide (KBr) reacts faster with AgCl than does AgBr. Ripeners (1,1,3,3-tetramethyl-2-thiourea, 3,6-dithia-1,8-octanediol) greatly increase the rate of halide conversion. 4-Hydroxy-6-methyl-1,3,3a,7-tetraazaindene greatly reduces the rate of halide conversion or can completely eliminate it using either soluble bromide or AgBr as the bromide source.

A Convenient Method for the Conversion of Halides to Alcohols

Abstract The displacement of halides in unactivated primary bromides and iodides, allylic and benzylic primary and secondary bromides, and primary and secondary α-bromoketones by formate, using triethylammonium formate as the formylating agent, followed by acid or base catalyzed hydrolysis has been found to be an efficient method for the conversion of halides to alcohols.

ChemInform Abstract: A Facile, High‐Yielding Method for the Conversion of Halides to Mercaptans.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Conversion of methyl halides to hydrocarbons on basic zeolites: a discovery by in situ NMR

It is shown that methyl halides (I, Br, Cl) react to form ethylene and other hydrocarbons on basic, alkali metal-exchanged zeolites at low temperatures. For example, methyl iodide is converted to ethylene on CsX zeolite at ca. 500 K. The order of reactivity of various catalyst/adsorbate combinations is consistent with the predictions of elementary chemical principles. The order of reactivity of the methyl halides follows the expected leaving-group trend. The activity of the catalyst framework correlates with its basicity (or nucleophilicity). All reactions were performed in a batch mode in sealed magic angle spinning (MAS) rotors while the contents were continuously monitored by in situ [sup 13]C NMR. Methyl iodide reacts on CsX below room temperature to form a framework-bound methoxy species in high yield. An analogous ethoxy species readily formed from ethyliodide. These species were characterized in detail. The ethoxy species was quantitatively converted to ethylene below 500 K. [sup 133]Cs MAS NMR was used to characterize the interactions of methyl iodide and other adsorbates with the cation in zeolite CsZSM-5. Solvation of the alkali metal cation was reflected in large, loading-dependent chemical shifts for [sup 133]Cs. Interactions between the cation and adsorbates were also reflected in the [supmore » 13]C shifts of the alkyl halides and ethylene. The cumulative evidence suggests a mechanism for carbon-carbon bond formation analogous to one proposed by Chang and co-workers for methanol-to-gasoline chemistry on acidic zeolites (J. Chem. Soc., Chem. Commun, 1987, 1320) that involves framework-bound methoxy and ethoxy species. The mechanism for methyl halide conversion is proposed to include roles for the basicity of the zeolite framework as well as the Lewis acidity of the cation. 68 refs., 18 figs., 2 tabs.« less

A facile, high-yielding method for the conversion of halides to mercaptans

An efficient, high-yield, one-pot preparation of alkyl and activated aryl mercaptans is presented. The method relies on sodium thiophosphate displacement of the halide, followed by mild hydrolysis of the intermediate phosphorothioate.

A new procedure for labeling alkylbenzenes with [ 18F]fluoride

A new procedure for labeling alkylbenzenes with no-carrier-added (nca) [ 18F]fluoride is reported. This will allow the use of [ 18F]-for-nitro aromatic nucleophilic displacement reaction for labeling aromatic compounds with no activating groups on the benzene ring. The new procedure involves (A) the [ 18F]-for-nitro displacement reaction on nitrophenones, and (B) the reduction of [ 18F]fluorophenones with triethylsilane and trifluoroacetic acid to alkylfluorobenzenes. The desired 18F-labeled alkylbenzenes were prepared in a synthesis time of 1 h with a radiochemical yield of 20% at end-of-synthesis. The procedure has been successfully applied to the synthesis of 18F-labeled alkylating agents, such as 4-[ 18F]fluorophenethyl bromide, 4, and 4-[ 18F]fluorophenbutyl chloride, 5. Using the reaction of piperidine and 4 as a model, the potential use of phenethylbromide 4 for labeling biologically important amines was examined. Initial results indicated that the desired alkylated piperidine was formed in low yields (<5%) due to the conversion of halide 4 to [ 18F]fluorostyrene (>85%) under basic conditions. The new procedure provides an easy method of labeling alkylbenzenes with fluorine-18.

Mechanism of halide conversion process of colloidal AgCl microcrystals by Br − ions : I. Observation of the dynamic changes in shape, structure, and composition

The mechanism of the halide conversion process in suspension of AgCl microcrystals by bromide ions was studied by electron microscopy, X-ray diffractometry, and electron-beam diffractometry. The typical conversion process after the introduction of Br − was found to consist of more than three distinctive steps. The first step was an almost instantaneous reaction within a few seconds for a surface conversion without apparent morphological change of the original particles. The second step was a very rapid epitaxial growth process of virtually pure AgBr crystals on every corner and partly on the edges of the AgCl cubic microcrystals with dissolution of their own {100} faces, which was finished in about 1 min at 25°C. The third step was a much slower process of about 2 h at 25°C (ca. 5 min at 45°C) for the formation of an AgCl 0.5Br 0.5 solid solution developing from the joints of AgBr guest and AgCl host by simultaneous dissolution of the guests and the hosts. After the complete dissolution of the AgBr guests, a further recrystallization process that formed a solid solution richer in chloride content followed. Finally, the conversion virtually stopped midway to yield double-structured particles of Ag(Cl, Br) shell/AgCl core. However, when the initial molar ratio of [Br −] 0 [AgCl] 0 was so high as to exceed unity, the original AgCl particles were totally decomposed into about eightfold AgBr particles in number. In this case the steps later than the second one were missing. Also, it was suggested from the subsidiary study on open systems, where bromide ions were added continuously, that the kinetics was basically controlled by the deposition rate of the solute of the AgBr component of the growing parts, though it was switched to being limited by the dissolution rate of the host AgCl crystals when their open surface area for dissolution was extremely diminished.