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Concept: Hydrogen chloride

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Both nitrate and pentachlorophenol (PCP) are familiar pollutants in aqueous environment. This research is focused on the simultaneous removal of nitrate and PCP from simulated contaminated groundwater using a laboratory-scale denitrification reactor packed with corncob as both carbon source and biofilm support. The reactor could be started up readily, and the removal efficiencies of nitrate and PCP reached up to approximately 98 % and 40-45 % when their initial concentrations were 50 mg N/L and 5 mg/L, respectively, after 15-day continuous operation at 10 h of hydraulic retention time (HRT) and 25 °C. Approximately 91 % of PCP removal efficiency was achieved, with 2.47 mg/L of chloride ion release at 24 h of HRT. Eighty-two percent of chlorine in PCP removed was ionized. The productions of 3-chlorophenol and phenol and chloride ion release indicate that the reductive dechlorination reaction is a major degradation pathway of PCP under the experimental conditions.

Concepts: Concentration, Chemistry, Water pollution, Sodium chloride, Ion, Chlorine, Chloride, Hydrogen chloride

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The cyanosporasides A-F are a collection of monochlorinated benzenoid derivatives isolated from the marine actinomycetes Salinispora and Streptomyces sp. All derivatives feature one of two types of cyanocyclopenta[a]indene frameworks, which are regioisomeric in the position of a single chlorine atom. It is proposed that these chloro-substituted benzenoids are formed biosynthetically through the cycloaromatization of a bicyclic nine-membered enediyne precursor. Herein, we report the synthesis of such a bicyclic precursor, its spontaneous transannulation into a p-benzyne, and its differential 1,4 hydrochlorination reactivity under either organochlorine or chloride-salt conditions. Our bioinspired approach culminated in the first regiodivergent total synthesis of the aglycons A/F and B/C, as well as cyanosporasides D and E. In addition, empirical insights into the site selectivity of a natural-like p-benzyne, calculated to be a ground-state triplet diradical, to hydrogen, chlorine, and chloride sources are revealed.

Concepts: Hydrogen, Atom, Total synthesis, Chlorine, The Marine, Hydrogen chloride, Streptomyces, Hydrochloric acid

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The structure of the gas-phase bimolecular complex formed between vinyl chloride and hydrogen fluoride is determined using Fourier transform microwave spectroscopy from 6.3 to 21.4 GHz. Although all previous examples of complexes formed between protic acids and haloethylenes are observed to have similar modes of binding regardless of the specific identity of the acid, HF, HCl, or HCCH, the planar vinyl chloride-HF complex has HF located at the “top” of the vinyl chloride with the secondary interaction occurring with the cis hydrogen atom as opposed to the “side” binding configuration found for vinyl chloride-HCCH. Nevertheless, the details of the structure, such as hydrogen bond length (2.32 Å) and amount of deviation from linearity (19.8°), do reflect the strength of the interaction and show clear correlations with the gas-phase acidity. Comparison with analogous complexes allows the determination of the relative importance of electrostatic interactions and steric requirements in leading to the observed structures.

Concepts: Oxygen, Acid, Fundamental physics concepts, Water, Hydrogen, Atom, Chlorine, Hydrogen chloride

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2-Arylbenzoyl chlorides undergo annulative coupling with internal alkynes in the presence of a catalyst system of [IrCl(cod)]2/P(t-Bu)3 to selectively afford the corresponding phenanthrene derivatives accompanied by elimination of carbon monoxide and hydrogen chloride. The reaction occurs without addition of any external base. Deuterium labeling experiments using 2-(d5-phenyl)benzoyl chloride suggest that the rate-determining step does not involve the C2'-H bond cleavage. Formation of a [(t-Bu)3PH][(biphenyl-2,2'-diyl)Ir(CO)Cl2] complex dimer, of which structure was determined by single-crystal X-ray analysis, from a stoichiometric reaction at 60 degC without adding alkyne also supports the facile C-H cleavage.

Concepts: Chemical reaction, Hydrogen, Carbon, Alkene, Carbon monoxide, Chlorine, Hydrogen chloride, Hydrochloric acid

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A dually activated ketene enolate, generated from an acid chloride, the unusual chelating nucleophile (1,8-naphthyridine), and a Lewis acid, reacts to afford a host of alpha,alpha-difluorinated products in the presence of a bench top stable fluorinating agent (Selectfluor). The use of this method to synthesize otherwise difficult to make products is highlighted along with computational and spectroscopic support for the proposed chelate.

Concepts: Amine, Gilbert N. Lewis, Carbonyl, Chlorine, Citric acid, Hydrogen chloride

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Internal sample conductivity in scanning electron microscopy can be a valuable alternative to metal coating. Proton conductivity may be used for this purpose. Many solid materials with active hydrogen atoms, such as hydrogen- and ammonium-salts, organic acids, and even ice, are protonic conductors or semiconductors. Here we present a method to generate proton conductivity in dry biological materials. A simple treatment with hydrogen chloride gas or hydrochloric acid vapour for a few minutes provides sufficient conductivity for many samples. After a removal of excess hydrogen chloride vapour with a vacuum desiccator, the objects may be examined in the SEM without metal coating. The use of internally conductive samples extends the range of easy-to-perform SEM preparation techniques. It is advantageous for material contrast imaging of uncoated samples, and it can be used in combination with metal coating to enhance conductivity on difficult samples with complex overlapping surfaces, where simple metal coating does not reliably eliminate charging problems.

Concepts: Electron, Acid, Hydrogen, Proton, Atom, Chlorine, Hydrogen chloride, Hydrochloric acid

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Chloromethane, accounting for approximately 16% of the tropospheric chlorine, is mainly coming from natural sources. However anthropogenic activities, such as combustion of biomass may contribute significantly as well. The present study focuses on the thermal solid state reaction between pectin, an important constituent of biomass, and chloride ions as found in alkali metal chlorides. The formation of chloromethane is evident with the amount formed being linear with respect to chloride if pectin is in great excess. Thus the reaction is explained as a pseudo first order SN2 reaction between the chloride ion and the methyl ester moiety in pectin. It is suggested that the polymeric nature of pectin plays an active role by an enhanced transport of halides along the carbohydrate chain. Optimal reaction temperature is around 210°C. At higher temperatures the yield of chloromethane decreases due to a thermal decomposition of the pectin. The possible influence of the type of cation is discussed.

Concepts: Ammonia, Nucleophilic substitution, Sodium chloride, Ion, Solid, Chlorine, Chloride, Hydrogen chloride

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Two-electron mixed-valence compounds promote the rearrangement of the two-electron bond photochemically. Such complexes are especially effective at managing the activation of hydrohalic acids (HX). Closed HX-splitting cycles require proton reduction to H2 and halide oxidation to X2 to be both accomplished, the latter of which is thermodynamically and kinetically demanding. Phosphazane-bridged Rh2 catalysts have been especially effective at activating HX via photogenerated ligand-bridged intermediates; such intermediates are analogues of the classical ligand-bridged intermediates proposed in binuclear elimination reactions. Herein, a new family of phosphazane-bridged Rh2 photocatalysts has been developed where the halide-bridged geometry is designed into the ground state. The targeted geometries were accessed by replacing previously used alkyl isocyanides with aryl isocyanide ligands, which provided access to families of Rh2L1 complexes. H2 evolution with Rh2 catalysts typically proceeds via two-electron photoreduction, protonation to afford Rh hydrides, and photochemical H2 evolution. Herein, we have directly observed each of these steps in stoichiometric reactions. Reactivity differences between Rh2 chloride and bromide complexes have been delineated. H2 evolution from both HCl and HBr proceeds with a halide-bridged Rh2 hydride photoresting state. The H2-evolution efficiency of the new family of halide-bridged catalysts is compared to a related catalyst in which ligand-bridged geometries are not stabilized in the molecular ground state, and the new complexes are found to more efficiently facilitate H2 evolution.

Concepts: Photosynthesis, Chemical reaction, Hydrogen, Chemistry, Hydrogenation, Organic reaction, Chlorine, Hydrogen chloride

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The recycling of platinum-group metals from wastes such as autocatalytic converters is getting growing attention due to the scarcity of these precious metals and the market pressure originated by increase of demand in current and emerging applications. Hydrometallurgical treatment of such wastes is an alternative way to the most usual pyrometallurgical processes based on smelter operations. This paper focuses on the development of a leaching process using cupric chloride as oxidising agent, in HCl media, for recovery of palladium and rhodium from a spent catalyst. The chloride media allows the adequate conditions for oxidising and solubilising the metals, as demonstrated by equilibrium calculations based on thermodynamic data. The experimental study of the leaching process revealed that Pd solubilisation is clearly easier than that of Rh. The factors temperature, time, and HCl and Cu(2+) concentrations were significant regarding Pd and Rh leaching, the latter requiring higher factor values to achieve the same results. Leaching yields of 95% Pd and 86% Rh were achieved under optimised conditions (T=80°C, t=4h, [HCl]=6M, [Cu(2+)]=0.3M).

Concepts: Hydrogen, Catalysis, Catalytic converter, Chlorine, Chloride, Palladium, Hydrogen chloride, Hydrochloric acid

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A high-throughput analytical method has been developed for the determination of seventeen 2,3,7,8-substituted congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in aqueous samples. A recently introduced octadecyl (C18) disk for semi-automated solid-phase extraction of PCDD/Fs in water samples with a high level of particulate material has been tested for the analysis of dioxins. A new type of C18 disk specially designed for the analysis of hexane extractable material (HEM), but never previously reported for use in PCDD/Fs analysis. This kind of disk allows a higher filtration flow, and therefore the time of analysis is reduced. The solid-phase extraction technique is used to change samples from liquid to solid, and therefore pressurized liquid extraction (PLE) can be used in the pre-treatment. In order to achieve efficient purification, extracts from the PLE are purified using an automated Power-prep system with disposable silica, alumina, and carbon columns. Quantitative analyses of PCDD/Fs were performed by GC-HRMS using multi-ion detection (MID) mode. The method was successfully applied to the analysis of water samples from the wastewater treatment system of a vinyl chloride monomer plant. The entire procedure is in agreement with EPA1613 recommendations regarding the blank control, MDLs (method detection limits), accuracy, and precision. The high-throughput method not only meets the requirements of international standards, but also shortens the required analysis time from 2weeks to 3d.

Concepts: Water, Analytical chemistry, Sewage treatment, Chlorine, Hydrogen chloride, Polychlorinated dibenzodioxins, Vinyl, Solid phase extraction