Chlorine Source Research Articles

NBS-Mediated C(sp2)-H Bond Chlorination of Enaminones: Using DCE as Chlorine Source

Commercial DCE is excavated as both a “Cl” source and a solvent for the vinyl C(sp2)-H chlorination. The strategy involves a metal-free NBS-mediated C(sp2)-H chlorination of enaminones, and affords diverse, functionalized α-chlorinated enaminones with a Z-configuration. This mild and effective approach not only advances the vinyl C(sp2)-H chlorination, employing DCE as the “Cl” source, but also provides a new strategy for accessing chlorinated enaminone derivatives.

Eco-friendly recovery and preparation of high purity nano silver powders from retired photovoltaic solar cells

With the increasing deployment of photovoltaic modules, recycling of waste photovoltaic has become a topic of great concern. Silver (Ag) represents a significant resource in retired crystalline silicon solar cells (RCSSC). However, conventional methods for the recovery of silver are based on the use of harmful inorganic acids, which give rise to environmental concerns. Furthermore, the use of unsuitable chlorine sources may result in the production of target products with a low level of purity. Herein, we reported a new method featured with eco-friendly mixed organic acid to extract and recycle Ag from retired crystalline silicon wafers. Single-factor experiments and response surface optimization experiments were carried out to find the optimal conditions in the leaching step. A process comprising chlorination precipitation, ammonia dissolution, and liquid phase reduction was constructed for the production of silver powder from the leaching solution. This approach resulted in a high silver leaching yield of 97.38 % and silver purity of 99.85 % before purification with an average particle size of 229.7 nm.

Recent Advances in Chlorination: Novel Reagents and Methods from the Last Decade

Chlorinated compounds are vital in organic synthesis, impacting nucleophilic substitutions, β-elimination, and C-H acidity. This review highlights recent advances in (hetero)arene chlorination, focusing on novel reagents and methods developed in the past decade. Traditional electrophilic agents like Cl₂ and PCl₅ have been expanded with new chlorinating agents such as Palau’chlor, as well as electrochemical and photochemical techniques. Biocatalyzed chlorination using FAD-dependent halogenases is also explored. Key trends include green chemistry with eco-friendly chlorine sources like NaCl and HCl. Although nucleophilic chlorination remains rare, electrochemical methods show promising, despite equipment limitations. This review emphasizes significant progress in the last decade towards more sustainable and efficient chlorination strategies.

Combined electrochemical in-situ activated chlorine production and photocatalytic for degradation of dimethyl phthalate using membrane filtration recycle TiO2

The ultraviolet (UV)/chlorine advanced oxidation process (AOP), involving addition of activated chlorine to the UV irradiation system to generate hydroxyl radicals (HO·) and chlorine radicals (Cl·), is promising in addressing refractory organic matters. Herein, activated chlorine was electrochemically in-situ generated under low concentrations of chloride ions (Cl−), serving as the chlorine source. A UV/electrochemistry/titanium dioxide (UV/E/TiO2) system was established by coupled membrane filtration. TiO2 was separated and circulated to remove dimethyl phthalate (DMP). Impacts of catalyst (TiO2), Cl− concentrations, and initial pH on DMP degradation were investigated under different conditions. The results revealed that compared with E and UV/TiO2 systems, the UV/E/TiO2 system substantially enhanced the DMP degradation (from 5.11 % and 22.54 % to 78.33 %), with a synergistic factor of 1.16. Radical quenching experiments confirmed that HO·and Cl·were the primary reactive substances for DMP degradation in the UV/E/TiO2 system. Fluorescence probe experiments, coupled with HPLC and LC–MS analysis, revealed a continuous decrease in Cl− in the UV/E/TiO2 system due to ongoing photolysis, generating more HO·for DMP degradation in contrast to the E/TiO2 system. In conclusion, the coupled UV/E/TiO2 system can promote the degradation of refractory organic pollutants in water environments, showcasing significant potential.

Selective Extraction of Valuable and Critical Metals in Cassiterite Concentrate by Dry Chlorination, Part I: Thermodynamic and Modelling Perspective.

The chlorination of oxides of major concern in cassiterite concentrate with various chlorinating agents is investigated in light of their thermodynamic feasibilities to extract and recover their valuable metal components. Mechanisms responsible for the processes and their Gibbs free energy changes as a function of temperature to selectively separate and/or recover the metal(s) of interest and unwanted ones as their metallic chlorides are identified. Attention is given to gaseous (Cl2 and Cl2 + CO mixture) and solid (CaCl2 and MgCl2) chlorine sources, from which Cl2 + CO shows no reaction selectivity for any of the oxides but a feasible metal chloride formation for all. Chlorine gas (Cl2), on the other hand, could selectively form chlorides with metals of +2 oxidation state in their oxides, leaving those of high oxidation state unreacted. MgCl2, unlike CaCl2, is found capable of producing calcium, ferrous, and stannic chloride from their metallic oxides with enhanced reaction tendencies in the presence of silicon dioxide (SiO2). An overall study of the thermodynamic feasibility of all chlorine sources looked at alongside operational and environmental viabilities suitably suggests MgCl2 for a selective extraction of the valuable metal components in a cassiterite concentrate, in which case, moderate temperatures seem promising.

Insight into the inhibition mechanisms of Ca-, N-, S-containing compounds on persistent organic pollutant formation from the thermal reaction of anthracene on copper chloride

Four inhibitors (CaO, CaS, CH4N2S, and (NH4)2SO4) were employed to inhibit the formation of multiple unintentional persistent organic pollutants (POPs) and environmentally persistent free radicals (EPFRs) using anthracene as a precursor, with CuCl2 serving as both a transition metal catalyst and chlorine source. The inhibition mechanisms were elucidated in terms of chlorine immobilization, catalyst deactivation, and free radical regulation. The inhibition efficiency of the four inhibitors on polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), and polychlorinated naphthalenes (PCNs) ranged from 64.7 % to 98.4 %, with the corresponding inhibition rates on toxic equivalency quantity ranging from 86.3 % to 99.7 %. The distribution of homologs shifted towards less chlorinated species, indicating effective suppression of chlorination. Calcium- and nitrogen-containing compounds consumed chlorine sources by forming CaCl2, CaClOH, and NH4Cl, while sulfur-containing compounds deactivated catalysts by forming CuSO4. EPFRs derived from anthracene were identified as carbon-centered anthracene-type and anthraquinone-type radicals. Positive correlations were observed between POPs and EPFRs concentrations, suggesting the pivotal role of organic free radicals as intermediates in POPs formation. Anthraquinones derived from anthracene underwent decomposition, recombination and chlorination, leading to the formation of PCDD/Fs and PCBs. The addition of inhibitors reduced EPFRs concentrations by 74.2–95.1 %. Sulfur- and nitrogen-containing inhibitors generated radicals that attacked POPs precursors and intermediates, forming heteroatomic compounds and inhibiting POPs formation. These findings enhanced the understanding of the source control mechanisms of POPs and provided theoretical and technical support for the synergistic inhibition of POPs and EPFRs in industrial thermal processes.

Global Mapping of HCl on Mars by IRTF/iSHELL

Hydrogen chloride (HCl)—a key marker of the chlorine cycle on Mars—has been recently discovered in the Martian atmosphere by the ExoMars/TGO mission. In-orbit data indicate that this molecule appears in the atmosphere only in a limited time period and specifically in the southern summer season. A snapshot global mapping of HCl is indispensable to examine its sources and sinks, but such observations are not currently possible from any orbiters. Here, we present the first spatially resolved map of HCl obtained with the ground-based NASA InfraRed Telescope Facility. We find clear features of HCl, demonstrating that HCl is present close to the surface. HCl is detected in the equatorial region for the first time, revealing that HCl is widely distributed on Mars. However, the spatial distribution of HCl is not uniform, and it is enhanced in the southern polar region. Interestingly, this nonuniform spatial distribution of HCl column abundance is strikingly similar to that of water vapor column abundance. This highlights the important role of water vapor in the evolution of HCl through the atmosphere, as previously noted, and suggests its potential involvement in the atmospheric chlorine source processes.

HCl/DMSO/HFIP-Mediated Chlorination of Pyrrolo[2,1-a]isoquinolines and Other Electron-Rich Heteroarenes.

An efficient oxidative chlorination of pyrrolo[2,1-a]isoquinolines has been established using HCl (aq) as the chlorine source and DMSO as the terminal oxidant in HFIP at ambient temperature. A variety of chlorinated pyrrolo[2,1-a]isoquinoline derivatives have been prepared readily in 23 to 99% yields. This chlorination strategy can be expanded to the functionalization of other electron-rich heteroarenes including substituted pyrroles, indoles, and naphthols.

Cu@CuFe2O4 nanoparticles catalyzed oxidative functionalization of alkynes: Access to α,α‐dichloro ketones

In this study, novel Cu@CuFe2O4 nanoparticles were prepared by virtue of a simple method. By utilizing a compatible system involving N‐chlorosuccinimide (NCS) as the chlorine source and Cu@CuFe2O4 magnetic nanoparticles (NPs) as recyclable catalyst, we present a novel and practical method for directly obtaining aryl α,α‐dichloroketones in aqueous trifluoroethanol (TFE). The catalyst was recovered and reused up to five times with no significant decrease in activity. The current study provides a foundational raw material for the subsequent synthesis of chlorinated functional molecules, which is achieved through a mild transformation of arylalkynes using readily available commercial feedstocks and exhibiting good tolerance with various substituents on the aromatic ring, including the aliphatic alkyne. This novel heterogeneous catalyst may be used in numerous industrial applications because of its merits, such as considerable recyclability, low requirement for catalyst loading, cost‐effectiveness, and ease of handling.

Repurposing of halogenated organic pollutants via alkyl bromide-catalysed transfer chlorination.

Halogenated organic pollutants (HOPs) are causing a significant environmental and human health crisis due to their high levels of toxicity, persistence and bioaccumulation. Urgent action is required to develop effective approaches for the reduction and reuse of HOPs. Whereas current strategies focus primarily on the degradation of HOPs, repurposing them is an alternative approach, albeit a challenging task. Here we discover that alkyl bromide can act as a catalyst for the transfer of chlorine using alkyl chloride as the chlorine source. We demonstrate that this approach has a wide substrate scope, and we successfully apply it to reuse HOPs that include dichlorodiphenyltrichloroethane, hexabromocyclododecane, chlorinated paraffins, chloromethyl polystyrene and poly(vinyl chloride) (PVC). Moreover, we show that the synthesis of essential non-steroidal anti-inflammatory drugs can be achieved using PVC and hexabromocyclododecane, and we demonstrate that PVC waste can be used directly as a chlorinating agent. Overall, this methodology offers a promising strategy for repurposing HOPs.

Markovnikov Hydrochlorination of Unactivated Alkenes with FeCl3 via a HAT/XAT Sequence.

Hydrochlorination of alkenes is a practical strategy for accessing organic chlorides. Herein, we report the hydrochlorination of unactivated alkenes via a hydrogen atom transfer/halogen atom transfer process using earth-abundant and biocompatible FeCl3 as a chlorine source under extraordinarily mild reaction conditions. The protocol is easy to operate with notable features such as excellent chemoselectivity, remarkable efficiency, a broad substrate scope, and good functional group tolerance. Importantly, the synthetic utility is highlighted by scaled-up reactions, late-stage derivatizations of products, and the modification of sulfonamides.

Catalyst‐free Chloroamination Cyclization Cascade with Sodium Hypochlorite: from N‐(Pentenyl)sulfonylamides to 2‐(1‐Chloromethyl)pyrrolidines

AbstractA mild and catalyst‐free protocol to obtain several 2‐chloromethylpyrrolidines by the use of a commercial solution of sodium hypochlorite is here reported, without the need for a light source. The choice of the solvent revealed to be crucial in the success of the reaction. Mechanistic studies, both experimental and computational, confirmed a radical mechanism, where the deprotonation step, followed by the oxidation of a N‐centered anion to the corresponding radical, allowed 2‐chloromethylpyrrolidines, by a very fast cyclization, to be obtained. Sodium hypochlorite plays the role of both the oxidant and the chlorine source.

Iron Photocatalysis Applied to Oxidative Amidation of Aldehydes with NaCl

AbstractA synthesis of amides from aldehydes promoted by the photoactive complex of Fe2SO4 with 2‐picolinic acid, NaCl as a chlorine source, and Na2S2O8 as a benign oxidant is reported. The reaction is mediated by visible light and is carried out at room temperature in the absence of additives. Fe2SO4 is a readily available earth‐abundant metal (EAMs) salt, which does not need to be prepared and is environmentally sustainable. Both aliphatic and aromatic aldehydes and mono‐ and disubstituted amines have been investigated for this transformation. This study opens intriguing perspectives for extending the application of photoactive complex iron salts toward halogenation processes as well as for C−H activation reactions and contributes to the field of earth‐abundant metal based catalysis.

Source analysis of chlorine in municipal solid waste under waste classification: a case study of Hangzhou, China.

Inorganic chlorine is susceptible to water and soil salinization due to its non-degradability and high mobility. To clarify the environmental risks associated with the active inorganic chlorine in municipal solid waste (MSW), the specific characteristics and contributions of inorganic chlorine in different MSW categories were investigated in this study. MSW samples were collected from eight representative waste classification residential areas in Hangzhou, China. It was found that the inorganic chlorine content in different MSW categories varied significantly (0-113 mg/g). Perishable waste, paper, and plastic were found to be the main sources of inorganic chlorine in MSW. A four-category classification system was used to quantify the contribution of inorganic chlorine from each waste category. It was found that the misclassification of inorganic chlorine contributions from perishable waste and other waste accounted for 51.96% and 48.04%, respectively. However, when correctly classified into the four-category system, their contributions were reduced to 67.14% and 30.65%, respectively. Therefore, MSW classification showed a significant reduction in the overall contribution of inorganic chlorine. The misclassification reduces the contribution of inorganic chlorine to 48.04%, while correct classification increases the reduction to 69.35%.

Photocatalytic chloride-to-chlorine conversion by ionic iron in aqueous aerosols: a combined experimental, quantum chemical, and chemical equilibrium model study

Abstract. Prior aerosol chamber experiments show that the ligand-to-metal charge transfer absorption in iron(III) chlorides can lead to the production of chlorine (Cl2/Cl). Based on this mechanism, the photocatalytic oxidation of chloride (Cl−) in mineral dust–sea spray aerosols was recently shown to be the largest source of chlorine over the North Atlantic. However, there has not been a detailed analysis of the mechanism that includes the aqueous formation equilibria and the absorption spectra of the iron chlorides nor has there been an analysis of which iron chloride is the main chromophore. Here we present the results of experiments measuring the photolysis of FeCl3 ⋅ 6H2O in specific wavelength bands, an analysis of the absorption spectra of FeCln3-n (n=1 … 4) made using density functional theory, and the results of an aqueous-phase model that predicts the abundance of the iron chlorides with changes in pH and iron concentrations. Transition state analysis is used to determine the energy thresholds of the dissociations of the species. Based on a speciation model with conditions extending from dilute water droplets and acidic seawater droplets to brine and salty crust, as well as the absorption rates and dissociation thresholds, we find that FeCl2+ is the most important species for chlorine production for a wide range of conditions. The mechanism was found to be active in the range of 400 to 530 nm, with a maximum around 440 nm. We conclude that iron chlorides will form in atmospheric aerosols from the combination of iron(III) cations with chloride and that they will be activated by sunlight, generating chlorine (Cl2/Cl) from chloride (Cl−) in a process that is catalytic in both chlorine and iron.

Microwave-Assisted One-Pot Telescoped Synthesis of 2-Amino-1,3-thiazoles, Selenazoles, Imidazo[1,2-a]pyridines, and Other Heterocycles from Alcohols.

Primary and secondary alcohols have been converted into 2-amino-1,3-thiazoles under microwave irradiation, employing trichloroisocyanuric acid (TCCA) as a dual oxidant and chlorine source, TEMPO as a co-oxidant, and thiourea. Secondary alcohols underwent a single-stage, one-pot conversion process, while primary alcohols required a two-stage, one-pot procedure. Both transformations were completed within minutes (25-45 min). The versatility of this protocol extends to the synthesis of other heterocycles, including 1,3-selenazoles, 2-aminoimidazoles, imidazo[1,2-a]pyridines, quinoxalines, and hydrazino thiazoles by replacing thiourea with the appropriate surrogates.

Visible-Light-Driven Oxidative Chlorination of Alkyl sp3 C–H Bonds with HCl/Air at Room Temperature

AbstractAn aerobic chlorination of alkyl sp3 C–H bonds of functionalized alkanes and simple alkanes has been established successfully under visible light at room temperature. The reaction is performed in the presence of catalytic NaNO2 using HCl or NaCl/acid as a chlorine source and air as a terminal oxidant under atmospheric pressure. It is suggested that NOCl from NaNO2/HCl is a crucial species in the catalytic cycle involving an aerobic oxidation and a photochemical radical chlorination.

Stereoselective Electrophilic Chlorination of β,β-Disubstituted Enesulfinamides with Chloramine-T: Asymmetric Synthesis of Acyclic α,α-Disubstituted α-Chlorinated Carbonyl Surrogates.

Enamine and iminium ion-mediated asymmetric organocatalysis was not successful in achieving highly stereoselective α-chlorination of acyclic α,α-disubstituted carbonyls. To address this limitation, an alternative method was developed, which involved the use of geometry-defined persubstituted enesulfinamides to intercept the electrophilic chlorinating reagent. This approach enables the asymmetric construction of challenging acyclic α,α-disubstituted α-chlorinated ketimines with a high degree of stereoselectivity. The use of chloramine-T, a cost-effective and stable chlorine source rarely utilized in asymmetric electrophilic chlorination, plays a crucial role in achieving superior stereocontrol.

Electrochemical Synthesis of Aryl Chlorides Using HCl as the Chlorine Source

Electrochemical Synthesis of Aryl Chlorides Using HCl as the Chlorine Source

Liquid Metal Mediated Heterostructure Fluoride Solid Electrolytes of High Conductivity and Air Stability for Sustainable Na Metal Batteries.

Fluoride-based solid electrolytes (SEs) have emerged as a promising component for high-energy-density rechargeable solid-state batteries (SSBs) in view of their wide electrochemical window, high air stability, and interface compatibility, but they still face the challenge of low ion conductivity and the lack of a desired structure for sodium metal SSBs. Here, we report a sodium-rich heterostructure fluoride SE, Na3GaF6-Ga2O3-NaCl (NGFOC-G), synthesized via in situ oxidation of liquid metal gallium and in situ chlorination using low-melting GaCl3. The distinctive features of NGFOC-G include single-crystal Na3GaF6 domains within an open-framework structure, composite interface decoration of Ga2O3 and NaCl with a concentration gradient, exceptional air stability, and high electrochemical oxidation stability. By leveraging the penetration of gallium at NaF grain boundaries and the in situ self-oxidation to form Ga2O3 nanodomains, the solid-phase reaction kinetics of NaF and GaF3 is activated for facilitating the synthesis of main component Na3GaF6. The introduction of a small amount of a chlorine source during synthesis further softens and modifies the boundaries of Na3GaF6 along with Ga2O3. Benefiting from the enhanced interface ion transport, the optimized NGFOC-G exhibits an ionic conductivity up to 10-4 S/cm at 40 °C, which is the highest level reported among fluoride-based sodium-ion SEs. This SE demonstrates a "self-protection" mechanism, where the formation of a high Young's modulus transition layer rich in NaF and Na2O under electrochemical driving prevents the dendrite growth of sodium metal. The corresponding Na/Na symmetric cells show minimal voltage hysteresis and stable cycling performance for at least 1000 h. The Na/NGFOC-G/Na3V2(PO4)3 cell demonstrates stable capacity release around 100 mAh/g at room temperature. The Na/NGFOC-G/FeF3 cell delivers a high capacity of 461 mAh/g with an excellent stability of conversion reaction cycling.