Journal articles: 'Halogen-free compounds'

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Sauerwein, Reiner. "Excellent Flow- and Conveyance- Behaviour, Low Dust Emission and Outstanding Properties of Halogen Free Flame Retardant Compounds Realized by a New Generation of Aluminium-Tri-Hydrate." Polymers and Polymer Composites 11, no. 2 (February 2003): 203–12. http://dx.doi.org/10.1177/096739110301100202.

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“A new non-post treated fine precipitated aluminium-tri-hydrate quality has been developed, offering the basis for the next generation of halogen free flame retardant compounds. The paper outlines the excellent powder handling properties and the outstanding performance of highly filled polymers” Halogen free flame retardant plastics for cable insulation and sheathing, known as LSFOH (low smoke, free of halogen) compounds became large volume products since the market introduction of fine precipitated aluminium-tri-hydrates (ATH) qualities in the beginning of the 80's. While former ATH improvements focused on product purity and electrical properties, recent developments responded to the growing importance of continuous compounding techniques. The focus on compound output and processing behaviour of fillers was answered by ATH qualities having higher bulk density and better flow properties. These improvements have been achieved by physical and chemical post treatments of the precipitated products. While giving the expected benefits in powder handling, detrimental effects have been observed for mechanical and especially for electrical compound properties. A new generation of non-post treated fine precipitated ATH has now been developed, offering excellent powder processing, but also outstanding compound properties. The paper outlines filler processing behaviour, presenting results of flow-, conveyance-, metering and dust-behaviour investigations. Special attention is given to compound user's benefits. Low melt viscosities and high extrusion speed in the production of LSFOH cables are identified as core properties of compounds filled with this new ATH quality.

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Wei, Ming, Daniel Murphy, Carol Barry, and Joey Mead. "HALOGEN-FREE FLAME RETARDANTS FOR WIRE AND CABLE APPLICATIONS." Rubber Chemistry and Technology 83, no. 3 (September 1, 2010): 282–302. http://dx.doi.org/10.5254/1.3525686.

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Abstract Flame retardants play a very important role in avoiding fire risks in wire and cable applications due to heat generation by current or outside sources. Halogen flame retardants are typically used to ensure good flammability. The halogen flame retardants, however, are under close scrutiny because of their potential to give off corrosive compounds when the materials are burned, as well as other safety, environmental, and health issues. For wire and cable industries, halogen-free flame retardant additives, such as nanoclays, nanotubes, aluminium trihydrate, or magnesium hydroxide are potential alternatives. Types of halogen-free flame retardant additives used in wire and cable constructions are reviewed and discussed.

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Gusarova, Nina K., Svetlana N. Arbuzova, and Boris A. Trofimov. "Novel general halogen-free methodology for the synthesis of organophosphorus compounds." Pure and Applied Chemistry 84, no. 3 (January 17, 2012): 439–59. http://dx.doi.org/10.1351/pac-con-11-07-11.

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The use of novel general halogen-free methodology for the synthesis of phosphines, phosphine chalcogenides, and phosphinic acids from elemental phosphorus and alkenes and alkynes in the superbase suspensions is described.

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Svatikov, A. Yu, and I. D. Simonov-Emelyanov. "THE THERMAL STABILITY OF POLYMER CABLE COMPOUNDS WITH A FLAME-RETARDING FILLER." Fine Chemical Technologies 13, no. 6 (December 28, 2018): 35–41. http://dx.doi.org/10.32362/2410-6593-2018-13-6-35-41.

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Currently, halogen-free cable compositions are becoming increasingly common in the manufacture of cable compositions. The concept of halogen-free or “zero halogen” becomes a symbol of fire resistance, low-smoke characteristics, low toxicity of volatile products of combustion, the absence of the toxic, corrosive and irritating gas - hydrogen chloride - and other hydrogen halides in the volatile products. More and more manufacturers of cable products are beginning to pay increasing attention to the problems of processing, toxicity and fire safety. It should be noted that the requirements for improving the fire safety of cable products are constantly becoming tougher, since the main problem of most of these polymeric materials is their flammability, high smoke generation and high flame spread rate. In this regard, there is a burning question to increase these characteristics and bring them to the level of compounds based on PVC. The main way to increase the flame-retardant characteristics of halogenfree cable compositions is to introduce mineral fire retardants into these compositions. The study of the composition and packaging of these mineral fillers-flame retardants makes it possible to increase the level of flame-retardant characteristics of halogen-free cable compositions. The paper presents the results of studies on the thermal stability of cable compositions based on PE + EVA mixtures containing magnesium hydroxide crystalline hydrate as a filler-flame retardant. It is shown that cable compositions containing magnesium hydroxide crystal hydrate are characterized by higher heat resistance and thermal stability (~ 2-fold) compared to a polymeric matrix based on PE + SEVA. This allows to process them at high temperatures (more than 200°C) by extrusion and pressure casting.

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Assim, K., M. Melzer, M. Korb, T. Rüffer, A. Jakob, J. Noll, C. Georgi, S. E. Schulz, and H. Lang. "Bis(β-diketonato)- and allyl-(β-diketonato)-palladium(ii) complexes: synthesis, characterization and MOCVD application." RSC Advances 6, no. 104 (2016): 102557–69. http://dx.doi.org/10.1039/c6ra22887a.

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Khan, Imad, Nasir Shehzad, Iftikhar Ahmad, Zahid Ali, and S. Jalali-Asadabadi. "First-principle studies of the optoelectronic properties of ASnF3 (A = Na, K, Rb and Cs)." International Journal of Modern Physics B 31, no. 21 (August 18, 2017): 1750148. http://dx.doi.org/10.1142/s021797921750148x.

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In this paper, we communicate a new type of Auger-free luminescence (AFL) compounds, alkali tin fluorides ASnF3 (A = Na, K, Rb and Cs). The luminescence in these compounds originates due to the electron transition from the top valence band (VB) of tin-[Formula: see text] orbital to the outermost core levels of halogen, i.e., halogen-[Formula: see text] orbital ([Formula: see text]-[Formula: see text] transitions). The AFL of these compounds is expected to be of L-type. Furthermore, the electronic band structures and optical properties such as dielectric functions, refractive index and energy loss function are also investigated using ab initio calculations.

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Edis, Haj Bloukh, Abu Sara, Bhakhoa, Rhyman, and Ramasami. "“Smart” Triiodide Compounds: Does Halogen Bonding Influence Antimicrobial Activities?" Pathogens 8, no. 4 (October 10, 2019): 182. http://dx.doi.org/10.3390/pathogens8040182.

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Antimicrobial agents containing symmetrical triiodides complexes with halogen bonding may release free iodine molecules in a controlled manner. This happens due to interactions with the plasma membrane of microorganisms which lead to changes in the structure of the triiodide anion. To verify this hypothesis, the triiodide complex [Na(12-crown-4)2]I3 was prepared by an optimized one-pot synthesis and tested against 18 clinical isolates, 10 reference strains of pathogens and five antibiotics. The antimicrobial activities of this symmetrical triiodide complex were determined by zone of inhibition plate studies through disc- and agar-well-diffusion methods. The triiodide complex proved to be a broad spectrum microbicidal agent. The biological activities were related to the calculated partition coefficient (octanol/water). The microstructural analysis of SEM and EDS undermined the purity of the triiodide complex. The anionic structure consists of isolated, symmetrical triiodide anions [I-I-I]- with halogen bonding. Computational methods were used to calculate the energy required to release iodine from [I-I-I]- and [I-I···I]-. The halogen bonding in the triiodide ion reduces the antibacterial activities in comparison to the inhibitory actions of pure iodine but increases the long term stability of [Na(12-crown-4)2]I3.

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Pravst, Igor, Marko Zupan, and Stojan Stavber. "Introduction of Halogen Atoms into Organic Compounds Under Solvent- Free Reaction Conditions." Current Organic Chemistry 13, no. 1 (January 1, 2009): 47–70. http://dx.doi.org/10.2174/138527209787193819.

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Ryu, Je Hong, Ki Seop Choi, and Whan Gun Kim. "Latent catalyst effects in halogen-free epoxy molding compounds for semiconductor encapsulation." Journal of Applied Polymer Science 96, no. 6 (2005): 2287–99. http://dx.doi.org/10.1002/app.21001.

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10

Markwart, Battig, Velencoso, Pollok, Schartel, and Wurm. "Aromatic vs. Aliphatic Hyperbranched Polyphosphoesters as Flame Retardants in Epoxy Resins." Molecules 24, no. 21 (October 29, 2019): 3901. http://dx.doi.org/10.3390/molecules24213901.

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The current trend for future flame retardants (FRs) goes to novel efficient halogen-free materials, due to the ban of several halogenated FRs. Among the most promising alternatives are phosphorus-based FRs, and of those, polymeric materials with complex shape have been recently reported. Herein, we present novel halogen-free aromatic and aliphatic hyperbranched polyphosphoesters (hbPPEs), which were synthesized by olefin metathesis polymerization and investigated them as a FR in epoxy resins. We compare their efficiency (aliphatic vs. aromatic) and further assess the differences between the monomeric compounds and the hbPPEs. The decomposition and vaporizing behavior of a compound is an important factor in its flame-retardant behavior, but also the interaction with the pyrolyzing matrix has a significant influence on the performance. Therefore, the challenge in designing a FR is to optimize the chemical structure and its decomposition pathway to the matrix, with regards to time and temperature. This behavior becomes obvious in this study, and explains the superior gas phase activity of the aliphatic FRs.

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Habibah, A. I. H. Dayang, and Abd Rahim Ruhida. "The Effects of Halogen-Free Flame Retardant Additives in Epoxidized Natural Rubber (ENR)." Advanced Materials Research 1107 (June 2015): 131–36. http://dx.doi.org/10.4028/www.scientific.net/amr.1107.131.

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Legislation on fire safety requirements especially in the USA and UK has been the driving force behind the use of halogen-free flame retardants (FR) in recent years. The present study describes the effect of inorganic fillers, namely aluminium hydroxides (ATH) on epoxidized natural rubber (ENR) in order to increase its flame retardant capability. Two different types of ATH, a standard type Apyral 60 CD (ATH 60) and a submicron sized Apyral 200 SM (ATH 200) were used. The flame-retardant ENR composite was characterized by limiting oxygen index (LOI), UL-94V, and thermogravimetric analysis (TGA) to study the combustion behavior and thermal stability. The finer particles size (ATH 200) as expected produced better flame retardant properties (measured by LOI) compared to ATH 60; however, the difference between the values is marginal. It was also observed that a combination of 100 pphr ATH 200 and 60 pphr ATH 60 gave the highest LOI value (29.4%) in ENR compounds. The compound was V0 rated in UL-94V burn test. Even at the higher loading, it was also found that the compound exhibited lower viscosity indicating its easier processability.

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Mishra, Nikita, and Dilip Vasava. "Recent developments in s-triazine holding phosphorus and nitrogen flame-retardant materials." Journal of Fire Sciences 38, no. 6 (September 3, 2020): 552–73. http://dx.doi.org/10.1177/0734904120952347.

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Flame retardants are chemical compounds when mixed or incorporated in to polymers provide varying degrees of flammability protection. Flammable polymeric materials are ubiquitous with a wide array of applications. However, recent studies have shown potential environmental and health concerns with certain halogen-containing flame retardants. Thus, it has now become a necessity to explore new and effective materials that are safer and environmentally benign. In this context, halogen-free phosphorus- and nitrogen-containing flame retardants have attracted much attention worldwide. Moreover, s-triazine is the central focus because of its excellent charring effect. General strategies for synthesizing s-triazine compounds mostly via nucleophilic substitution reaction have been highlighted. This review provides a comprehensive description on design and synthesis of flame-retardant materials with significant flammability performance.

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13

Moon, SungCheal, ByungWook Jo, and Richard J. Farris. "Flame resistance and foaming properties of NBR compounds with halogen-free flame retardants." Polymer Composites 30, no. 12 (December 2009): 1732–42. http://dx.doi.org/10.1002/pc.20794.

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14

Gusarova, Nina K., Svetlana N. Arbuzova, and Boris A. Trofimov. "ChemInform Abstract: Novel General Halogen-Free Methodology for the Synthesis of Organophosphorus Compounds." ChemInform 43, no. 44 (October 4, 2012): no. http://dx.doi.org/10.1002/chin.201244240.

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15

Luyt, Adriaan Stephanus, Sarah Shahid Malik, Soumia Abderrazak Gasmi, Athanasios Porfyris, Anna Andronopoulou, Dimitrios Korres, Stamatina Vouyiouka, et al. "Halogen-Free Flame-Retardant Compounds. Thermal Decomposition and Flammability Behavior for Alternative Polyethylene Grades." Polymers 11, no. 9 (September 10, 2019): 1479. http://dx.doi.org/10.3390/polym11091479.

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The effect of six halogen-free flame retardant (FR) formulations was investigated on the thermal stability of two low-density polyethylenes (LDPE) and one linear low-density polyethylene (LLDPE), by means of thermogravimetric analysis (TGA) under nitrogen and air atmosphere. The relative data were combined with flammability properties and the overall performance of the FRs was correlated with the type of branching in the polyethylene grades and to their processing behavior. The thermal degradation kinetics was further determined based on the Kissinger and Coats-Redfern methods. In terms of flammability, the addition of a triazine derivative and ammonium polyphosphate at a loading of 35 wt. %. was found to be the most efficient, leading to UL 94 V0 ranking in the case of the LDPE grade produced in an autoclave reactor.

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16

Kim, Woojung, and Dong Quy Hoang Thi. "Organo-phosphorus flame retardants when applied to acrylonitrile-butadiene-styrene copolymer." Science and Technology Development Journal - Natural Sciences 1, no. 6 (December 7, 2018): 192–96. http://dx.doi.org/10.32508/stdjns.v1i6.629.

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In order to find an effective halogen-free flame retardant for acrylonitrile-butadienestyrene copolymer (ABS), organo-phosphorus compounds were studied and their flame retarding performances were determined by UL 94 vertical test. It is found that the flame retardancy strongly depends on phosphorus (P) content of organophosphorus compounds. Only the mixture of ABS with 2-(6-oxido-6Hdibenz< c,e><1,2>oxaphosphorin-6-yl) methyl diethyl phosphinate (ODOPM-DE), which has the highest P content, i.e., 17.68 % gives V-0 rating for the 70/30 composition.

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Naskar, K., S. Mohanty, and G. B. Nando. "Development of thin-walled halogen-free cable insulation and halogen-free fire-resistant low-smoke cable-sheathing compounds based on polyolefin elastomer and ethylene vinyl acetate blends." Journal of Applied Polymer Science 104, no. 5 (2007): 2839–48. http://dx.doi.org/10.1002/app.25870.

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Hwang, Chan-Yun, Jong-Seok Yang, Baek-Yong Sung, Ji-Yeon Kim, and Dae-Hee Park. "A Study on Mechanical Properties Improvement of Halogen-free Flame Retardant Compounds by Nanoclay Addition." Journal of the Korean Institute of Electrical and Electronic Material Engineers 28, no. 2 (February 1, 2015): 126–30. http://dx.doi.org/10.4313/jkem.2015.28.2.126.

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Kikushima, Kotaro, Haruka Koyama, Kazuki Kodama, and Toshifumi Dohi. "Nucleophilic Aromatic Substitution of Polyfluoroarene to Access Highly Functionalized 10-Phenylphenothiazine Derivatives." Molecules 26, no. 5 (March 4, 2021): 1365. http://dx.doi.org/10.3390/molecules26051365.

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Nucleophilic aromatic substitution (SNAr) reactions can provide metal-free access to synthesize monosubstituted aromatic compounds. We developed efficient SNAr conditions for p-selective substitution of polyfluoroarenes with phenothiazine in the presence of a mild base to afford the corresponding 10-phenylphenothiazine (PTH) derivatives. The resulting polyfluoroarene-bearing PTH derivatives were subjected to a second SNAr reaction to generate highly functionalized PTH derivatives with potential applicability as photocatalysts for the reduction of carbon–halogen bonds.

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Marx, Rupert, and Hans Michael Mayer. "Darstellung und Lithiumteilstruktur von Lithiumnitridtribromid, Li6NBr3 und Lithiumnitridtriiodid, Li6NI3 / Preparation and Lithium Sublattice of Lithium Nitride Trihalides, Li6NHal3 (Hal = Br, I)." Zeitschrift für Naturforschung B 51, no. 4 (April 1, 1996): 525–30. http://dx.doi.org/10.1515/znb-1996-0415.

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Abstract Single phase Li6NBr3 was prepared by the reaction of Li3N and dry, OH-free LiBr at 450°C. It is the most bromide rich compound in the quasi binary system Li3-2xN1-xBrx. The crystal structures of Li6NBr3 and of isotypic Li6NI3, have been redetermined from neutron powder diffraction data. Both compounds crystallize in the cubic space group Fm3m (No. 225), a(Li6NBr3) = 894.18(7), a(Li6NI3) = 951.7(1) pm with 4 formula units per unit cell. The anion sublattice comprises a rock salt like arrangement of N with one of the three halogen atoms (Hal1), with the remaining halogen atoms in the resulting N4Hal4 cubes. The structure may be regarded as an ordered AX3 variation of a body-centered packing. The lithium atoms are disordered over the 96 (distorted) tetrahedral NX3 holes in such a way that of the four neighbouring, face-sharing NBr3 tetrahedra along an N-H all-connection line only one is occupied. The resulting Li coordination polyhedron around N (and Hal1) is a distorted octahedron with 6 equidistant Li atoms. Hal2 is surrounded by 12 Li atoms. The Li6NHal3 structure may be regarded as an anti-form of the cryolite structure.

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Nishad, Ravi K., Karuna S. Shukla, and Pooja A. Chawla. "Design and Synthesis of 2-Substituted Benzothiazole Derivatives as Antioxidant and Antimicrobial Agents." Current Bioactive Compounds 16, no. 8 (November 10, 2020): 1242–48. http://dx.doi.org/10.2174/1573407216666200128160438.

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Background: An upsurge in the number of antibiotic-resistant microbial infections has warranted the discovery and development of new antibiotics. This is a matter of great concern for effective therapy for a search of novel antimicrobial agents. Literature has a number of reports of involvement of oxidative stress due to an imbalance between the generation and neutralization of free radicals in many diseases. Heterocyclic compounds have been involved in the treatment of various disorders. Benzothiazole is one such heterocyclic nucleus having benzene ring merged with the thiazole ring. Among the various substitutions possible in this nucleus, substitutions at position-2 have already been reported with potential bioactivities. Thus, different substituted compounds have been synthesized which could serve as antimicrobials and antioxidants. Methods: Benzothiazole derivatives (B1-B7) were synthesized by two-step reactions and the structures were confirmed through infrared, mass and NMR spectroscopy. The compounds were evaluated for in vitro antioxidant and antimicrobial activities using standard methods. Results: The results of antibacterial and antifungal activity showed that compound B4 exhibited maximum activity against all the tested strains of microorganisms with the zone of inhibition 17.1-18.5 mm and MIC value 1.1-1.5 μg/mL. Compound B5 exhibited potent antioxidant activity. Conclusion: The compounds substituted with halogen on the aryl ring showed increased antimicrobial activity as seen in the case of compound B4 (6-fluoro). The compounds substituted with a hydroxyl group (B5) exhibited good antioxidant activity.

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Thirumal, M., Dipak Khastgir, G. B. Nando, Y. P. Naik, and Nikhil K. Singha. "Halogen-free flame retardant PUF: Effect of melamine compounds on mechanical, thermal and flame retardant properties." Polymer Degradation and Stability 95, no. 6 (June 2010): 1138–45. http://dx.doi.org/10.1016/j.polymdegradstab.2010.01.035.

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KICKO-WALCZAK, EWA. "Novel halogen-free flame retardants - flame retardation of unsaturated polyester resins with use of boron compounds." Polimery 53 (February 2008): 126–32. http://dx.doi.org/10.14314/polimery.2008.126.

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24

Gargala, Gilles, Laetitia Le Goff, Jean-Jacques Ballet, Loic Favennec, Andrew V. Stachulski, and Jean-François Rossignol. "Evaluation of New Thiazolide/Thiadiazolide Derivatives Reveals Nitro Group-Independent Efficacy against In Vitro Development of Cryptosporidium parvum." Antimicrobial Agents and Chemotherapy 54, no. 3 (January 4, 2010): 1315–18. http://dx.doi.org/10.1128/aac.00614-09.

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ABSTRACT Thirty-nine new thiazolide/thiadiazolide compounds were compared with the nitrothiazole nitazoxanide for activity against Cryptosporidium parvum development in HCT-8 cells. Twenty-seven agents exerted ≥90% inhibition. Agents with a lower 50% inhibitory concentration (IC50) than nitazoxanide were either NO2 or halogen 5 substituted on the thiazole moiety. Other 5 substitutions such as methyl, C3H7, C6H11, H, SO2CH3, and SCH3 negatively impacted activity. Five-substituted deacetylated analogues exhibited higher IC50s than their acetylated counterparts. Halogeno-thiazolide/thiadiazolides may provide valuable nitro-free alternatives to nitazoxanide.

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Rossi, Laura I., and Manuel I. Velasco. "Alternatives to free molecular halogens as chemoselective reactants: Catalysis of organic reactions with reusable complexes of halogen metal salts." Pure and Applied Chemistry 84, no. 3 (February 6, 2012): 819–26. http://dx.doi.org/10.1351/pac-con-11-07-13.

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Organometallic complexes of halogen metallic salts have been used as catalysts in different organic reactions, mainly the oxidation of organic compounds. Their use has not only allowed the reduction of the amounts of catalyst (since they can be reused) but also a lower generation of byproducts and wastes. The different reaction media developed through the research were analyzed by several green parameters, and the best results were obtained with complexes that have cyclodextrins as organic ligands. The proposed methodology is an alternative to use of molecular halogen as oxidant or catalyst when halogens are significant chemoselective reactants.

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Hu, Yixin, Lihong Zhou, and Wenjun Lu. "Transition-Metal- and Halogen-Free Oxidation of Benzylic sp3 C–H Bonds to Carbonyl Groups Using Potassium Persulfate." Synthesis 49, no. 17 (June 6, 2017): 4007–16. http://dx.doi.org/10.1055/s-0036-1588429.

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Aryl carbonyl compounds including acetophenones, benzophenones, imides, and benzoic acids are prepared from benzyl substrates using potassium persulfate as oxidant with catalytic pyridine in acetonitrile under mild conditions. Neither transition metals nor halogens are involved in the reactions.

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Hwang, Chan-Yun, Jong-Seok Yang, Baeg-Yong Seong, Ji-Yeon Kim, and Dae-Hee Park. "A Study on Perpendicular Flame Retardant Characteristic Improvement of Halogen-free Flame Retardant Compounds by Nanoclay Addition." Journal of the Korean Institute of Electrical and Electronic Material Engineers 28, no. 1 (January 1, 2015): 51–56. http://dx.doi.org/10.4313/jkem.2015.28.1.51.

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Cogen, Jeffrey M., Thomas S. Lin, and Richard E. Lyon. "Correlations between pyrolysis combustion flow calorimetry and conventional flammability tests with halogen-free flame retardant polyolefin compounds." Fire and Materials 33, no. 1 (January 2009): 33–50. http://dx.doi.org/10.1002/fam.980.

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Martínez-Cifuentes, Maximiliano, Boris Weiss-López, and Ramiro Araya-Maturana. "Theoretical Study about the Effect of Halogen Substitution on the Reactivity of Antitumor 3-Formylchromones and Their Free Radicals." Journal of Chemistry 2017 (2017): 1–5. http://dx.doi.org/10.1155/2017/9254831.

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The mandatory presence of a chlorine atom on the aromatic ring of 6-hydroxy-3-formyl angular chromones, on the respiration inhibition of mammary carcinoma mouse, is explained through a computational study of these compounds. This study analyzes the reactivity of the neutral molecules and their free radicals, in gas phase and with water solvation, incorporated by the polarizable continuum medium (PCM) approach. Electrophilic reactivities were evaluated using Fukui (f+) and Parr (P+) functions. The stabilities of radical species formed by the abstraction of a hydrogen atom from the O-H bond were evaluated by bond dissociation enthalpy (BDE) and spin density (SD) calculations. This study has potential implications for the design of chromone analogues as anticancer compounds.

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Linh, Pham Thi Thuy, and Hoang Thi Dong Quy. "Thermoplastic polyurethane flame retardant using phosphorus/phosphorus-nitrogen compounds." Science and Technology Development Journal - Natural Sciences 2, no. 1 (January 6, 2019): 91–95. http://dx.doi.org/10.32508/stdjns.v2i1.680.

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In order to improve fire performance of thermoplastic polyurethane (TPU) material, halogen-free flame retardants (triphenylphosphate- TPP and diamonium hydrogen phosphate-DAP) were studied in an attempt to obtain UL-94V ratings. The fire behaviors and thermal stability properties were evaluated using UL-94 vertical test and thermogravimetric analysis (TGA). The UL- 94V results showed that V-0 ratings were achieved at 5 wt% of DAP or 7.5 wt% loading of TPP. The incorporation of these flame retardant (FR) increases the flame retardant properties as well as the amounts of charred residues protecting the mixture from further degradation. This assertion could be accepted when observing that the char residual of TPU/DAP mixture at 500–600oC was much higher than that of neat TPU. The char layer limited the amount of fuel available and insulate the underlying composite material from the flame and, thus, make further degradation more difficult. The mechanism of flame retardants was also discussed in this study.

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Baby, Aloshy, Svetlana Tretsiakova-McNally, Malavika Arun, Paul Joseph, and Jianping Zhang. "Reactive and Additive Modifications of Styrenic Polymers with Phosphorus-Containing Compounds and Their Effects on Fire Retardance." Molecules 25, no. 17 (August 19, 2020): 3779. http://dx.doi.org/10.3390/molecules25173779.

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Polystyrene, despite its high flammability, is widely used as a thermal insulation material for buildings, for food packaging, in electrical and automotive industries, etc. A number of modification routes have been explored to improve the fire retardance and boost the thermal stability of commercially important styrene-based polymeric products. The earlier strategies mostly involved the use of halogenated fire retardants. Nowadays, these compounds are considered to be persistent pollutants that are hazardous to public and environmental health. Many well-known halogen-based fire retardants, regardless of their chemical structures and modes of action, have been withdrawn from built environments in the European Union, USA, and Canada. This had triggered a growing research interest in, and an industrial demand for, halogen-free alternatives, which not only will reduce the flammability but also address toxicity and bioaccumulation issues. Among the possible options, phosphorus-containing compounds have received greater attention due to their excellent fire-retarding efficiencies and environmentally friendly attributes. Numerous reports were also published on reactive and additive modifications of polystyrene in different forms, particularly in the last decade; hence, the current article aims to provide a critical review of these publications. The authors mainly intend to focus on the chemistries of phosphorous compounds, with the P atom being in different chemical environments, used either as reactive, or additive, fire retardants in styrene-based materials. The chemical pathways and possible mechanisms behind the fire retardance are discussed in this review.

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Vaz, Patrícia A. A. M., João Rocha, Artur M. S. Silva, and Samuel Guieu. "Benzimidazole-Based N,O Boron Complexes as Deep Blue Solid-State Fluorophores." Materials 14, no. 15 (July 31, 2021): 4298. http://dx.doi.org/10.3390/ma14154298.

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Benzimidazole-based boranils were designed and synthesized in order to assess the influence of halogen substituents on their optoelectronic properties. All compounds are photoluminescent in solution and solid state. Compared to the free ligands, the new boranils emit at a lower wavelength, by elimination of the excited-state intramolecular proton transfer observed with the ligands. In the solid state, some of the boranils exhibit a deep blue emission, presenting Commission Internationale de l’Éclairage (CIE) coordinates with an x-component of less than 0.16 and a y-component smaller than 0.04, highly desired values for the development of blue emitting materials.

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McGuigan, C., S. Turner, S. R. Nicholls, T. J. O'Connor, and D. Kinchington. "Haloalkyl Phosphate Derivatives of AZT as Inhibitors of HIV: Studies in the Phosphate Region." Antiviral Chemistry and Chemotherapy 5, no. 3 (June 1994): 162–68. http://dx.doi.org/10.1177/095632029400500304.

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Novel haloalkyl phosphate derivatives of the anti-HIV nucleoside analogue AZT were prepared by phosphorochloridate chemistry. These materials were designed to act as labile membrane-soluble prodrugs of the bio-active free nucleotides. In vitro evaluation revealed the compounds to have a pronounced and selective antiviral action, which varied greatly with the structure of the phosphate moiety. By comparison to simple dialkyl phosphates, which are inactive against HIV-1, the introduction of halogen atoms into the alkyl (phosphate) chains led to anti-HIV activity. Although halogen substitution in just one alkyl chain was sufficient for biological activity, substitution in the second alkyl chain further enhanced activity. Conversely, stabilization of the second chain, by conversion to a phosphonate, led to a reduction in activity. In one case, the diastereo-isomers resulting from mixed stereochemistry at the phosphate centre were separated, and found to differ in activity by one order of magnitude. Lastly, the bis(mono- and di-chloroethyl) phosphates were prepared and found to display moderate anti-HIV activity.

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Lehrer, E., G. Hönninger, and U. Platt. "The mechanism of halogen liberation in the polar troposphere." Atmospheric Chemistry and Physics Discussions 4, no. 3 (June 28, 2004): 3607–52. http://dx.doi.org/10.5194/acpd-4-3607-2004.

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Abstract. Sudden depletions of tropospheric ozone during spring were reported from the Arctic and also from Antarctic coastal sites. Field studies showed that those depletion events are caused by reactive halogen species, especially bromine compounds. However the source and seasonal variation of reactive halogen species is still not completely understood. There are several indications that the halogen mobilisation from the sea ice surface of the polar oceans may be the most important source for the necessary halogens. Here we present a 1-D model study aimed at determining the primary source of reactive halogens. The model includes gas phase and heterogeneous bromine and chlorine chemistry as well as vertical transport between the surface and the top of the boundary layer. The autocatalytic Br release by photochemical processes (bromine explosion) and subsequent rapid bromine catalysed ozone depletion is well reproduced in the model and the major source of reactive bromine appears to be the sea ice surface. The sea salt aerosol alone is not sufficient to yield the high levels of reactive bromine in the gas phase necessary for fast ozone depletion. However, the aerosol efficiently 'recycles' less reactive bromine species (e.g. HBr) and feeds them back into the ozone destruction cycle. Isolation of the boundary layer air from the free troposphere by a strong temperature inversion was found to be critical for boundary layer ozone depletion to happen. The combination of strong surface inversions and presence of sunlight occurs only during polar spring.

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Nguyen, Hung Kim, Wataru Sakai, and Congtranh Nguyen. "Preparation of a Novel Flame Retardant Formulation for Cotton Fabric." Materials 13, no. 1 (December 20, 2019): 54. http://dx.doi.org/10.3390/ma13010054.

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A novel halogen-free flame-retardant formulation was prepared and coated onto cotton fabrics. The structure of phosphorus compounds in the system was characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and nuclear magnetic resonance spectroscopy (1H-NMR). Results from the ATR-FTIR spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) analyses presented that the flame retardant was coated successfully onto a cotton surface. We investigated the thermal stability and fire-retardant behaviors of cotton fabrics using thermal gravimetric analysis (TGA) and the vertical flame test. We also discuss the mechanism of flame retardance of coated cotton fabrics.

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Perin, Gelson, Patrick Nobre, Daniela Mailahn, Márcio Silva, Thiago Barcellos, Raquel Jacob, Eder Lenardão, Claudio Santi, and Juliano Roehrs. "Synthesis of 4-Organoselanyl-1H-pyrazoles: Oxone®-Mediated Electrophilic Cyclization of α,β-Alkynyl Hydrazones by Using Diorganyl Diselenides." Synthesis 51, no. 11 (March 14, 2019): 2293–304. http://dx.doi.org/10.1055/s-0037-1611747.

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A simple and efficient method for the synthesis of 4‑organoselanyl-1H-pyrazoles has been developed, taking place under metal- and halogen-free conditions. Electrophilic species of selenium were easily generated in situ by the reaction of diorganyl diselenides with Oxone® in ethanol as solvent in an open-flask at 70 °C. These electrophilic selenium species were employed in the selenylation/cyclization of α,β-alkynyl hydrazones, giving the title compounds in moderate to excellent yields. The final species of selenium obtained from the reaction of diphenyl diselenide with Oxone® were characterized by 77Se NMR spectroscopy and high-resolution mass spectrometry (HRMS).

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Koo, J. H., Y. Wang, T. P. Kurosu, K. Chance, A. Rozanov, A. Richter, S. J. Oltmans, et al. "Characteristics of tropospheric ozone depletion events in the Arctic spring: analysis of the ARCTAS, ARCPAC, and ARCIONS measurements and satellite BrO observations." Atmospheric Chemistry and Physics Discussions 12, no. 7 (July 2, 2012): 16219–57. http://dx.doi.org/10.5194/acpd-12-16219-2012.

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Abstract. Arctic ozone depletion events (ODEs) are due to catalytic ozone loss driven by halogen chemistry. The presence of ODEs is affected not only by in situ chemistry but also by transport including advection of ozone-poor air mass and vertical mixing. To better characterize the ODEs, we analyze the combined set of surface, ozonesonde, and aircraft in situ measurements of ozone and bromine compounds during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) and the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) experiments (April 2008). Tropospheric BrO columns retrieved from satellite measurements and back trajectories calculations are used to investigate the characteristics of observed ODEs. The implications of the analysis results for the validation of the retrieval of tropospheric column BrO are also discussed. Time-lagged correlation analysis between in situ (surface and ozonesonde) measurements of ozone and satellite derived tropospheric BrO indicates that the ODEs are due to either local halogen-driven ozone loss or short-range (~1 day) transport from nearby regions with ozone depletion. The effect of in situ halogen-driven loss is also evident in the diurnal variation of surface ozone concentrations at Alert, Canada. High-BrO regions revealed by satellite measurements tend to be collocated with first-year sea ice, particularly over the Chukchi Sea. Aircraft observations indicate low-ozone air mass transported from these high-BrO regions. Correlation analyses of ozone with potential temperature and time-lagged tropospheric BrO column show that the vertical extent of local ozone loss is surprisingly deep (1–2 km) at Resolute and Churchill, Canada. The unstable boundary layer during ODEs at Churchill could potentially provide a source of free tropospheric BrO through convective transport and explain the significant negative correlation between free tropospheric ozone and tropospheric BrO column at this site.

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Lehrer, E., G. Hönninger, and U. Platt. "A one dimensional model study of the mechanism of halogen liberation and vertical transport in the polar troposphere." Atmospheric Chemistry and Physics 4, no. 11/12 (December 6, 2004): 2427–40. http://dx.doi.org/10.5194/acp-4-2427-2004.

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Abstract. Sudden depletions of tropospheric ozone during spring were reported from the Arctic and also from Antarctic coastal sites. Field studies showed that those depletion events are caused by reactive halogen species, especially bromine compounds. However the source and seasonal variation of reactive halogen species is still not completely understood. There are several indications that the halogen mobilisation from the sea ice surface of the polar oceans may be the most important source for the necessary halogens. Here we present a one dimensional model study aimed at determining the primary source of reactive halogens. The model includes gas phase and heterogeneous bromine and chlorine chemistry as well as vertical transport between the surface and the top of the boundary layer. The autocatalytic Br release by photochemical processes (bromine explosion) and subsequent rapid bromine catalysed ozone depletion is well reproduced in the model and the major source of reactive bromine appears to be the sea ice surface. The sea salt aerosol alone is not sufficient to yield the high levels of reactive bromine in the gas phase necessary for fast ozone depletion. However, the aerosol efficiently "recycles" less reactive bromine species (e.g. HBr) and feeds them back into the ozone destruction cycle. Isolation of the boundary layer air from the free troposphere by a strong temperature inversion was found to be critical for boundary layer ozone depletion to happen. The combination of strong surface inversions and presence of sunlight occurs only during polar spring.

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39

Gilman, J. B., J. F. Burkhart, B. M. Lerner, E. J. Williams, W. C. Kuster, P. D. Goldan, P. C. Murphy, et al. "Ozone variability and halogen oxidation within the Arctic and sub-Arctic springtime boundary layer." Atmospheric Chemistry and Physics Discussions 10, no. 6 (June 29, 2010): 15885–919. http://dx.doi.org/10.5194/acpd-10-15885-2010.

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Abstract. The influence of halogen oxidation on the variabilities of ozone (O3) and volatile organic compounds (VOCs) within the Arctic and sub-Arctic atmospheric boundary layer was investigated using field measurements from multiple campaigns conducted in March and April 2008 as part of the POLARCAT project. For the ship-based measurements, a high degree of correlation (r=0.98 for 544 data points collected north of 68° N) was observed between the acetylene to benzene ratio, used as a marker for halogen oxidation, and O3 signifying the vast influence of bromine oxidation throughout the ice-free regions of the North Atlantic. Concurrent airborne and ground-based measurements in the Alaskan Arctic substantiated this correlation and were used to demonstrate that halogen oxidation influenced O3 variability throughout the Arctic boundary layer during these springtime studies. Measurements aboard the R/V "Knorr" in the North Atlantic and Arctic Oceans provided a unique view of the transport of O3-poor air masses from the Arctic Basin to latitudes as far south as 52° N. FLEXPART, a Lagrangian transport model, was used to quantitatively determine the exposure of air masses encountered by the ship to first-year ice (FYI), multi-year ice (MYI), and total ICE (FYI+MYI). O3 anti-correlated with the modeled total ICE tracer (r=−0.86) indicating that up to 73% of the O3 variability measured in the Arctic marine boundary layer could be related to sea ice exposure.

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40

Gilman, J. B., J. F. Burkhart, B. M. Lerner, E. J. Williams, W. C. Kuster, P. D. Goldan, P. C. Murphy, et al. "Ozone variability and halogen oxidation within the Arctic and sub-Arctic springtime boundary layer." Atmospheric Chemistry and Physics 10, no. 21 (November 2, 2010): 10223–36. http://dx.doi.org/10.5194/acp-10-10223-2010.

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Abstract. The influence of halogen oxidation on the variabilities of ozone (O3) and volatile organic compounds (VOCs) within the Arctic and sub-Arctic atmospheric boundary layer was investigated using field measurements from multiple campaigns conducted in March and April 2008 as part of the POLARCAT project. For the ship-based measurements, a high degree of correlation (r = 0.98 for 544 data points collected north of 68° N) was observed between the acetylene to benzene ratio, used as a marker for chlorine and bromine oxidation, and O3 signifying the vast influence of halogen oxidation throughout the ice-free regions of the North Atlantic. Concurrent airborne and ground-based measurements in the Alaskan Arctic substantiated this correlation and were used to demonstrate that halogen oxidation influenced O3 variability throughout the Arctic boundary layer during these springtime studies. Measurements aboard the R/V Knorr in the North Atlantic and Arctic Oceans provided a unique view of the transport of O3-poor air masses from the Arctic Basin to latitudes as far south as 52° N. FLEXPART, a Lagrangian transport model, was used to quantitatively determine the exposure of air masses encountered by the ship to first-year ice (FYI), multi-year ice (MYI), and total ICE (FYI+MYI). O3 anti-correlated with the modeled total ICE tracer (r = −0.86) indicating that up to 73% of the O3 variability measured in the Arctic marine boundary layer could be related to sea ice exposure.

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41

Karaaslan, Cigdem, Hande Gurer-Orhan, Sibel Suzen, Luciano Saso, Omidreza Firuzi, Marjan Tavakkoli, and Elif Ince. "Behaviour of 9-Ethyl-9H-carbazole Hydrazone Derivatives Against Oxidant Systems." Croatica chemica acta 92, no. 1 (2019): 87–94. http://dx.doi.org/10.5562/cca3481.

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Antioxidants are helpful in prevention of several diseases related with oxidative stress including neurodegenerative disorders. In recent studies, carbazoles were given proof of promising antioxidant activities. In this article, 9-ethyl-9H-carbazole hydrazone derivatives were synthesized, characterized and their in vitro antioxidant activity and possible cytotoxic effects were investigated. Furthermore, protective effect of the synthesized derivatives against amyloid β-induced damage in PC12 neuronal cells was examined by using MTT assay. The newly synthesized carbazoles were found to have radical scavenging activity with a varying potency both in cell-free and cell-based in vitro assays. Several compounds, especially such as 3d and 3e, 3m and 3n bearing two halogen groups on the phenyl ring, were found to have cytotoxic activity. However, their cytotoxic activities were not higher than that of melatonin. Several compounds also significantly protected neuronal PC12 cells against amyloid β-induced damage, which can be defined as neuroprotective agents. (4-(2-((9-Ethyl-9H-carbazol-3-yl)methylene)hydrazinyl)benzonitrile) 3r was found as the most active compound with both radical scavenging activity and neuroprotective effects against amyloid β-induced damage. These findings might provide an alternative strategy for developing novel carbazole derivatives for management of neurodegenerative diseases, such as Alzheimer's disease.

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Niu, Ying Jian, and Ling Yang. "Thermogravimetric Evaluation of Magnesium Hydroxide and Red Phosphorous Flame Retarded Methyl Vinyl Silicone Rubber." Advanced Materials Research 396-398 (November 2011): 162–65. http://dx.doi.org/10.4028/www.scientific.net/amr.396-398.162.

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Halogen free fire-retardant silicon rubber compounds were prepared, using red phosphorus combined with magnesium hydroxide as flame retardants. The flame retardant mechanisms of red phosphorus, magnesium hydroxide were studied by means of comprehensive decomposition studies and combustion tests. The study is intended to illuminate prerequisites and the potential of red phosphorus as a fire retardant for silicone rubber in the condensed phase. The flammability was determined by limited oxygen indices （LOI） and UL 94 test. Thermo-oxidative decomposition kinetics were characterized by thermo-gravimetric analysis (TG). The activation energies were determined using the Friedman method, which do not require knowledge of the reaction mechanism (RM). The results show that the MVMQ/MH/RP composite has a higher thermal stability and lower flammability.

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43

SINGH, SUNDAR, and FAREED AHMAD. "Synthesis, Properties and Applications of Lead-Free Perovskites:A Review." Journal of Ultra Scientist of Physical Sciences Section A 33, no. 6 (October 7, 2021): 74–83. http://dx.doi.org/10.22147/jusps-a/330601.

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Perovskites are the materials or compounds having a structure similar to calcium titanium oxide (CaTiO3). These materials possess the basic structure of ABX3, in which A & B are the cations with +1 and +2 electron vacancy and X is an anion which may be either halogen or oxygen. Perovskites are chiefly being used in solar cells in the photo absorbing layer for solar to electrical energy conversion with relatively high efficiencies, besides their use in LEDs, photodetectors, X-ray detectors, lasers etc. The power conversion efficiency (PCE) of Perovskite solar cell (PSC) has increased from 10% in the year 2012 to 29.1% in 2020 and are promising to cross the theoretical maximum (Shockley-Queisser) limit of 33% for conventional silicon solar cells, besides having great thermal and mechanical stability values. Toxicity due to the presence of lead and associated instability of PSCs have led to the intensive research in lead-free perovskite solar cells (LF-PSCs). In this review article we have tried to explore the current status of synthesis, properties and applications of perovskites in PSCs,particularly lead-free perovskites, and will suggest future prospects in this widely attracted field of non-conventional energy generation.

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Mphahlele, Malose J., Emmanuel N. Agbo, Samantha Gildenhuys, and Itumeleng B. Setshedi. "Exploring Biological Activity of 4-Oxo-4H-furo[2,3-h]chromene Derivatives as Potential Multi-Target-Directed Ligands Inhibiting Cholinesterases, β-Secretase, Cyclooxygenase-2, and Lipoxygenase-5/15." Biomolecules 9, no. 11 (November 13, 2019): 736. http://dx.doi.org/10.3390/biom9110736.

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A series of 5-oxo-5H-furo[3,2-g]chromene-6-carbaldehydes and their hydrazone derivatives were evaluated as potential multi-target-directed ligands in vitro against cholinesterases, β-secretase, cyclooxygenase-2, and lipoxygenase-15 (LOX-15), as well as for free radical-scavenging activities. The most active compounds against LOX-15 were also evaluated for activity against the human lipoxygenase-5 (LOX-5). Kinetic studies against AChE, BChE, and β-secretase (BACE-1) were performed on 2-(3-fluorophenyl)- (3b) and 2-(4-chlorophenyl)-6-[(4-trifluoromethylphenyl)hydrazonomethyl]furo[3,2-h]chromen-5-one (3e) complemented with molecular docking (in silico) to determine plausible protein-ligand interactions on a molecular level. The docking studies revealed hydrogen and/or halogen bonding interactions between the strong electron-withdrawing fluorine atoms of the trifluoromethyl group with several residues of the enzyme targets, which are probably responsible for the observed increased biological activity of these hydrazone derivatives. The two compounds were found to moderately inhibit COX-2 and lipoxygenases (LOX-5 and LOX-15). Compounds 3b and 3e were also evaluated for cytotoxicity against the breast cancer MCF-7 cell line and Hek293-T cells.

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Moskaeva, Elena, Ahina Mosharenkova, Sergey Shekhovtsov, and Nikolay Mchedlov-Petrossyan. "PROTOLYTIC EQUILIBRIUM OF TETRA- AND PENTANITROFLUORESCEINS IN A BINARY SOLVENT ACETONITRILE – DIMETHYL SULFOXIDE (MASS RATIO 96 : 4)." Ukrainian Chemistry Journal 87, no. 5 (June 25, 2021): 25–37. http://dx.doi.org/10.33609/2708-129x.87.05.2021.25-37.

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In this paper, the acid-base and tautomeric equilibria of four nitrofluorescein dyes, 2,4,5,7-tetranitrofluorescein, 2,4,5,7,4’-pentanitrofluorescein, 2,4,5,7,5’-pentanitrofluorescein, and 2,4,5,7-tetranitrofluorescein methyl ester, were studied. As reaction media, a binary solvent acetonitrile – dimethyl sulfoxide (96 : 4 by mass) was used. The acidity scale in this solvent was established previously. The indices of the dissociation constants of the dyes were determined using the spectrophotometric method. Interpreting the values requires an understanding of the state of tautomeric equilibria. The behavior of these compounds differs significantly from that of other fluorescein dyes, e.g., halogen derivatives. In the case of the first three compounds, i.e., for dyes with a free carboxylic group, the lactonic structure is predominant not only for the neutral form, but even for the double-charged anion. The single-charged anionic form exists as an equilibrium mixture of a colored (and fluorescent) tautomer and an almost colorless lactone. The fourth compound with esterified carboxylic group exhibits extreme stability in its anionic form. Evaluation of the tautomerization constants made it possible to calculate the microscopic equilibrium constants of the stepwise dissociation of dye lactones, k1L and k2L. The consideration of the difference (pk2L – pk1L) allowed estimating the effective relative permittivity of the space between the ionizing groups basing on the Bjerrum – Kirkwood – Westheimer equation. Tautomerism of anions was discussed from the point of view of stabilization of symmetric structures.

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Heinz, Michael, Christoph Callsen, Waldemar Stöcklein, Volker Altstädt, and Holger Ruckdäschel. "Halogen‐free flame‐retardant cable compounds: Influence of magnesium‐di‐hydroxide filler and coupling agent on EVA / LLDPE blend system morphology." Polymer Engineering & Science 62, no. 2 (December 9, 2021): 461–71. http://dx.doi.org/10.1002/pen.25858.

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47

Liu, Quanyi, Donghui Wang, Zekun Li, Zhifa Li, Xiaoliang Peng, Chuanbang Liu, Yu Zhang, and Penglun Zheng. "Recent Developments in the Flame-Retardant System of Epoxy Resin." Materials 13, no. 9 (May 6, 2020): 2145. http://dx.doi.org/10.3390/ma13092145.

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With the increasing emphasis on environmental protection, the development of flame retardants for epoxy resin (EP) has tended to be non-toxic, efficient, multifunctional and systematic. Currently reported flame retardants have been capable of providing flame retardancy, heat resistance and thermal stability to EP. However, many aspects still need to be further improved. This paper reviews the development of EPs in halogen-free flame retardants, focusing on phosphorus flame retardants, carbon-based materials, silicon flame retardants, inorganic nanofillers, and metal-containing compounds. These flame retardants can be used on their own or in combination to achieve the desired results. The effects of these flame retardants on the thermal stability and flame retardancy of EPs were discussed. Despite the great progress on flame retardants for EP in recent years, further improvement of EP is needed to obtain numerous eco-friendly high-performance materials.

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Saito, Akio. "Hypervalent Iodine-mediated/Catalyzed Oxidative Cycloisomerization/Annulation of Alkynes for Metal-free Synthesis of Oxazoles." Current Organic Chemistry 24, no. 18 (November 18, 2020): 2048–69. http://dx.doi.org/10.2174/1385272824999200510232438.

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Since oxazoles have found widespread applications not only as synthetic intermediates but also as biologically active compounds, much effort has been focused on developing novel and efficient methods for the synthesis of this heterocycle. From the viewpoint of green and sustainable chemistry, hypervalent iodine and other halogen reagents have gained increasing popularity in metal-free oxidative transformation due to their low toxicity, transition-metal-like reactivity, high stability, easy handling and other benefits. In this account, our two approaches to the metal-free synthesis of oxazoles by means of a peculiar activation of alkynes by iodine species are described with the related contexts. One is iodine(III)-mediated/catalyzed oxidative cycloisomerization reactions of N-propargyl amides for the preparation of oxazoles bearing various functional groups at their side chains. In these reactions, iodine(III) species works as a donor of various heteroatomic functional groups as well as an activator of carbon-carbon triple bonds in a single step. Furthermore, this methodology can be extended to iodine(III)-mediated/catalyzed oxidative annulation of alkynes and nitriles as another approach, in which heteroatoms on iodine(III) species are incorporated in the azole rings.

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Basylevska, M., and V. Bogillo. "The impact of volcanic emission of halogenated compounds on the Southern Hemisphere and Antarctic environment." Ukrainian Antarctic Journal, no. 2 (2021): 12–34. http://dx.doi.org/10.33275/1727-7485.2.2021.675.

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The study aims to estimate and compare the global emission for 20 halocarbons from volcanic and hydrothermal sources into the Earth’s atmosphere. It follows from the results that the contribution of volcanic emission for these species in the depletion of stratospheric ozone in the catalytic halogen cycles does not exceed 0.1%. Still, they significantly impair the level of tropospheric ozone near the volcanoes. The scheme of gas-phase free radical chain halogenation of the hydrocarbons is proposed and confirmed by thermodynamic and kinetic calculations. This explains the experimental ratios between concentrations of CH3I : CH3Br : CH3Cl and CCl4 : CHCl3 : CH2Cl2 : CH3Cl in the volcanic gases. The possible volcanic emission of halocarbons from Erebus and explosive eruptions in the Southern Hemisphere during the Holocene do not have a notable impact on their content in the Antarctic ice. However, volcanic emission of hydrogen halides (HX, X = Cl, Br or I) from powerful eruptions in the Southern Hemisphere during Holocene could deplete the stratospheric ozone substantially, causing a drastic impact of the harmful UV-B radiation on the biota of continents and ocean. We calculated the injected Equivalent Effective Stratospheric Chlorine values and estimated the column ozone percentage change, Δ%O3, for 20 known volcano eruptions in the tropical belt and Southern latitudes. The estimates lead to more than 50% depletion of stratospheric ozone after past powerful volcanic eruptions. The range is estimated for possible ozone depletion after the eruption of Deception Island’s volcano occurred near 4000 BP (from 44 to 56%), which is comparable with those from Krakatoa, Samalas, and Tambora eruptions. A similar analysis was carried out for 192 yrs series of Mt Takahe (West Antarctica) halogen-rich volcanic eruptions at 17,7 kyr, showing extensive stratospheric ozone depletion over Antarctica. Crude estimations of stratospheric ozone depletion (Δ%O3) after Ferrar Large Igneous Province eruptions (183 Ma) in Antarctica were performed, considering the whole LIP volume of basaltic lavas, and they range from 49 to 83%. Given the very low emission rate of HCl due to non-eruptive degassing of the Mt. Erebus volcano, the volcanic emission of Erebus could not be a fundamental reason for modern springtime ozone hole formation over Antarctica.

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Fuhlbrügge, Steffen, Birgit Quack, Susann Tegtmeier, Elliot Atlas, Helmke Hepach, Qiang Shi, Stefan Raimund, and Kirstin Krüger. "The contribution of oceanic halocarbons to marine and free tropospheric air over the tropical West Pacific." Atmospheric Chemistry and Physics 16, no. 12 (June 21, 2016): 7569–85. http://dx.doi.org/10.5194/acp-16-7569-2016.

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Abstract. Emissions of halogenated very-short-lived substances (VSLSs) from the oceans contribute to the atmospheric halogen budget and affect tropospheric and stratospheric ozone. Here, we investigate the contribution of natural oceanic VSLS emissions to the marine atmospheric boundary layer (MABL) and their transport into the free troposphere (FT) over the tropical West Pacific. The study concentrates on bromoform, dibromomethane and methyl iodide measured on ship and aircraft during the SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) campaign in the South China and Sulu seas in November 2011. Elevated oceanic concentrations for bromoform, dibromomethane and methyl iodide of on average 19.9, 5.0 and 3.8 pmol L−1, in particular close to Singapore and to the coast of Borneo, with high corresponding oceanic emissions of 1486, 405 and 433 pmol m−2 h−1 respectively, characterise this tropical region as a strong source of these compounds. Atmospheric mixing ratios in the MABL were unexpectedly relatively low with 2.08, 1.17 and 0.39 ppt for bromoform, dibromomethane and methyl iodide. We use meteorological and chemical ship and aircraft observations, FLEXPART trajectory calculations and source-loss estimates to identify the oceanic VSLS contribution to the MABL and to the FT. Our results show that the well-ventilated MABL and intense convection led to the low atmospheric mixing ratios in the MABL despite the high oceanic emissions. Up to 45 % of the accumulated bromoform in the FT above the region originates from the local South China Sea area, while dibromomethane is largely advected from distant source regions and the local ocean only contributes 20 %. The accumulated methyl iodide in the FT is higher than can be explained with local contributions. Possible reasons, uncertainties and consequences of our observations and model estimates are discussed.

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Journal articles on the topic 'Halogen-free compounds'

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